Achieving the Outage Capacity of the Diamond Relay Network to Within One Bit and Even Less

A new forwarding strategy is proposed for the wireless diamond relay network under slow fading. The key feature is that it can adaptively switch between decode–forward and compress–forward according to the instantaneous received signal strength. It has four control parameters, which can be optimized by an alternating optimization procedure. Its outage performance is compared with two lower bounds. Analytically, it is proven to achieve the outage capacity to within 1 bit and within 50% for any signal-to-noise ratio (SNR). Empirically, it is shown to be nearly optimal for some fading scenarios.