EURASIP Journal on Applied Signal Processing 2004:5, 772–782 c © 2004 Hindawi Publishing Corporation Multiple ARQ Processes for MIMO Systems

We propose a new automatic repeat request (ARQ) scheme for MIMO systems with multiple transmit and receive antennas. The substreams emitted from various transmit antennas encounter distinct propagation channels and thus have different error statis-tics. When per-antenna encoders are used, separating ARQ processes among the substreams results in a throughput improvement. Moreover, it facilitates the interference cancellation in certain MIMO techniques. Quantitative results from UMTS simulations demonstrate that the proposed multiple ARQ structure yields more than 30 % gain in link throughput