Storage-performance tradeoff for receivers of MIMO systems using hybrid ARQ

Hybrid automatic repeat request (HARQ) improves the throughput performance of ARQ by combining retransmission of packets with forward error correction coding. In MIMO systems employing HARQ and equalization, optimal performance at the receiver is obtained when the signals corresponding to each transmission are combined before the equalizer. Performance can be exchanged for reduced receiver memory by first equalizing the signals after each individual reception and then combining them. For systems that use bit-level combining, post-equalization combining may be the only option for equalizer-based receiver implementation. In this paper the performance limit of post-equalization combining is derived for both linear and decision feedback equalizers used by receivers of HARQ MIMO systems. Moreover, pre-equalization combining and post-equalization combining architectures are compared in terms of the storage-performance tradeoff that they achieve.