Spectral efficiency of a non‐orthogonal FH‐CDMA system

Abstract

Fast frequency hopping code division multiple access (FH-CDMA) is a low complexity option for multiuser communication in fast, frequency selective fading channels such as in mobile mmWave communications. The original, orthogonal FH-CDMA has low spectral efficiency and up to now lacks a non-orthogonal version. In this work, a soft input soft output, non-orthogonal multiuser detector is designed using factor graphs. Extrinsic Information Transfer (EXIT) chart analysis of this detector allows determination of which multiple access code length maximises system spectral efficiency. Results show that when the access code length is reduced to an ideal length, spectral efficiency is maximised. Another conclusion is that maximum spectral efficiency is similar in value to a system with no multiple access method.