An Improved Space-Division Multiple-Access Strategy for Rayleigh-Fading Channels

We propose a new transmission strategy for the Rayleigh-fading multiple-access channel called space-time active rotation (STAR). STAR is a simple enhancement of the traditional space-division multiple-access (SDMA) strategy that enables a successive-cancellation (SC) decoder to approach the outage probability of the underlying multiple-access channel. We derive the outage probability of a STAR system with SC decoding and propose an ordering algorithm that minimizes this outage probability. We derive an upper bound on the diversity-multiplexing tradeoff of the system. We present numerical results for a 4-user Rayleigh-fading multiple-access channel, with 2 transmit antennas per user and 8 receive antennas, which show that the STAR strategy with SC decoding falls only 1.6 dB short of the optimum outage probability. When restricted to SC decoding, STAR outperforms conventional SDMA by 8.2 dB