In this paper, reconfigurable intelligent surface (RIS)-assisted generalized receive quadrature spatial modulation (RIS-GRQSM) is proposed to improve the spectral efficiency of RIS-aided quadrature spatial modulation (QSM) systems by utilizing the concept of generalized spatial modulation (GSM). That is, multiple antennas are activated at the receiver independently for both the real and imaginary parts. We propose a max-min optimization problem to adjust the phase shifts of all RIS elements to maximize the relevant signal-to-noise ratios (SNRs) at all activated receive antennas. Using Lagrange duality, the non-convex optimization problem involving the phase shifts of all RIS elements reduces to a convex optimization involving a number of variables equal to the number of activated receive antennas. A successive greedy detector (GD) can be used at the receiver to detect the active antennas, which simplifies the detection process. The numerical results show that the proposed scheme outperforms the benchmark schemes in terms of error rate performance, especially in systems with a larger number of receive antennas. In the special case where each receive antenna corresponds to a user and is activated, the RIS-GRQSM system becomes a multicast communication system. In this context, in contrast to existing phase shift optimization algorithms which exhibit an impractical level of complexity, our proposed solution offers the advantage of low complexity and practical feasibility of implementation.

翻译：本文提出了一种可重构智能表面（RIS）辅助的广义接收正交空间调制（RIS-GRQSM）方案，通过利用广义空间调制（GSM）的概念，旨在提升RIS辅助正交空间调制（QSM）系统的频谱效率。具体而言，接收端对实部和虚部分别独立激活多个天线。我们提出了一种最大-最小优化问题，通过调整所有RIS单元的相位偏移，最大化所有激活接收天线处的相关信噪比（SNR）。利用拉格朗日对偶性，涉及所有RIS单元相位偏移的非凸优化问题可简化为一个凸优化问题，其变量个数等于激活接收天线的数量。接收端可采用逐次贪婪检测器（GD）来检测激活天线，从而简化检测过程。数值结果表明，所提方案在误码率性能方面优于基准方案，尤其是在接收天线数量较多的系统中。在特殊情况下，当每个接收天线对应一个用户且被激活时，RIS-GRQSM系统成为多播通信系统。在此背景下，与现有复杂度不切实际的相位偏移优化算法相比，我们提出的解决方案具有低复杂度和实际可实现的优势。