Department of Computer Engineering Kasetsart University 01204325 Data Communications and Computer Networks Based on lecture materials from Data Communications and Networking 5 th ed Behrouz A ID: 1030716
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1. Analog TransmissionChaiporn JaikaeoDepartment of Computer EngineeringKasetsart University01204325 Data Communications and Computer NetworksBased on lecture materials from Data Communications and Networking, 5th ed.,Behrouz A. Forouzan, McGraw Hill, 2012.Revised 2019-08-20
2. OutlineAspects of Digital-to-Analog ConversionAmplitude Shift KeyingFrequency Shift KeyingPhase Shift KeyingQuadrature Amplitude Modulation
3. Digital-to-Analog ConversionRequired to send digital data over a band-pass channelAlso known as modulation(band-pass channel)https://en.wikipedia.org/wiki/Modem
4. Carrier SignalsCarrier signal is a high-frequency signal acting as a base for information signalAlso known as Carrier Frequency
5. Simplest form of periodic signalGeneral form: periodT = 1/fpeakamplitudetimesignal strengthSine Waves: Revisitedphase / phase shift
6. Conversion Techniques
7. Bit Rate vs. Baud RateBit rate the number of bits per secondBaud rate the number of signal elements (symbols) per secondIn the analog transmission of digital data, the baud rate is less than or equal to the bit rate
8. Binary Amplitude Shift KeyingOr Binary ASKRepresent bits by amplitudes; fix frequency and phaseSimplest form On-Off Keying (OOK)fc : Carrier frequency0 < d < 1
9. Implementation of Binary ASKAn everyday example: IR remote
10. Frequency Spectrum of ASK (1)Consider a digital signal of the formAfter modulation with the carrier frequency fc
11. Frequency Spectrum of ASK (2)Using trigonometric identities ffnBandband signalffcfc+fnfc– fnModulated signalDemo on Desmos
12. Example – ASK Bit RateGiven bandwidth of 100 kHz, spanning from 200 kHz to 300 kHzModulate data using ASK with communication circuitry that requires bandwidth of 2 Hz/baudWhat is the carrier frequency and the bit rate?Solution:
13. Binary Frequency Shift KeyingOr Binary FSKRepresent bits by frequencies; fix amplitude and phase
14. Implementation of Binary FSK
15. Multilevel FSKUse one frequency to send more than one bit at a timeE.g., the whole bandwidth divided into 8 frequency rangesEach frequency can represent 3 bits000001010011100101110111
16. Binary Phase Shift KeyingOr Binary PSKRepresent bits by phase shifts; fix amplitude and frequency
17. Implementation of Binary PSK
18. Quadrature PSKEach signal element carries 2 bits
19. Example – QPSK BandwidthFind the bandwidth for a signal transmitting at 12 Mbps for QPSKAssume the communication circuitry requires 1 Hz/baudSolutionFor QPSK, two bits is carried by one signal element. This means 1 baud = 2 bits per second
20. Implementation of QPSKData Bits00011011Phase-135135-4545
21. Constellation DiagramsA constellation diagram helps define the amplitude and phase of a signal elementPhasor Visualization
22. Example – Constellation DiagramShow the constellation diagrams for OOK, BPSK, and QPSK modulations
23. Constellation Diagram for 8-PSK
24. Quadrature Amplitude ModulationQAM – Quadrature Amplitude ModulationA combination of ASK and PSK
25. QAM Modulation Process
26. QAM Demodulation Process
27. Telephone Line Bandwidth
28. V.32 and V.32bis Modem Standards
29. Analog-to-Analog ConversionProcess of transmitting analog information by an analog signalAlthough the signal is already analog, modulation is needed if a band-pass channel is available to us.
30. Types of Analog-to-Analog Modulations
31. Amplitude Modulation (AM)
32. AM Band Allocation
33. Frequency Modulation (FM)
34. FM Band Allocation
35. Phase Modulation (PM)Considered a variation of FM
36. SummaryBand-pass channels require signals modulated into specific frequency rangeThree properties of sine wave can be altered to represent the original data bitsAmplitude-shift keying (ASK)Frequency-shift keying (FSK)Phase-shift keying (PSK)Quadrature Amplitude Modulation (QAM) combines both ASK and PSK