Optimizing Multi-User Vasm Systems: A Novel Approach for Transmit Antenna Selection

Abstract

Variable active antenna spatial modulation (VASM) schemes have demonstrated superiority over conventional spatial modulation techniques in terms of enhancing spectral efficiency and system configuration flexibility in multiple-input multiple-output (MIMO) systems. To meet the increasing demands of users, it is crucial to extend this scheme from point-to-point single-user transmission to multi-user (MU) transmission. By incorporating non-orthogonal multiple access (NOMA) into VASM, NOMA-VASM schemes have been proposed to further enhance spectral efficiency and flexibility for downlink MU transmission systems. However, BER performance degrades when many users are involved. In this study, we propose a novel scheme for the downlink MU-VASM system, where each user employs a set of transmit antennas at the base station. We utilize a combination of precoders and equalizers to effectively eliminate multi-user interference in this system. Moreover, we introduce two novel transmit antenna selection (TAS) algorithms: hierarchical (Hi)-TAS, which offers low complexity while significantly improving BER performance, and one-by-one (ObO)-TAS, which ensures fairness among users. In addition, we also propose the reuse of transmit antennas among different users to optimize the system’s performance.

Keywords: Variable active antenna spatial modulation (VASM), transmit antenna selection (TAS), multi-user MIMO system, precoding and equalizer