Turbo receiver design for MIMO relay ARQ transmissions

In this paper, we investigate practical turbo receiver design for throughput-efficient relay ARQ transmissions over broadband cooperative MIMO channels. Our setup is comprised of three multi-antenna nodes: a source, a destination, and a relay node operating under the amplify-and-forward half-duplex relaying mode. To attain higher system average throughput, we adopt a two-slot transmission strategy where the ARQ mechanism is activated on top of the amplify-and-forward protocol. We derive a soft sub-packet combiner allowing the destination node to jointly perform sub-packet combining (over both time-slots and multiple ARQ rounds) and frequency domain (FD) MMSE filtering. Its computational load is then smoothly relaxed via a recursive implementation alleviating the memory requirements when the number of ARQ rounds increases. Simulation results show that the proposed transmission strategy along with turbo sub-packet combining at the destination side achieves significant average throughput performance gain compared with conventional ARQ-based cooperative relaying, especially in situations where the relay node is close to the source node.