Reconfigurable intelligent surface (RIS)-assisted index modulation system schemes are considered a promising technology for sixth-generation (6G) wireless communication systems, which can enhance various system capabilities such as coverage and reliability. However, obtaining perfect channel state information (CSI) is challenging due to the lack of a radio frequency chain in RIS. In this paper, we investigate the RIS-assisted full-duplex (FD) two-way space shift keying (SSK) system under imperfect CSI, where the signal emissions are augmented by deploying RISs in the vicinity of two FD users. The maximum likelihood detector is utilized to recover the transmit antenna index. With this in mind, we derive closed-form average bit error probability (ABEP) expression based on the Gaussian-Chebyshev quadrature (GCQ) method and provide the upper bound and asymptotic ABEP expressions in the presence of channel estimation errors. To gain more insights, we also derive the outage probability and provide the throughput of the proposed scheme with imperfect CSI. The correctness of the analytical derivation results is confirmed via Monte Carlo simulations. It is demonstrated that increasing the number of elements of RIS can significantly improve the ABEP performance of the FD system over the half-duplex (HD) system. Furthermore, in the high SNR region, the ABEP performance of the FD system is better than that of the HD system.

翻译：可重构智能表面（RIS）辅助的索引调制系统方案被视为第六代（6G）无线通信系统的有前景技术，能够增强覆盖范围、可靠性等多种系统能力。然而，由于RIS缺乏射频链路，获取完美信道状态信息（CSI）面临挑战。本文研究了非完美CSI下RIS辅助的全双工（FD）双向空间移位键控（SSK）系统，其中通过在两个FD用户附近部署RIS来增强信号发射。采用最大似然检测器恢复发射天线索引。基于此，我们利用高斯-切比雪夫求积（GCQ）方法推导了平均误比特概率（ABEP）的闭式表达式，并给出了信道估计误差存在时的上界和渐近ABEP表达式。为获得更深入见解，我们还推导了中断概率并提供了非完美CSI下所提方案的吞吐量。通过蒙特卡洛仿真验证了分析推导结果的正确性。研究表明，增加RIS单元数量可显著提升FD系统相较于半双工（HD）系统的ABEP性能。此外，在高信噪比区域，FD系统的ABEP性能优于HD系统。