Capacity-Approaching Signal Constellations for the Additive Exponential Noise Channel

TL;DR

This paper introduces log constellations for additive exponential noise channels, achieving near-capacity performance with coded modulation and highlighting limitations of BICM in this context.

Contribution

The paper proposes a new family of log constellations that closely approximate the optimal input distribution for AEN channels, improving capacity achievement.

Findings

Log constellations outperform existing signal sets in CM by over 0.5 dB.

Error performance within 0.12 dB of AEN capacity with CM.

BICM offers limited performance gains and may not be suitable for AEN channels.

Abstract

We present a new family of signal constellations, called log constellations, that can be used to design near-capacity coded modulation schemes over additive exponential noise (AEN) channels. Log constellations are designed by geometrically approximating the input distribution that maximizes the AEN channel capacity. The mutual information achievable over AEN channels with both coded modulation (CM) and bit-interleaved coded modulation (BICM) approaches is evaluated for various signal sets. In the case of CM, the proposed log constellations outperform, sometimes by over half a decibel, the best existing signal sets available from the literature, and can display error performance within only 0.12 dB of the AEN channel capacity. In the context of BICM, log constellations do not offer significant performance advantages over the best existing constellations. As the potential performance degradation resulting from the use of BICM instead of CM is larger than 1 dB, BICM may however not be a suitable design approach over AEN channels.