65 research outputs found
Repair Scheduling in Wireless Distributed Storage with D2D Communication
We consider distributed storage (DS) for a wireless network where mobile
devices arrive and depart according to a Poisson random process. Content is
stored in a number of mobile devices, using an erasure correcting code. When
requesting a piece of content, a user retrieves the content from the mobile
devices using device-to-device communication or, if not possible, from the base
station (BS), at the expense of a higher communication cost. We consider the
repair problem when a device that stores data leaves the network. In
particular, we introduce a repair scheduling where repair is performed (from
storage devices or the BS) periodically. We derive analytical expressions for
the overall communication cost of repair and download as a function of the
repair interval. We illustrate the analysis by giving results for maximum
distance separable codes and regenerating codes. Our results indicate that DS
can reduce the overall communication cost with respect to the case where
content is only downloaded from the BS, provided that repairs are performed
frequently enough. The required repair frequency depends on the code used for
storage and the network parameters. In particular, minimum bandwidth
regenerating codes require very frequent repairs, while maximum distance
separable codes give better performance if repair is performed less frequently.
We also show that instantaneous repair is not always optimal.Comment: To be presented at IEEE Information Theory Workshop (ITW) 2015, Jeju
Island, Korea, October 201
Backhaul-Aware Caching Placement for Wireless Networks
As the capacity demand of mobile applications keeps increasing, the backhaul
network is becoming a bottleneck to support high quality of experience (QoE) in
next-generation wireless networks. Content caching at base stations (BSs) is a
promising approach to alleviate the backhaul burden and reduce user-perceived
latency. In this paper, we consider a wireless caching network where all the
BSs are connected to a central controller via backhaul links. In such a
network, users can obtain the required data from candidate BSs if the data are
pre-cached. Otherwise, the user data need to be first retrieved from the
central controller to local BSs, which introduces extra delay over the
backhaul. In order to reduce the download delay, the caching placement strategy
needs to be optimized. We formulate such a design problem as the minimization
of the average download delay over user requests, subject to the caching
capacity constraint of each BS. Different from existing works, our model takes
BS cooperation in the radio access into consideration and is fully aware of the
propagation delay on the backhaul links. The design problem is a mixed integer
programming problem and is highly complicated, and thus we relax the problem
and propose a low-complexity algorithm. Simulation results will show that the
proposed algorithm can effectively determine the near-optimal caching placement
and provide significant performance gains over conventional caching placement
strategies.Comment: 6 pages, 3 figures, accepted to IEEE Globecom, San Diego, CA, Dec.
201
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