Enhancing Reliability in Sparse Code Multiple Access Systems through Hybrid Automatic Repeat Request with Chase Combining

This letter proposes a novel hybrid automatic repeat request with chase combining assisted sparse code multiple access (HARQ-CC-SCMA) scheme to improve the reliability of SCMA systems. Two multi-user detection algorithms, factor graph aggregation (FGA) and log-likelihood ratio combination (LLRC), are developed to effectively combine the current and previous erroneous packets.