4,088 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
Distributed Storage in Mobile Wireless Networks with Device-to-Device Communication
We consider the use of distributed storage (DS) to reduce the communication
cost of content delivery in wireless networks. Content is stored (cached) in a
number of mobile devices using an erasure correcting code. Users retrieve
content from other devices using device-to-device communication or from the
base station (BS), at the expense of higher communication cost. We address the
repair problem when a device storing data leaves the cell. We introduce a
repair scheduling where repair is performed periodically and derive analytical
expressions for the overall communication cost of content download and data
repair as a function of the repair interval. The derived expressions are then
used to evaluate the communication cost entailed by DS using several erasure
correcting codes. Our results show that DS can reduce the communication cost
with respect to the case where content is downloaded only from the BS, provided
that repairs are performed frequently enough. If devices storing content arrive
to the cell, the communication cost using DS is further reduced and, for large
enough arrival rate, it is always beneficial. Interestingly, we show that MDS
codes, which do not perform well for classical DS, can yield a low overall
communication cost in wireless DS.Comment: After final editing for publication in TCO
Secure Partial Repair in Wireless Caching Networks with Broadcast Channels
We study security in partial repair in wireless caching networks where parts
of the stored packets in the caching nodes are susceptible to be erased. Let us
denote a caching node that has lost parts of its stored packets as a sick
caching node and a caching node that has not lost any packet as a healthy
caching node. In partial repair, a set of caching nodes (among sick and healthy
caching nodes) broadcast information to other sick caching nodes to recover the
erased packets. The broadcast information from a caching node is assumed to be
received without any error by all other caching nodes. All the sick caching
nodes then are able to recover their erased packets, while using the broadcast
information and the nonerased packets in their storage as side information. In
this setting, if an eavesdropper overhears the broadcast channels, it might
obtain some information about the stored file. We thus study secure partial
repair in the senses of information-theoretically strong and weak security. In
both senses, we investigate the secrecy caching capacity, namely, the maximum
amount of information which can be stored in the caching network such that
there is no leakage of information during a partial repair process. We then
deduce the strong and weak secrecy caching capacities, and also derive the
sufficient finite field sizes for achieving the capacities. Finally, we propose
optimal secure codes for exact partial repair, in which the recovered packets
are exactly the same as erased packets.Comment: To Appear in IEEE Conference on Communication and Network Security
(CNS
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