Multiple ARQ Processes for MIMO Systems

We propose a more efficient Automatic Retransmission reQuest (ARQ) for MIMO systems with multiple transmit and multiple receive antennas. The substreams emitted from various transmit antennas encounter distinct propagation channels and thus have different error statistics. Using multiple per-antenna encoders, separating ARQ processes among the substreams results in effective throughput improvement. It can further facilitate the interference cancellation, which is essential in MIMO performance. Quantitative results from UMTS HSDPA simulations demonstrate that the proposed multiple ARQ processes yield more than 30% gain in single user link throughput.