An Improved Stage-Combined Belief Propagation Decoding of Polar Codes

Belief Propagation (BP) algorithm is an alternative decoding method to Successive Cancellation (SC) decoding of polar codes with an advantage of higher throughput and lesser latency. BP algorithm is performed over the factor graph of a polar code, and its throughput is oppositely proportional to the number of stages of the factor graph. The stage-combining idea can be applied to the factor graph of a polar code to halve the number of stages, and thus to double the decoding throughput. By this idea, every two adjacent stages of a factor graph are combined and processed in a single step. In this paper, we propose a modified stage-combined BP decoding method that is able to improve the Bit-Error Rate (BER) performance of the decoding algorithm. This improvement is almost 0.5 dB at low to intermediate SNRs, and much more considerable at high SNRs, since the undesired phenomenon of error floor is mitigated as a result of the proposed stage-combining mechanism.