Transmission of digital data over a Rayleigh fading channel

In a microwave mobile telecommunications system, a digital message must be transmitted several times to overcome the effects of Rayleigh fades that characterize this channel, and thus ensure a high probability that the message is received error-free. Obviously, there are many different transmission schemes that may be suitable for this channel. We present an analytic approach to an evaluation of their comparative performance in terms of the probability of a transmission failure, and provide a basis for the design of an efficient scheme. In the first part, we present some fade statistics that have been used in our analysis. Next, we derive upper bounds on the probability of the transmission failure for three different schemes. The actual failure rates as determined in an experimental simulation are then shown for those schemes that our theoretical study predicts to be acceptable. It is shown that an efficient scheme for the Rayleigh fading channel is the block-protected one in which a message is transmitted four times, each transmission 4-ms long and spaced 4-ms apart. The spacing is obtained by interleaving a similar transmission of another message. The receiver discards a transmission if it fails the parity checks.