Variable-Rate Transmission for Rayleigh Fading Channels

A modulation system is proposed that continuously adjusts its data rate in response to signal strength variations in a fading channel. The optimum variation of data rate with channel conditions is determined, and includes the effects of feedback channel time delay, the interval between rate changes, and restriction of the number of allowable rates. Application of these results to a full duplex situation allows determination of the optimum fraction of the data stream to be devoted to service information. Comparison of this scheme with diversity transmission on the basis of error probability and bandwidth utilization reveals a reduction on the order of 14 dB in transmitter power for a typical duplex link.