Abstract
Abstract The recent ubiquitous deployment of Wi-Fi access points (APs) has offered vehicles to use the high-speed and low-cost Internet service via the roadside APs. However, the high mobility of vehicles and the limited coverage of APs render some challenges. First, it results in frequent handoffs, thus leading to long delay and low service availability. Second, the available AP sets and their channel quality change dynamically, making the AP selection problem even harder. Therefore, there is a strong need to develop an efficient association control mechanism that provides efficient vehicular Wi-Fi access. In this paper, we present a theoretical framework to formulate the optimal association problem through non-linear integer programming, whose objective function is to maximize the throughput or to minimize the handoff overhead. We show that this problem holds the totally unimodular (TU) property and is thus solvable in polynomial time. Then, we study the optimality of association control by comparing existing online algorithms through real trace-based simulations. The results show that there exists a large performance gap between the performance of existing online algorithms and the optimal one. We also observe that the association control algorithm can be further improved if it has access to future knowledge. Particularly, the offline optimal with future AP information improves the performance of the local optimal by up to 10%.
Highlights
Wi-Fi access technology for moving vehicles has drawn considerable attention, since it has been shown that Wi-Fi connectivity is feasible even at vehicular speed [1,2,3,4,5,6,7,8,9]
We prove that the optimal association problems satisfy the totally unimodular (TU) property, and we validate that these problems are solvable in polynomial time
One interesting observation is that if we predict the access points (APs) information 15 s ahead in the future, we achieve 97% compared to the offline optimal performance
Summary
Wi-Fi access technology for moving vehicles has drawn considerable attention, since it has been shown that Wi-Fi connectivity is feasible even at vehicular speed [1,2,3,4,5,6,7,8,9]. 2 Related work Related work falls under two categories: (i) techniques for improving the reliability and performance of vehicular Wi-Fi Internet access, and (ii) studies addressing the association and handoff problems of mobile users. We can utilize the ad hoc communication in this paper, for simplicity, we only consider the single-hop communication between vehicles and APs. There are various approaches to improve the mobile user performance by association control. They consider AP-quality scores as well as channel quality to associate with the APs. The AP-quality scores are determined by average load and backhaul connectivity. Equation 2 is provided since the vehicle can associate with at most one AP among the available APs according to the system model given above
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