Enhanced Generalized Spatial Modulation for STAR-RIS-Aided Vehicular Communication System

In this paper, a novel scheme is proposed by introducing the concept of generalized spatial modulation (GSM) and space-time block code (STBC) into simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) for vehicular communication system. To improve spectral efficiency and diversity gain of vehicular system, STAR-RIS array elements are categorized into reflective and transmissive blocks, establishing a mapping relationship with the index bits by using GSM. Subsequently, the modulated symbols are reflected or transmitted based on the predetermined allocation patterns of the blocks. Specifically, to enhance the reliability of signal reception, one of the most renowned STBC schemes, the Alamouti code, is employed at the STAR-RIS surface by receiving and detecting signals across two consecutive time slots. Furthermore, the new design of leveraging STAR-RIS as an access point (AP) is proposed, which plays the role of source in the communication scenario. The mathematical formulas and theoretical average bit error rate (BER) of the scheme are derived based on preceding analysis. According to simulation results, the suggested scheme can outperform conventional schemes in terms of BER performance. In addition, the proposed redesigned scheme further improves the BER performance with better channel conditions, exhibiting excellent performance advantages.