Optimum Asymptotic Multiuser Efficiency of Pseudo-Orthogonal Randomly Spread CDMA

TL;DR

This paper analyzes the high signal-to-noise ratio performance of a pseudo-orthogonal CDMA system, deriving its asymptotic multiuser efficiency and demonstrating near-optimal performance at low system loads.

Contribution

It introduces a pseudo-orthogonal CDMA model and derives its asymptotic multiuser efficiency, showing near-optimal performance in large systems with low loads.

Findings

AME is close to 1 for loads below 0.1

AME is bounded below by 1/4 for higher loads

Efficiency is comparable to optimal multiuser detectors

Abstract

A $K$-user pseudo-orthogonal (PO) randomly spread CDMA system, equivalent to transmission over a subset of $K'\leq K$ single-user Gaussian channels, is introduced. The high signal-to-noise ratio performance of the PO-CDMA is analyzed by rigorously deriving its asymptotic multiuser efficiency (AME) in the large system limit. Interestingly, the $K'$-optimized PO-CDMA transceiver scheme yields an AME which is practically equal to 1 for system loads smaller than 0.1 and lower bounded by 1/4 for increasing loads. As opposed to the vanishing efficiency of linear multiuser detectors, the derived efficiency is comparable to the ultimate CDMA efficiency achieved for the intractable optimal multiuser detector.