Selective Diversity for Rayleigh Fading Channels With a Feedback Link

A feedback scheme for regulating error probability on slowly fading communication channels is described and analyzed. In this selective diversity system, only the best of available diversity subchannels are used, the selection being revised from moment to moment. Comparison with conventional diversity transmission on an 8-channel system shows a performance improvement ranging from 20.8 to 9.5 dB, where the low figure corresponds to constant power operation of the transmitter and a typical value of round-trip delay. A novel feature of selective diversity is that, for moderate SNR, the error probability decreases to zero as a strong inverse power of , the order of diversity, which contrasts with behavior of conventional systems in which increasing causes the error probability to decrease to a nonzero lower bound. The implication is that the figures quoted above can be improved indefinitely by increasing the order of diversity.