On the other hand, this loss must be discussed in the
context of implementation complexity. In some cases the more critical issue may be receiver complexity
and in this case the price paid is performance. However as discussed above, this loss in Eb/No
must be considered in the overall communication system link budget. Various parameters can be optimized
to help reduce or eliminate this loss such as: coding gain, output power, noise figure, antenna
gain, cell size, and so on.
In the next noncoherent detection technique we show how this 3 dB performance gap can be made
smaller by increasing the complexity of this simple noncoherent receiver. In other words, by widening
the observation window from 2 symbols for the conventional differential detector to a larger value,
performance gain can be obtained. Hence we begin to close the performance gap shown in Fig. 4.28.
4.3.2 Multiple Symbol DD
In this noncoherent technique the observation window used to estimate the transmitted signal is
increased resulting in desirable performance improvement [44??“51]. The conventional DD discussed
in the previous section has an observation window of 2 symbols. In other words, we observe 2 symbols
to make a decision on 1 symbol.
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