Soft-Output Successive Cancellation Stack Polar Decoder

Polar coding has been ratified for employment inthe 3GPP New Radio standard and several soft-decision decodersachieved comparable performance to that of the state-of-the-artsuccessive cancellation list decoder. Aiming for further improvingthe performance of the soft-decision polar decoders, we proposea soft-output successive cancellation stack (SSCS) polar decoder,which jointly exploits the benefits of the depth-first search ofthe stack decoder and the soft information output of the beliefpropagation decoder. This has the substantial benefit of facilitatingsoft-input soft-output (SISO) decoding and seamless iterativeinformation exchange in turbo-style receivers. As a further contribution,we intrinsically amalgamate our SSCS decoder into polarcodedlarge-scale multiple-input multiple-output (MIMO) systemsand conceive an iterative turbo receiver, operating on the basis oflogarithmic likelihood ratios (LLRs). Our simulation results showthat the proposed SSCS decoder is capable of outperforming thestate-of-the-art SISO polar decoders, despite requiring a lowercomplexity at moderate to high signal-to-noise ratios (SNRs).Additionally, compared with the non-iterative hard-output SCSdecoder, our SSCS scheme attained 1.5 dB SNR gain at a biterror ratio level of 10^-5, when decoding the [256; 512] polar codeof a (64 * 64) MIMO system