Soft-Out Successive Cancellation Decoding and Its List Version for Polar Codes

Unlike the standard successive cancellation (SC) decoding of polar codes, soft cancellation (SCAN) decoding could provide soft outputs, which are required in iterative processing for concatenated polar-coded systems. However, its performance is largely limited due to the absence of a list version. This letter first proposes a novel soft-out SC (SoSC) algorithm, where the left-to-right message-passing akin to the SCAN decoding is performed to get soft outputs whenever the partial-sum update is activated during the SC decoding. This SoSC inherits the mechanism of hard-decisions along the path, which allows us to propose its list version, namely, soft-out SC list (SoSCL) decoding. Compared to the existing SCL-based soft decoding algorithms, the proposed SoSCL has a more rigorous mathematical interpretation and could achieve sound gain in iterative processing for various concatenated polar-coded systems.