The concept of age of information (AoI) has been proposed to quantify information freshness, which is crucial for time-sensitive applications. However, in millimeter wave (mmWave) communication systems, the link blockage caused by obstacles and the severe path loss greatly impair the freshness of information received by the user equipments (UEs). In this paper, we focus on reconfigurable intelligent surface (RIS)-assisted mmWave communications, where beamforming is performed at transceivers to provide directional beam gain and a RIS is deployed to combat link blockage. We aim to maximize the system sum rate while satisfying the information freshness requirements of UEs by jointly optimizing the beamforming at transceivers, the discrete RIS reflection coefficients, and the UE scheduling strategy. To facilitate a practical solution, we decompose the problem into two subproblems. For the first per-UE data rate maximization problem, we further decompose it into a beamforming optimization subproblem and a RIS reflection coefficient optimization subproblem. Considering the difficulty of channel estimation, we utilize the hierarchical search method for the former and the local search method for the latter, and then adopt the block coordinate descent (BCD) method to alternately solve them. For the second scheduling strategy design problem, a low-complexity heuristic scheduling algorithm is designed. Simulation results show that the proposed algorithm can effectively improve the system sum rate while satisfying the information freshness requirements of all UEs.

翻译：信息年龄（AoI）概念已被提出用于量化信息新鲜度，这对时间敏感型应用至关重要。然而，在毫米波通信系统中，障碍物引起的链路阻塞和严重的路径损耗会极大损害用户设备接收信息的新鲜度。本文聚焦于可重构智能表面辅助的毫米波通信，其中收发端通过波束赋形提供定向波束增益，并部署RIS以应对链路阻塞问题。我们旨在通过联合优化收发端波束赋形、离散RIS反射系数及UE调度策略，在满足用户信息新鲜度要求的同时最大化系统总和速率。为便于实际求解，我们将原始问题分解为两个子问题：针对首个单用户数据速率最大化问题，进一步将其拆解为波束赋形优化子问题和RIS反射系数优化子问题。考虑到信道估计的困难，前者采用分层搜索方法，后者采用局部搜索方法，并采用块坐标下降法交替求解。针对第二个调度策略设计问题，设计了低复杂度启发式调度算法。仿真结果表明，所提算法能在满足所有用户信息新鲜度要求的同时有效提升系统总和速率。