Age of Information Minimization for Opportunistic Channel Access

This paper investigates how to suppress the Age of Information (AoI) in an opportunistic channel access system, which allows multiple mobile devices to access a base station without central coordination while being aware of instant channel quality. An optimization problem is formulated to minimize the average AoI by optimizing each mobile device's probability of contending for channel access opportunity and the threshold of offload rate. We derive the exact expression of the average AoI and generate a reformulated optimization problem. Although being non-convex, the reformulated problem is tackled by the following operations. First, we leverage the Dinkelbach method and the block coordinate descent method to convert the reformulated problem into an iterative solving procedure of two non-convex sub-problems, which optimize the contending probability and the threshold of offload rate respectively. Second, for each non-convex sub-problem, we explore the piecewise differential monotonicity for the cost function, and achieve the associated optimal solution by transforming them into standard monotonic optimization problems. Numerical results can verify the effectiveness of the proposed method through the comparison with benchmark methods.