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
R
of
L
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
L
, the order of diversity, which contrasts with behavior of conventional systems in which increasing
L
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.