When s ?‰¤ 2l, the REQ message is bound
to meet the DATA message. The advantage is that parameters s and l can
253 Chapter 10 Location Service, Info. Dissemination and Object Tracking
Dan-Dan Liu and Xiao-Hua Jia
be adjusted depending on frequencies of events and queries in the system,
dynamically. However, in an irregular network, the REQ messages can hardly
follow a comb shape, and the comb may miss the needle (i.e., the success rate
of an REQ finding its matched data is poor). This problem will be even more
severe in the presence of ???void areas??? in the network.
S
D
Fig. 9. Comb-needle model.
5 Conclusion
In this chapter, we tried to present an overview of the quorum method applied
to three main problems in wireless networks. They are: location service,
information dissemination and object tracking. Location service is the general
obstacle for distributed networks, since the current location of a destination
node should be known before any data can be delivered correctly. The main
goal of wireless sensor networks is to provide required and latest data sensed
at a source node to any other nodes that are interested in the data. Therefore,
the central issue that needs to be addressed is to develop energy e?±cient
protocols to disseminate information. Object tracking in a military battlefield
situation is one of the most important applications of sensor networks. It is
a combination of the other two problems and can be dealt with by similar
methods.
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