Bit-interleaved coded modulation in the wideband regime

TL;DR

This paper analyzes the capacity of bit-interleaved coded modulation (BICM) in the wideband regime, deriving formulas for energy efficiency and bandwidth trade-offs, and compares its performance to coded modulation schemes.

Contribution

It provides a low-SNR expansion for BICM capacity, revealing its suboptimality and quantifying the power-bandwidth trade-offs in the wideband regime.

Findings

BICM is suboptimal compared to coded modulation in the wideband regime.

The minimum energy per bit for BICM approaches -0.34 dB as M increases.

A trade-off between power and bandwidth is characterized at low SNR.

Abstract

The wideband regime of bit-interleaved coded modulation (BICM) in Gaussian channels is studied. The Taylor expansion of the coded modulation capacity for generic signal constellations at low signal-to-noise ratio (SNR) is derived and used to determine the corresponding expansion for the BICM capacity. Simple formulas for the minimum energy per bit and the wideband slope are given. BICM is found to be suboptimal in the sense that its minimum energy per bit can be larger than the corresponding value for coded modulation schemes. The minimum energy per bit using standard Gray mapping on M-PAM or M^2-QAM is given by a simple formula and shown to approach -0.34 dB as M increases. Using the low SNR expansion, a general trade-off between power and bandwidth in the wideband regime is used to show how a power loss can be traded off against a bandwidth gain.