Enhanced Security Index Modulation for STAR-RIS Aided Intelligent Autonomous Transport Networks

As a promising technology, simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) is proposed to improve the transmission quality and coverage, which is considered to be widely applied to intelligent automated transportation (IAT) systems. However, due to the open environment and 360° omnidirectional transmission, security issues have always been a major difficulty hindering the implementation of STAR-RIS aided IAT systems. To tackle this challenge, we propose an enhanced security index modulation (ESIM) scheme in this paper, which combines well-known IM and higher-order linear decoding quasi-orthogonal space-time block coding (LD-QO-STBC) techniques to improve the system security performance. Specifically, the information bits and transmit antennas are organized into four distinct sets, with each subset of antennas activated by individual IM. Subsequently, the STAR-RIS is employed to meticulously craft the LD-QO-STBC scheme, which involves determining the phase of the unmodulated carrier. In a strategic move to thwart eavesdropping attempts, the eavesdroppers are subjected to continuously varying and disruptive continuous artificial noise (CAN) and is thus unable to reliably decode the transmitted information, which collectively achieves secure communications amidst potential eavesdropping threats. In addition, the theoretical analysis of both the bit error rate (BER) and secrecy capacity are derived to explore the potential of ESIM-LD-QO-STBC. Numerical results reveal that our proposed method excels in achieving a substantial diversity gain while maintaining low computational complexity. Furthermore, our proposed scheme enhances secrecy capacity by at least 50%, offering a marked improvement over conventional physical layer security (PLS) schemes.