Abstract
Pre-caching popular files at mobile users with the aid of device-to-device (D2D) communications can offload the data traffic to low-cost D2D links and reduce the network transmission cost. This leads to additional cache leasing cost brought by the lease of storage from mobile users. Besides, newly-emerging video-related applications also pose strict requirement on the network delay. Thus, it is of great significance to design caching strategies considering the transmission cost, the cache leasing cost and the delay. As the movement of mobile users can improve the communication opportunities among different users and increase the cache hit ratio, in this paper, mobility-aware caching strategies are designed to minimize the network cost including both the transmission cost and the cache leasing cost with the delay constraint. In specific, by characterizing the user mobility as an inter-contact model, analytical expressions of the average network cost and the average file delivery delay are derived and a cost-oriented mobility-aware caching problem is formulated. To handle this mixed integer nonlinear programming (MINLP) problem, we first relax the binary cache placement indicator as a continuous one and prove that both the average network cost and the average file delivery delay are convex. Hence, an iterative caching algorithm is proposed with the successive convex approximation method. Moreover, to lower the complexity, combinatorial optimization method is adopted. Firstly, to make the caching problem tractable, the average file delivery delay constraint is implicitly added in the cost objective function as a penalty term. Then, the reformulated objective function is proved to have the non-monotone submodular property and thus a modified low-complexity greedy caching strategy is proposed. Simulation results show that, compared with the most popular caching strategy, our proposed mobility-aware caching strategy can reduce the average cost by 46% when the user speed is high.
Highlights
INTRODUCTIONThe wireless data traffic is growing tremendously and the main driver of it has been fundamentally changed from text and voice to the data-craving applications, such as high-definition video, online games, virtual reality
In recent years, the wireless data traffic is growing tremendously and the main driver of it has been fundamentally changed from text and voice to the data-craving applications, such as high-definition video, online games, virtual realityThe associate editor coordinating the review of this manuscript and approving it for publication was Yunlong Cai .and so on
SIMULATION RESULTS Simulation results are given to evaluate the performance of our proposed mobility-aware caching strategies
Summary
The wireless data traffic is growing tremendously and the main driver of it has been fundamentally changed from text and voice to the data-craving applications, such as high-definition video, online games, virtual reality. These two time durations are random variables characterized by user mobility traces in real-world With this mobility model, mobilityaware caching strategies are proposed in [15], [16] to maximize the traffic offloaded by D2D links. This paper designs cost-oriented mobility-aware and delay-aware caching strategies to minimize the average network cost comprising both the transmission cost and the cache leasing cost with average file delivery delay constraint. The dwelling time of the inter-contact state is assumed to follow the exponential distribution, which is verified by the real-world mobility traces Based on this mobility model, analytical expressions of the average network cost and the average file delivery delay are obtained and cost-oriented mobility-aware and delay-aware caching strategies are designed. It is worth pointing out that contact processes for different user pairs are assumed to be independent
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