Performance of Spatial Modulation Aided OTFS under Channel Imperfections

Orthogonal Time Frequency Space (OTFS) modulation and Spatial Modulation (SM) have emerged as promising candidates for high-mobility communication systems, such as those envisioned for beyond 5G and 6G networks. OTFS excels in mitigating the effects of Doppler shifts and channel variations by operating in the delay-Doppler domain, while SM enhances spectral efficiency and reduces system complexity by using antenna indices to convey additional information. However, practical systems often encounter challenges related to imperfect channel state information (CSI) due to errors in channel estimation and rapidly varying channel conditions, which can severely degrade system performance. This paper investigates the performance of an SM-OTFS system under imperfect CSI, addressing a critical yet unexplored issue in current research. Simulations of SM-OTFS whilst considering channel estimation error are simulated and compared with simulations of SM-OTFS without estimation error while using zero-forcing (ZF) equalisationat the receiver. The results show that the proposed SM-OTFS system has a significantly different BER performance compared to one where CSI error was not considered. These findings provide valuable insights for the practical implementation of OTFS-SM in real-world high-mobility communication environments, such as vehicular and satellite networks.