The Gateway Channel: Outage Analysis

We consider a relay that simultaneously assists multiple source-destination pairs that do not have a direct link, which we denote the gateway channel, and explore the sum capacity of this network in the presence of quasi-static fading. In the absence of transmitter-side channel state information (CSI), we study superpostion as well as orthogonal channel access. In the presence of transmitter CSI, we consider opportunistic channel access with full CSI, as well as limited CSI via a 1- bit feedback (per user). In each case, the outage capacity and the diversity-multiplexing tradeoff are calculated. It is observed that orthogonal channel access is almost as good as superposition coding, and that opportunistic access provides significant gains. It is shown that a 1-bit feedback per user captures most of the gains available in opportunistic communication.