An Optimal Query Assignment for Wireless Sensor Networks

TL;DR

This paper develops an optimal query assignment policy for wireless sensor networks balancing query waiting time and data freshness, using a Markov decision process and dynamic programming, outperforming heuristics in simulations and real traffic.

Contribution

It introduces a novel optimal policy for query assignment in wireless sensor networks based on a continuous-time Markov decision process and uniformization, improving over existing heuristics.

Findings

Optimal policy reduces average assignment costs.

Policy outperforms common heuristics in simulations.

Significant cost savings in real query traffic.

Abstract

A trade-off between two QoS requirements of wireless sensor networks: query waiting time and validity (age) of the data feeding the queries, is investigated. We propose a Continuous Time Markov Decision Process with a drift that trades-off between the two QoS requirements by assigning incoming queries to the wireless sensor network or to the database. To compute an optimal assignment policy, we argue, by means of non-standard uniformization, a discrete time Markov decision process, stochastically equivalent to the initial continuous process. We determine an optimal query assignment policy for the discrete time process by means of dynamic programming. Next, we assess numerically the performance of the optimal policy and show that it outperforms in terms of average assignment costs three other heuristics, commonly used in practice. Lastly, the optimality of the our model is confirmed also in the case of real query traffic, where our proposed policy achieves significant cost savings compared to the heuristics.