Cooperation in Outage-Limited Multiple-Access Channels

Abstract

We consider three variants of the multiple-access (MA) channel and propose protocols that simultaneously achieve the corresponding full-diversity and full-multiplexing gains. The three variants considered in this work are the scalar cooperative MA (CMA) channel, the scalar MA relay (MAR) channel and the vector automatic retransmission request CMA (ARQ-CMA) channel. For the scalar CMA channel, we propose a recursive amplify and forward (AF) protocol and prove its optimality with respect to the diversity-multiplexing tradeoff (DMT). For the scalar MAR channel, we characterize the performance of the dynamic decode and forward (DDF) protocol. This characterization proves that DDF simultaneously achieves the full-diversity and full-multiplexing gains. It also shows that the protocol is DMT optimal, over the range of multiplexing gains 0.5 ges r ges 0. The last variant considered in this paper is the vector ARQ-CMA channel. For this scenario, we propose a protocol and characterize its achieved tradeoff. This characterization reveals that the devised protocol achieves both, the full-diversity and full-multiplexing gains. It also establishes the asymptotic optimality of the proposed protocol as the number of transmission rounds grows to infinity