13-11-2012, 03:49 PM
Caching Strategies Based on Information Density Estimation in Wireless Ad Hoc Networks
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INTRODUCTION
PROVIDING information to users on the move is one of the
most promising directions of the infotainment business,
which rapidly becomes a market reality, because infotainment
modules are deployed on cars and handheld devices. The ubiquity
and ease of access of third- and fourth-generation (3G
or 4G) networks will encourage users to constantly look for
content that matches their interests. However, by exclusively
relying on downloading from the infrastructure, novel applications
such as mobile multimedia are likely to overload the
wireless network (as recently happened to AT&T following
the introduction of the iPhone [1]). It is thus conceivable
that a peer-to-peer system could come in handy, if used in
conjunction with cellular networks, to promote content sharing
using ad hoc networking among mobile users [2].
Content Diversity
Similar to Hamlet, in [6], mobile nodes cache data items
other than their neighbors to improve data accessibility. In
particular, the solution in [6] aims at caching copies of the same
content farther than a given number of hops. Such a scheme,
however, requires the maintenance of a consistent state among
nodes and is unsuitable for mobile network topologies. The
concept of caching different content within a neighborhood is
also exploited in [7], where nodes with similar interests and
mobility patterns are grouped together to improve the cache hit
rate, and in [8], where neighboring mobile nodes implement
a cooperative cache replacement strategy. In both works, the
caching management is based on instantaneous feedback from
the neighboring nodes, which requires additional messages.
The estimation of the content presence that we propose, instead,
avoids such communication overhead.
SYSTEM OUTLINE AND ASSUMPTIONS
Hamlet is a fully distributed caching strategy for wireless
ad hoc networks whose nodes exchange information items in
a peer-to-peer fashion. In particular, we address a mobile ad
hoc network whose nodes may be resource-constrained devices,
pedestrian users, or vehicles on city roads. Each node runs an
application to request and, possibly, cache desired information
items. Nodes in the network retrieve information items from
other users that temporarily cache (part of) the requested items
or from one or more gateway nodes, which can store content or
quickly fetch it from the Internet.
HAMLET FRAMEWORK
The Hamlet framework allows wireless users to take caching
decisions on content that they have retrieved from the network.
The process that we devise allows users to take such decisions
by leveraging a node’s local observation, i.e., the node’s
ability to overhear queries and information messages on the
wireless channel. In particular, for each information item, a
node records the distance (in hops) of the node that issues the
query, i.e., where a copy of the content is likely to be stored,
and the distance of the node that provides the information.
Based on such observations, the node computes an index of the
information presence in its proximity for each of the I items.