A destination
search packet from the source is forwarded in a similar fashion. It is first
broadcasted to the easternmost and westernmost neighbors of the source, and
retransmitted along its east-west direction (forming a row) until it reaches
the end. The location update and destination search process can form a cross
shape inside the network (Figure 1).
Figure 1 (a) is the best situation that quorum method is used in a regular
grid system. Obviously, a row and a column are bound to intersect. Figure 1
(b) shows the situation that the quorum method is applied to common wireless
sensor networks. Sensors along the north-south direction and the east-west
direction form the column and row respectively. Intuitively, queries can be
answered by at least one rendezvous.
241 Chapter 10 Location Service, Info. Dissemination and Object Tracking
Dan-Dan Liu and Xiao-Hua Jia
D
S
D
(a) (b)
S
Fig. 1. Illustration of the quorum-based location management.
In a comparatively sparse network, rows and columns will be more likely
formed in a diagonal or zigzag way, not vertically or horizontally as desired.
Thus the probability of intersection will decrease as the density decreases. To
increase the reliability of quorum intersection, each ???column??™ and ???row??™ can be
expanded to a thicker quorum. Face routing on the perimeter of the network
can be added as well, which will be discussed specifically in the following subsection,
to make sure the intersection between read and write quorums exists.
Pages:
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396