Performance Analysis of Index Modulation Scheme Combining RIS Sub-Blocks and Receiving Antennas

‍ ‍The reconfigurable intelligent surface （RIS）， designed by numerous passive reflective devices， presents the advantages of expanding wireless communication coverage， reducing system costs/power consumption， and improving future communication system performance. Moreover， index modulation （IM） realizes the implicit transmission of information by activating a subset of communication resources， which was expected to provide higher spectral efficiency and energy efficiency for wireless communication. To further improve the performance of future wireless communication systems， this paper thus proposes an IM scheme by combining the RIS and IM technologies. In this scheme， RIS reflection elements are divided into sub-blocks based on the adjacent principle. Additional information is transmitted concurrently through both the RIS sub-block index and the receiving antenna index. Specifically， transmitted bit sequences are divided into three parts： the first bit is modulated into constellation symbols， the second indicates RIS sub-block divisions， and the third denotes the receiving antenna index. Based on the analytical form of paired error probability （PEP） of maximum likelihood （ML） detection， the corresponding moment-generating function was theoretically derived in four cases， and the analytical expression of unconditional PEP was obtained. Finally， the upper bound of the mean bit error rate （ABER） performance of ML detection for this scheme was obtained. Simulation results show that the proposed scheme has advantages in terms of system reachable rate and system error performance compared with the existing RIS-assisted IM schemes and verify that the ABER upper bound of ML detection has strict consistency as well.