Moreover, if this window was increased to 5 the
overall performance gain would be increased to 1.5 dB. Thus we can further close the performance
gap between noncoherent detection and coherent detection with differential decoding (see Fig. 4.42).
Next the BER performance for 8DPSK is presented. The results show when increasing the observation
window from 2 symbols to 3 symbols there is a gain of 0.8 dB. An additional gain of 0.7 dB
can be seen when we further increased the observation window to 5 symbols, totaling 1.5 dB. This
has closed the 2.5 dB performance gap between coherent and noncoherent detection to approximately
1 dB. The differential detector performance of DQPSK is also shown in Fig. 4.43 for sake of
reference.
Lastly, the performance of the MBO detectors are shown here for CD using the upper bounds
defined in [26] for the theoretical coherent detection curve. A point worth noting is that these
results assumed a BFSK modulation index, b 0.715 (for reasons already discussed in Chap. 2)
(see Fig. 4.44).
Here we see increasing the observation window from 1 bit to 2 bits gives approximately 2.4 dB of
gain. Increasing this further to 3 bits gives an additional gain of approximately 1 dB. Moreover, a
5-bit observation window gives another 0.
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