Optimization of sequences in CDMA systems: a statistical-mechanics approach

TL;DR

This paper applies a statistical mechanics approach, specifically the replica method, to optimize spreading sequences in CDMA systems, demonstrating that WBE sequences maximize average mutual information.

Contribution

It introduces a novel application of the replica method to optimize CDMA spreading sequences based on mutual information.

Findings

WBE sequences maximize average mutual information

Statistical mechanics approach effectively analyzes CDMA system performance

Optimization criterion based on mutual information

Abstract

Statistical mechanics approach is useful not only in analyzing macroscopic system performance of wireless communication systems, but also in discussing design problems of wireless communication systems. In this paper, we discuss a design problem of spreading sequences in code-division multiple-access (CDMA) systems, as an example demonstrating the usefulness of statistical mechanics approach. We analyze, via replica method, the average mutual information between inputs and outputs of a randomly-spread CDMA channel, and discuss the optimization problem with the average mutual information as a measure of optimization. It has been shown that the average mutual information is maximized by orthogonally-invariant random Welch bound equality (WBE) spreading sequences.