Aggregation-Assisted Combining for MIMO Multiple ARQ Systems

This letter proposes an aggregation-assisted combining (AAC) for multiple-input multiple-output multiple automatic repeat request systems. The proposed AAC can be considered as a hybrid scheme of the symbol-level combining (SLC) and bit-level combining (BLC), which consists of the aggregation-assisted log-likelihood ratio (LLR) calculation and subsequent LLR combining stages. The aggregation-assisted LLR calculation stage is performed in a similar manner on the SLC except that the interference-to-noise reformulation is performed instead of the terminated-packet elimination; thus, the remaining interference from the terminated packets is regarded as additional noise. This additional noise can degrade the LLR quality from the aggregation-assisted LLR calculation stage. Therefore, the proposed AAC combines the currently calculated LLRs with the previously calculated LLRs similar to the BLC when the previously calculated LLRs have less LLR contaminations, i.e., they experience fewer numbers of terminated packets. The simulation results verify that the proposed AAC outperforms the BLC and even achieves a performance comparable with the SLC with simplified reception procedures.