Simplified Metric Sorting for Multi-Bit Successive Cancellation List Decoding of Polar Codes

Ping Luo, Wu Guan, Liping Liang, Xin Qiu

Abstract: This letter focuses on the metric sorting step for multi-bit successive cancellation list (SCL) decoders of polar codes, which is an important part of the whole decoder. We propose a primary-secondary exchange sorting (PSES) method. In the primary sorting, most of the survivals, ${L}$ paths are selected from the first minor 2L candidates. In the secondary sorting, a small number of ${N}$ paths are extracted from the other huge number of candidates to remedy the missing survivals. The ${N}$ paths in the secondary stage are exchanged with the largest ${N}$ elements in the first ${L}$ paths. Due to the minor candidates in the primary stage and the few survivals in the secondary stage, this method reduces the complexity with negligible performance loss. Additionally, a sorting network based on compare-and-swap unit (CASU) PSES (CPSES) and a sorting network based on Radix-2L PSES (RPSES) are proposed to improve secondary sorting. The evaluation results show that compared with state-of-the-art metric sorting methods, the proposed CPSES architecture significantly reduces hardware resources, and the proposed RPSES architecture significantly reduces the latency.