Transmit antenna selection for multi-user VASM systems: Simplicity and fairness

Variable Active Antenna Spatial Modulation (VASM) systems have been shown to offer higher spectral efficiency and greater flexibility than conventional spatial modulation systems. In VASM systems, since a part of the information is carried on the indices of activated antennas, the transmit antenna selection (TAS) problem significantly impacts the systems' quality. In this article, we propose two new TAS methods for multi-user VASM systems, namely, Hi-TAS and ObO-TAS. Specifically, Hi-TAS aims to reduce the system's computational complexity, which is a hierarchical combination of two popular TAS methods, i.e., channel gain-based TAS (CG -TAS) and Euclidean distance-based TAS (ED-TAS). Meanwhile, the ObO-TAS alternately chooses each transmit antenna one by one for every user to ensure fairness among them. In addition, we propose the idea of reusable TAs to improve the quality of the system. The calculation and simulation results show that the proposed Hi -TAS has a computational complexity of only 7.74% compared to ED-TAS while achieving better average bit error rate performance for the system than ED-TAS. The proposed ObO-TAS also demonstrates the advantage of ensuring fairness among users, namely that the difference in bit error rate among users is very small compared to other TAS methods.