Analysis and simulation of a multiaccess scheme over flat slow fading channels

Two factors that need to be considered jointly in multi-access communications are: random arrival of messages for transmission and the noise and interference affecting the communication process. Telatar and Gallager (1995) and Telatar (1992) proposed a multi-access scheme over a no-fading AWGN channel and considered both these factors jointly. By formulating this scheme as a processor sharing queue with a single class of customers, the expected duration of signal (encoded messages) transmission for a given probability of decoding error was determined. Along similar lines, we analyse the multi-access scheme over flat slow fading channels and show that the multi-access scheme formulates as a processor sharing queueing system with multiple classes of customers with each customer belonging to a class determined by the SNR value at which it is received. The performance measures of interest in our study are: (a) the maximum stable throughput, and (b) the signaling duration for a tolerable message. We also conjecture the stability condition of the processor sharing queue. We simulate the scheme to obtain average delays over Rayleigh fading channels, Rician fading channels with Rician factors K=1 and K=1000 and no-fading AWGN channels. The results for the different fading channels are compared for equal values of average received SNR. We find that there is a threshold for the average received SNR, above which the average delay for the fading channel is less than that for the no-fading channel.