Throughput-Based Design for Polar-Coded Modulation

Typically, forward error correction (FEC) codes are designed based on the minimization of the error rate for a given code rate. However, for applications that incorporate hybrid automatic repeat request (HARQ) protocol and adaptive modulation and coding, the throughput is a more important performance metric than the error rate. Polar codes, a new class of FEC codes with simple rate matching, can be optimized efficiently for maximization of the throughput. In this paper, we aim to design HARQ schemes using multilevel polar-coded modulation (MLPCM). Thus, we first develop a method to determine a set-partitioning-based bit-to-symbol mapping for high-order quadrature amplitude modulation (QAM) constellations. We simplify the log-likelihood ratio estimation of set-partitioned QAM constellations for a multistage decoder, and we introduce a set of algorithms to design throughput-maximizing MLPCM for the successive cancellation decoding (SCD). These codes are specifically useful for non-combining, chase-combining, and incremental redundancy HARQ protocols. Furthermore, since optimized codes for SCD are not optimal for SC list decoders (SCLDs), we propose a rate matching algorithm to find the best rate for SCLD while using the polar codes optimized for SCD. The resulting codes provide throughput close to the capacity with low decoding complexity when used with HARQ protocols.