Outage probability and goodput with ARQ in multiple access channels

We consider a block fading multiple access channel with N users transmitting information to a single receiver. We assume channel state is known only at the receiver and ARQ is used to combat fading and improve the transmission reliability. The overall goodput for such a system is a function of user transmission rates and outage probabilities. In this paper, we provide approximations for common and individual outage probability for a general N user symmetric Gaussian MAC channel based on the geometry of the capacity region. Using these approximations, we analyse the optimal goodput as a function of the number of MAC users and the signal-to-noise ratio (SNR). With common outage, we observe a SNR threshold above which the optimal outage probability (for optimal goodput) decreases with the number of users, and below which the optimal outage probability increases with users. When individual outage is considered, the optimal outage probability decreases with increasing users for all SNRs. © VDE VERLAG GMBH ·Berlin· offenbach.