Improving the Diversity-Multiplexing Tradeoff with Repetition-Coded Relaying in Wireless Downlink

Repetition-coded relaying using half-duplex relays offers an easy way of achieving cooperative diversity that works well with apparently any source transmission schemes, but at the same time presents a potentially serious problem of inefficient spectrum utilization. Poor diversity-multiplexing tradeoff (DMT) is often reported. This paper investigates efficient ways of using repetition-type decode-and-forward relaying to improve the DMT of users in a wireless downlink. We deliberately align the relaying operation of one user with the source transmission for another user and show that the arisen inter-user and inter-relay interference could be efficiently managed without the need of transmit-side channel state information thanks to the downlink network topology and simple user scheduling. The effects of different interfering signal flows are analyzed in detail. We show that interference does not necessarily lead to system performance degradation, which is metric-specific, and good DMT is obtained both with and without the presence of the direct path.