CRC Aided Short-Cycle Free BP Decoding for Polar Codes

In this paper, a novel scheme that utilizes soft decision LLR values of CRC bits to aid BP decoding in polar codes is proposed. We show that the proposed periodic CRC scheduling for the factor graphs of BP decoding, combined with relaxation operations can prevent short cycles and improve FER performance of BP decoding. The proposed scheme provides around 0.75 dB gain over CASCL decoder and 1 dB gain over conventional BP decoder at a FER of 10^-4 for N=1024 and R=0.5.