An Advanced Index Modulation Scheme for V2I Communications: Reflection Modulation-Assisted Adaptive Space Shift Keying

In Intelligent Transportation Systems (ITS), reliable Vehicle-to-Infrastructure (V2I) communication is critical for real-time traffic management, collision avoidance, and environmental monitoring in high-mobility urban scenarios. To support real-time intersection collision-warning and traffic-signal-priority in ITS, we propose an RIS-assisted index modulation scheme that simultaneously increases road-safety message reliability and reduces roadside unit deployment density, termed Reflection Modulation-Assisted Adaptive Space Shift Keying (RM-ASSK). The RM-ASSK scheme leverages reconfigurable intelligent surface (RIS) technology to enhance the efficiency and reliability of wireless communication within transportation systems. By integrating RIS with adaptive space shift keying, the scheme aims to improve spectral efficiency and reduce bit-error rate performance. Meanwhile, we present theoretical analyses of the scheme's spectral efficiency, average BER upper bounds, detection complexity, and ergodic channel capacity lower bounds. These analyses demonstrate the RM-ASSK scheme's superior performance in terms of spectral efficiency, reduced complexity, and improved BER. Besides, to further enhance the scheme's effectiveness and flexibility, we propose a novel antenna-combination selection algorithm, mixture optimized antenna combination selection, and a reflection-element subset design. These innovations optimize BER performance while balancing the trade-off between performance and complexity. Simulations show that RM-ASSK reduces data error rates by up to 25% in Nakagami-m and Rayleigh fading channels typical of urban V2I, enabling 15-20% faster dissemination of traffic alerts and improving vehicle throughput by supporting 30% more connected devices without spectral congestion.