Resource allocation for RIS-aided mmWave system with cooperative and non-cooperative base stations

The emergence of reconfigurable intelligent surfaces (RIS) represents a notable technological advancement that has gained considerable interest within the wireless communication domain. However, due to cost and privacy concerns, different operators may not make an agreement on cooperatively utilizing RISs and sharing resources. In the presence of non-cooperative base stations (BSs) from different operators, conventional resource allocation and RIS design are rendered inapplicable. Motivated by this fact, we explore the resource allocation scheme for RIS-assisted millimeter wave (mmWave) systems with cooperative and non-cooperative BSs. We first delineate between the cooperation and non-cooperation modes of BSs, based on their agreement concerning the joint utilization of RISs. We then formulate the joint optimization problem of the reflection coefficients of RISs, active beamforming, power allocation, and user association at BSs. The objective is to maximize the sum rates for users served by cooperative BSs while ensuring the channel gain constraints between non-cooperative BSs and their associated users so as to mitigate the effects of RISs on the communication of non-cooperative BSs. To address the mixed binary optimization problem, we leverage the block coordinate descent (BCD) technique to decompose the original problem into several sub-problems, each iteratively optimized until convergence is achieved. Simulation results validate the effectiveness of RISs in improving sum rate performance, while also providing additional benefits by mitigating their impact on non-cooperative BSs and their associated users.