Optimization of Information Freshness in Multi-RIS Cooperative Assisted Wireless Sensor Network
Long Qu, An Huang, Maurice Khabbaz · IEEE Transactions on Wireless Communications · 2024
Wireless Sensor Networks (WSNs) require timely information updates for safety and operational efficiency. The Age of Information (AoI) quantifies the freshness of information exchanged among WSN nodes. However, in the presence of noise and fading, sensors communicating with each other as well as with Access Points (APs) may suffer from degraded communication reliability. Here, Reconfigurable Intelligent Surfaces (RISs) are capable of enhancing communication links and, thus, maintaining information freshness. This paper aims at minimizing the AoI perceived by communicating sensors in multi-RIS-assisted WSNs. Precisely, an original AoI-minimal, Deadline-constrained and Cooperative Multi-RIS-assisted (ADCMR) wireless sensor communication framework is presented. This framework embeds a convoluted Integer Linear Program (ILP) formulation aiming at optimizing the schedules of collaborative data transfers subject to deadline and RIS selection constraints. Owing to this ILP’s remarkable complexity, a GReedy Algorithm (GRA) is proposed to generate acceptable sub-optimal schedules with a maximum of 6.66% performance difference compared to their optimal counterparts. GRA, though, is not scalable. This problem is resolved using a Lagrange Relaxation Algorithm (LRA). The difference between LRA and the optimal solution is 2.2%. Also, for large-scale networks, LRA outperforms GRA by 24.8%. Extensive simulations and numerical analyses are conducted to gauge LRA’s benefits and highlight its notable AoI performance improvements over existing benchmarks.