ADV contains description information, which is much shorter
than complete data. Thus write and read operations take much less consumption
than the previous quorum method without negotiation. They achieve
further energy e?±ciency.
B. Recovery Scheme
However, forming quorums only by row and column is not su?±cient for
their intersection. There are a couple of technical problems that should be
addressed.
Now, suppose that a node v receives an ADV from node w that should
be forwarded northward, but all its neighbors have smaller y-coordinates than
itself. In this case Figure 4(a), the ADV reaches a local maximum with respect
to the direction to the north (i.e., a node without any better neighbors). This
situation will occur when the deployment of sensor nodes has some ???void
areas??? (i.e., the small areas that do not have any sensor nodes).
This failure of further forwarding is due to the inherence of greedy algorithms.
Greedy algorithms work in phases. In each phase, a decision is made
that appears to be the best, without regard for future consequences. There
245 Chapter 10 Location Service, Info. Dissemination and Object Tracking
Dan-Dan Liu and Xiao-Hua Jia
are three basic greedy algorithms, known as: DIR [13], [14], [30], GEDIR [34],
[35] and MFR [36].
In order to direct the message to leave out of the local maximum v, the
protocol should execute a recovery scheme. So it applies the right-hand rule of
face routing [30] on the Gabriel graph [32].
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