1. EE 3220: Digital Communication Dr Hassan Yousif 1 Dr. Hassan Yousif Ahmed Department of Electrical Engineering College of Engineering at Wadi Aldwasser Slman bin Abdulaziz University Lec-7: Bandpass modulation and Coherent and non- coherent detection

2. Today, we are going to talk about: Dr Hassan Yousif 2 Some bandpass modulation schemes used in DCS for transmitting information over channel M-PAM, M-PSK, M-FSK, M-QAM How to detect the transmitted information at the receiver Coherent detection Non-coherent detection

3. Block diagram of a DCS Dr Hassan Yousif 3 Format Source encode Format Source decode Channel encode Pulse modulate Bandpass modulate Channel decode Demod. Sample Detect Channel Digital modulation Digital demodulation

4. Bandpass modulation Dr Hassan Yousif 4 Bandpass modulation: The process of converting a data signal to a sinusoidal waveform where its amplitude, phase or frequency, or a combination of them, are varied in accordance with the transmitting data. Bandpass signal: where is the baseband pulse shape with energy. We assume here (otherwise will be stated): is a rectangular pulse shape with unit energy. Gray coding is used for mapping bits to symbols. denotes average symbol energy given by

5. Demodulation and detection Dr Hassan Yousif 5 Demodulation: The receiver signal is converted to baseband, filtered and sampled. Detection: Sampled values are used for detection using a decision rule such as the ML detection rule. Decision circuits (ML detector)‏

6. Coherent detection Dr Hassan Yousif 6 Coherent detection requires carrier phase recovery at the receiver and hence, circuits to perform phase estimation. Sources of carrier-phase mismatch at the receiver: Propagation delay causes carrier-phase offset in the received signal. The oscillators at the receiver which generate the carrier signal, are not usually phased locked to the transmitted carrier.

7. Coherent detection.. Dr Hassan Yousif 7 Circuits such as Phase-Locked-Loop (PLL) are implemented at the receiver for carrier phase estimation ( ). PLL Oscillator 90 deg. Used by correlators I branch Q branch

8. Bandpass Modulation Schemes Dr Hassan Yousif 8 One dimensional waveforms Amplitude Shift Keying (ASK) ‏ M-ary Pulse Amplitude Modulation (M-PAM) ‏ Two dimensional waveforms M-ary Phase Shift Keying (M-PSK) ‏ M-ary Quadrature Amplitude Modulation (M-QAM) ‏ Multidimensional waveforms M-ary Frequency Shift Keying (M-FSK)

9. One dimensional modulation, demodulation and detection Dr Hassan Yousif 9 Amplitude Shift Keying (ASK) modulation: 0 “0”“1” On-off keying (M=2):

10. One dimensional mod.,… Dr Hassan Yousif 10 M-ary Pulse Amplitude modulation (M-PAM) ‏ 4-PAM: 0 “00”“01”“11”“10”

11. Example of bandpass modulation: Binary PAM Dr Hassan Yousif 11

12. One dimensional mod.,...–cont’d Dr Hassan Yousif 12 Coherent detection of M-PAM ML detector (Compare with M-1 thresholds)‏

13. Two dimensional modulation, demodulation and detection (M-PSK) ‏ Dr Hassan Yousif 13 M-ary Phase Shift Keying (M-PSK) ‏

14. Two dimensional mod.,… (MPSK) ‏ Dr Hassan Yousif 14 “0”“1” “110” “000” “001” “011” “010” “101” “111” “100” “00” “11”“10” “01” QPSK (M=4)‏ BPSK (M=2)‏ 8PSK (M=8)‏

15. Two dimensional mod.,…(MPSK) ‏ Dr Hassan Yousif 15 Coherent detection of MPSK ComputeChoose smallest

16. Two dimensional mod.,… (M-QAM) ‏ Dr Hassan Yousif 16 M-ary Quadrature Amplitude Mod. (M-QAM) ‏

17. Two dimensional mod.,… (M-QAM) ‏ Dr Hassan Yousif 17 “0000” “0001” “0011” “0010” 13-3 “1000” “1001” “1011” “1010” “1100” “1101” “1111” “1110” “0100” “0101” “0111” “0110” 1 3 -3 16-QAM

18. Two dimensional mod.,… (M-QAM) ‏ Dr Hassan Yousif 18 Coherent detection of M-QAM ML detector Parallel-to-serial converter

19. Multi-dimensional modulation, demodulation & detection Dr Hassan Yousif 19 M-ary Frequency Shift keying (M-FSK) ‏

20. Multi-dimensional mod.,…(M-FSK) ‏ Dr Hassan Yousif 20 ML detector: Choose the largest element in the observed vector

21. Non-coherent detection Dr Hassan Yousif 21 Non-coherent detection: No need for a reference in phase with the received carrier Less complexity compared to coherent detection at the price of higher error rate.

22. Non-coherent detection … Dr Hassan Yousif 22 Differential coherent detection Differential encoding of the message The symbol phase changes if the current bit is different from the previous bit. 0 0 1 2 3 4 5 6 7 1 1 0 1 0 1 1 1 1 1 0 0 1 1 1 00 Symbol index: Data bits: Diff. encoded bits Symbol phase:

23. Non-coherent detection … Dr Hassan Yousif 23 Coherent detection for diff encoded mod. assumes slow variation in carrier-phase mismatch during two symbol intervals. correlates the received signal with basis functions uses the phase difference between the current received vector and previously estimated symbol

24. Non-coherent detection … Dr Hassan Yousif 24 Optimum differentially coherent detector Sub-optimum differentially coherent detector oPerformance degradation about 3 dB by using sub-optimal detector Decision Delay T Decision Delay T

25. Non-coherent detection … Dr Hassan Yousif 25 Energy detection Non-coherent detection for orthogonal signals (e.g. M-FSK) ‏ Carrier-phase offset causes partial correlation between I and Q branches for each candidate signal. The received energy corresponding to each candidate signal is used for detection.

26. Non-coherent detection … Dr Hassan Yousif 26 Non-coherent detection of BFSK Decision stage: + -