How Long Can RIS Work Effectively: An Electronic Reliability Perspective

In this paper, from an electronic reliability perspective, non-residual stochastic hardware aging (HA) effects are introduced to reconfigurable intelligent surfaces (RISs) aided communication systems, for characterizing the life cycle of the RIS. Different from traditional residual impairment factors such as RIS phase imperfections and transceiver noises, the impact of the stochastic HA effect on the RIS is related to RIS runtimes and lifetimes. Given this background, we first propose a Rician channel model for the RIS-aided system with the stochastic HA effect. Then, the definition for the lifetime of the RIS is mathematically given as the time at which 63.2% of the elements expire. Besides, closed-form achievable rate expression is also derived. Analytical and simulated results unveil an important insight that throughout the life cycle of the RIS, the residual impairment dominates when the runtime is shorter than the lifetime, otherwise the stochastic HA effect should be paid more attention to. This work can be regarded as the first guideline for evaluating and predicting the whole life cycle performance of the RIS-assisted system.