This paper investigates the benefits of integrating multiple reconfigurable intelligent surfaces (RISs) in enhancing the timeliness performance of uplink Internet-of-Things (IoT) network, where IoT devices (IoTDs) upload their time-stamped status update information to a base station (BS) using non-orthogonal multiple access (NOMA). Accounting to the potential unreliable wireless channels due to the impurities of the propagation environments, such as deep fading, blockages, etc., multiple RISs are deployed in the considered IoT network to mitigate the propagation-induced impairments, to enhance the quality of the wireless links, and to ensure that the required freshness of information is achieved. In this setup, an optimization problem has been formulated to minimize the average sum Age of Information (AoI) by optimizing the transmit power of the IoTDs, the IoTDs clustering policy, and the RISs configurations. The formulated problem ends up to be a mixed-integer non-convex problem. In order to tackle this challenge, the RISs configurations are first obtained by adopting a semi-definite relaxation (SDR) approach. Then, the joint power allocation and user-clustering problem is solved using the concept of bi-level optimization, where the original problem is decomposed into an outer IoTDs clustering problem and an inner power allocation problem. Optimal closed-form expressions are derived for the inner problem and the Hungarian method is invoked to solve the outer problem. Numerical results demonstrate that our proposed approach achieves lowest AoI compared to the other baseline approaches.
翻译:本文考察了将多种可重新校正的智能表面(RIS)整合起来的好处,这些表面(RIS)可以提高互联网上链路(IoT)网络的及时性性能,因为IoT设备(IoTDs)使用非orogon 多重访问(NOMA)向基地站(BS)上传了时间标记状态更新信息。考虑到由于传播环境的杂质(如深度淡化、阻塞等)而可能造成的不可靠的无线频道,在被考虑的 IoT 网络中部署多种RIS,以缓解传播导致的缺陷,提高无线链接的质量,并确保实现所要求的信息新鲜性。在这一设置中,一个优化问题是为了通过优化 IoTDs 的传输能力、 IoTDs 组合政策和RINS 配置问题, 形成一种混合内向非convex的问题。为了应对这个挑战, 将Oilalalalal- electoral 连接起来, 将一个内部动力配置的系统配置方法展示为一种内部结构, IMISDR 配置是采用一种内部配置, IMF 。