Example ASK FSK PSK QAM Binary digital modulation Multilevel digital modulation Amplitude Shift Keying BinaryASK BASK Or OnOff Keying OOK Uses two amplitude levels for the modulated carrier ID: 1030718
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1. Digital Modulation
2. Digital modulation Example: ASK, FSK, PSK, QAMBinary digital modulationMultilevel digital modulation
3. Amplitude Shift KeyingBinary-ASK --- BASKOr On-Off Keying OOKUses two amplitude levels for the modulated carrier Frequency and phase of the carrier are kept constantASK modulation and demodulation processes are relatively inexpensiveASK is commonly used to transmit digital data over optical fiber
4. ASK signal
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6. Constellation diagram
7. Original ASK signal
8. Power Spectral Density PSD
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10. Modified ASK signal
11. DemodulationCoherent demodulationnon Coherent demodulation envelop detector
12. Others:Spectral efficiency BandwidthAdvantage and disadvantages
13. Phase Shift Keying PSKInformation signal modulates the phase of the carrier signalBPSK uses two of phases, each assigned 1 bit of binary digits
14. Constellation DiagramIn PSK, the constellation points chosen are usually positioned with uniform angular spacing around a circle
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16. Original BPSKUnmodulated carrier is not exist
17. Band limited BPSK
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19. PSK DemodulationCoherent demodulation Synchronous detection of PSK signals is required, due to the absence of a large carrier component. A coherent reference for synchronous detection cannot be obtained by an ordinary cct., since there are no spectral line components at ± fcCarrier signal
20. However, the signal has a spectrum that is symmetric with respect to the (suppressed) carrier frequency, a squaring loop can be used to obtain synchronization Carrier recovery is more complex and expensive.
21. Differential PSK (DPSK)
22. DPSK demodulation
23. Frequency Shift Keying FSKFSK is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier wave
24. FSK= ASKf1 + ASKf2
25. Binary FSK
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27. Discontinuous FSK
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30. Spectrum of BFSK
31. BFSK Modulator
32. FSK Demodulator
33. Synchronous or coherent detection
34. PLL as FSK demodulator
35. Error Performance The order of performance, from worst to best, is Non coherent ASK Coherent ASKNon coherent FSK Coherent FSK DPSK Coherent PSK.The three most widely used digital modulation methods for communication systems are PSK, DPSK, and non coherent FSK.