Active Fully-connected RIS Based on Index Modulation for High Rate and Energy-Efficient Systems

In this paper, a novel active fully-connected reconfigurable intelligent surface assisted space shift keying and code index modulation (AFRIS-SCIM) scheme is proposed. On one hand, by introducing joint space-code index modulation while maintaining low power consumption and complexity, the proposed scheme achieves higher data rates compared to existing one-dimensional index modulation. On the other hand, the proposed active fully-connected architecture achieves a desirable trade-off between reliability and power consumption compared to conventional passive RIS and active RIS architectures. Additionally, to reduce detection complexity at the receiver, a low-complexity detection algorithm is proposed and the upper bound for the bit error rate (BER) of the system is derived. Mathematical models characterizing the system complexity and power consumption are also established to analyze the overall performance. Both theoretical analyses and simulation results demonstrate that the AFRIS-SCIM scheme outperforms existing RIS-IM schemes as well as multidimensional index modulation systems in terms of BER performance.