Code division multiple access Steps in CDMA Modulation CDMA is a spread spectrum multiple access technique httpsstoretheartofservicecomthemodulationtoolkithtml Code division multiple access Steps in CDMA Modulation ID: 935097
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Slide1
Modulation
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Slide2Code division multiple access Steps in CDMA Modulation
CDMA is a spread spectrum multiple access technique
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Slide3Code division multiple access Steps in CDMA Modulation
Each user in a CDMA system uses a different code to modulate their signal
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Slide4Code division multiple access Steps in CDMA Modulation
An analogy to the problem of multiple access is a room (channel) in which people wish to talk to each other simultaneously
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Slide5Code division multiple access Steps in CDMA Modulation
In general, CDMA belongs to two basic categories: synchronous (orthogonal codes) and asynchronous (pseudorandom codes).
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Slide6Radar - Frequency modulation
Another form of distance measuring radar is based on frequency modulation. Frequency comparison between two signals is considerably more accurate, even with older electronics, than timing the signal. By measuring the frequency of the returned signal and comparing that with the original, the difference can be easily measured.
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Slide7Radar - Frequency modulation
This technique can be used in continuous wave radar and is often found in aircraft radar altimeters
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Slide8Radar - Frequency modulation
Since the signal frequency is changing, by the time the signal returns to the aircraft the transmit frequency has changed. The amount of frequency shift is used to measure distance.
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Slide9Radar - Frequency modulation
The modulation index riding on the receive signal is proportional to the time delay between the radar and the reflector
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Slide10Radar - Frequency modulation
A further advantage is that the radar can operate effectively at relatively low frequencies. This was important in the early development of this type when high frequency signal generation was difficult or expensive.
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Slide11Radar - Frequency modulation
Terrestrial radar uses low-power FM signals that cover a larger frequency range. The multiple reflections are analyzed mathematically for pattern changes with multiple passes creating a computerized synthetic image. Doppler effects are used which allows slow moving objects to be detected as well as largely eliminating "noise" from the surfaces of bodies of water.
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Slide12Telecommunication - Modulation
In addition, there are combinations of phase-shift keying and amplitude-shift keying which is called (in the jargon of the field) "quadrature amplitude modulation" (QAM) that are used in high-capacity digital radio communication systems.
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Slide13Telecommunication - Modulation
In addition, modulation has the advantage of being about to use frequency division multiplexing (FDM)
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Slide14Bipolar junction transistor - Base-width modulation
As the collector–base voltage () varies, the collector–base depletion region varies in size. An increase in the collector–base voltage, for example, causes a greater reverse bias across the collector–base junction, increasing the collector–base depletion region width, and decreasing the width of the base. This variation in base width often is called the "Early effect" after its discoverer James M. Early.
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Slide15Bipolar junction transistor - Base-width modulation
Narrowing of the base width has two consequences:
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Slide16Bipolar junction transistor - Base-width modulation
The charge gradient is increased across the base, and consequently, the current of minority carriers injected across the emitter junction increases.
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Slide17Bipolar junction transistor - Base-width modulation
Both factors increase the collector or "output" current of the transistor in response to an increase in the collector–base voltage.
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Slide18Bipolar junction transistor - Base-width modulation
In the forward-active region, the Early effect modifies the collector current () and the forward common emitter current gain () as given by:
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Slide19Bipolar junction transistor - Base-width modulation
is forward common-emitter current gain when = 0 V
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Slide20Bipolar junction transistor - Base-width modulation
is the output impedance
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Slide21Infrared - Photobiomodulation
Near-infrared light, or photobiomodulation, is used for treatment of chemotherapy-induced oral ulceration as well as wound healing. There is some work relating to anti-herpes virus treatment. Research projects include work on central nervous system healing effects via cytochrome c oxidase upregulation and other possible mechanisms.
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Slide22Powered exoskeleton - Power control and modulation
Control and modulation of excessive and unwanted movement is a third large problem
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Slide23Powered exoskeleton - Power control and modulation
A single-speed assist mechanism which is slowed down to prevent oscillation is then restrictive on the agility of the wearer. Sudden unexpected movements such as tripping or being pushed over requires fast precise movements to recover and prevent falling over, but a slow assist mechanism may simply collapse and injure the user inside. (This is known as an overdamped servo.)
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Slide24Powered exoskeleton - Power control and modulation
Fast and accurate assistive positioning is typically done using a range of speeds controlled using computer position sensing of both the exoskeleton and the wearer, so that the assistive motion only moves as fast or as far as the motion of the wearer and does not overshoot or undershoot
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Slide25Diode - Radio demodulation
The first use for the diode was the demodulation of amplitude modulated (AM) radio broadcasts
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Slide26Global Positioning System - Demodulation and decoding
Because all of the satellite signals are modulated onto the same L1 carrier frequency, the signals must be separated after demodulation. This is done by assigning each satellite a unique binary sequence known as a Gold code. The signals are decoded after demodulation using addition of the Gold codes corresponding to the satellites monitored by the receiver.
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Slide27Global Positioning System - Demodulation and decoding
If the almanac information has previously been acquired, the receiver picks the satellites to listen for by their PRNs, unique numbers in the range 1 through 32
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Slide28Global Positioning System - Demodulation and decoding
Processing of the navigation message enables the determination of the time of transmission and the satellite position at this time. For more information see Demodulation and Decoding, Advanced.
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Slide29Holography - Amplitude and phase modulation holograms
An amplitude modulation hologram is one where the amplitude of light diffracted by the hologram is proportional to the intensity of the recorded light. A straightforward example of this is photographic emulsion on a transparent substrate. The emulsion is exposed to the interference pattern, and is subsequently developed giving a transmittance which varies with the intensity of the pattern - the more light that fell on the plate at a given point, the darker the developed plate at that point.
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Slide30Holography - Amplitude and phase modulation holograms
A phase hologram is made by changing either the thickness or the refractive index of the material in proportion to the intensity of the holographic interference pattern. This is a phase grating and it can be shown that when such a plate is illuminated by the original reference beam, it reconstructs the original object wavefront. The efficiency (i.e. the fraction of the illuminated beam which is converted to reconstructed object beam) is greater for phase than for amplitude modulated holograms.
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Slide31Modulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal ( High Frequency Signal), with a modulating signal which typically contains information to be transmitted.
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Slide32Modulation
In telecommunications, modulation is the process of conveying a message signal, for example a digital bit stream or an analog audio signal, inside another signal that can be physically transmitted. Modulation of a sine waveform is used to transform a baseband message signal into a passband signal.
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Slide33Modulation
A device that performs modulation is known as a modulator and a device that performs the inverse operation of modulation is known as a demodulator (sometimes detector or demod). A device that can do both operations is a modem (from "modulator–demodulator").
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Slide34Modulation
The aim of digital modulation is to transfer a digital bit stream over an analog bandpass channel, for example over the public switched telephone network (where a bandpass filter limits the frequency range to between 300 and 3400 Hz), or over a limited radio frequency band.
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Slide35Modulation
The aim of analog modulation is to transfer an analog baseband (or lowpass) signal, for example an audio signal or TV signal, over an analog bandpass channel at a different frequency, for example over a limited radio frequency band or a cable TV network channel.
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Slide36Modulation
Analog and digital modulation facilitate frequency division multiplexing (FDM), where several low pass information signals are transferred simultaneously over the same shared physical medium, using separate passband channels (several different carrier frequencies).
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Slide37Modulation
The aim of digital baseband modulation methods, also known as line coding, is to transfer a digital bit stream over a baseband channel, typically a non-filtered copper wire such as a serial bus or a wired local area network.
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Slide38Modulation
The aim of pulse modulation methods is to transfer a narrowband analog signal, for example a phone call over a wideband baseband channel or, in some of the schemes, as a bit stream over another digital transmission system.
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Slide39Modulation
In music synthesizers, modulation may be used to synthesise waveforms with an extensive overtone spectrum using a small number of oscillators. In this case the carrier frequency is typically in the same order or much lower than the modulating waveform. See for example frequency modulation synthesis or ring modulation synthesis.
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Slide40Modulation - Analog modulation methods
In analog modulation, the modulation is applied continuously in response to the analog information signal. Common analog modulation techniques are:
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Slide41Modulation - Analog modulation methods
Amplitude modulation (AM) (here the amplitude of the carrier signal is varied in accordance to the instantaneous amplitude of the modulating signal)
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Slide42Modulation - Analog modulation methods
Double-sideband modulation (DSB)
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Slide43Modulation - Analog modulation methods
Double-sideband modulation with carrier (DSB-WC) (used on the AM radio broadcasting band)
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Slide44Modulation - Analog modulation methods
Double-sideband suppressed-carrier transmission (DSB-SC)
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Slide45Modulation - Analog modulation methods
Double-sideband reduced carrier transmission (DSB-RC)
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Slide46Modulation - Analog modulation methods
Single-sideband modulation (SSB, or SSB-AM)
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Slide47Modulation - Analog modulation methods
SSB suppressed carrier modulation (SSB-SC)
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Slide48Modulation - Analog modulation methods
Vestigial sideband modulation (VSB, or VSB-AM)
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Slide49Modulation - Analog modulation methods
Angle modulation, which is approximately constant envelope
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Slide50Modulation - Analog modulation methods
Frequency modulation (FM) (here the frequency of the carrier signal is varied in accordance to the instantaneous amplitude of the modulating signal)
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Slide51Modulation - Analog modulation methods
Phase modulation (PM) (here the phase shift of the carrier signal is varied in accordance to the instantaneous amplitude of the modulating signal)
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Slide52Modulation - Digital modulation methods
In digital modulation, an analog carrier signal is modulated by a discrete signal. Digital modulation methods can be considered as digital-to-analog conversion, and the corresponding demodulation or detection as analog-to-digital conversion. The changes in the carrier signal are chosen from a finite number of M alternative symbols (the modulation alphabet).
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Slide53Modulation - Digital modulation methods
A simple example: A telephone line is designed for transferring audible sounds, for example tones, and not digital bits (zeros and ones)
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Slide54Modulation - Digital modulation methods
According to one definition of digital signal, the modulated signal is a digital signal, and according to another definition, the modulation is a form of digital-to-analog conversion. Most textbooks would consider digital modulation schemes as a form of digital transmission, synonymous to data transmission; very few would consider it as analog transmission.
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Slide55Modulation - Fundamental digital modulation methods
The most fundamental digital modulation techniques are based on keying:
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Slide56Modulation - Fundamental digital modulation methods
PSK (phase-shift keying): a finite number of phases are used.
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Slide57Modulation - Fundamental digital modulation methods
FSK (frequency-shift keying): a finite number of frequencies are used.
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Slide58Modulation - Fundamental digital modulation methods
ASK (amplitude-shift keying): a finite number of amplitudes are used.
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Slide59Modulation - Fundamental digital modulation methods
QAM (quadrature amplitude modulation): a finite number of at least two phases and at least two amplitudes are used.
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Slide60Modulation - Fundamental digital modulation methods
In QAM, an inphase signal (or I, with one example being a cosine waveform) and a quadrature phase signal (or Q, with an example being a sine wave) are amplitude modulated with a finite number of amplitudes, and then summed. It can be seen as a two-channel system, each channel using ASK. The resulting signal is equivalent to a combination of PSK and ASK.
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Slide61Modulation - Fundamental digital modulation methods
In all of the above methods, each of these phases, frequencies or amplitudes are assigned a unique pattern of binary bits. Usually, each phase, frequency or amplitude encodes an equal number of bits. This number of bits comprises the symbol that is represented by the particular phase, frequency or amplitude.
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Slide62Modulation - Fundamental digital modulation methods
If the alphabet consists of alternative symbols, each symbol represents a message consisting of N bits. If the symbol rate (also known as the baud rate) is symbols/second (or baud), the data rate is bit/second.
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Slide63Modulation - Fundamental digital modulation methods
For example, with an alphabet consisting of 16 alternative symbols, each symbol represents 4 bits. Thus, the data rate is four times the baud rate.
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Slide64Modulation - Fundamental digital modulation methods
In the case of PSK, ASK or QAM, where the carrier frequency of the modulated signal is constant, the modulation alphabet is often conveniently represented on a constellation diagram, showing the amplitude of the I signal at the x-axis, and the amplitude of the Q signal at the y-axis, for each symbol.
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Slide65Modulation - Modulator and detector principles of operation
PSK and ASK, and sometimes also FSK, are often generated and detected using the principle of QAM. The I and Q signals can be combined into a complex-valued signal I+jQ (where j is the imaginary unit). The resulting so called equivalent lowpass signal or equivalent baseband signal is a complex-valued representation of the real-valued modulated physical signal (the so-called passband signal or RF signal).
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Slide66Modulation - Modulator and detector principles of operation
These are the general steps used by the modulator to transmit data:
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Slide67Modulation - Modulator and detector principles of operation
Group the incoming data bits into codewords, one for each symbol that will be transmitted.
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Slide68Modulation - Modulator and detector principles of operation
Map the codewords to attributes, for example amplitudes of the I and Q signals (the equivalent low pass signal), or frequency or phase values.
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Slide69Modulation - Modulator and detector principles of operation
Adapt pulse shaping or some other filtering to limit the bandwidth and form the spectrum of the equivalent low pass signal, typically using digital signal processing.
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Slide70Modulation - Modulator and detector principles of operation
Perform digital to analog conversion (DAC) of the I and Q signals (since today all of the above is normally achieved using digital signal processing, DSP).
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Slide71Modulation - Modulator and detector principles of operation
Carry out the modulation, for example by multiplying the sine and cosine waveform with the I and Q signals, resulting in the equivalent low pass signal being frequency shifted to the modulated passband signal or RF signal
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Slide72Modulation - Modulator and detector principles of operation
Amplification and analog bandpass filtering to avoid harmonic distortion and periodic spectrum
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Slide73Modulation - Modulator and detector principles of operation
At the receiver side, the demodulator typically performs:
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Slide74Modulation - Modulator and detector principles of operation
Automatic gain control, AGC (to compensate for attenuation, for example fading).
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Slide75Modulation - Modulator and detector principles of operation
Frequency shifting of the RF signal to the equivalent baseband I and Q signals, or to an intermediate frequency (IF) signal, by multiplying the RF signal with a local oscillator sinewave and cosine wave frequency (see the superheterodyne receiver principle).
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Slide76Modulation - Modulator and detector principles of operation
Sampling and analog-to-digital conversion (ADC) (Sometimes before or instead of the above point, for example by means of undersampling).
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Slide77Modulation - Modulator and detector principles of operation
Equalization filtering, for example a matched filter, compensation for multipath propagation, time spreading, phase distortion and frequency selective fading, to avoid intersymbol interference and symbol distortion.
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Slide78Modulation - Modulator and detector principles of operation
Detection of the amplitudes of the I and Q signals, or the frequency or phase of the IF signal.
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Slide79Modulation - Modulator and detector principles of operation
Quantization of the amplitudes, frequencies or phases to the nearest allowed symbol values.
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Slide80Modulation - Modulator and detector principles of operation
Mapping of the quantized amplitudes, frequencies or phases to codewords (bit groups).
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Slide81Modulation - Modulator and detector principles of operation
Pass the resultant bit stream on for further processing such as removal of any error-correcting codes.
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Slide82Modulation - Modulator and detector principles of operation
As is common to all digital communication systems, the design of both the modulator and demodulator must be done simultaneously. Digital modulation schemes are possible because the transmitter-receiver pair have prior knowledge of how data is encoded and represented in the communications system. In all digital communication systems, both the modulator at the transmitter and the demodulator at the receiver are structured so that they perform inverse operations.
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Slide83Modulation - Modulator and detector principles of operation
Non-coherent modulation methods do not require a receiver reference clock signal that is phase synchronized with the sender carrier wave. In this case, modulation symbols (rather than bits, characters, or data packets) are asynchronously transferred. The opposite is coherent modulation.
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Slide84Modulation - List of common digital modulation techniques
The most common digital modulation techniques are:
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Slide85Modulation - List of common digital modulation techniques
Quadrature PSK (QPSK), using M=4 symbols
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Slide86Modulation - List of common digital modulation techniques
Audio frequency-shift keying (AFSK)
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Slide87Modulation - List of common digital modulation techniques
Multi-frequency shift keying (M-ary FSK or MFSK)
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Slide88Modulation - List of common digital modulation techniques
Dual-tone multi-frequency (DTMF)
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Slide89Modulation - List of common digital modulation techniques
M-ary vestigial sideband modulation, for example 8VSB
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Slide90Modulation - List of common digital modulation techniques
Quadrature amplitude modulation (QAM) - a combination of PSK and ASK:
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Slide91Modulation - List of common digital modulation techniques
Polar modulation like QAM a combination of PSK and ASK.
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Slide92Modulation - List of common digital modulation techniques
Continuous phase modulation (CPM) methods:
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Slide93Modulation - List of common digital modulation techniques
Continuous-phase frequency-shift keying (CPFSK)
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Slide94Modulation - List of common digital modulation techniques
Orthogonal frequency-division multiplexing (OFDM) modulation:
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Slide95Modulation - List of common digital modulation techniques
discrete multitone (DMT) - including adaptive modulation and bit-loading.
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Slide96Modulation - List of common digital modulation techniques
Wavelet modulation
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Slide97Modulation - List of common digital modulation techniques
Trellis coded modulation (TCM), also known as trellis modulation
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Slide98Modulation - List of common digital modulation techniques
Chirp spread spectrum (CSS) according to IEEE 802.15.4a CSS uses pseudo-stochastic coding
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Slide99Modulation - List of common digital modulation techniques
Frequency-hopping spread spectrum (FHSS) applies a special scheme for channel release
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Slide100Modulation - List of common digital modulation techniques
SIM31 (SIM) New digital Mode SIM31 SIM63 tks SWL Tunisian
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Slide101Modulation - List of common digital modulation techniques
MSK and GMSK are particular cases of continuous phase modulation. Indeed, MSK is a particular case of the sub-family of CPM known as continuous-phase frequency-shift keying (CPFSK) which is defined by a rectangular frequency pulse (i.e. a linearly increasing phase pulse) of one symbol-time duration (total response signaling).
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Slide102Modulation - List of common digital modulation techniques
OFDM is considered as a modulation technique rather than a multiplex technique, since it transfers one bit stream over one communication channel using one sequence of so-called OFDM symbols
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Slide103Modulation - List of common digital modulation techniques
Nevertheless, even though switching amplifiers are completely unsuitable for normal QAM constellations, often the QAM modulation principle are used to drive switching amplifiers with these FM and other waveforms, and sometimes QAM demodulators are used to receive the signals put out by these switching amplifiers.
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Slide104Modulation - Automatic digital modulation recognition (ADMR)
Obviously, with no knowledge of the transmitted data and many unknown parameters at the receiver, such as the signal power, carrier frequency and phase offsets, timing information, etc., blind identification of the modulation is a difficult task
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Slide105Modulation - Automatic digital modulation recognition (ADMR)
There are two main approaches to automatic modulation recognition. The first approach uses likelihood-based methods to assign an input signal to a proper class. Another recent approach is based on feature extraction.
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Slide106Modulation - Digital baseband modulation or line coding
The term digital baseband modulation (or digital baseband transmission) is synonymous to line codes. These are methods to transfer a digital bit stream over an analog baseband channel (a.k.a. lowpass channel) using a pulse train, i.e. a discrete number of signal levels, by directly modulating the voltage or current on a cable. Common examples are unipolar, non-return-to-zero (NRZ), Manchester and alternate mark inversion (AMI) codings.
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Slide107Modulation - Pulse modulation methods
These are not modulation schemes in the conventional sense since they are not channel coding schemes, but should be considered as source coding schemes, and in some cases analog-to-digital conversion techniques.
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Slide108Modulation - Pulse modulation methods
Pulse-amplitude modulation (PAM)
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Slide109Modulation - Pulse modulation methods
Pulse-width modulation (PWM) AND Pulse-depth modulation (PDM)
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Slide110Modulation - Pulse modulation methods
Pulse-position modulation (PPM)
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Slide111Modulation - Pulse modulation methods
Pulse-code modulation (PCM)
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Slide112Modulation - Pulse modulation methods
Delta modulation (DM or Δ-modulation)
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Slide113Modulation - Pulse modulation methods
Delta-sigma modulation (∑Δ)
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Slide114Modulation - Pulse modulation methods
Continuously variable slope delta modulation (CVSDM), also called Adaptive-delta modulation (ADM)
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Slide115Modulation - Pulse modulation methods
Pulse-density modulation (PDM)
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Slide116Modulation - Miscellaneous modulation techniques
The use of on-off keying to transmit Morse code at radio frequencies is known as continuous wave (CW) operation.
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Slide117Modulation - Miscellaneous modulation techniques
Space modulation A method whereby signals are modulated within airspace, such as that used in Instrument landing systems.
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Slide118Modulation - Further reading
Multipliers vs. Modulators Analog Dialogue, June 2013
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Slide119Pulse-width modulation
Pulse-width modulation
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Slide120Pulse-width modulation
Although this modulation technique can be used to encode information for transmission, its main use is to allow the control of the power supplied to electrical devices, especially to inertial loads such as motors
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Slide121Pulse-width modulation
The average value of voltage (and current) fed to the load is controlled by turning the switch between supply and load on and off at a fast pace. The longer the switch is on compared to the off periods, the higher the power supplied to the load is.
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Slide122Pulse-width modulation
The PWM switching frequency has to be much faster than what would affect the load, which is to say the device that uses the power. Typically switchings have to be done several times a minute in an electric stove, 120 Hz in a lamp dimmer, from few kilohertz (kHz) to tens of kHz for a motor drive and well into the tens or hundreds of kHz in audio amplifiers and computer power supplies.
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Slide123Pulse-width modulation
The term duty cycle describes the proportion of 'on' time to the regular interval or 'period' of time; a low duty cycle corresponds to low power, because the power is off for most of the time. Duty cycle is expressed in percent, 100% being fully on.
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Slide124Pulse-width modulation
The main advantage of PWM is that power loss in the switching devices is very low. When a switch is off there is practically no current, and when it is on, there is almost no voltage drop across the switch. Power loss, being the product of voltage and current, is thus in both cases close to zero. PWM also works well with digital controls, which, because of their on/off nature, can easily set the needed duty cycle.
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Slide125Pulse-width modulation
PWM has also been used in certain communication systems where its duty cycle has been used to convey information over a communications channel.
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Slide126Pulse-width modulation - History
In the past, when only partial power was needed (such as for a sewing machine motor), a rheostat (located in the sewing machine's foot pedal) connected in series with the motor adjusted the amount of current flowing through the motor, but also wasted power as heat in the resistor element
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Slide127Pulse-width modulation - History
For about a century, some variable-speed electric motors have had decent efficiency, but they were somewhat more complex than constant-speed motors, and sometimes required bulky external electrical apparatus, such as a bank of variable power resistors or rotating converter such as Ward Leonard drive.
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Slide128Pulse-width modulation - History
However, in addition to motor drives for fans, pumps and robotic servos, there was a great need for compact and low cost means for applying adjustable power for many devices, such as electric stoves and lamp dimmers.
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Slide129Pulse-width modulation - History
One early application of PWM was in the Sinclair X10, a 10 W audio amplifier available in kit form in the 1960s. At around the same time PWM started to be used in AC motor control.
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Slide130Pulse-width modulation - Principle
Pulse-width modulation uses a rectangular pulse wave whose pulse width is modulated resulting in the variation of the average value of the waveform. If we consider a pulse waveform with a low value , a high value and a duty cycle D (see figure 1), the average value of the waveform is given by:
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Slide131Pulse-width modulation - Principle
As is a pulse wave, its value is for and for . The above expression then becomes:
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Slide132Pulse-width modulation - Principle
This latter expression can be fairly simplified in many cases where as . From this, it is obvious that the average value of the signal () is directly dependent on the duty cycle D.
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Slide133Pulse-width modulation - Principle
The simplest way to generate a PWM signal is the intersective method, which requires only a sawtooth or a triangle waveform (easily generated using a simple oscillator) and a comparator. When the value of the reference signal (the red sine wave in figure 2) is more than the modulation waveform (blue), the PWM signal (magenta) is in the high state, otherwise it is in the low state.
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Slide134Pulse-width modulation - Delta
In the use of delta modulation for PWM control, the output signal is integrated, and the result is compared with limits, which correspond to a Reference signal offset by a constant. Every time the integral of the output signal reaches one of the limits, the PWM signal changes state. Figure 3
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Slide135Pulse-width modulation - Delta-sigma
In delta-sigma modulation as a PWM control method, the output signal is subtracted from a reference signal to form an error signal. This error is integrated, and when the integral of the error exceeds the limits, the output changes state. Figure 4
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Slide136Pulse-width modulation - Space vector modulation
Space vector modulation
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Slide137Pulse-width modulation - Space vector modulation
Space vector modulation is a PWM control algorithm for multi-phase AC generation, in which the reference signal is sampled regularly; after each sample, non-zero active switching vectors adjacent to the reference vector and one or more of the zero switching vectors are selected for the appropriate fraction of the sampling period in order to synthesize the reference signal as the average of the used vectors.
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Slide138Pulse-width modulation - Direct torque control (DTC)
Direct torque control is a method used to control AC motors. It is closely related with the delta modulation (see above). Motor torque and magnetic flux are estimated and these are controlled to stay within their hysteresis bands by turning on new combination of the device's semiconductor switches each time either of the signal tries to deviate out of the band.
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Slide139Pulse-width modulation - Time proportioning
Many digital circuits can generate PWM signals (e.g., many microcontrollers have PWM outputs)
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Slide140Pulse-width modulation - Time proportioning
The incremented and periodically reset counter is the discrete version of the intersecting method's sawtooth. The analog comparator of the intersecting method becomes a simple integer comparison between the current counter value and the digital (possibly digitized) reference value. The duty cycle can only be varied in discrete steps, as a function of the counter resolution. However, a high-resolution counter can provide quite satisfactory performance.
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Slide141Pulse-width modulation - Types
Three types of pulse-width modulation (PWM) are possible:
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Slide142Pulse-width modulation - Types
The pulse center may be fixed in the center of the time window and both edges of the pulse moved to compress or expand the width.
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Slide143Pulse-width modulation - Types
The lead edge can be held at the lead edge of the window and the tail edge modulated.
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Slide144Pulse-width modulation - Types
The tail edge can be fixed and the lead edge modulated.
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Slide145Pulse-width modulation - Spectrum
The resulting spectra (of the three cases) are similar, and each contains a dc component, a base sideband containing the modulating signal and phase modulated carriers at each harmonic of the frequency of the pulse
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Slide146Pulse-width modulation - Spectrum
On the contrary, the delta modulation is a random process that produces continuous spectrum without distinct harmonics.
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Slide147Pulse-width modulation - PWM sampling theorem
The theorem states that "Any bandlimited baseband signal within ±0.637 can be represented by a pulsewidth modulation (PWM) waveform with unit amplitude
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Slide148Pulse-width modulation - Telecommunications
In telecommunications, PWM is a form of signal modulation where the widths of the pulses correspond to specific data values encoded at one end and decoded at the other.
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Slide149Pulse-width modulation - Telecommunications
Pulses of various lengths (the information itself) will be sent at regular intervals (the carrier frequency of the modulation).
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Slide150Pulse-width modulation - Telecommunications
The inclusion of a clock signal is not necessary, as the leading edge of the data signal can be used as the clock if a small offset is added to the data value in order to avoid a data value with a zero length pulse.
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Slide151Pulse-width modulation - Power delivery
PWM can be used to control the amount of power delivered to a load without incurring the losses that would result from linear power delivery by resistive means. Potential drawbacks to this technique are the pulsations defined by the duty cycle, switching frequency and properties of the load. With a sufficiently high switching frequency and, when necessary, using additional passive electronic filters, the pulse train can be smoothed and average analog waveform recovered.
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Slide152Pulse-width modulation - Power delivery
High frequency PWM power control systems are easily realisable with semiconductor switches
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Slide153Pulse-width modulation - Power delivery
Modern semiconductor switches such as MOSFETs or Insulated-gate bipolar transistors (IGBTs) are well suited components for high efficiency controllers. Frequency converters used to control AC motors may have efficiencies exceeding 98%. Switching power supplies have lower efficiency due to low output voltage levels (often even less than 2 V for microprocessors are needed) but still more than 70–80% efficiency can be achieved.
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Slide154Pulse-width modulation - Power delivery
Variable-speed fan controllers for computers usually use PWM, as it is far more efficient when compared to a potentiometer or rheostat. (Neither of the latter is practical to operate electronically; they would require a small drive motor.)
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Slide155Pulse-width modulation - Power delivery
Light dimmers for home use employ a specific type of PWM control
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Slide156Pulse-width modulation - Power delivery
These rather simple types of dimmers can be effectively used with inert (or relatively slow reacting) light sources such as incandescent lamps, for example, for which the additional modulation in supplied electrical energy which is caused by the dimmer causes only negligible additional fluctuations in the emitted light
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Slide157Pulse-width modulation - Power delivery
In electric cookers, continuously variable power is applied to the heating elements such as the hob or the grill using a device known as a Simmerstat. This consists of a thermal oscillator running at approximately two cycles per minute and the mechanism varies the duty cycle according to the knob setting. The thermal time constant of the heating elements is several minutes, so that the temperature fluctuations are too small to matter in practice.
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Slide158Pulse-width modulation - Voltage regulation
PWM is also used in efficient voltage regulators. By switching voltage to the load with the appropriate duty cycle, the output will approximate a voltage at the desired level. The switching noise is usually filtered with an inductor and a capacitor.
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Slide159Pulse-width modulation - Voltage regulation
One method measures the output voltage. When it is lower than the desired voltage, it turns on the switch. When the output voltage is above the desired voltage, it turns off the switch.
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Slide160Pulse-width modulation - Audio effects and amplification
PWM is sometimes used in sound (music) synthesis, in particular subtractive synthesis, as it gives a sound effect similar to chorus or slightly detuned oscillators played together
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Slide161Pulse-width modulation - Audio effects and amplification
A new class of audio amplifiers based on the PWM principle is becoming popular
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Slide162Pulse-width modulation - Audio effects and amplification
Historically, a crude form of PWM has been used to play back PCM digital sound on the PC speaker, which is driven by only two voltage levels, typically 0 V and 5 V. By carefully timing the duration of the pulses, and by relying on the speaker's physical filtering properties (limited frequency response, self-inductance, etc.) it was possible to obtain an approximate playback of mono PCM samples, although at a very low quality, and with greatly varying results between implementations.
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Slide163Pulse-width modulation - Audio effects and amplification
In more recent times, the Direct Stream Digital sound encoding method was introduced, which uses a generalized form of pulse-width modulation called pulse density modulation, at a high enough sampling rate (typically in the order of MHz) to cover the whole acoustic frequencies range with sufficient fidelity. This method is used in the SACD format, and reproduction of the encoded audio signal is essentially similar to the method used in class-D amplifiers.
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Slide164Pulse-width modulation - Electrical
SPWM (Sine–triangle pulse width modulation) signals are used in micro-inverter design (used in solar or wind power applications)
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Slide165Telecommunications in North America - Modulation
In addition, there are combinations of phase-shift keying and amplitude-shift keying which is called (in the jargon of the field) quadrature amplitude modulation (QAM) that are used in high-capacity digital radio communication systems.
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Slide166Telecommunications in North America - Modulation
In addition, modulation has the advantage of being about to use frequency division multiplexing (FDM).
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Slide167GPS - Demodulation and decoding
If the almanac information has previously been acquired, the receiver picks the satellites to listen for by their PRNs, unique numbers in the range1 through 32
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Slide168Composite video - Signal modulation
Composite video can easily be directed to any broadcast channel simply by modulating the proper RF carrier frequency with it
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Slide169Composite video - Demodulation loss
The process of modulating RF with the original video signal, and then demodulating the original signal again in the TV, introduces several losses
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Slide170Composite video - Demodulation loss
Dot crawl is a defect that results from crosstalk due to the intermodulation of the chrominance and luminance components of the signal
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Slide171CDMA - Steps in CDMA Modulation
CDMA is a spread spectrum multiple access technique
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Slide172CDMA - Steps in CDMA Modulation
Each user in a CDMA system uses a different code to modulate their signal
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Slide173CDMA - Steps in CDMA Modulation
An analogy to the problem of multiple access is a room (channel) in which people wish to talk to each other simultaneously
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Slide174Neuromodulation (medicine)
'Neuromodulation', defined by the International Neuromodulation Society as “the alteration of nerve activity through the delivery of electrical stimulation or chemical agents to targeted sites of the body,” is carried out to normalize – or modulate – nerve function. Neuromodulation can involve a range of electromagnetic stimuli such as a strong magnetic field (repetitive transcranial magnetic stimulation), a very small electric current or, potentially, light (optogenetics).
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Slide175Neuromodulation (medicine)
Neuromodulation, Vol
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Slide176Neuromodulation (medicine) - Spinal cord stimulation
A form of neuromodulation therapy in common use since the 1980s is spinal cord stimulation, a reversible, non-pharmacological therapy for chronic pain management that delivers mild electrical pulses to the spinal cord.Mekhail NA, Cheng J, Narouze S, Kapural L, Mekhail MN, Deer T
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Slide177Neuromodulation (medicine) - Deep brain stimulation
Another commonly used neuromodulation treatment developed in the 1980s is deep brain stimulation, which may be used to help limit symptoms of movement disorder in Parkinson’s disease, dystonia, or essential tremor.Bronstein JM, Tagliati M, Alterman RL, et al. Deep Brain Stimulation for Parkinson Disease: An Expert Consensus and Review of Key Issues. Arch Neurol. 2011;68(2):165. doi:10.1001/archneurol.2010.260.
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Slide178Neuromodulation (medicine) - Other
Neuromodulation: Technology at the Neural Interface, 16: 10–24
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Slide179Neuromodulation (medicine) - Other
Neuromodulation: Technology at the Neural Interface, 16: 349–354
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Slide180Neuromodulation (medicine) - Other
Some types of neuromodulation, and their usual acronyms, are:
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Slide181Neuromodulation (medicine) - Other
* Brain computer interface (BCI, which has been investigated as a type of functional electrical stimulation for patients with tetraplegia)
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Slide182Neuromodulation (medicine) - Other
* Deep brain stimulation (DBS)
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Slide183Neuromodulation (medicine) - Other
* Functional electrical stimulation (FES)
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Slide184Neuromodulation (medicine) - Other
* Intrathecal drug delivery systems (ITDS, which may deliver micro-doses of painkiller or anti-spasm medicine directly to the site of action)
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Slide185Neuromodulation (medicine) - Other
* Occipital nerve stimulation (ONS)
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Slide186Neuromodulation (medicine) - Other
* Peripheral nerve stimulation (PNS, which refers to simulation of nerves beyond the spine or brain, and may be considered to include occipital or sacral nerve stimulation)
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Slide187Neuromodulation (medicine) - Other
* Repetitive transcranial magnetic stimulation (rTMS)
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Slide188Neuromodulation (medicine) - Other
* Sacral nerve stimulation (SNS or SNM for “sacral neuromodulation”)
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Slide189Neuromodulation (medicine) - Other
* Transcranial direct current stimulation (tDCS)
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Slide190Neuromodulation (medicine) - Other
* Vagus nerve stimulation (VNS)
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Slide191Alzheimer's disease research - Gamma secretase modulation
R-flurbiprofen|Tarenflurbil (MPC-7869, formerly R-flubiprofen) is a gamma secretase modulator sometimes called a selective amyloid beta 42 lowering agent. It is believed to reduce the production of the toxic amyloid beta in favor of shorter forms of the peptide.Tarenflurbil:
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Slide192Alzheimer's disease research - Gamma secretase modulation
* Negative results were announced regarding tarenflurbil in July 2008 and further development was canceled.
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Slide193Neural oscillation - Neuromodulation
In addition to fast direct synapse|synaptic interactions between neurons forming a network, oscillatory activity is modulated by neurotransmitters on a much slower time scale
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Slide194Neural oscillation - Asymmetric amplitude modulation
This model implies that slow event-related responses are created as a direct consequence of amplitude modulations in ongoing brain oscillations
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Slide195Chirp - Chirp modulation
Chirp modulation, or linear frequency modulation for digital communication was patented by Sidney Darlington in 1954 with significant later work performed by Winkler in 1962. This type of modulation employs sinusoidal waveforms whose instantaneous frequency increases or decreases linearly over time. These waveforms are commonly referred to as linear chirps or simply chirps.
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Slide196Chirp - Chirp modulation
Hence the rate at which their frequency changes is called the chirp rate. In binary chirp modulation, binary data is transmitted by mapping the bits into chirps of opposite chirp rates. For instance, over one bit period 1 is assigned a chirp with positive rate a and 0 a chirp with negative rate −a. Chirps have been heavily used in radar applications and as a result advanced sources for transmission and matched filters for reception of linear chirps are available.
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Slide197Hologram - Amplitude and phase modulation holograms
A phase hologram is made by changing either the thickness or the refractive index of the material in proportion to the intensity of the holographic interference pattern
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Slide198Neural engineering - Neuromodulation
Neuromodulation (medicine)|Neuromodulation aims to treat disease or injury by employing medical device technologies that would enhance or suppress activity of the nervous system with the delivery of pharmaceutical agents, electrical signals, or other forms of energy stimulus to re-establish balance in impaired regions of the brain
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Slide199Neural engineering - Neuromodulation
Neuromodulation is appealing as treatment for varying defects because it focuses in on treating highly specific regions of the brain only, contrasting that of systemic treatments that can have side effects on the body. Neuromodulator stimulators such as microelectrode arrays can stimulate and record brain function and with further improvements are meant to become adjustable and responsive delivery devices for drugs and other stimuli. (2012a)
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Slide200E85 - Excessive fuel pulse width modulation
Ethanol promoters claim that today's FFV are much too inexact in measuring the ethanol content because car companies will not pay the high patent royalties demanded for fuel content sensors. They state that some FFV have use wastefully high-flow fuel injectors which are not necessary and waste fuel all the time on either fuel. The technical term is excessive fuel pulse width modulation.
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Slide201E85 - Excessive fuel pulse width modulation
Other ethanol advocates also state that it is a mistake to base ethanol engine design on gasoline engine design, but that ethanol engines should be based on diesel engine design parameters instead. Using this approach, the EPA has produced an ethanol-only engine which achieves much higher brake thermal efficiency levels than gasoline engines achieve (Footnote 21).
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Slide202E85 - Excessive fuel pulse width modulation
In contrast, ethanol critics contest the benefits of E85 by focusing on the fact that E85 has 33% less Energy content of biofuel|energy content than 100% gasoline (and 30% less than the E10 gasohol blend that is sold by almost all retailers in the US).[http://www.eia.gov/tools/faqs/faq.cfm?id=27t=4 Frequently Asked Questions: How much ethanol is in gasoline and how does it affect fuel economy?] era.gov Retrieved March 15, 2012 The amount of reduction in mileage, therefore, is highly dependent upon the particulars of the vehicle design, exact composition of the ethanol-gasoline blend, and state of engine tune (primarily Air–fuel ratio|fuel-air mixture and compression ratio)
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Slide203E85 - Excessive fuel pulse width modulation
So in order to save money at the pump with current FFV available in the United States, the price of E85 must be much lower than gasoline. E85 was at least 20% less expensive in most areas, as recently as 2011. However as of March 2012, the difference in the retail price between E85 and gasoline is 15% or less in the vast majority of the United States.
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Slide204E85 - Excessive fuel pulse width modulation
E85 also gets less MPG, at least in FFV. In one test, a Chevy Tahoe FFV averaged 18 MPG [U.S. gallons] for gasoline and 13 MPG for E85, or 28% fewer MPG than gasoline. In that test, the cost of gas averaged $3.42, while the cost for E85 averaged $3.09, or 90% of the cost of gasoline. In another test, however, a fleet of Ford Tauruses averaged only about 6% fewer miles per gallon in the ethanol-based vehicles as compared to traditional, gas-powered Tauruses.
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Slide205Analog signal - Modulation
Another method of conveying an analog signal is to use modulation. In this, some base signal (e.g., a sinusoidal carrier signal) has one of its properties modulated: amplitude modulation involves altering the amplitude of a sinusoidal voltage waveform by the source information, frequency modulation changes the frequency. Other techniques, such as changing the phase (waves)|phase of the base signal also work.
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Slide206Analog signal - Modulation
Analog circuits do not involve Quantization (signal processing)|quantisation of information into digital format. The concept being measured over the circuit, whether sound, light, pressure, temperature, or an exceeded limit, remains from end to end.
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Slide207Analog signal - Modulation
Sources: Parts of an earlier version of this article were originally taken from Federal Standard 1037C in support of MIL-STD-188.
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Slide208Enzymes - Allosteric modulation
Allosteric sites are sites on the enzyme that bind to molecules in the cellular environment. The sites form weak, noncovalent bonds with these molecules, causing a change in the conformation of the enzyme. This change in conformation translates to the active site, which then affects the reaction rate of the enzyme. Allosteric interactions can both inhibit and activate enzymes and are a common way that enzymes are controlled in the body.
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Slide209Pulse-position modulation
'Pulse-position modulation' ('PPM') is a form of signal modulation in which M message bits are encoded by transmitting a single pulse in one of 2^M possible time-shifts. This is repeated every T seconds, such that the transmitted bit rate is M/T bits per second. It is primarily useful for optical communications systems, where there tends to be little or no Multipath propagation|multipath interference.
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Slide210Pulse-position modulation - History
An ancient use of pulse position modulation was the Hydraulic telegraph#Greek hydraulic semaphore system|Greek hydraulic semaphore system invented by Aeneas Stymphalus around 350 B.C
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Slide211Pulse-position modulation - History
In modern times, pulse position modulation has origins in telegraph time-division multiplexing which dates back to 1853, and evolved alongside pulse code modulation and pulse width modulation. In the early 1960s, Don Mathers and Doug Spreng of NASA invented Pulse Position Modulation used in Radio Control (R/C) systems. PPM is currently being used in fiber optic communications, deep space communications, and continues to be used in R/C systems.
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Slide212Pulse-position modulation - Synchronization
Therefore, it is often implemented differentially as differential pulse-position modulation, whereby each pulse position is encoded relative to the previous, such that the receiver must only measure the difference in the arrival time of successive pulses
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Slide213Pulse-position modulation - Sensitivity to multipath interference
Aside from the issues regarding receiver synchronization, the key disadvantage of PPM is that it is inherently sensitive to multipath interference that arises in channels with frequency-selective fading, whereby the receiver's signal contains one or more echoes of each transmitted pulse. Since the information is encoded in the time of arrival (either differentially, or relative to a common clock), the presence
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Slide214Pulse-position modulation - Sensitivity to multipath interference
of one or more echoes can make it extremely difficult, if not impossible, to accurately determine the correct pulse position corresponding to the transmitted pulse.
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Slide215Pulse-position modulation - Sensitivity to multipath interference
Multipath in Pulse Position Modulation systems can be easily mitigated by using the same techniques that are used in Radar systems that rely totally on synchronization and time of arrival of the received pulse to obtain their range position in the presence of echoes.
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Slide216Pulse-position modulation - Non-coherent detection
The only other common M-ary non-coherent modulation technique is Multiple frequency-shift keying|M-ary Frequency Shift Keying (M-FSK), which is the frequency-domain dual to PPM.
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Slide217Pulse-position modulation - PPM vs. M-FSK
PPM and M-FSK systems with the same bandwidth, average power, and transmission rate of M/T bits per second have identical performance in an AWGN (Additive White Gaussian Noise) channel
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Slide218Pulse-position modulation - PPM vs. M-FSK
Optical communications systems (even wireless ones) tend to have weak multipath distortions, and PPM is a viable modulation scheme in many such applications.
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Slide219Pulse-position modulation - Applications for RF communications
Narrowband RF (radio frequency) channels with low power and long wavelengths (i.e., low frequency) are affected primarily by Fading#Flat_versus_frequency-selective_fading|flat fading, and PPM is better suited than M-FSK to be used in these scenarios
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Slide220Pulse-position modulation - Applications for RF communications
(Model aircraft require parts that are as lightweight as possible).
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Slide221Pulse-position modulation - Applications for RF communications
Servomechanism|Servos made for model radio control include some of the electronics required to convert the pulse to the motor position – the receiver is merely required to multiplexing|demultiplex the separate channels and feed the pulses to each servo.
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Slide222Pulse-position modulation - Applications for RF communications
More sophisticated R/C systems are now often based on pulse-code modulation, which is more complex but offers greater flexibility and reliability.
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Slide223Pulse-position modulation - Applications for RF communications
Pulse position modulation is also used for communication to the ISO/IEC 15693 contactless smart card as well as the High frequency|HF implementation of the Electronic Product Code (EPC) Class 1 protocol for RFID tags.
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Slide224Immune modulation
'Immunotherapy' is a medical term defined as the Therapy|treatment of disease by inducing, enhancing, or suppressing an immune response. Immunotherapies designed to elicit or amplify an immune response are classified as 'activation immunotherapies,' while immunotherapies that reduce or suppress are classified as 'Immunosuppression|suppression immunotherapies.'
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Slide225Immune modulation - T-cell adoptive transfer
Adoptive cell transfer uses T cell-based cytotoxic responses to attack cancer cells
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Slide226Immune modulation - T-cell adoptive transfer
Thus far, a 51% objective response rate has been observed; and in some patients, tumors shrank to undetectable size.
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Slide227Immune modulation - T-cell adoptive transfer
The initial studies of adoptive cell transfer using TIL, however, revealed that persistence of the transferred cells in vivo was too short
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Slide228Immune modulation - T-cell adoptive transfer
Clinical trials based on adoptive cell transfer of TILs for patients with metastatic melanoma are currently ongoing at the National Cancer Institute (Bethesda,MD,USA), Moffitt Cancer Center (Tampa,FL,USA), MD Anderson Cancer Center (Houston,TX,USA), Sheba Medical Center (Tel Hashomer,Israel), Herlev University Hospital (Herlev,Denmark) and NKI Antonie van Leeuwenhoek (Amsterdam, Netherlands).
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Slide229Immune modulation - Genetically engineered T cells
Genetically engineered T cells are created by infecting patient's cells with a virus that contain a copy of a T cell receptor (TCR) gene that is specialised to recognise tumour antigens
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Slide230Immune modulation - Genetically engineered T cells
In one case study, United States doctors from the Clinical Research Division, led by Dr
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Slide231Immune modulation - Immune tolerance
Immune tolerance is the process by which the body naturally does not launch an immune system attack on its own tissues
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Slide232Radars - Frequency modulation
This technique can be used in continuous wave radar and is often found in aircraft radar altimeters
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Slide233Radars - Frequency modulation
The Frequency modulation#Modulation index|modulation index riding on the receive signal is proportional to the time delay between the radar and the reflector
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Slide234Metabotropic glutamate receptor - Modulation of other receptors
Metabotropic glutamate receptors are known to act as modulators of (affect the activity of) other receptors. For example, group I mGluRs are known to increase the activity of NMDA receptor|N-methyl-D-aspartate receptors (NMDARs), a type of ion channel-linked receptor that is central in a neurotoxicity|neurotoxic process called excitotoxicity. Proteins called PDZ proteins frequently anchor mGluRs near enough to NMDARs to modulate their activity.
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Slide235Metabotropic glutamate receptor - Modulation of other receptors
It has been suggested that mGluRs may act as regulators of neurons' vulnerability to excitotoxicity (a deadly neurochemical process involving glutamate receptor overactivation) through their modulation of NMDARs, the receptor most involved in that process
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Slide236Metabotropic glutamate receptor - Modulation of other receptors
Group II and III mGluRs tend to protect neurons from excitotoxicity, possibly by reducing the activity of NMDARs.
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Slide237Metabotropic glutamate receptor - Modulation of other receptors
Metabotropic glutamate receptors are also thought to affect dopaminergic and adrenergic neurotransmission.Wang J-Q, Brownell A-L (2007). [http://www.ingentaconnect.com/content/ben/cmir/2007/00000003/00000003/art00006 Development of metabotropic glutamate receptor ligands for neuroimaging.] Current Medical Imaging Reviews '3' (3): 186-205. Retrieved on January 20, 2008.
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Slide238Allosteric modulation
In biochemistry, 'allosteric regulation' is the regulation of an enzyme or other protein by binding an Effector (biology)|effector molecule at the protein's allosteric site (that is, a site other than the protein's active site)
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Slide239Allosteric modulation - Models of allosteric regulation
Most allosteric effects can be explained by the concerted MWC model put forth by Monod, Wyman, and Jean-Pierre Changeux|Changeux,J
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Slide240Allosteric modulation - Concerted model
The concerted model of allostery, also referred to as the symmetry model or MWC model, postulates that enzyme subunits are connected in such a way that a conformational change in one subunit is necessarily conferred to all other subunits
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Slide241Allosteric modulation - Sequential model
The sequential model of allosteric regulation holds that subunits are not connected in such a way that a conformational change in one induces a similar change in the others
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Slide242Allosteric modulation - Sequential model
* subunits need not exist in the same conformation
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Slide243Allosteric modulation - Sequential model
* molecules of substrate bind via induced-fit protocol
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Slide244Allosteric modulation - Sequential model
* conformational changes are not propagated to all subunits
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Slide245Allosteric modulation - Morpheein model
The morpheein model of allosteric regulation is a dissociative concerted model.
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Slide246Allosteric modulation - Morpheein model
A morpheein is a homo-oligomeric structure that can exist as an ensemble of physiologically significant and functionally different alternate quaternary assemblies. Transitions between alternate morpheein assemblies involve oligomer dissociation, conformational change in the dissociated state, and reassembly to a different oligomer. The required oligomer disassembly step differentiates the morpheein model for allosteric regulation from the classic MWC and KNF models.
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Slide247Allosteric modulation - Morpheein model
The discovery of morpheeins has revealed a previously unforeseen mechanism to target universally essential enzymes for species-specific drug design and discovery. A morpheein-based inhibitor would function by binding to and stabilizing the inactive morpheein form of the enzyme, thereby shifting the equilibrium to favor that form.
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Slide248Allosteric modulation - Allosteric database
Allostery is a direct and efficient means for regulation of biological macromolecule function, produced by the binding of a ligand at an allosteric site topographically distinct from the orthosteric site
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Slide249Allosteric modulation - Positive modulation
Positive allosteric modulation (also known as allosteric activation) occurs when the binding of one ligand enhances the attraction between substrate molecules and other binding sites
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Slide250Allosteric modulation - Negative modulation
Negative allosteric modulation (also known as allosteric inhibition) occurs when the binding of one ligand decreases the affinity for substrate at other active sites. For example, when 2,3-bisphosphoglycerate|2,3-BPG binds to an allosteric site on hemoglobin, the affinity for oxygen of all subunits decreases. This is when a regulator is absent from the binding site.
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Slide251Allosteric modulation - Negative modulation
Another example is strychnine, a Seizure|convulsant poison, which acts as an allosteric inhibitor of the glycine receptor
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Slide252Allosteric modulation - Negative modulation
Another instance in which negative allosteric modulation can be seen is between Adenosine triphosphate|ATP and the enzyme Phosphofructokinase within the negative feedback loop that regulates glycolysis
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Slide253Allosteric modulation - Homotropic
A homotropic allosteric modulator is a substrate (biochemistry)|substrate for its target enzyme, as well as a regulatory molecule of the enzyme's activity. It is typically an activator of the enzyme. For example, O2 is a homotropic allosteric modulator of hemoglobin.
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Slide254Allosteric modulation - Heterotropic
A heterotropic allosteric modulator is a regulatory molecule that is not also the enzyme's substrate. It may be either an activator or an inhibitor of the enzyme. For example, H+, CO2, and 2,3-bisphosphoglycerate are heterotropic allosteric modulators of hemoglobin.
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Slide255Allosteric modulation - Heterotropic
Some allosteric proteins can be regulated by both their substrates and other molecules. Such proteins are capable of both homotropic and heterotropic interactions.
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Slide256Allosteric modulation - Non-regulatory allostery
A non-regulatory allosteric site refers to any non-regulatory component of an enzyme (or any protein), that is not itself an amino acid
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Slide257Allosteric modulation - Pharmacology
Allosteric modulation of a receptor results from the binding of allosteric modulators at a different site (a regulatory site) from that of the Ligand (biochemistry)|endogenous ligand (an active site) and enhances or inhibits the effects of the endogenous ligand
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Slide258Allosteric modulation - Pharmacology
For example, the GABAA receptor|GABAA receptor has two active sites that the neurotransmitter gamma-aminobutyric acid (GABA) binds, but also has benzodiazepine and general anaesthetic|general anaesthetic agent regulatory binding sites. These regulatory sites can each produce positive allosteric modulation, Synergy|potentiating the activity of GABA. Diazepam is an agonist at the benzodiazepine regulatory site, and its antidote flumazenil is an antagonist.
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Slide259Allosteric modulation - Pharmacology
More recent examples of drugs that allosterically modulate their targets include the calcium-mimicking cinacalcet and the HIV treatment maraviroc.
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Slide260Allosteric modulation - Allosteric sites as drug targets
Allosteric sites may represent a novel Drug discovery#Targets: New and Established|drug target
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Slide261Gene therapy of the human retina - Modulation of expression
Different methods have been utilized for the expression modulation
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Slide262Amygdala - Memory modulation
The amygdala is also involved in the modulation of memory consolidation
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Slide263Amygdala - Memory modulation
During the consolidation period, the memory can be modulated
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Slide264Amygdala - Memory modulation
The amygdala, especially the basolateral nuclei, are involved in mediating the effects of emotional arousal on the strength of the memory for the event, as shown by many laboratories including that of James McGaugh
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Slide265Amygdala - Memory modulation
Buddhist monks who do metta|compassion meditation have been shown to modulate their amygdala, along with their temporoparietal junction and Insular cortex|insula, during their practice.Cultivating compassion: Neuroscientific and behavioral approaches a talk given by Richard J
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Slide266Amygdala - Memory modulation
Amygdala activity at the time of encoding information correlates with retention for that information
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Slide267Amygdala - Memory modulation
Research using Rorschach test blot 03 finds that the number of unique responses to this random figure links to larger sized amygdalae. The researchers note, Since previous reports have indicated that unique responses were observed at higher frequency in the artistic population than in the nonartistic normal population, this positive correlation suggests that amygdalar enlargement in the normal population might be related to creative mental activity.
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Slide268Intensity modulation
In optical communications, 'intensity modulation' ('IM') is a form of modulation in which the optical Power (physics)|power output of a source is varied in accordance with some characteristic of the modulating Signal (information theory)|signal. The envelope of the modulated optical signal is an analog of the modulating signal in the sense that the instantaneous power of the envelope is an analog of the characteristic of interest in the modulating signal.
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Slide269Intensity modulation
Recovery of the modulating signal is usually by direct detection, not Heterodyne|heterodyning
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Slide270Carrier wave - Carrierless modulation systems
Newer forms of radio communication (such as spread spectrum and ultra-wideband) do not use a conventional sinusoidal carrier wave, nor does Orthogonal frequency-division multiplexing|OFDM (which is used in Digital subscriber line|DSL and in the European standard for High-definition television|HDTV).
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Slide271Carrier wave - Carrierless modulation systems
* Orthogonal frequency-division multiplexing|OFDM may be thought of as an array of symmetrical carrier waves. The rules governing carrier-wave propagation affect OFDM differently than 8VSB.
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Slide272Carrier wave - Carrierless modulation systems
* Some forms of spread spectrum transmission (and most forms of ultra-wideband) are mathematically defined as being devoid of carrier waves. Transmitter implementations typically produce residual carriers which may (or may not) be detectable or transmitted.
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Slide273Brainwave synchronization - Music Modulation and Audio Filtering
Modulating sound is a way to produce brainwave entrainment using something as complex as a musical track. In effect, this is embedding brainwave entrainment into the audio. Any sound can be used, from nature sounds to white noise to a full classical symphony.
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Slide274Brainwave synchronization - Music Modulation and Audio Filtering
Modulation works by rhythmically adjusting a component in the sound. For example, volume modulation would be used to increase and decreases the volume to create the rhythmic stimulus necessary for entrainment to occur.
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Slide275Brainwave synchronization - Music Modulation and Audio Filtering
The problem with modulation (above) is that it can often distort the audio, particularly when used with music or certain nature sounds like rain. Frequency band selection solves this problem by selectively modulating certain parts of an audio file, instead of the whole of it.
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Slide276Brainwave synchronization - Music Modulation and Audio Filtering
The brainwave entrainment is embedded into a lower frequency range only– affecting parts of the bass, but leaving the mid and treble alone. Frequency band selection can be used to affect only one part of a sound file. Multiple frequency bands can also be selected.
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Slide277Brainwave synchronization - Music Modulation and Audio Filtering
Frequency band selection is an important advancement, allowing entrainment to be embedded into any sound file with virtually no negative effect on the existing audio. Because it allows for much higher intensity levels, the effectiveness of the session is actually increased.
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Slide278Modulating retro-reflector - Inherent Maximum Modulation Rate vs. Aperture Size
The fundamental limit in the switching speed of the modulator is the resistance-capacitance limit. A key trade is area of the modulator vs. area of the clear aperture. If the modulator area is small, the capacitance is small, hence the modulation rate can be faster. However, for longer application ranges on the order of several hundred meters, larger apertures are needed to close the link. For a given modulator, the speed of the shutter scales inversely as the square of the modulator diameter.
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Slide279Therapeutic gene modulation
'Therapeutic gene modulation' refers to the practice of altering the Gene expression|expression of a gene at one of various stages, with a view to alleviate some form of ailment. It differs from gene therapy in that gene modulation seeks to alter the expression of an endogenous gene (perhaps through the introduction of a gene encoding a novel modulatory protein) whereas gene therapy concerns the introduction of a gene whose product aids the recipient directly.
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Slide280Therapeutic gene modulation
Modulation of gene expression can be mediated at the level of Transcription (genetics)|transcription by DNA-binding agents (which may be artificial transcription factors), small molecules, or Oligonucleotide synthesis|synthetic oligonucleotides. It may also be mediated post-transcriptionally through RNA interference.
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Slide281Therapeutic gene modulation - Transcriptional gene modulation
An approach to therapeutic modulation utilizes agents that modulate endogenous transcription by specifically targeting those genes at the Genome|gDNA level. The advantage to this approach over modulation at the mRNA or protein level is that every cell contains only a single gDNA copy. Thus the target copy number is significantly lower allowing the drugs to theoretically be administered at much lower doses.
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Slide282Therapeutic gene modulation - Transcriptional gene modulation
This is not anticipated to be a problem for transcriptional modulation as it acts on endogenous DNA.
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Slide283Therapeutic gene modulation - Transcriptional gene modulation
There are three major categories of agents that act as transcriptional gene modulators: triplex-forming oligonucleotides (TFOs), synthetic polyamides (SPAs), and DNA-binding protein|DNA binding proteins.
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Slide284Therapeutic gene modulation - What are they
Triplex-forming oligonucleotides (TFO) are one potential method to achieve therapeutic gene modulation. TFOs are approximately 10-40 base pairs long and can bind in the DNA|major groove in duplex DNA which creates a third strand or a triple helix. The binding occurs at polypurine or polypyrimidine regions via Hoogsteen hydrogen bonds to the purine (A / G) bases on the double stranded DNA that is already in the form of the Nucleic acid double helix|Watson-Crick helix.
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Slide285Therapeutic gene modulation - How they work
TFOs can be either polypurine or polypyrimidine molecules and bind to one of the two strands in the double helix in either parallel or Antiparallel (biochemistry)|antiparallel orientation to target polypurine or polypyrimidine regions
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Slide286Therapeutic gene modulation - Complications and limitations
In order for TFO motifs to bind in a parallel fashion and create hydrogen bonds, the nitrogen atom at position 3 on the cytosine residue needs to be Protonation|protonated, but at pH|physiological pH levels it is not, which could prevent parallel binding.
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Slide287Therapeutic gene modulation - Complications and limitations
Another limitation is that TFOs can only bind to purine-rich target strands and this would limit the choice of Endogeny|endogenous gene target sites to polypurine-polypyrimidine stretches in duplex DNA
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Slide288Therapeutic gene modulation - Complications and limitations
Other limitations include concerns regarding Ligand (biochemistry)|binding affinity and specifity, in vivo stability, and uptake into cells
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Slide289Therapeutic gene modulation - What can they do
Scientists are still refining the technology to turn TFOs into a Therapeutic effect|therapeutic product and much of this revolves around their potential applications in antigene therapy
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Slide290Therapeutic gene modulation - What can they do
In model systems TFOs can inhibit gene expression at the DNA level as well as induce targeted mutagenesis in the model. TFO-induced inhibition of transcription elongation on endogenous targets have been tested on cell cultures with success. However, despite much in vitro success, there has been limited achievement in cellular applications potentially due to target accessibility.
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Slide291Therapeutic gene modulation - What can they do
TFOs have the potential to silence Gene silencing|silence gene by targeting transcription initiation or elongation, arresting at the triplex binding sites, or introducing permanent changes in a target sequence via stimulating a cell's inherent repair pathways
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Slide292Therapeutic gene modulation - Synthetic polyamides
Synthetic polyamides are a set of small molecules that form specific hydrogen bonds to the DNA#Grooves|minor groove of DNA. They can exert an effect either directly, by binding a regulatory region or transcribed region of a gene to modify transcription, or indirectly, by designed conjugation with another agent that makes alterations around the DNA target site.
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Slide293Slow-scan television - Modulation
SSTV uses analogue frequency modulation, in which every different value of brightness in the image gets a different audio frequency. In other words, the signal frequency shifts up or down to designate brighter or darker pixels, respectively. Color is achieved by sending the brightness of each color component (usually red, green and blue) separately. This signal can be fed into an single-sideband modulation|SSB transmitter, which in part modulates the carrier wave.
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Slide294Slow-scan television - Modulation
There are a number of different modes of transmission, but the most common ones are Martin M1 (popular in Europe) and Scottie S1 (used mostly in the USA). Using one of these, an image transfer takes 114 (M1) or 110 (S1) seconds. Some black and white modes take only 8 seconds to transfer an image.
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Slide295Edge network - EDGE modulation and coding scheme (MCS)
The channel encoding process in GPRS as well as EGPRS/EDGE consists of two steps: first, a cyclic code is used to add parity bits, which are also referred to as the Block Check Sequence, followed by coding with a possibly punctured convolutional code
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Slide296Edge network - EDGE modulation and coding scheme (MCS)
In all EGPRS Modulation and Coding Schemes, a convolutional code of rate 1/3 is used, and puncturing is used to achieve the desired code rate
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Slide297Télé Distribution Française - Phase modulation pattern
Since the phase is the integral of the frequency, this triangular phase modulation corresponds to a square frequency modulation with a deviation of about 6Hz.
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Slide298Télé Distribution Française - Phase modulation pattern
Both the average phase and the average frequency deviation are thus zero. Additional non-timing data is sent by phase modulation during the rest of each second. But the second marker (and data bit) is always preceded by 100 ms without any phase modulation. The signal is not phase-modulated at all during the 59th second past the minute.
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Slide299Human voice - Voice modulation in spoken language
Human spoken language makes use of the ability of almost all persons in a given society to dynamically modulate certain parameters of the laryngeal voice source in a consistent manner
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Slide300Human voice - Voice modulation in spoken language
The ability to vary the ab/adduction of the vocal folds quickly has a strong genetic component, since vocal fold adduction has a life-preserving function in keeping food from passing into the lungs, in addition to the covering action of the epiglottis
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Slide301Human voice - Voice modulation in spoken language
If an abductory movement or adductory movement is strong enough, the vibrations of the vocal folds will stop (or not start)
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Slide302Human voice - Voice modulation in spoken language
An adductory gesture is also identified by the change in voice spectral energy it produces. Thus, a speech sound having an adductory gesture may be referred to as a glottal stop even if the vocal fold vibrations do not entirely stop.
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Slide303Human voice - Voice modulation in spoken language
Other aspects of the voice, such as variations in the regularity of vibration, are also used for communication, and are important for the trained voice user to master, but are more rarely used in the formal phonetic code of a spoken language.
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Slide304Modulation and Coding Scheme
For example, Enhanced Data Rates for GSM Evolution|EDGE uses a rate adaptation algorithm that adapts the modulation and coding scheme (MCS) according to the quality of the radio channel, and thus the bit rate and robustness of data transmission
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Slide305Modulation and Coding Scheme
Especially over fading channels which model wireless propagation environments, adaptive modulation systems exhibit great performance enhancements compared to systems that do not exploit channel knowledge at the transmitter.
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Slide306Modulation and Coding Scheme - Example
* Choice of modulation type -- the link can employ QPSK for noisy channels and Quadrature amplitude modulation|16QAM for clearer channels. The former is more robust and can tolerate higher levels of interference but has lower transmission bit rate. The latter has twice higher bit rate but is more prone to errors due to interference and noise hence it requires stronger forward error correction (FEC) coding which in turn means more redundant bits and lower information bit rate;
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Slide307Modulation and Coding Scheme - Example
* Choice of FEC code rate -- the FEC code used has a rate of 1/3, but it can be varied effectively by bit puncturing and hybrid automatic repeat request (HARQ) with incremental redundancy
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Slide308Modulation and Coding Scheme - Example
Thus HSDPA adapts to achieve very high bit rates, of the order of 14 megabit/sec, on clear channels using 16-QAM and close to 1/1 coding rate. On noisy channels HSDPA adapts to provide reliable communications using QPSK and 1/3 coding rate but the information bit rate drops to about 2.4 megabit/sec. This adaptation is performed up to 500 times per second.
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Slide309WWVB - Modulation format
WWVB transmits binary data at 1 bit per second, using 60 seconds to encode the current time of day and date within a century.
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Slide310WWVB - Modulation format
There are two independent time codes used for this purpose: An amplitude-modulated time code, which has been in use with minor changes since 1962, and a phase-modulated time code added in late 2012.
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Slide311WWVB - Amplitude modulation
The amplitude modulated code reduces the transmitter power at the beginning of each UTC second, and restores it to full power some time during the second. The duration of the reduced carrier power encodes one trinary digit (having value of zero, one, or marker) per second.
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Slide312WWVB - Amplitude modulation
* If the period of reduced power is four-fifths of a second (0.8s), this indicates a marker.
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Slide313WWVB - Amplitude modulation
* If the period of reduced power is one-fifth of a second (0.2s), this indicates a data bit with value zero or not set.
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Slide314WWVB - Amplitude modulation
* If the period of reduced power is one-half of a second (0.5s), this indicates a data bit with value one or set.
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Slide315WWVB - Amplitude modulation
Each minute, seven markers are transmitted in a regular pattern. The other 53 seconds are filled with data bits which encode the current time.
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Slide316WWVB - Modulation depth
At the start of each UTC second, the WWVB 60kHz carrier, which has a normal ERP of 70 kW, is reduced in power by 17 Decibel|dB (to 1.4kW). Before July 12, 2005, when WWVB's maximum ERP was 50kW, the power reduction was 10 dB, resulting in a 5kW signal. This change in modulation depth was part of a series of experiments to increase coverage without increasing transmitter power.
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Slide317WWVB - Phase modulation
An independent time code is transmitted by Phase-shift keying#Binary phase-shift keying (BPSK)|binary phase-shift keying of the WWVB carrier. A 1bit is encoded by inverting the phase (a 180° phase shift) of the last 0.9 seconds of each UTC second. A 0bit is encoded with no phase shift.
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Slide318WWVB - Phase modulation
The use of phase-shift keying allows a more sophisticated (but still very simple by modern electronics standards) receiver to distinguish 0 and 1 bits far more clearly, allowing improved reception on the East Coast of the United States where the WWVB signal level is weak, radio frequency noise is high, and the MSF time signal from the U.K. also interferes sometimes.
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Slide319WWVB - Phase modulation
Because the amplitude-modulated marker bits only provide 0.2s of full-strength carrier, they are more difficult to receive reliably, and the phase modulation time code avoids using them for important information.
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Slide320Cable television headend - Modulation
Cable television signals are then mixed in accordance with the cable system's channel numbering scheme using a series of cable modulators (one for each channel), which is in turn fed into a frequency multiplexer or signal combiner. The mixed signals are sent into a broadband amplifier, then sent into the cable system by the trunk line and continuously re-amplified as needed.
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Slide321Cable television headend - Modulation
Modulators essentially take an input signal and attach it to a specific frequency. For example in North America, NTSC standards dictate that CH2 is a 6MHz wide channel with its luminance carrier at 55.25MHz, so the modulator for channel 2 will impose the appropriate input signal on to the 55.25MHz frequency to be received by any TV tuned to Channel 2.
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Slide322Cable television headend - Modulation
Using QAM (Quadrature Amplitude Modulation), a CATV operator can place usually up to eight channels on one specific frequency so channel 2 may actually be carrying channels 1 - 58 in a viewer's city
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Slide323GPS signals - Demodulation and decoding
This is done by assigning each satellite a unique binary sequence known as a Gold code, and the signals are decoded, after demodulation, using modulo 2 addition of the Gold codes corresponding to satellites n1 through nk, where k is the number of channels in the GPS receiver and n1 through nk are the PRN identifiers of the satellites
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Slide324GPS signals - Demodulation and decoding
There are 1,025 different Gold codes of length 1,023 bits, but only 32 are used. These Gold codes are quite often referred to as pseudo random noise since they contain no data and are said to look like random sequences.[http://www.kowoma.de/en/gps/signals.htm GPS - explained (Signals)] However, this may be misleading since they are actually deterministic sequences.
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Slide325GPS signals - Demodulation and decoding
If the almanac information has previously been acquired, the receiver picks which satellites to listen for by their PRNs
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Slide326GPS signals - Demodulation and decoding
The receiver uses the C/A Gold code with the same PRN number as the satellite to compute an offset, O, that generates the best correlation
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Slide327GPS signals - Demodulation and decoding
Since the carrier frequency received can vary due to Doppler effect|Doppler shift, the points where received PRN sequences begin may not differ from O by an exact integral number of milliseconds
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Slide328GPS signals - Demodulation and decoding
As the receiver continues to read successive PRN sequences, it will encounter a sudden change in the phase of the 1,023 bit received PRN signal
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Slide329GPS signals - Demodulation and decoding
After a subframe has been read and interpreted, the time the next subframe was sent can be calculated through the use of the clock correction data and the HOW
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Slide330GPS signals - Demodulation and decoding
Then the orbital position data, or ephemeris, from the navigation message is used to calculate precisely where the satellite was at the start of the message. A more sensitive receiver will potentially acquire the ephemeris data more quickly than a less sensitive receiver, especially in a noisy environment.
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Slide331DCF77 - Amplitude modulation
The DCF77 signal uses amplitude-shift keying to transmit digitally coded time information by reducing the amplitude of the carrier to 15% of normal (−16½decibel|dB) for 0.1 or 0.2 seconds at the beginning of each second. A 0.1 second reduction (7750 cycles of the 77500Hz carrier amplitude) denotes a binary 0; a 0.2 second reduction denotes a binary 1. As a special case, the last second of every minute is marked with no carrier power reduction.
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Slide332DCF77 - Amplitude modulation
There was also a morse code station identification until 2006, sent during minutes 19, 39 and 59 of each hour, however this was discontinued as the station is easily identifiable by the characteristic signal. A 250Hz tone was generated by square wave modulating the carrier between 100% and 85% power, and that tone was used to send one letter per second, between the second marks. During seconds 20–32, the call sign DCF77 was transmitted twice.
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Slide333ATSC tuner - Demodulation
It is separation of a standard baseband signal from the RF carrier that was used to transmit it through the air (or down a coaxial cable or other long-distance medium.) ATSC as implemented in the US uses 8VSB modulation, which requires less power to transmit, as opposed to the also proposed COFDM modulation (used in European DVB-T, which is less prone to multipath interference|multipath distortion and therefore better received in mobile installations).
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Slide334Broadcast television systems - Modulation
Given all of these parameters, the result is a mostly-continuous analog signal which can be modulated onto a radio-frequency carrier and transmitted through an antenna. All analog television systems use vestigial sideband modulation, a form of amplitude modulation in which one sideband is partially removed. This reduces the bandwidth of the transmitted signal, enabling narrower channels to be used.
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Slide335Modulational instability
In the fields of nonlinear optics and fluid dynamics, 'modulational instability' or 'sideband instability' is a phenomenon whereby deviations from a periodic waveform are reinforced by nonlinearity, leading to the generation of Frequency spectrum|spectral-sidebands and the eventual breakup of the waveform into a train of wave packet|pulses. Concluded with a discussion by Klaus Hasselmann.
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Slide336Modulational instability
The phenomenon was first discovered − and modelled − for periodic surface gravity waves (Stokes waves) on deep water by T. Brooke Benjamin and Jim E. Feir, in 1967. Therefore, it is also known as the 'Benjamin−Feir instability'. It is a possible mechanism for the generation of rogue waves.
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Slide337Modulational instability - Initial instability and gain
Modulation instability only happens under certain circumstances. The most important condition is anomalous group velocity dispersion relation|dispersion, whereby pulses with shorter wavelengths travel with higher group velocity than pulses with longer wavelength. (This condition assumes a focussing Kerr nonlinearity, whereby refractive index increases with optical intensity.) There is also a threshold power, below which no instability will be seen.
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Slide338Modulational instability - Initial instability and gain
The instability is strongly dependent on the frequency of the perturbation
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Slide339Modulational instability - Initial instability and gain
The tendency of a perturbing signal to grow makes modulation instability a form of amplifier|amplification. By tuning an input signal to a peak of the gain spectrum, it is possible to create an optical amplifier.
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Slide340Modulational instability - Mathematical derivation of gain spectrum
The gain spectrum can be derived by starting with a model of modulation instability based upon the Nonlinear Schrödinger equation
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Slide341Modulational instability - Mathematical derivation of gain spectrum
which describes the evolution of a Slowly varying envelope approximation|slowly varying envelope A with time t and distance of propagation z. The model includes group velocity dispersion described by the parameter \beta_2, and Kerr nonlinearity with magnitude \gamma. A waveform of constant power P is assumed. This is given by the solution
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Slide342Modulational instability - Mathematical derivation of gain spectrum
where the oscillatory e^ phase factor accounts for the difference between the linear refractive index, and the modified refractive index, as raised by the Kerr effect. The beginning of instability can be investigated by perturbing this solution as
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Slide343Modulational instability - Mathematical derivation of gain spectrum
where \epsilon\left(t,z\right) is the perturbation term (which, for mathematical convenience, has been multiplied by the same phase factor as A). Substituting this back into the Nonlinear Schrödinger equation gives a perturbation theory|perturbation equation of the form
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Slide344Modulational instability - Mathematical derivation of gain spectrum
where the perturbation has been assumed to be small, such that \epsilon^2\approx 0. Instability can now be discovered by searching for solutions of the perturbation equation which grow exponentially. This can be done using a trial function of the general form
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Slide345Modulational instability - Mathematical derivation of gain spectrum
where \omega_m and k_m are the frequency and wavenumber of a perturbation, and c_1 and c_2 are constants
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Slide346Modulational instability - Mathematical derivation of gain spectrum
This dispersion relation is vitally dependent on the sign of the term within the square root, as if positive, the wavenumber will be real number|real, corresponding to mere oscillations around the unperturbed solution, whilst if negative, the wavenumber will become imaginary number|imaginary, corresponding to exponential growth and thus instability. Therefore, instability will occur when
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Slide347Modulational instability - Mathematical derivation of gain spectrum
where as noted above, \omega_m is the difference between the frequency of the perturbation and the frequency of the initial light.
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Slide348Modulational instability - Breakup
The waveform will eventually break up into a train of pulses.
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Slide349576i - Modulation for TVRO transmission
576i when it is transmitted over Television receive-only|free-to-air satellite signals is transmitted substantially differently from terrestrial transmission.
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Slide350576i - Modulation for TVRO transmission
* Luma signal is FM modulated, but with a 50Hz dithering signal to spread out energy over the transponder
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Slide351576i - Modulation for TVRO transmission
* Chroma is phase modulated
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Slide352576i - Modulation for TVRO transmission
* An FM subcarrier of 4.50, 5.50, 6.0, 6.50 or 6.65MHz is added for mono sound
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Slide353576i - Modulation for TVRO transmission
* Other FM subcarriers (usually 7.02, 7.20, 7.38, 7.56, 7.74 and 7.92MHz) are added for a true stereo service and can also carry multi-lingual sound and radio services. These additional subcarriers are normally narrower bandwidth than the main mono subcarrier and are companded using Panda 1 or similar to preserve the signal to noise ratio
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Slide354576i - Modulation for TVRO transmission
* Data subcarriers may also be added
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Slide355576i - Modulation for TVRO transmission
* All of the above is done, but signal is bandwidth limited to 18MHz
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Slide356576i - Modulation for TVRO transmission
* The bandwidth limiting does not affect audio subcarriers
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Slide357Photonics - Modulation
Modulation of a light source is used to encode information on a light source. Modulation can be achieved by the light source directly. One of the simplest examples is to use a flashlight to send Morse code. Another method is to take the light from a light source and modulate it in an external optical modulator.
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Slide358Photonics - Modulation
An additional topic covered by modulation research is the modulation format. On-off keying has been the commonly used modulation format in optical communications. In the last years more advanced modulation formats like phase-shift keying or even orthogonal frequency-division multiplexing have been investigated to counteract effects like dispersion (optics)|dispersion that degrade the quality of the transmitted signal.
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Slide359Self phase modulation
'Self-phase modulation' (SPM) is a Nonlinear optics|nonlinear optical effect of light-matter interaction.
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Slide360Self phase modulation
An ultrashort pulse of light, when travelling in a medium, will induce a varying refractive index of the medium due to the optical Kerr effect. This variation in refractive index will produce a phase (waves)|phase shift in the pulse, leading to a change of the pulse's frequency spectrum.
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Slide361Self phase modulation
Self-phase modulation is an important effect in optics|optical systems that use short, intense pulses of light, such as lasers and optical fiber|optical fibre communications systems.
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Slide362Self phase modulation - Theory
For an ultrashort pulse with a Gaussian shape and constant phase, the intensity at time t is given by I(t):
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Slide363Self phase modulation - Theory
where I0 is the peak intensity, and τ is half the pulse duration.
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Slide364Self phase modulation - Theory
If the pulse is travelling in a medium, the optical Kerr effect produces a refractive index change with intensity:
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Slide365Self phase modulation - Theory
where n0 is the linear refractive index, and n2 is the second-order nonlinear refractive index of the medium.
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Slide366Self phase modulation - Theory
As the pulse propagates, the intensity at any one point in the medium rises and then falls as the pulse goes past. This will produce a time-varying refractive index:
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Slide367Self phase modulation - Theory
This variation in refractive index produces a shift in the instantaneous phase of the pulse:
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Slide368Self phase modulation - Theory
where \omega_0 and \lambda_0 are the carrier frequency and (vacuum) wavelength of the pulse, and L is the distance the pulse has propagated.
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Slide369Self phase modulation - Theory
The phase shift results in a frequency shift of the pulse. The instantaneous frequency ω(t) is given by:
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Slide370Self phase modulation - Theory
and from the equation for dn/dt above, this is:
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Slide371Self phase modulation - Theory
Plotting ω(t) shows the frequency shift of each part of the pulse. The leading edge shifts to lower frequencies (redder wavelengths), trailing edge to higher frequencies (bluer) and the very peak of the pulse is not shifted. For the centre portion of the pulse (between t = ±τ/2), there is an approximately linear frequency shift (chirp) given by:
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Slide372Self phase modulation - Theory
It is clear that the extra frequencies generated through SPM broaden the frequency spectrum of the pulse symmetrically
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Slide373Self phase modulation - Theory
A similar analysis can be carried out for any pulse shape, such as the Hyperbolic function|hyperbolic secant-squared (sech2) pulse profile generated by most ultrashort pulse lasers.
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Slide374Self phase modulation - Theory
If the pulse is of sufficient intensity, the spectral broadening process of SPM can balance with the temporal compression due to anomalous dispersion and reach an equilibrium state. The resulting pulse is called an optical soliton.
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Slide375Self phase modulation - Applications of SPM
Self-phase modulation has stimulated many applications in the field of ultrashort pulse including to cite a few:
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Slide376Self phase modulation - Applications of SPM
* spectral broadening and supercontinuum
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Slide377Self phase modulation - Applications of SPM
* temporal pulse compression
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Slide378Self phase modulation - Applications of SPM
* spectral pulse compression
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Slide379Self phase modulation - Applications of SPM
The nonlinear properties of Kerr nonlinearity has also been beneficial for various optical pulse processing techniques such as optical regeneration or wavelength conversion.
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Slide380Self phase modulation - Mitigation strategies in DWDM systems
In long-haul single-channel and DWDM systems SPM is one of the most important reach limiting nonlinear effects. It can be reduced by:
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Slide381Self phase modulation - Mitigation strategies in DWDM systems
* Dispersion management, because dispersion can partly mitigate the SPM effect
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Slide382FM broadcasting - Modulation
Frequency modulation is a form of modulation which conveys information over a carrier wave by varying its frequency (contrast this with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant). In analog applications, the instantaneous frequency of the carrier is directly proportional to the instantaneous value of the input signal. This form of modulation is commonly used in the FM broadcast band.
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Slide383Laser video projector - Laser signal modulation
The video Signalling (telecommunication)|signal is introduced to the laser beam by an acousto-optic modulator (AOM) that uses a photorefractive effect|photorefractive crystal to separate the beam at distinct diffraction angles. The beam must enter the crystal at the specific Bragg diffraction|Bragg angle of that AOM crystal. A piezoelectric element transforms the video signal into vibrations in the crystal to create an image
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Slide384Digital Audio Broadcasting - Modulation
Immunity to fading and inter-symbol interference (caused by multipath propagation) is achieved without equalization by means of the OFDM and DQPSK modulation techniques. For details, see the OFDM system comparison table.
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Slide385Digital Audio Broadcasting - Modulation
Using values for the most commonly used transmission mode on DAB, Transmission Mode I (TM I), the OFDM modulation consists of 1,536 subcarriers that are transmitted in parallel
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Slide386Shortwave radio - Types of modulation
Several different types of modulation are used to impress information on a short-wave transmission.
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Slide387Shortwave radio - Types of modulation
Amplitude modulation is the simplest type and the most commonly used for shortwave broadcasting. The instantaneous amplitude of the carrier is controlled by the amplitude of the signal (speech, or music, for example). At the receiver, a simple detector (radio)|detector recovers the desired modulation signal from the carrier.
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Slide388Shortwave radio - Types of modulation
Single sideband transmission is a form of amplitude modulation but in effect filters the result of modulation
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Slide389Shortwave radio - Types of modulation
Vestigal sideband transmits the carrier and one complete side-band, but filters out the redundant side-band. It is a compromise between AM and SSB, allowing simple receivers to be used but requiring almost as much transmitter power as AM. One advantage is that only half the bandwidth of an AM signal is used. It can be heard in the transmission of certain radio time signal stations.
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Slide390Shortwave radio - Types of modulation
Continuous wave (CW) is on-and-off keying of a carrier, used only for Morse code communications.
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Slide391Shortwave radio - Types of modulation
Regulations limit the Bandwidth (signal processing)|bandwidth of a signal transmitted in the HF bands, and the advantages of frequency modulation are greatest if the FM signal is allowed to have a wider bandwidth
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Slide392Shortwave radio - Types of modulation
Digital Radio Mondiale (DRM) is a digital modulation for use on bands below 30MHz.
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Slide393Shortwave radio - Types of modulation
Radioteletype, fax, digital, slow-scan television and other systems use forms of frequency-shift keying or audio subcarriers on a shortwave carrier. These generally require special equipment to decode, such as software on a computer equipped with a sound card.
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Slide394Medtronic - Neuromodulation (medicine)|Neuromodulation
Products include neurostimulation systems and implantable drug delivery systems for chronic pain, common movement disorders, and urologic and gastrointestinal disorders.
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Slide395Modulator - Analog modulation methods
In analogue signal|analog modulation, the modulation is applied continuously in response to the analog information signal. Common analog modulation techniques are:
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Slide396Modulator - Analog modulation methods
*Amplitude modulation (AM) (here the amplitude of the carrier signal is varied in accordance to the instantaneous amplitude of the modulating signal)
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Slide397Modulator - Analog modulation methods
**Double-sideband modulation (DSB)
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Slide398Modulator - Analog modulation methods
***Double-sideband modulation with carrier (DSB-WC) (used on the AM radio broadcasting band)
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Slide399Modulator - Analog modulation methods
***Double-sideband suppressed-carrier transmission (DSB-SC)
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Slide400Modulator - Analog modulation methods
***Double-sideband reduced carrier transmission (DSB-RC)
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Slide401Modulator - Analog modulation methods
**Single-sideband modulation (SSB, or SSB-AM)
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Slide402Modulator - Analog modulation methods
***SSB suppressed carrier modulation (SSB-SC)
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Slide403Modulator - Analog modulation methods
**Vestigial sideband modulation (VSB, or VSB-AM)
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Slide404Modulator - Analog modulation methods
**Quadrature amplitude modulation (QAM)
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Slide405Modulator - Analog modulation methods
*Angle modulation, which is approximately constant envelope
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Slide406Modulator - Analog modulation methods
**Frequency modulation (FM) (here the frequency of the carrier signal is varied in accordance to the instantaneous amplitude of the modulating signal)
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Slide407Modulator - Analog modulation methods
**Phase modulation (PM) (here the phase shift of the carrier signal is varied in accordance with the instantaneous amplitude of the modulating signal)
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Slide408Modulator - Digital modulation methods
In Digital data|digital modulation, an analog carrier signal is modulated by a discrete signal. Digital modulation methods can be considered as digital-to-analog conversion, and the corresponding demodulation or detection as analog-to-digital conversion. The changes in the carrier signal are chosen from a finite number of M alternative symbols (the modulation alphabet).
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Slide409Modulator - Digital modulation methods
'A simple example:' A telephone line is designed for transferring audible sounds, for example tones, and not digital bits (zeros and ones)
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Slide410Modulator - Fundamental digital modulation methods
* Phase-shift keying|PSK (phase-shift keying): a finite number of phases are used.
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Slide411Modulator - Fundamental digital modulation methods
* Frequency-shift keying|FSK (frequency-shift keying): a finite number of frequencies are used.
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Slide412Modulator - Fundamental digital modulation methods
* Amplitude-shift keying|ASK (amplitude-shift keying): a finite number of amplitudes are used.
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Slide413Modulator - Fundamental digital modulation methods
* Quadrature amplitude modulation|QAM (quadrature amplitude modulation): a finite number of at least two phases and at least two amplitudes are used.
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Slide414Modulator - Fundamental digital modulation methods
In all of the above methods, each of these phases, frequencies or amplitudes are assigned a unique pattern of Binary numeral system|binary bits. Usually, each phase, frequency or amplitude encodes an equal number of bits. This number of bits comprises the symbol that is represented by the particular phase, frequency or amplitude.
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Slide415Modulator - Fundamental digital modulation methods
If the alphabet consists of M = 2^N alternative symbols, each symbol represents a message consisting of N bits. If the symbol rate (also known as the Baud|baud rate) is f_ symbols/second (or baud), the data rate is N f_ bit/second.
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Slide416Modulator - List of common digital modulation techniques
**Quadrature PSK (QPSK), using M=4 symbols
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Slide417Modulator - List of common digital modulation techniques
**Audio frequency-shift keying (AFSK)
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Slide418Modulator - List of common digital modulation techniques
**Multi-frequency shift keying (M-ary FSK or MFSK)
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Slide419Modulator - List of common digital modulation techniques
**Dual-tone multi-frequency (DTMF)
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Slide420Modulator - List of common digital modulation techniques
**M-ary vestigial sideband modulation, for example 8VSB
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Slide421Modulator - List of common digital modulation techniques
**Polar modulation like QAM a combination of PSK and ASK.
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Slide422Modulator - List of common digital modulation techniques
*Continuous phase modulation (CPM) methods:
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Slide423Modulator - List of common digital modulation techniques
**Continuous-phase frequency-shift keying (CPFSK)
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Slide424Modulator - List of common digital modulation techniques
*Orthogonal frequency-division multiplexing (OFDM) modulation:
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Slide425Modulator - List of common digital modulation techniques
** Discrete multitone modulation|discrete multitone (DMT) - including adaptive modulation and bit-loading.
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Slide426Modulator - List of common digital modulation techniques
*Wavelet modulation
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Slide427Modulator - List of common digital modulation techniques
*Trellis coded modulation (TCM), also known as trellis modulation
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Slide428Modulator - List of common digital modulation techniques
** Chirp spread spectrum (CSS) according to IEEE 802.15.4a CSS uses pseudo-stochastic coding
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Slide429Modulator - List of common digital modulation techniques
** Frequency-hopping spread spectrum (FHSS) applies a special scheme for channel release
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Slide430Modulator - List of common digital modulation techniques
** [http://www.on4nb.be/sim31.htm#English SIM31] (SIM) New digital Mode SIM31 SIM63 tks SWL Tunisian
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Slide431Modulator - List of common digital modulation techniques
Minimum-shift keying|MSK and GMSK are particular cases of continuous phase modulation. Indeed, MSK is a particular case of the sub-family of CPM known as continuous-phase frequency-shift keying (CPFSK) which is defined by a rectangular frequency pulse (i.e. a linearly increasing phase pulse) of one symbol-time duration (total response signaling).
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Slide432Modulator - List of common digital modulation techniques
OFDM is considered as a modulation technique rather than a multiplex technique, since it transfers one bit stream over one communication channel using one sequence of so-called OFDM symbols
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Slide433Modulator - List of common digital modulation techniques
Nevertheless, even though switching amplifiers are completely unsuitable for normal QAM constellations, often the QAM modulation principle are used to drive switching amplifiers with these FM and other waveforms, and sometimes QAM demodulators are used to receive the signals put out by these switching amplifiers.
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Slide434Modulator - Digital baseband modulation or line coding
The term 'digital baseband modulation' (or digital baseband transmission) is synonymous to line codes. These are methods to transfer a digital bit stream over an analog baseband channel (a.k.a. lowpass channel) using a pulse train, i.e. a discrete number of signal levels, by directly modulating the voltage or current on a cable. Common examples are unipolar encoding|unipolar, non-return-to-zero (NRZ), Manchester coding|Manchester and alternate mark inversion (AMI) codings.
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Slide435Modulator - Pulse modulation methods
These are not modulation schemes in the conventional sense since they are not channel coding schemes, but should be considered as source coding schemes, and in some cases analog-to-digital conversion techniques.
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Slide436Modulator - Pulse modulation methods
* Pulse-amplitude modulation (PAM)
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Slide437Modulator - Pulse modulation methods
* Pulse-width modulation (PWM) AND Pulse-depth modulation (PDM)
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Slide438Modulator - Pulse modulation methods
* Pulse-position modulation (PPM)
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Slide439Modulator - Pulse modulation methods
* Pulse-code modulation (PCM)
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Slide440Modulator - Pulse modulation methods
* Delta modulation (DM or Δ-modulation)
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Slide441Modulator - Pulse modulation methods
* Delta-sigma modulation (∑Δ)
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Slide442Modulator - Pulse modulation methods
* Continuously variable slope delta modulation (CVSDM), also called Adaptive-delta modulation (ADM)
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Slide443Modulator - Pulse modulation methods
* Pulse-density modulation (PDM)
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Slide444Modulator - Miscellaneous modulation techniques
* The use of on-off keying to transmit Morse code at radio frequency|radio frequencies is known as continuous wave (CW) operation.
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Slide445Modulator - Miscellaneous modulation techniques
* Adaptive modulation
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Slide446Modulator - Miscellaneous modulation techniques
*Space modulation A method whereby signals are modulated within airspace, such as that used in Instrument landing systems.
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Slide447Long-term potentiation - Modulation
As described previously, the molecules that underlie LTP can be classified as mediators or modulators. A mediator of LTP is a molecule, such as the NMDA receptor or calcium, whose presence and activity is necessary for generating LTP under nearly all conditions. By contrast, a modulator is a molecule that can alter LTP but is not essential for its generation or expression.
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Slide448Long-term potentiation - Modulation
In addition to the signaling pathways described above, hippocampal LTP may be altered by a variety of modulators
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Slide449Amplitude modulation
This contrasts with frequency modulation, in which the frequency of the carrier signal is varied, and phase modulation, in which its Phase (waves)|phase is varied, by the modulating signal.
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Slide450Amplitude modulation
AM was the earliest modulation method used to transmit voice by radio. It was developed during the first two decades of the 20th century beginning with Reginald Fessenden's radiotelephone experiments in 1900. It remains in use today in many forms of communication; for example it is used in portable two way radios, Airband|VHF aircraft radio and in computer modems. AM is often used to refer to mediumwave AM broadcasting|AM radio broadcasting.
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Slide451Amplitude modulation - Forms of amplitude modulation
In electronics and telecommunications, modulation means varying some aspect of a higher frequency continuous wave carrier signal with an information-bearing modulation waveform, such as an audio signal which represents sound, or a video signal which represents images, so the carrier will carry the information. When it reaches its destination, the information signal is extracted from the modulated carrier by demodulation.
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Slide452Amplitude modulation - Forms of amplitude modulation
Standard AM is thus sometimes called double-sideband amplitude modulation (DSB-AM) to distinguish it from more sophisticated modulation methods also based on AM.
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Slide453Amplitude modulation - Forms of amplitude modulation
This is in contrast to frequency modulation (FM) and digital radio where the effect of such noise following demodulation is strongly reduced so long as the received signal is well above the threshold for reception
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Slide454Amplitude modulation - Forms of amplitude modulation
The receiver may regenerate a copy of the carrier frequency (usually as shifted to the intermediate frequency) from a greatly reduced pilot carrier (in reduced-carrier transmission or DSB-RC) to use in the demodulation process
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Slide455Amplitude modulation - Forms of amplitude modulation
However it is absolutely undesired for music or normal broadcast programming, where a faithful reproduction of the original program, including its varying modulation levels, is expected.
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Slide456Amplitude modulation - Forms of amplitude modulation
A trivial form of AM which can be used for transmitting Digital data|binary data is on-off keying, the simplest form of amplitude-shift keying, in which Binary numeral system|ones and zeros are represented by the presence or absence of a carrier. On-off keying is likewise used by radio amateurs to transmit Morse code where it is known as continuous wave (CW) operation, even though the transmission is not strictly continuous.
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Slide457Amplitude modulation - anchor|AM demodulation methods Demodulation methods
The simplest form of AM demodulator consists of a diode which is configured to act as envelope detector. Another type of demodulator, the product detector, can provide better-quality demodulation with additional circuit complexity.
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Slide458Miniature helicopter - Modulation
Early Radio Controls Systems used AM (Amplitude Modulation) to transmit their signals. In the late 70's, FM (Frequency Modulation) became more commonplace.
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Slide459Digital Terrestrial Multimedia Broadcast - Modulation
The DTMB standard uses many advanced technologies to improve their performance, for example, a Pseudorandom number sequence|pseudo-random noise code (PN) as a guard interval that allows faster synchronization system and a more accurate channel estimation, Low-density parity-check code|Low-Density Parity Check (LDPC) encoding to protect against mistakes, modulation Time Domain Synchronization - Orthogonal Frequency Division Multiplexing (TDS-OFDM) which allows the combination of broadcasting in SD, HD and multimedia services, etc.
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Slide460Digital Terrestrial Multimedia Broadcast - Modulation
This system gives flexibility to the services offered to support the combination of single-frequency networks (SFN) and multi-frequency networks (MFN). The different modes and parameters can be chosen depending on the type of service and network's environment.
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Slide461Digital Terrestrial Multimedia Broadcast - Modulation
The sequence of pseudo-random pattern is defined in time domain and the information of the Discrete Fourier transform (DFT) is defined in the frequency domain. The two frames are multiplexed in the time domain, resulting in Time domain synchronization (TDS).
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Slide462Amplitude modulation signalling system
The 'amplitude modulation signalling system' ('AMSS' or the 'AM signalling system') is a Digital data|digital system for adding low bit rate information to an analog signal|analogue amplitude modulation|amplitude modulated broadcasting|broadcast signal in the same manner as the Radio Data System (RDS) for frequency modulation|frequency modulated (FM) broadcast signals.
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Slide463Amplitude modulation signalling system - Broadcasting
** Deutschlandradio Kultur: 990kHz
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Slide464Amplitude modulation signalling system - Broadcasting
Formerly it was also used by:
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Slide465Frequency modulation
In telecommunications and signal processing, 'frequency modulation' ('FM') is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. (Compare with amplitude modulation, in which the amplitude of the carrier wave varies, while the frequency remains constant.)
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Slide466Frequency modulation
In analog signal applications, the difference between the instantaneous and the base frequency of the carrier is directly proportional to the instantaneous value of the input-signal amplitude.
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Slide467Frequency modulation
Digital data can be encoded and transmitted via a carrier wave by shifting the carrier's frequency among a predefined set of frequencies—a technique known as frequency-shift keying (FSK). FSK is widely used in modems and fax modems, and can also be used to send Morse code. Radioteletype also uses FSK.
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Slide468Frequency modulation
In radio systems, frequency modulation with sufficient Bandwidth (signal processing)|bandwidth provides an advantage in cancelling naturally-occurring noise.
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Slide469Frequency modulation
Frequency modulation is known as phase modulation when the carrier phase modulation is the time integral of the FM signal.
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Slide470Frequency modulation - Theory
If the information to be transmitted (i.e., the baseband signal) is x_m(t) and the sinusoidal carrier is x_c(t) = A_c \cos (2 \pi f_c t)\,, where fc is the carrier's base frequency, and Ac is the carrier's amplitude, the modulator combines the carrier with the baseband data signal to get the transmitted signal:
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Slide471Frequency modulation - Theory
:y(t) = A_c \cos \left( 2 \pi \int_^ f(\tau) d \tau \right)
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Slide472Frequency modulation - Theory
::= A_ \cos \left( 2 \pi \int_^ \left[ f_ + f_ x_(\tau) \right] d \tau \right)
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Slide473Frequency modulation - Theory
:: = A_ \cos \left( 2 \pi f_ t + 2 \pi f_ \int_^x_(\tau) d \tau \right)
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Slide474Frequency modulation - Theory
In this equation, f(\tau)\, is the instantaneous phase#Instantaneous frequency|instantaneous frequency of the oscillator and f_\, is the frequency deviation, which represents the maximum shift away from fc in one direction, assuming xm(t) is limited to the range ±1.
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Slide475Frequency modulation - Theory
While most of the energy of the signal is contained within fc ± fΔ, it can be shown by Fourier analysis that a wider range of frequencies is required to precisely represent an FM signal. The frequency spectrum of an actual FM signal has components extending infinitely, although their amplitude decreases and higher-order components are often neglected in practical design problems.
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Slide476Non-contact atomic force microscopy - Frequency modulation
Frequency modulation, introduced by Albrecht et al. in 1991,
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Slide477Non-contact atomic force microscopy - Frequency modulation
is a mode of nc-AFM where the change in resonant frequency of the sensor is tracked directly, by always exciting the sensor on resonance
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Slide478Non-contact atomic force microscopy - Frequency modulation
During frequency modulated images, an additional feedback loop is normally used to keep the amplitude of resonance constant, by adjusting the drive amplitude. By recording the drive amplitude during the scan (usually refereed to as the damping channel as the need for a higher drive amplitude corresponds to more damping in the system) a complementary image is recorded showing only non-conservative forces. This allows conservative and non-conservative forces in the experiment to be separated.
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Slide479Non-contact atomic force microscopy - Amplitude modulation
Amplitude modulation was one of the original modes of operation introduced by Binnig and Quate in their seminal 1986 AFM paper, in this mode the sensor is excited just off resonance
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Slide480Non-contact atomic force microscopy - Amplitude modulation
Another potential problem with amplitude modulation is that a sudden change to a more repulsive (less attractive) force can shift the resonance past the drive frequency causing it to decrease again
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Slide481Non-contact atomic force microscopy - Amplitude modulation
An advantage of amplitude modulation is that there is only one feedback loop (the topography feedback loop) compared to three in frequency modulation (the phase/frequency loop, the amplitude loop, and the topography loop), making both operation and implementation much easier. Amplitude modulation, however, is rarely used in vacuum as the Q factor|Q of the sensor is usually so high that the sensor oscillates many times before the amplitude settles to its new value, thus slowing down operation.
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Slide482Carrierless Amplitude Phase Modulation
The modulation of the baseband signal with the quadrature carriers is not necessary with CAP, because it is part of the transmit pulse.
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Slide483Carrierless Amplitude Phase Modulation - Applications
The standardized variants of ADSL, ANSI T1.413 Issue 2 and G.DMT, as well as the successors ADSL2, ADSL2+, VDSL2, and G.fast, do not specify CAP, but rather discrete multi-tone modulation|discrete multi-tone (DMT) modulation.
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Slide484Carrierless Amplitude Phase Modulation - Applications
CAP used for ADSL divides the available frequency spectrum into three bands. The range from 0 to 4kHz is allocated for Plain old telephone service|POTS transmissions. The range of 25kHz to 160kHz is allocated for uplink|upstream data traffic and the range of 240kHz to 1.5MHz is allocated for downlink|downstream data traffic, in a frequency-division duplexing (FDD) scheme.
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Slide485Demodulation
'Demodulation' is the act of extracting the original information-bearing signal from a modulated carrier wave.
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Slide486Demodulation
A 'demodulator' is an electronic circuit (or computer program in a software-defined radio) that is used to recover the information content from the modulated carrier wave
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Slide487Demodulation
The demodulator takes the digital data and, using the staircase maker and the delay
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Slide488Demodulation
unit, creates the analog signal. The created analog signal, however, needs to pass
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Slide489Demodulation
through a low-pass filter for smoothing
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Slide490Demodulation
These terms are traditionally used in connection with radio receiver (radio)|receivers, but many other systems use many kinds of demodulators. Another common one is in a modem, which is a contraction of the terms modulator/demodulator.
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Slide491Demodulation - History
Since the early days of radio when all transmissions were in Morse Code, a demodulator has also been called a detector (radio)|detector. Early demodulators had only to detect the presence (or absence) of a radio wave using a device such as a coherer, without necessarily making it audible. This alternative term has survived despite the greater sophistication of modern circuits.
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Slide492Demodulation - Techniques
On the other hand, for a signal modulated with an angular modulation, we must use an FM (Frequency Modulation) demodulator or a PM (Phase Modulation) demodulator
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Slide493Demodulation - Techniques
Many techniques—such as carrier recovery, clock recovery, bit slip, frame synchronization, rake receiver, pulse compression, Received Signal Strength Indication, error detection and correction, etc. --
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Slide494Demodulation - Techniques
are only performed by demodulators, although any specific demodulator may perform only some or none of these techniques.
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Slide495Demodulation - AM radio
An amplitude modulation|AM signal encodes the information onto the carrier wave by varying its amplitude in direct sympathy with the analog signal|analogue signal to be sent. There are two methods used to Detector (radio)|demodulate AM signals.
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Slide496Demodulation - AM radio
The crystal radio receiver|crystal set exploits the simplicity of AM modulation to produce a receiver with very few parts, using the crystal as the rectifier, and the limited frequency response of the headphones as the filter.
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Slide497Demodulation - AM radio
The 'product detector' multiplies the incoming signal by the signal of a local oscillator with the same frequency and phase as the carrier of the incoming signal. After filtering, the original audio signal will result. This method will decode both AM and Single-sideband modulation|SSB, although if the phase cannot be determined a more complex setup is required.
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Slide498Demodulation - AM radio
An Amplitude modulation|AM signal can be rectified without requiring a Coherence (physics)|coherent demodulator. For example, the signal can be passed through an envelope detector (a diode rectifier and a low-pass filter). The output will follow the same curve as the input baseband signal. There are forms of AM in which the suppressed carrier|carrier is reduced or suppressed entirely, which require coherent demodulation. For further reading, see sideband.
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Slide499Demodulation - FM radio
Frequency modulation or FM is more complex. It has numerous advantages over AM, such as better fidelity and noise immunity. However, it is much more complex to both modulate and demodulate a carrier wave with FM, and AM predates it by several decades.
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Slide500Demodulation - FM radio
* The Detector (radio)#Quadrature detector|quadrature detector, which phase (waves)|phase shifts the signal by 90 degrees and multiplies it with the unshifted version. One of the terms that drops out from this operation is the original information signal, which is selected and amplified.
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Slide501Demodulation - FM radio
* The signal is fed into a PLL and the error signal is used as the demodulated signal.
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Slide502Demodulation - FM radio
* The most common is a Foster-Seeley discriminator. This is composed of an electronic filter which decreases the amplitude of some frequencies relative to others, followed by an AM demodulator. If the filter response changes linearly with frequency, the final analog output will be proportional to the input frequency, as desired.
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Slide503Demodulation - FM radio
* A variant of the Foster-Seeley discriminator called the Detector (radio)#Ratio detector|ratio detector [http://www.tpub.com/neets/book12/51d.htm The ratio detector]
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Slide504Demodulation - FM radio
* Another method uses two AM demodulators, one tuned to the high end of the band and the other to the low end, and feed the outputs into a difference amp.
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Slide505Demodulation - FM radio
* Using a digital signal processor, as used in software-defined radio.
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Slide506Demodulation - QAM
QAM demodulation requires a coherent receiver.
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Slide507Pulse width modulation
Although this modulation technique can be used to encode information for transmission, its main use is to allow the control of the power supplied to electrical devices, especially to inertial loads such as motors
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Slide508Pulse width modulation
The average value of voltage (and current) fed to the Electrical load|load is controlled by turning the switch between supply and load on and off at a fast pace. The longer the switch is on compared to the off periods, the higher the power supplied to the load is.
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Slide509Pulse width modulation
PWM has also been used in certain Signalling (telecommunication)|communication systems where its duty cycle has been used to convey information over a communications channel.
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Slide510Pulse width modulation - History
However, in addition to motor drives for fans, pumps and robotics|robotic Servomechanism|servos, there was a great need for compact and low cost means for applying adjustable power for many devices, such as electric stoves and lamp dimmers.
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Slide511Pulse width modulation - History
One early application of PWM was in the Sinclair Radionics|Sinclair X10, a 10W audio amplifier available in kit form in the 1960s. At around the same time PWM started to be used in AC motor control.
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Slide512Pulse width modulation - Principle
Pulse-width modulation uses a rectangular wave|rectangular pulse wave whose pulse width is modulated resulting in the variation of the average value of the waveform. If we consider a pulse waveform f(t), with period T, low value y_, a high value y_ and a duty cycle D (see figure 1), the average value of the waveform is given by:
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Slide513Pulse width modulation - Principle
As f(t) is a pulse wave, its value is y_ for 0 t\\
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Slide514Pulse width modulation - Principle
This latter expression can be fairly simplified in many cases where y_=0 as \bar y=D\cdot y_. From this, it is obvious that the average value of the signal (\bar y) is directly dependent on the duty cycle D.
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Slide515Pulse width modulation - Principle
The simplest way to generate a PWM signal is the intersective method, which requires only a Sawtooth wave|sawtooth or a Triangle wave|triangle waveform (easily generated using a simple Electronic oscillator|oscillator) and a comparator. When the value of the reference signal (the red sine wave in figure 2) is more than the modulation waveform (blue), the PWM signal (magenta) is in the high state, otherwise it is in the low state.
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Slide516Pulse width modulation - Time proportioning
When the counter value is more than the reference value, the PWM output changes state from high to low (or low to high).[http://www.netrino.com/Embedded-Systems/How-To/PWM-Pulse-Width-Modulation www.netrino.comndash; Introduction to Pulse Width Modulation (PWM)] This technique is referred to as 'time proportioning,' particularly as 'time-proportioning control'Fundamentals of HVAC Control Systems, by Robert McDowall, [http://books.google.com/books?id=UMk1EUp-W-UCpg=PA21dq=%22time+proportioning%22 p
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Slide517Pulse width modulation - Types
#The pulse center may be fixed in the center of the time window and both signal edge|edges of the pulse moved to compress or expand the width.
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Slide518Pulse width modulation - Types
#The lead edge can be held at the lead edge of the window and the tail edge modulated.
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Slide519Pulse width modulation - Types
#The tail edge can be fixed and the lead edge modulated.
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Slide520Pulse width modulation - Spectrum
The resulting spectrum|spectra (of the three cases) are similar, and each contains a Direct current|dc component, a base sideband containing the modulating signal and phase modulated Carrier wave|carriers at each harmonic of the frequency of the pulse. The amplitudes of the harmonic groups are restricted by a \sin x / x envelope (sinc function) and extend to infinity.
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Slide521Pulse width modulation - PWM sampling theorem
The theorem states that Any bandlimited baseband signal within ±0.637 can be represented by a pulsewidth modulation (PWM) waveform with unit amplitude
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Slide522Pulse width modulation - Telecommunications
In telecommunications, PWM is a form of signal modulation#Pulse_modulation_methods|modulation where the widths of the pulses correspond to specific data values encoded at one end and decoded at the other.
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Slide523Pulse width modulation - Power delivery
In electric cookers, continuously variable power is applied to the heating elements such as the hob or the grill using a device known as a Energy regulator|Simmerstat. This consists of a thermal oscillator running at approximately two cycles per minute and the mechanism varies the duty cycle according to the knob setting. The thermal time constant of the heating elements is several minutes, so that the temperature fluctuations are too small to matter in practice.
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Slide524Pulse width modulation - Audio effects and amplification
PWM is sometimes used in sound (music) synthesis, in particular subtractive synthesis, as it gives a sound effect similar to chorus or slightly detuned oscillators played together
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Slide525Pulse width modulation - Audio effects and amplification
A new class of audio amplifiers based on the PWM principle is becoming popular
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Slide526Pulse width modulation - Electrical
SPWM (Sine–triangle pulse width modulation) signals are used in micro-inverter design (used in solar or wind power applications)
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Slide527Hard X-ray Modulation Telescope
'Hard X-ray Modulation Telescope' ('HXMT') is a planned X-ray space observatory from China.
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Slide528Hard X-ray Modulation Telescope
The spacecraft is planned for launch between 2014 and 2016.SpaceDaily, [http://www.spacedaily.com/reports/China_unveils_ambitious_space_projects_999.html China unveils ambitious space projects], Xinhua, 23 August 2012 It will be China's first astronomy satellite.SpaceDaily, [http://www.spacedaily.com/reports/China_Focus_Timeline_for_Chinas_space_research_revealed_999.html China Focus: Timeline for China's space research revealed], Xinhua, 4 September 2012 It is based on the JianBing 3 imagery reconnaissance satellite series platform.
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Slide529Hard X-ray Modulation Telescope
The main scientific instrument is an array of 18 NaI(Tl)/CsI(na) slat-collimated Phoswich Detector|phoswich scintillation detectors, collimated to 5.7°×1° overlapping fields of view.HXMT.cn, [http://www.hxmt.cn/english/engineering/instruments.php Configuration] (Hard X-ray telescope design) c.2004
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Slide530Hard X-ray Modulation Telescope
Data analysis is planned to be by a direct algebraic method, direct demodulation,HXMT.cn, [http://www.hxmt.cn/english/engineering/imagingmethod.php The direct demodulation method] (Imaging by direct deconvolution) c.2004 which has shown promise in de-convolving the raw data into images while preserving excellent angular and energy resolution.
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Slide531Hard X-ray Modulation Telescope
The project, a joint collaboration of the Ministry of Science and Technology of China, the Chinese Academy of Sciences, and Tsinghua University, has been under development since 2000.
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Slide532HSDPA - Adaptive modulation and coding
The modulation scheme and coding are changed on a per-user basis, depending on signal quality and cell usage
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Slide533Pulse amplitude modulation
'Pulse-amplitude modulation' ('PAM'), is a form of signal modulation where the message information is encoded in the amplitude of a series of signal pulses. It is an analog pulse modulation scheme in which the amplitudes of a train of carrier pulses are varied according to the sample value of the message signal.
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Slide534Pulse amplitude modulation
Demodulation is performed by detecting the amplitude level of the carrier at every symbol period.
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Slide535Pulse amplitude modulation - Generation of PAM
PAM is also useful for demodulation of PWM.
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Slide536Pulse amplitude modulation - Generation of PAM
These are all come under pulse amplitude modulation..
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Slide537Pulse amplitude modulation - Types
There are two types of pulse amplitude modulation:
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Slide538Pulse amplitude modulation - Types
# Single polarity PAM: In this a suitable fixed DC bias is added to the signal to ensure that all the pulses are positive.
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Slide539Pulse amplitude modulation - Types
# Double polarity PAM: In this the pulses are both positive and negative.
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Slide540Pulse amplitude modulation - Types
Pulse-amplitude modulation is widely used in baseband transmission of digital data, with non-baseband applications having been largely replaced by pulse-code modulation, and, more recently, by pulse-position modulation.
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Slide541Pulse amplitude modulation - Types
In particular, all telephone modems faster than 300 bit/s use quadrature amplitude modulation (QAM). (QAM uses a two-dimensional constellation diagram|constellation).
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Slide542Pulse amplitude modulation - Use in Ethernet
In particular, the Fast Ethernet 100BASE-T2 medium (now defunct), running at 100 Mbit/s, uses five-level PAM modulation (PAM-5) running at 25 megapulses/sec over two wire pairs
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Slide543Pulse amplitude modulation - Use in Ethernet
The IEEE 802.3an standard defines the wire-level modulation for 10 Gigabit Ethernet#10GBASE-T|10GBASE-T as a Tomlinson-Harashima Precoded (THP) version of pulse-amplitude modulation with 16 discrete levels (PAM-16), encoded in a two-dimensional checkerboard pattern known as DSQ128. Several proposals were considered for wire-level modulation, including PAM with 12 discrete levels (PAM-12), ten levels (PAM-10), or eight levels (PAM-8), both with and without Tomlinson-Harashima Precoding (THP).
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Slide544Pulse amplitude modulation - Use in photo biology
The concept is also used for the study of photosynthesis using a specialized instrument that involves a fluorescence spectroscopy|spectrofluorometric measurement of the kinetics of fluorescence rise and decay in the light-harvesting antenna of thylakoid membranes, thus querying various aspects of the state of the photosystems under different environmental conditions.
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Slide545Pulse amplitude modulation - Use in electronic drivers for LED lighting
Pulse-amplitude modulation has also been developed for the control of light-emitting diodes (LEDs), especially for lighting applications. LED drivers based on the PAM technique offer improved energy efficiency over systems based upon other common driver modulation techniques such as pulse-width modulation (PWM) as the forward current passing through an LED is relative to the intensity of the light output and the LED efficiency increases as the forward current is reduced.
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Slide546Pulse amplitude modulation - Use in electronic drivers for LED lighting
Pulse-amplitude modulation LED drivers are able to synchronize pulses across multiple LED channels to enable perfect colour matching. Due to the inherent nature of PAM in conjunction with the rapid switching speed of LEDs it is possible to use LED lighting as a means of wireless data transmission at high speed.
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Slide547Radiofrequency MASINT - Covert modulation for digital surveillance
The RED signal, at a low power level, may be intercepted directly, or there may be intermodulation between the RED and BLACK signals.
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Slide548Radiofrequency MASINT - Covert modulation for digital surveillance
HIJACK is a more advanced threat, where the RED signal modulates a RF signal generated within the secure area, such as a cellular telephone. While HIJACK targets RF, NONSTOP targets the pulses of a digital device, typically a computer.
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Slide549Trellis modulation
Trellis modulation was invented by Gottfried Ungerboeck working for IBM in the 1970s, and first described in a conference paper in 1976; but it went largely unnoticed until he published a new detailed exposition in 1982 which achieved sudden widespread recognition.
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Slide550Trellis modulation
In the late 1980s, modems operating over plain old telephone service (POTS) typically achieved 9.6kbit/s by employing 4 bits per symbol quadrature amplitude modulation|QAM modulation at 2,400 baud (symbols/second)
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Slide551Trellis modulation - A new modulation method
Finally, in 1982, Ungerboeck published a paper describing the principles of trellis modulation.
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Slide552Trellis modulation - A new modulation method
A flurry of research activity ensued, and by 1990 the International Telecommunication Union had published modem standards for the first trellis-modulated modem at 14.4kilobits/s (2,400 baud and 6 bits per symbol)
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Slide553Trellis modulation - A new modulation method
Once manufacturers introduced modems with trellis modulation, transmission rates increased to the point where interactive transfer of multimedia over the telephone became feasible (a 200 kilobyte image and a 5 megabyte song could be downloaded in less than 1 minute and 30 minutes, respectively). Sharing a floppy disk via a BBS could be done in just a few minutes, instead of an hour. Thus Ungerboeck's invention played a key role in the Information Age.
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Slide554Modified Frequency Modulation
'Modified Frequency Modulation', commonly 'MFM', is a run-length limited (RLL) coding scheme used to encode the actual data-bits on most floppy disks. It was first introduced in disk drives with the IBM 3330 hard disk drive in 1970. Floppy disk drive hardware examples include Amiga, most CP/M operating system|CP/M machines as well as IBM PC compatibles.
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Slide555Modified Frequency Modulation
MFM is a modification to the original FM (frequency modulation) scheme for encoding data on single-density floppy disks and some early hard disk drives
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Slide556Modified Frequency Modulation - Coding
As is standard when discussing hard drive encoding schemes, FM and MFM encodings produce a bit stream which is Non-return-to-zero|NRZI encoded when written to disk. A 1 bit represents a magnetic transition, and a 0 bit no transition. Data encoding has to balance two factors:
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Slide557Modified Frequency Modulation - Coding
* there are limits on the minimum and maximum number of 0 bits that the hardware can detect between consecutive 1 bits, and the encoding must not exceed this limit;
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Slide558Modified Frequency Modulation - Coding
* there are limits on the maximum number of 1 bits that the hardware can detect in a given amount of time. If a disk is encoded with a higher (average) number of magnetic transitions per bit, the bits will have to be wider and fewer sectors will fit each track;
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Slide559Modified Frequency Modulation - Coding
Both FM and MFM encodings can also be thought of as having data bits separated by clock bits, but with different rules for encoding the bits. Still, both formats encode each data bit as two bits on disk (because of delimiters that are required at the beginning and end of a sequence, the actual density is slightly lower).
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Slide560Modified Frequency Modulation - Coding
The basic encoding rule for FM is that all clock bits are 1: zeros are encoded as 10, ones are encoded as 11. The number of magnetic transitions per bit is on average 1.5 (50%*1 + 50%*2).
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Slide561Modified Frequency Modulation - Coding
The basic encoding rule for MFM is that (x, y, z, ...) encodes to (x, x Logical NOR|NOR y, y, y NOR z, z, z NOR...). A zero is encoded as 10 if preceded by a zero, and 00 if preceded by a one (each of these cases occurs 25% of the time); a one is always encoded as 01 (which happens 50% of the time); thus the number of magnetic transitions is on average 0.75 (25%*1 + 25%*0 + 50%*1).
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Slide562Modified Frequency Modulation - Coding
Note that the surrounding clock bits are sometimes known, but sometimes require knowledge of the adjacent data bits. A longer example:
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Slide563Modified Frequency Modulation - Coding
In FM encoding, the number of 0 bits that may appear between consecutive 1 bits is either 0 or 1. In MFM encoding there is a minimum of 1 zero bit between adjacent ones (there are never two adjacent one bits), and the maximum number of zeros in a row is 3. Thus, FM is a (0,1) Run length limited|RLL code, while MFM is a (1,3) code.
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Slide564Modified Frequency Modulation - Coding
A special “sync mark” is used to allow the disk controller to figure out where the data starts
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Slide565Modified Frequency Modulation - MMFM
'MMFM', (Modified Modified Frequency Modulation), also abbreviated 'M²FM', or 'M2FM', is similar to MFM, but suppresses additional clock bits, producing a longer maximum run length (a (1,4) RLL code). In particular, a clock pulse is only inserted between a pair of adjacent 0 bits if the first bit of the pair did not have a clock pulse inserted before it. In the example below, clock bits that would have been present in MFM are noted in bold:
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Slide566Modified Frequency Modulation - MMFM
In this system, sync marks are made by inserting additional clock pulses between adjacent zero bits (following the MFM rule) where they would normally be omitted. In particular, the data bit pattern 10001 has a clock pulse inserted in the middle, where it would normally be omitted:
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Slide567Baseband - Modulation
Some transmission schemes such as frequency modulation use even more bandwidth.
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Slide568Baseband - Modulation
The figure shows what happens with AM modulation:
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Slide569Baseband - Modulation
Some signals can be treated as baseband or not, depending on the situation
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Slide570Baseband - Modulation
The simplest definition is that a signal's baseband bandwidth is its bandwidth before modulation and multiplexing, or after demultiplexing and demodulation.
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Slide571Baseband - Modulation
The composite video signal created by devices such as most newer VCRs, game consoles and DVD players is a commonly used baseband signal.
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Slide572Sound chip - Frequency modulation synthesis (FM synth)
**Jerry, in addition to wavetable and PCM capabilities. Used in the Atari Jaguar.
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Slide573Sound chip - Frequency modulation synthesis (FM synth)
**Memory management controller#VRC7|Konami VRC7 A modified derivative of Yamaha's YM2413, used in the Famicom cartridge Lagrange Point
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Slide574Sound chip - Frequency modulation synthesis (FM synth)
** Yamaha YM2413 (a.k.a. OPLL), used in the MSX in MSX Music cartridges like the FM-PAC and internally in several Japanese models by Panasonic, Sony and Sanyo; also used in the Sega Master System|Sega Mark III (Japanese version of the Master System)
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Slide575Sound chip - Frequency modulation synthesis (FM synth)
** Yamaha YM2151 (a.k.a. OPM), used in the X68000|Sharp X68000 and the Yamaha SFG-01 and SFG-05 FM Sound Synthesizer Unit cartridges for the MSX as well as extensive use in mid 80's - early mid 90's Arcade games (the most prolific FM chip used in the arcade)
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Slide576Sound chip - Frequency modulation synthesis (FM synth)
** Yamaha YM2203 (a.k.a. OPN), used in the NEC PC-88|PC-88 and in some Arcade games.
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Slide577Sound chip - Frequency modulation synthesis (FM synth)
** Yamaha YM2608 (a.k.a. OPNA), used in the NEC PC-88|PC-88 and NEC PC-98|PC-98
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Slide578Sound chip - Frequency modulation synthesis (FM synth)
** Yamaha YM2610 (a.k.a. OPNB), used in the Neo Geo (console)|SNK Neo Geo
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Slide579Sound chip - Frequency modulation synthesis (FM synth)
** Yamaha YM2612 (a.k.a. OPN2), used in the Mega Drive|Sega Mega Drive / Genesis and FM Towns/ FM Towns Marty Marty|FM Towns
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Slide580Sound chip - Frequency modulation synthesis (FM synth)
*** Yamaha Y8950, (a.k.a. MSX-AUDIO, very similar to Yamaha YM3526) used in MSX-Audio cartridges for the MSX: Panasonic FS-CA1, Toshiba HX-MU900 and Philips NMS-1205
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Slide581Sound chip - Frequency modulation synthesis (FM synth)
** Yamaha YM3812 (a.k.a. OPL2), used in AdLib and early Sound Blaster sound cards
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Slide582Sound chip - Frequency modulation synthesis (FM synth)
** Yamaha YMF262 (a.k.a. OPL3), used in Sound Blaster Pro 2.0 and later cards
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Slide583Sound chip - Frequency modulation synthesis (FM synth)
** Yamaha YMF278 (a.k.a. OPL4), used in the Moonsound cartridge for the MSX
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Slide584Sound chip - Frequency modulation synthesis (FM synth)
** Yamaha YMF288 (a.k.a. OPN3), used in the NEC PC-98|PC-98
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Slide585Sound chip - Frequency modulation synthesis (FM synth)
** Yamaha YMF7xx (Embedded audio chipset in some laptops and soundcards)
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Slide586Sound chip - Pulse-code modulation (PCM, Digital sampler|sample-based)
*Original_Amiga_chipset#Paula|MOS Technology 8364 Paula, used in the Commodore Amiga
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Slide587Sound chip - Pulse-code modulation (PCM, Digital sampler|sample-based)
*Sony SPC700, used in the Super Nintendo Entertainment System
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Slide588Sound chip - Pulse-code modulation (PCM, Digital sampler|sample-based)
*Ricoh RF5c68, used in the Fujitsu FM Towns computer and Sega arcade boards
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Slide589Sound chip - Pulse-code modulation (PCM, Digital sampler|sample-based)
*OKI MSM6258, used in the Sharp X68000
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Slide590Sound chip - Pulse-code modulation (PCM, Digital sampler|sample-based)
*Atari Jerry, in addition to FM and wavetable synthesis. Used in the Atari Jaguar.
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Slide591Yamaha YMF278 - Frequency modulation synthesis component
The FM part is essentially a Yamaha YMF262|YMF262 (OPL3) block; thus, it is also backwards-compatible with the Yamaha YM3526|YM3526 (OPL) and the Yamaha YM3812|YM3812 (OPL2). Like the OPL3, it can operate in one of four ways:
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Slide592Yamaha YMF278 - Frequency modulation synthesis component
* absolute sine
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Slide593Yamaha YMF278 - Frequency modulation synthesis component
Unlike the OPL3, which has four channels for sound output, the OPL4 features six channels.
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Slide594Pulse-code modulation
'Pulse-code modulation' ('PCM') is a method used to Digital signal|digitally represent sampled analog signals. It is the standard form of digital audio in computers, Compact Discs, digital telephony and other digital audio applications. In a PCM stream, the amplitude of the analog signal is sampled regularly at uniform intervals, and each sample is Quantization (signal processing)|quantized to the nearest value within a range of digital steps.
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Slide595Pulse-code modulation
PCM streams have two basic properties that determine their fidelity to the original analog signal: the sampling rate, which is the number of times per second that samples are taken; and the Audio bit depth|bit depth, which determines the number of possible digital values that each sample can take.
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Slide596Pulse-code modulation - History
This was TDM, but pulse-amplitude modulation (PAM) rather than PCM.
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Slide597Pulse-code modulation - History
In 1926, Paul M
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Slide598Pulse-code modulation - History
The first transmission of Speech communication|speech by digital techniques was the SIGSALY encryption equipment used for high-level Allied communications during World War II
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Slide599Pulse-code modulation - History
Goodall, Television by Pulse Code Modulation, Bell Sys
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Slide600Pulse-code modulation - History
In the United States, the National Inventors Hall of Fame has honored Bernard M. Oliver
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Slide601Pulse-code modulation - History
as described in 'Communication System Employing Pulse Code Modulation,' filed in 1946 and 1952, granted in 1956. Another patent by the same title was filed by John R. Pierce in 1945, and issued in 1948: . The three of them published The Philosophy of PCM in 1948.
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Slide602Pulse-code modulation - History
PCM was used in Japan by Denon in 1972 for the recording and mastering of analogue phonograph records, using a Quadruplex videotape|2-inch Quadruplex-format video recorder for the PCM signal, but this was never intended to be a consumer product.
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Slide603Pulse-code modulation - Modulation
In the diagram, a sine wave (red curve) is sampled and quantized for PCM
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Slide604Pulse-code modulation - Modulation
The PCM process is commonly implemented on a single integrated circuit generally referred to as an analog-to-digital converter (ADC).
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Slide605Pulse-code modulation - Demodulation
To recover the original signal from the sampled data, a demodulator can apply the procedure of modulation in reverse
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Slide606Pulse-code modulation - Demodulation
The electronics involved in producing an accurate analog signal from the discrete data are similar to those used for generating the digital signal. These devices are Digital-to-analog converters (DACs). They produce a voltage or Electric current|current (depending on type) that represents the value presented on their digital inputs. This output would then generally be filtered and amplified for use.
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Slide607Pulse-code modulation - Limitations
There are potential sources of impairment implicit in any PCM system:
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Slide608Pulse-code modulation - Limitations
* Choosing a discrete value that is near but not exactly at the analog signal level for each sample leads to quantization error.Quantization error swings between -q/2 and q/2. In the ideal case (with a fully linear ADC) it is uniform distribution (continuous)|uniformly distributed over this interval, with zero mean and variance of q2/12.
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Slide609Pulse-code modulation - Limitations
* Between samples no measurement of the signal is made; the sampling theorem guarantees non-ambiguous representation and recovery of the signal only if it has no energy at frequency fs/2 or higher (one half the sampling frequency, known as the Nyquist frequency); higher frequencies will generally not be correctly represented or recovered.
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Slide610Pulse-code modulation - Limitations
* As samples are dependent on time, an accurate clock is required for accurate reproduction
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Slide611Pulse-code modulation - Digitization as part of the PCM process
In conventional PCM, the analog signal may be processed (e.g., by amplitude compression) before being digitized. Once the signal is digitized, the PCM signal is usually subjected to further processing (e.g., Digital data|digital data compression).
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Slide612Pulse-code modulation - Digitization as part of the PCM process
PCM with linear quantization is known as Linear PCM (LPCM).
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Slide613Pulse-code modulation - Digitization as part of the PCM process
Some forms of PCM combine signal processing with coding. Older versions of these systems applied the processing in the analog domain as part of the analog-to-digital process; newer implementations do so in the digital domain. These simple techniques have been largely rendered obsolete by modern transform-based audio compression (data)|audio compression techniques.
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Slide614Pulse-code modulation - Digitization as part of the PCM process
* DPCM encodes the PCM values as differences between the current and the predicted value. An algorithm predicts the next sample based on the previous samples, and the encoder stores only the difference between this prediction and the actual value. If the prediction is reasonable, fewer bits can be used to represent the same information. For audio, this type of encoding reduces the number of bits required per sample by about 25% compared to PCM.
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Slide615Pulse-code modulation - Digitization as part of the PCM process
* Adaptive DPCM (ADPCM) is a variant of DPCM that varies the size of the quantization step, to allow further reduction of the required bandwidth for a given signal-to-noise ratio.
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Slide616Pulse-code modulation - Digitization as part of the PCM process
* Delta modulation is a form of DPCM which uses one bit per sample.
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Slide617Pulse-code modulation - Digitization as part of the PCM process
In telephony, a standard audio signal for a single phone call is encoded as 8,000 analog samples per second, of 8 bits each, giving a 64 kbit/s digital signal known as DS0
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Slide618Pulse-code modulation - Digitization as part of the PCM process
Where circuit costs are high and loss of voice quality is acceptable, it sometimes makes sense to compress the voice signal even further. An ADPCM algorithm is used to map a series of 8-bit µ-law or A-law PCM samples into a series of 4-bit ADPCM samples. In this way, the capacity of the line is doubled. The technique is detailed in the G.726 standard.
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Slide619Pulse-code modulation - Digitization as part of the PCM process
Later it was found that even further compression was possible and additional standards were published. Some of these international standards describe systems and ideas which are covered by privately owned patents and thus use of these standards requires payments to the patent holders.
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Slide620Pulse-code modulation - Digitization as part of the PCM process
Some ADPCM techniques are used in Voice over IP communications.
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Slide621Pulse-code modulation - Encoding for serial transmission
PCM can be either return-to-zero (RZ) or non-return-to-zero (NRZ). For a NRZ system to be synchronized using in-band information, there must not be long sequences of identical symbols, such as ones or zeroes. For binary PCM systems, the density of 1-symbols is called ones-density.Stallings, William, [http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=01091872 Digital Signaling Techniques], December 1984, Vol. 22, No. 12, IEEE IEEE Communications Magazine|Communications Magazine
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Slide622Pulse-code modulation - Encoding for serial transmission
Ones-density is often controlled using precoding techniques such as Run Length Limited encoding, where the PCM code is expanded into a slightly longer code with a guaranteed bound on ones-density before modulation into the channel. In other cases, extra framing bits are added into the stream which guarantee at least occasional symbol transitions.
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Slide623Pulse-code modulation - Encoding for serial transmission
Another technique used to control ones-density is the use of a Scrambler (randomizer)|scrambler polynomial on the raw data which will tend to turn the raw data stream into a stream that looks pseudorandom|pseudo-random, but where the raw stream can be recovered exactly by reversing the effect of the polynomial. In this case, long runs of zeroes or ones are still possible on the output, but are considered unlikely enough to be within normal engineering tolerance.
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Slide624Pulse-code modulation - Encoding for serial transmission
In other cases, the long term direct current|DC value of the modulated signal is important, as building up a DC offset will tend to bias detector circuits out of their operating range. In this case special measures are taken to keep a count of the cumulative DC offset, and to modify the codes if necessary to make the DC offset always tend back to zero.
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Slide625Pulse-code modulation - Encoding for serial transmission
Many of these codes are bipolar codes, where the pulses can be positive, negative or absent. In the typical alternate mark inversion code, non-zero pulses alternate between being positive and negative. These rules may be violated to generate special symbols used for framing or other special purposes.
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Slide626Pulse-code modulation - Nomenclature
This perhaps is a natural consequence of this technique having evolved alongside two analog methods, pulse width modulation and pulse position modulation, in which the information to be encoded is in fact represented by discrete signal pulses of varying width or position, respectively
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Slide627Frequency modulation synthesis
:where f_c\,,\,f_m\, are frequencies of carrier and modulator, I\, is modulation index, and J_k(I)\, is k\,-th Bessel function#Bessel functions of the first kind : Jα|Bessel function of first kind, respectively.
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Slide628Computer security compromised by hardware failure - The Modulation Technique
Harmonics compromising electromagnetic emissions come from unintentional emanations such as radiations emitted by the clock, non-linear elements, crosstalk, ground pollution, etc
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Slide629Reward system - Modulation by drugs
Almost all drugs causing drug addiction increase the dopamine release in the mesolimbic pathway, e.g. opioids, nicotine, amphetamine, ethanol, and cocaine. After prolonged use, psychological drug tolerance and sensitization arises.
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Slide630Reward system - Modulation by drugs
Drugs have many different effects on the brain; however, they all follow the same path
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Slide631For More Information, Visit:
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