Abstract: In view of the fact that the current successive cancellation list bit-flip (SCLF) does not fully consider the influence of the previous bits decoding on the current bit decoding, this paper proposes a successive cancellation list bit-flip algorithm based on the improved first critical set (IFCS-SCLF). The algorithm takes the first critical set (FCS) as the initial critical set. Then, the theoretical bit unreliability is calculated by the channel error probability and the actual decoding bit unreliability is calculated by the path metric obtained through the cyclic redundancy check aided SCL (CA-SCL). If the bits with actual unreliability is higher than the theoretical value, the error possibility of the bits are higher and will be selected from the SC path status in the first critical set and arranged in ascending order of channel reliability to construct the improved first critical set (IFCS). Finally, the decision results on the SC state path in IFCS are exchanged when the first CA-SCL decoding fails. Simulation results show that the proposed algorithm has better bit error performance and lower complexity than the RCS-SCLF and the D-Post SCLF decoding algorithms, and it can be combined with CA-SCL decoder of small list size to achieve the similar decoding performance of large list size.

Key words: Polar codes, First critical set, Successive cancellation list, Bit-flip