Transmit Antenna Selection-Based SM-OTFS System for Green Communication

Orthogonal time frequency space (OTFS) is a novel modulation technique that improves the transmission reliability of the system in high-mobility scenarios. Spatial modulation (SM) appears as a green communication technique to enhance the spectral efficiency (SE) and energy efficiency (EE) of the system. In this paper, we propose the transmit antenna selection (TAS) based SM-OTFS system to improve the transmit diversity (TD) and reliability in mobile communication environments. TAS is performed based on the Euclidean distances (EDTAS) of the transmit antenna (TA) subset. Further, we present low-complexity TAS based on a tree search scheme (LCTAS-TSS) for a small-scale SM-OTFS system. We show norm and antenna correlation (N-AC) based TAS scheme (LCTAS-N-AC) to reduce the search complexity of LCTAS-TSS further. The complexities of EDTAS, LCTAS-TSS, and LCTAS-N-AC are analyzed. Analytical expressions of TD for EDTAS are verified using simulation results. Simulation results show that LCTAS-TSS attains the same BER performance as the EDTAS scheme offers at reduced complexity. Moreover, results show that LCTAS-N-AC provides substantial complexity reduction compared to LCTAS-TSS and performs better than the conventional OTFS and SM-OTFS for comparable configurations.