Single-User MIMO ML Successive Interference Canceling Receiver with HARQ-IR Protocol

Incremental Redundancy Hybrid Automatic Repeat Request (HARQ-IR) retransmission protocol was developed to reduce the transmission errors over fading channels through multiple retransmissions. In this paper, we implement HARQ-IR for Single User MIMO systems with Successive Interference Canceling (SIC) receiver. We perform the throughput and reliability analysis for the MIMO system with Closed Loop Spatial Multiplexing (TM4) with two codewords (CW) and compare the results for SIC and Parallel Interference Aware (PIA) receiver. Our SIC receiver benefits from the log-likelihood ratios combining for the second transport block, accessed through the multi-round SIC procedure a posteriori to all the previous rounds once the first CW has been decoded, while PIA receiver treats both CWs in the same manner. The SIC receiver achieves higher throughput in frequency selective environment, receiving most of the gain in the first two retransmission rounds. For both receivers, the first transport block enjoys huge performance improvement in the low SNR regime thanks to HARQ at the price of spectral efficiency degradation due to reuse of the space-frequency resources. We also investigate the optimal retransmission scheme for TM4 in the scenarios with one successfully decoded CW, while another one is in error.