Ant-Colony-Based Multiuser Detection for Multifunctional-Antenna-Array-Assisted MC DS-CDMA Systems

A novel ant colony optimization (ACO)-based multiuser detector (MUD) is designed for the synchronous multifunctional antenna array (MFAA)-assisted multicarrier direct-sequence code-division multiple-access (MC DS-CDMA) uplink, which supports both receiver diversity and receiver beamforming. The ACO-based MUD aims to achieve a bit-error-rate performance approaching that of the optimum maximum-likelihood (ML) MUD, without carrying out an exhaustive search of the entire MC DS-CDMA search space constituted by all possible combinations of the received multiuser vectors. We will demonstrate that regardless of the number of the subcarriers or of the MFAA configuration, the system employing the proposed ACO-based MUD is capable of supporting 32 users with the aid of 31-chip Gold codes used as the T-domain spreading sequence without any significant performance degradation when compared to the single-user system. As a further benefit, the number of floating-point operations per second imposed by the proposed ACO-based MUD is a factor of lower than that of the ML MUD. We will also show that at a given increase of the complexity, the MFAA will allow the ACO-based MUD to achieve a higher signal-to-noise ratio gain than the single-input-single-output MC DS-CDMA system.