Outage Probabilities and Finite-SNR Diversity Gains in Rate-Adaptive Fading Multiple Access Channels

In this paper, bounds on the outage probability and estimates of the diversity gain at finite signal-to-noise ratios (SNRs) are obtained for quasi-static fading multiple access channels in which user data rates increase with SNR. The data rate of each user is equal to the multiplexing gain multiplied by the capacity of an additive white Gaussian noise (AWGN) channel. Given the user multiplexing gains, the finite-SNR diversity gain is defined in terms of the slope of the common outage probability versus SNR at a particular point. This nonasymptotic framework represents an extension of previous work for point-to-point multiantenna channels to rate-adaptive multiple access channels. In contrast to asymptotic diversity-multiplexing tradeoffs as the SNR tends to infinity, finite-SNR analysis provides useful insight into achievable multiple access performance with different transmit power, path loss, and shadowing among users