Type-1 hybrid-ARQ using MTCM spatio-temporal vector coding for MIMO systems

A system that combines MTCM modified for type-I hybrid-ARQ error control with Spatio-Temporal Vector Coding (STVC) for use over a slowly varying MIMO channel is presented. An idealistic retransmission protocol is defined that maximizes the channel utilization is described and analyzed. Numerical examples, based on a set of simple 8-state trellis codes providing a granularity of 0.5 bit per 2-dimensional symbol, demonstrate that this simple type-I hybrid-ARQ system can reduce the code gap by the same amount as an FEC system based on a set of 64-state trellis codes. This shows that type-I hybrid-ARQ STVC can close the code gap (the SNR gap between actual performance and channel capacity) without an increase in the code complexity or a decrease in performance. We also demonstrate the limitations of this approach: as the bit error rate increases and the probability of retransmission increases, the channel utilization drops. As a consequence, the code gap does not decrease or even increases.