Joint Admission Control and Beamforming for Intelligent Reflecting Surface Aided Wireless Networks

Intelligent reflecting surface (IRS) is a promising technique that can enhance the spectral-efficiency and energy-efficiency of wireless networks. The existing studies on resource allocation in IRS-aided wireless networks have a common assumption that the quality-of-service (QoS) requirements of all users can be satisfied. However, when the number of users is large and/or the QoS requirement is stringent, the resource allocation problem may be infeasible. In this paper, we study the joint multi-user admission control and transmit beamforming problem in an IRS-aided downlink cellular network. We aim to simultaneously maximize the number of users that can be served with certain QoS requirements and minimize the transmit power required to serve the admitted users. The formulated problem turns out to be NP-hard. To ensure the feasibility of the transformed problem, we introduce auxiliary variables to the objective function and QoS constraints. We decouple the transformed single-stage problem into two subproblems and reformulate the subproblems as semidefinite programming problems. To deal with the rank-one constraints, we introduce a difference-of-convex representation, which is added to the objective function as a penalty term. We solve the resulting subproblems using successive convex relaxation, followed by proposing an effective algorithm to solve the joint problem. Simulation results show that the proposed algorithm achieves near-optimal performance and also outperforms the benchmark algorithms in terms of the number of admitted users and the per-user power consumption.