Proposal of a Hierarchical Combination of CG-TAS and ED-TAS to Improve BER Performance at Low Complexity for VASM Systems

The spatial modulation (SM) technique has been extended with various variants, one of which is variable active antenna spatial modulation (VASM), where the count of activated transmit antennas varies according to the input bit sequence. This approach offers significant enhancements to the spectral efficiency and flexibility of VASM in comparison to conventional SM systems. Channel gain (CG) and Euclidean distance (ED) are widely adopted criteria for transmit antenna selection (TAS) in SM systems. CG-TAS provides low computational complexity; however, it exhibits a slight improvement in bit error rate (BER) performance. Conversely, ED-TAS optimally enhances BER performance at the cost of higher computational complexity. This paper proposes a novel low-complexity TAS method, named HC-TAS, that hierarchically combines CG-TAS with ED-TAS for the VASM systems. A comprehensive analysis of computational complexity demonstrates HC-TAS’s superiority over ED-TAS in alleviating the workload burden. Furthermore, Monte Carlo simulation results indicate that HC-TAS outperforms CG-TAS and approximates ED-TAS in enhancing BER performance.