This letter proposes an analytical framework for multi-reconfigurable intelligent surface (RIS) aided networks with limited backhaul capacity, where a simple symmetric structure is considered to explore the characteristics of multi-RIS systems with coherent transmissions. By using the Gamma distribution to model the composite RIS-aided channels, closed-form expressions in terms of the outage probability and the ergodic rate are derived. The theoretical results provide two design guidelines: 1) the minimum outage can be achieved by deploying the assisted RISs at certain locations; 2) the rate performance is bounded, and an optimal number of assisted RISs exists for rate maximization. Simulations verify our analysis and demonstrate the backhaul capacity is the bottleneck for multi-RIS systems. Compared with single-RIS systems, multi-RIS systems require a minimal backhaul capacity to ensure the performance gain.

中文翻译：

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回程受限网络中的下行链路多 RIS 辅助传输

这封信提出了一个用于回程容量有限的多可重构智能地面 (RIS) 辅助网络的分析框架，其中考虑了一个简单的对称结构来探索具有相干传输的多 RIS 系统的特性。通过使用 Gamma 分布对复合 RIS 辅助通道进行建模，导出了关于中断概率和遍历率的闭式表达式。理论结果提供了两个设计指南：1）通过在某些位置部署辅助RIS可以实现最小的中断；2）速率性能是有界的，并且存在用于速率最大化的辅助RIS的最佳数量。仿真验证了我们的分析并证明回程容量是多 RIS 系统的瓶颈。与单RIS系统相比，