Block Orthogonal Sparse Superposition Codes for Ultra-Reliable Low-Latency Communications

TL;DR

This paper introduces block orthogonal sparse superposition (BOSS) codes for ultra-reliable low-latency communications, featuring efficient encoding, a low-latency approximate MAP decoder, and analytical performance evaluation, outperforming polar codes in key regimes.

Contribution

The paper proposes a novel BOSS code family with a new encoding method, an efficient approximate MAP decoder, and analytical BLER expressions, advancing coding for URLLC.

Findings

CA-BOSS with list decoding outperforms CA-polar codes in low-rate, finite-blocklength regimes.

CA-BOSS approaches finite-blocklength capacity within 1 dB SNR.

The proposed decoding reduces latency significantly while maintaining complexity.

Abstract

Low-rate and short-packet transmissions are important for ultra-reliable low-latency communications (URLLC). In this paper, we put forth a new family of sparse superposition codes for URLLC, called block orthogonal sparse superposition (BOSS) codes. We first present a code construction method for the efficient encoding of BOSS codes. The key idea is to construct codewords by the superposition of the orthogonal columns of a dictionary matrix with a sequential bit mapping strategy. We also propose an approximate maximum a posteriori probability (MAP) decoder with two stages. The approximate MAP decoder reduces the decoding latency significantly via a parallel decoding structure while maintaining a comparable decoding complexity to the successive cancellation list (SCL) decoder of polar codes. Furthermore, to gauge the code performance in the finite-blocklength regime, we derive an exact analytical expression for block-error rates (BLERs) for single-layered BOSS codes in terms of relevant code parameters. Lastly, we present a cyclic redundancy check aided-BOSS (CA-BOSS) code with simple list decoding to boost the code performance. Our experiments verify that CA-BOSS with the simple list decoder outperforms CA-polar codes with SCL decoding in the low-rate and finite-blocklength regimes while achieving the finite-blocklength capacity upper bound within one dB of signal-to-noise ratio.