A Synchro-Set-Aided Breadth-First Sphere Decoder for Polar-Coded MIMO Systems

The joint optimization of multiple-input-multiple-output (MIMO) detection and polar decoding has become a research hotspot for future communication systems. The error-correction performance of the separate detection and decoding (SDD) is far from the Shannon capacity, which cannot meet the requirements of communication scenarios such as ultra-reliable and low latency communications (URLLC). The existing joint detection and decoding (JDD) using breadth-first sphere decoding (BFSD) improves the reliability over SDD but still has a huge performance loss on low-rate codes. In this paper, JDD using synchro-set-aided BFSD (SA-BFSD) is proposed to greatly improve the error-correction performance for polar-coded MIMO systems. We first propose a method to generate the symbol synchro sets through the concept of frozen symbols, then refine the symbol synchro sets based on the characteristics analysis of the channel matrix. We optimize the enumerating order of the symbols and reduce the enumerating levels. The frame error rate (FER) and the bit error rate of the proposed algorithms are significantly improved especially for the low-rate codes. The proposed SA-BFSD JDD achieves an up to 7.8 dB performance gain over BFSD at FER
$=10^{-3}$
. The hardware architecture of the polar JDD scheme is first implemented with SMIC 40-nm CMOS technology for MIMO systems. The reliability and latency of SA-BFSD are much better than those of the existing works, which could meet the requirements of URLLC.