A Family of Likelihood Ascent Search Multiuser Detectors: an Upper Bound of Bit Error Rate and a Lower Bound of Asymptotic Multiuser Efficiency

TL;DR

This paper analyzes the bit error rate and asymptotic efficiency of likelihood ascent search multiuser detectors, providing bounds and demonstrating potential for high efficiency in CDMA systems.

Contribution

It introduces bounds on BER and AME for LAS detectors, showing their potential to achieve high efficiency regardless of user count.

Findings

Upper bound on BER using fixed point region analysis

Lower bound on asymptotic multiuser efficiency (AME)

LAS detectors can achieve unit AME in certain CDMA channels

Abstract

In this paper, the bit error performance of a family of likelihood ascent search (LAS) multiuser detectors is analyzed. An upper bound on the BER of any LAS detector is obtained by bounding the fixed point region with the worst initial detector. The concept of indecomposable errors developed by Verdu is applied to tighten the upper bound. In a special instance, the upper bound is reduced to that for all the local maximum likelihood detectors. The upper bound is comparable with that of the optimum detector obtained by Verdu. A lower bound on the asymptotic multiuser efficiency (AME) is then obtained. It is shown that there are nontrivial CDMA channels such that a LAS detector can achieve unit AME regardless of user number. The AME lower bound provides a means for further seeking a good set of spreading sequences and power distribution for spectral and power efficient CDMA.