THESIS
2017
xvii, 155 pages : illustrations ; 30 cm
Abstract
The mobile data traffic is growing at an exponential rate, among which mobile video accounts for more than a half. Network densification is commonly adopted to accommodate
the increasing demand, which incurs a heavy burden on the backhaul links. Cache-enabled
content-centric networking (CCN) is considered as a promising approach to alleviate backhaul burden, as well as improving the user experience of video streaming applications. Moreover, caching at mobile devices can facilitate device-to-device (D2D) communications, which
can significantly improve spectral efficiency. The cache-assisted D2D network operates in two phases: cache placement and content delivery. Cache placement deals with where to
cache, what to cache, and how to update; while content delivery deals with network res...[
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The mobile data traffic is growing at an exponential rate, among which mobile video accounts for more than a half. Network densification is commonly adopted to accommodate
the increasing demand, which incurs a heavy burden on the backhaul links. Cache-enabled
content-centric networking (CCN) is considered as a promising approach to alleviate backhaul burden, as well as improving the user experience of video streaming applications. Moreover, caching at mobile devices can facilitate device-to-device (D2D) communications, which
can significantly improve spectral efficiency. The cache-assisted D2D network operates in two phases: cache placement and content delivery. Cache placement deals with where to
cache, what to cache, and how to update; while content delivery deals with network resource
allocation among the base station, caching mobile, content-requesting mobile.
While designing the cache placement, most previous works ignored user mobility, thus
having limited practical applications. In this thesis, we take advantage of the user mobility
pattern and propose mobility-aware cache placement strategies to maximize the data offloading ratio, which is defined as the percentage of the requested data that can be delivered via
D2D links rather than through base stations (BSs). We consider that the timeline of each user
pair is divided into contact durations, when the two users are in contact, and inter-contact
durations, which are the time intervals between two consecutive contact durations. Firstly,
by utilizing the statistical information of inter-contact durations, a cache placement problem
is formulated. To solve the NP-hard caching problem, we propose an optimal dynamic programming (DP) algorithm to obtain a performance benchmark, as well as a time-efficient
greedy algorithm, which achieves an approximation ratio as 1/2 . Then, we explicitly consider both the users’ contact and inter-contact durations via an alternating renewal process. A tractable expression of the data offloading ratio is derived, which is proved to be increasing with the user moving speed. The analytical results are then used to develop an effective
mobility-aware caching strategy.
Due to the selfishness of mobile users, incentive mechanisms will be needed to motivate
device caching in the cache placement phase. By taking advantage of the user mobility information, we design an incentive mechanism in a cache-assisted D2D network. A Stackelberg
game is formulated, where each user plays as a follower aiming at maximizing its own utility and the mobile network operator (MNO) plays as a leader aiming at minimizing the overall
cost. Assuming that user responses can be predicted by the MNO, a cost minimization
problem is formulated. Since this problem is NP-hard, we reformulate it as a non-negative
submodular maximization problem and develop a
(1/4+ϵ)
-approximation local search algorithm
to solve it.
In the content delivery phase, the user requests are served via D2D links. However, without
appropriate network design, severe interference will be generated between the cellular
and D2D links. Dynamic resource allocation is effective for managing interference in D2D
networks. We therefore propose effective channel assignment algorithms for network utility
maximization in a cellular network with underlaying D2D communications. A major innovation
is the consideration of partial channel state information (CSI), i.e., the BS is assumed
to be able to acquire partial instantaneous CSI of the cellular and D2D links, as well as, the
interference links. In contrast to existing works, multiple D2D links are allowed to share the
same channel, and the quality of service (QoS) requirements for both the cellular and D2D
links are enforced. Furthermore, with D2D communications, mobile user may operate in
cellular mode and D2D mode. Accordingly, effective mode selection schemes are needed.
While mode selection and resource allocation are typically separately designed, we consider
to jointly optimize the mode selection and channel assignment in a cellular network with
underlaying D2D communications.
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