Reconfigurable intelligent surface (RIS) is promising for future 6G wireless communications. However, the increased number of RIS elements results in the high overhead for channel acquisition and the non-negligible power consumption. Therefore, how to improve the system capacity with limited RIS elements is essential. Unlike the classical regular RIS whose elements are arranged on a regular grid, in this paper, we propose an irregular RIS structure. The key idea is to irregularly configure a given number of RIS elements on an enlarged surface, which provides extra spatial degrees of freedom compared with the regular RIS. In this way, the received signal power can be enhanced, and thus the system capacity can be improved. Then, we formulate a joint topology and precoding optimization problem to maximize the capacity for irregular RIS-aided communication systems. Accordingly, a joint optimization algorithm with low complexity is proposed to alternately optimize the RIS topology and the precoding design. Particularly, a tabu search-based method is used to design the irregular RIS topology, and a neighbor extraction-based cross-entropy method is introduced to optimize the precoding design. Simulation results demonstrate that, subject to the constraint of limited RIS elements, the proposed irregular RIS can significantly enhance the system capacity.
翻译:对未来6G无线通信而言,重新配置的智能表面(RIS)很有希望。然而,增加的RIS元素数量导致获取频道的高管理费和不可忽略的电能消耗。因此,如何用有限的RIS元素提高系统能力至关重要。与传统的常规性RIS(其元素在常规网格上排列)不同,我们在本文件中提议了一个不规则的RIS结构。关键的想法是在扩大的表面不规则地配置一定数量的RIS元素,与常规的IRS相比,它提供了额外的空间自由度。这样,收到的信号能量可以得到加强,从而系统能力可以得到改善。然后,我们制定了一种联合的表层和预编码优化问题,以最大限度地增加不规则性RIS辅助通信系统的能力。因此,建议采用一种低复杂性的联合优化算法,以替代优化RIS的表层和预编码设计。特别是,采用基于表格的搜索方法来设计不规则的RIS表层,并采用基于邻居的提取方法来优化前置系统设计,从而可以改进系统的能力。Simulate 结果可以显著地加强拟议的不规则性风险评估。