In this paper, we investigate a practical structure of reconfigurable intelligent surface (RIS)-based double spatial scattering modulation (DSSM) for millimeter-wave (mmWave) multiple-input multiple-output (MIMO) systems. A suboptimal detector is proposed, in which the beam direction is first demodulated according to the received beam strength, and then the remaining information is demodulated by adopting the maximum likelihood algorithm. Based on the proposed suboptimal detector, we derive the conditional pairwise error probability expression. Further, the exact numerical integral and closed-form expressions of unconditional pairwise error probability (UPEP) are derived via two different approaches. To provide more insights, we derive the upper bound and asymptotic expressions of UPEP. In addition, the diversity gain of the RIS-DSSM scheme was also given. Furthermore, the union upper bound of average bit error probability (ABEP) is obtained by combining the UPEP and the number of error bits. Simulation results are provided to validate the derived upper bound and asymptotic expressions of ABEP. We found an interesting phenomenon that the ABEP performance of the proposed system-based phase shift keying is better than that of the quadrature amplitude modulation. Additionally, the performance advantage of ABEP is more significant with the increase in the number of RIS elements.

翻译：本文研究了基于可重构智能表面（RIS）的双空间散射调制（DSSM）在毫米波（mmWave）多输入多输出（MIMO）系统中的实用结构。提出了一种次优检测器，首先根据接收波束强度解调波束方向，然后采用最大似然算法解调剩余信息。基于所提出的次优检测器，推导了条件成对错误概率表达式。进一步，通过两种不同方法推导了无条件的成对错误概率（UPEP）的精确数值积分和闭式表达式。为提供更深入的理解，推导了UPEP的上界和渐近表达式。此外，还给出了RIS-DSSM方案的分集增益。进而，结合UPEP与错误比特数，得到了平均比特错误概率（ABEP）的联合上界。仿真结果验证了所推导的ABEP上界与渐近表达式。我们观测到一个有趣的现象：基于相移键控的所提系统的ABEP性能优于正交幅度调制。此外，随着RIS单元数量的增加，ABEP的性能优势更加显著。