Quantization for Soft-Output Demodulators in Bit-Interleaved Coded Modulation Systems

TL;DR

This paper explores the quantization of LLRs in BICM systems, proposing a design that makes quantizer outputs equiprobable, and evaluates its impact on capacity and error rates.

Contribution

It introduces a novel quantizer design for LLRs in BICM systems that aims to optimize capacity and error performance.

Findings

Equiprobable quantizer outputs improve capacity estimates.

Quantization impacts ergodic and outage capacity.

Bit error rate performance is maintained with the proposed quantization.

Abstract

We study quantization of log-likelihood ratios (LLR) in bit-interleaved coded modulation (BICM) systems in terms of an equivalent discrete channel. We propose to design the quantizer such that the quantizer outputs become equiprobable. We investigate semi-analytically and numerically the ergodic and outage capacity over single- and multiple-antenna channels for different quantizers. Finally, we show bit error rate simulations for BICM systems with LLR quantization using a rate 1/2 low-density parity-check code.