5.48), there is significant performance
improvement that can be achieved. It is not readily apparent how these improvements can be
obtained by other FEC techniques provided earlier in this chapter. It is for these reasons why next generation
digital cellular systems have adopted the turbo coding principle.
In an effort to provide some closure on the performance comparison of the FEC codes presented,
in Fig. 5.49 we compare the performance of the convolutional code to that of concatenated coding and
lastly to the turbo coding.
Pb>Dfree # Qa?„2 # dfree # R # Eb
No b
5.2 RECEIVE SPATIAL ANTENNA DIVERSITY
COMBINING TECHNIQUES
In the ???Multipath Fading Channel??? Chapter 3 we discussed how severe the wireless channel can
become. Thus far we have assumed a single transmit antenna and a single receive antenna in the communication
system. Performance degradation was observed when the received signal encountered a
fade or destructive interference. In this section, we introduce a technique where multiple-receive
antennas are used to aid the detection or demodulation of the transmitted signal. The level of performance
improvement highly depends on the signals at each of the receive antennas being independent
and uncorrelated from each other.
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