Diversity-Multiplexing-Delay Tradeoff in Half-Duplex ARQ Relay Channels

In this paper, we present an efficient protocol for the delay-limited fading ARQ single relay half duplex channel. The source is using an ARQ retransmission protocol to send data to the relay and the destination. When the relay is able to decode, both the relay and the source send the same data to the destination providing additional gains. The proposed protocol exploits two kinds of diversity: (i) space diversity available through the cooperative (relay) terminal, which retransmits the source’s signals, (ii) ARQ diversity obtained by leveraging the retransmission delay to enhance the reliability. The performance characterization is in terms of the achievable diversity, multiplexing gain and delay tradeoff for a high signal-to-noise ratio (SNR) regime. Then, by letting the source’s power level vary over the retransmission rounds, we show the benefits of power control on the diversity.