Caching popular contents at mobile devices, assisted by device-to-device(D2D) communications, is considered as a promising technique for mobile contentdelivery. It can effectively reduce backhaul traffic and service cost, as wellas improving the spectrum efficiency. However, due to the selfishness of mobileusers, incentive mechanisms will be needed to motivate device caching. In thispaper, we investigate incentive mechanism design in cache-assisted D2Dnetworks, taking advantage of the user mobility information. An inter-contactmodel is adopted to capture the average time between two consecutive contactsof each device pair. A Stackelberg game is formulated, where each user plays asa follower aiming at maximizing its own utility and the mobile network operator(MNO) plays as a leader aiming at minimizing the cost. Assuming that userresponses can be predicted by the MNO, a cost minimization problem isformulated. Since this problem is NP-hard, we reformulate it as a non-negativesubmodular maximization problem and develop$(\frac{1}{4+\epsilon})$-approximation local search algorithm to solve it. Inthe simulation, we demonstrate that the local search algorithm provides nearoptimal performance. By comparing with other caching strategies, we validatethe effectiveness of the proposed incentive-based mobility-aware cachingstrategy.
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