Impact of Half-duplex Radios and Decoding Latencies on MIMO Relay Channel

摘要

In this paper, we study achievable rates for the fading relay channel with multiple antennas, without channel state information at the transmitters. Our main motivation is understanding how much of theoretically predicted gains are achievable in real implementations of relay-based networks. Two "imperfections" are considered in this paper. First, we study how commonly used half-duplex radios affect the performance of the relay channel-As shown in this paper, half-duplex radios can significantly reduce the peak gains compared to the relay network using full-duplex radios, but still retain significant superiority over the direct link without the relay. More importantly, we find that simple data forwarding (sending to relay and relay forwarding to destination) performs reasonably close to upper bound on half-duplex relay channels, thus making multi-hop communication in distributed networks not too far from optimal. We also find that decode-and-forward is near-optimal for the half-duplex relay channel in many geometries, and thus, is the coding scheme of choice to achieve high data rates. But decoding at the relay introduces decoding latencies, which is the topic of our second "imperfection." Our analysis of full-duplex and half-duplex relay channels indicate that the full-duplex relay channel is more seriously affected by finite decoding latencies compared to half-duplex. In fact, with appropriate choice of codelengths, the half-duplex relay channel need not suffer any rate losses.