Fairness-Oriented Multiple RIS-Aided mmWave Transmission: Stochastic Optimization Methods

In millimeter wave (mmWave) systems, it is challenging to ensure reliable communication links due the high sensitivity presence of blockages. order improve robustness mmWave systems in random blockages, we consider deployment multiple reconfigurable intelligent surfaces (RISs) enhance spatial diversity gain, and design robust beamforming schemes based on stochastic optimization methods that minimize maximum outage probability among users so as fairness. Under framework, adopt majorization–minimization (SMM) method successive convex approximation (SSCA) construct deterministic surrogate problems at each iteration, obtain closed-form solutions precoding matrix base station (BS) vectors RISs. Both are proved converge set stationary points original problems. Simulation results show proposed for RIS-aided can effectively compensate performance loss caused by especially when blockage high.