BER Evaluation Based SCFlip Algorithm for Polar Codes Decoding

Xueting Zhang,Shaoping Chen,Yingzhuang Liu

doi:10.1109/access.2019.2962003

Abstract

Successive cancellation (SC) decoding of polar codes may bring about error propagation that needs to be mitigated. In this paper, we present a new SC Flipping (SCFlip) decoder, named bit error rate (BER) evaluation based SCFlip (BER-SCFlip), which can accurately target the first error bit and correct it with a high probability. Thus, a high error correction capability and a low decoding complexity can be achieved. First, we propose a new criterion to find out the most suspicious error bit. Those non-frozen bits that have higher decoding BERs derived from log-likelihood-ratios (LLRs) after SC decoding than the corresponding expected ones estimated via Gaussian Approximation (GA), are collected into the flip-bits set. These candidate bits will be flipped one by one according to their SC decoding orderings in extra decoding attempts until the decoded codeword passes cyclic redundancy check (CRC) or a predetermined maximum number of extra attempts is reached. We then propose an extended version of BER-SCFlip, named BER-SCFlip-w with the capability to correct up to w error bits in each extra decoding attempt. By combining our criterion for the flip-bits selection with that of Dynamic SCFlip (D-SCFlip), the proposed BER-SCFlip-w significantly reduces decoding complexity and latency while maintaining the superior error-correction performance close to that of D-SCFlip-w. The simulation results show that the proposed schemes are competitive among existing SCFlip algorithms and could achieve the error-correction performance approaching that of CRC-aided SCL decoding under list size L = 16 while maintaining low complexity.

Highlights

Polar codes are the first family of channel codes that are proved theoretically to achieve the capacity of binaryinput discrete memory-less channels (B-DMCs) under a low-complexity successive cancellation (SC) decoding when code lengths go to infinity [1]
The other focused on enhancing the performance of SC decoding, e.g., the SC list (SCL) decoder proposed in [6], [7] to significantly improve the error-correction performance of polar codes at finite lengths
The bit error rate (BER)-SC Flipping (SCFlip) decoder presented in the previous section has a limited error-correction capability, for only one suspicious bit is flipped in each decoding attempt

Summary

INTRODUCTION

Polar codes are the first family of channel codes that are proved theoretically to achieve the capacity of binaryinput discrete memory-less channels (B-DMCs) under a low-complexity successive cancellation (SC) decoding when code lengths go to infinity [1]. X. Zhang et al.: BER Evaluation-Based SCFlip Algorithm for Polar Codes Decoding decoding attempts, SCFlip decoder could achieve a better error correction performance than SC decoder at a cost of a minor increase in the decoding complexity. By adjusting the critical set progressively during the decoding, the proposed Progressive SCFlip could rival SCL decoding with a lower average complexity It was observed from simulations in [20] that the first error was distributed non-uniformly, and an adaptive threshold was employed to screen possible flipping candidates. We sort the indexes according to their orderings in the standard SC decoding Based on this criterion, we propose a BER evaluation based SCFlip (BER-SCFlip) decoder that can achieve a good error-correction performance. To constrain the scope of the flip-bits and avoid unnecessary iterations, we set the maximum number of new decoding attempts as T , which is investigated in the later section

ALGORITHM DESCRIPTION

THE PERFORMANCE ANALYSIS

THE SIMULATIONS AND ANALYSIS

CONCLUSION