an AWGN (static) channel for BPSK, QPSK, DPSK, and DQPSK modulation schemes. Coherent
detection was used for BPSK/QPSK and noncoherent detection was used for DPSK/DQPSK.
Here we see that we have sacrificed 2.5 dB of Eb/No when the receiver phase offset was neglected,
not estimated nor compensated. The mathematical equations used to plot Fig. 4.27 are given in
Appendix 4A.
Similarly, we can plot the BER performance in a flat fading (dynamic) channel below for BPSK,
QPSK, DPSK, and DQPSK modulation schemes (see Fig. 4.28).
MODULATION DETECTION TECHNIQUES 193
Comparison of Coherent and Noncoherent
Detection in AWGN
1.E??“4
1.E??“3
1.E??“2
1.E??“1
8 6 4 20 1012
Eb/No (dB)
Probability of Bit Error (Pb)
Pb(BPSK/QPSK)
DPSK
DQPSK
FIGURE 4.27 Comparison of coherent and noncoherent detection in AWGN.
Comparison of Coherent and Noncoherent
Detection in Flat Fading Channel
1.E??“4
1.E??“3
1.E??“2
1.E??“1
0 5 10 15 20 25 30 35 40
Eb/No (dB)
Probability of Bit Error (Pb)
Pb (BPSK)
Pb (DPSK)
Pb (DQPSK)
FIGURE 4.28 Comparison of coherent and noncoherent detection in Rayleigh
fading.
Here we see approximately 3 dB penalty in Eb/No when we use noncoherent detection instead of
coherent detection. In many communication systems this loss is significant and must be made up (or
compensated for) elsewhere in the link budget.
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