Efficient Soft-Output List Decoding of Polar Codes for Iterative Detection and Decoding in MIMO System

Polar-coded multiple-input multiple-output (MIMO) system has obtained increasing attention recently, in which iterative detection and decoding (IDD) brings improved performance compared to separate detection and decoding (SDD) schemes. IDD requires the exchange of soft information between the detector and decoder, but the best-performing decoding algorithm for polar codes, the cyclic redundancy check (CRC)-aided successive cancellation list (CA-SCL) algorithm, cannot generate soft outputs by itself. To address this issue, existing high-performance soft-output decoders combine the CA-SCL decoder with the belief propagation (BP) or soft cancellation (SCAN) decoding process to generate soft outputs, leading to high computational complexity and memory requirements. In this work, an efficient partial sum-based soft-output SCL (PS-SSCL) decoder is proposed, which utilizes the inherent partial sums generated during the CA-SCL decoding process to calculate soft outputs without introducing any additional decoding procedure. For the 5G (256,128) polar code, the proposed PS-SSCL decoder achieves a 57% reduction in memory requirements and a 62% reduction in computational complexity compared to the state-of-the-art soft-output list (SOL) polar decoder. Additionally, the PS-SSCL decoder can also bring more than 0.2 dB gain over the SOL decoder, when integrated into the IDD receiver with the linear minimum mean square error (LMMSE) detector.