Index modulation schemes for reconfigurable intelligent surfaces (RIS)-assisted systems are envisioned as promising technologies for fifth-generation-advanced and sixth-generation (6G) wireless communication systems to enhance various system capabilities such as coverage area and network capacity. In this paper, we consider a receive diversity RIS-assisted wireless communication system employing IM schemes, namely, space-shift keying (SSK) for binary modulation and spatial modulation (SM) for M-ary modulation for data transmission. The RIS lies in close proximity to the transmitter, and the transmitted data is subjected to a fading environment with a prominent line-of-sight component modeled by a Rician distribution. A receiver structure based on a greedy detection rule is employed to select the receive diversity branch with the highest received signal energy for demodulation. The performance of the considered system is evaluated by obtaining a series-form expression for the probability of erroneous index detection (PED) of the considered target antenna using a characteristic function approach. In addition, closed-form and asymptotic expressions at high and low signal-to-noise ratios (SNRs) for the bit error rate (BER) for the SSK-based system, and the SM-based system employing M-ary phase-shift keying and M-ary quadrature amplitude modulation schemes, are derived. The dependencies of the system performance on the various parameters are corroborated via numerical results. The asymptotic expressions and results of PED and BER at high and low SNR values lead to the observation of a performance saturation and the presence of an SNR value as a point of inflection, which is attributed to the greedy detector's structure.

翻译：摘要：针对可重构智能表面(RIS)辅助系统的索引调制方案，被视为增强第五代增强版和第六代(6G)无线通信系统覆盖范围与网络容量等系统能力的前沿技术。本文考虑采用空间移位键控(SSK)二进制调制与空间调制(SM)M进制调制的接收分集RIS辅助无线通信系统。RIS紧邻发射端，传输数据经历具有显著视距分量的莱斯分布衰落环境。采用基于贪心检测准则的接收机结构，选择具有最高接收信号能量的分集支路进行解调。通过特征函数方法推导目标天线索引检测错误概率(PED)的级数表达式来评估系统性能。此外，推导了基于SSK系统及采用M进制相移键控与M进制正交幅度调制方案的SM系统在高、低信噪比(SNR)下的误码率(BER)闭合渐近表达式。通过数值结果验证了系统性能对多种参数的依赖关系。高、低SNR下的PED与BER渐近表达式及结果表明，存在性能饱和现象及作为拐点的SNR值，该现象归因于贪心检测器的结构特性。