wireless ad hoc networking

22 Wireless Ad Hoc Networking
R t =2R s
R s
R t =1.5R s
s 2 s 4
R s s 2
s 4
s 1
s 1
s 3
s 3
s 5
s 5
(a)
(b)
Figure 1.13 An example of the CCP + SPAN execution result. Solid circles mean
sensing ranges R s , and dotted circles mean transmission ranges R t . The dotted
lines between sensors represent communication links between sensors. (a) When
R t = 2R s , 1-coverage implies 1-connectivity, so sensor s 1 can be turned off.
(b) When R t = 1.5R s , sensor s 1 has to stay active to maintain the communication
backbone.
connectivity maintenance protocol. SPAN tries to maintain a communication
backbone to provide connectivity while sensors not on the backbone are
kept in the sleep mode. The CCP-SPAN-integrated protocol decides a sensor
to be active if it satisfies the active principle in CCP or SPAN. Otherwise,
it can enter the sleep mode. For example, in Figure 1.13(b), the R t < 2R s
condition makes the network probably not connected after the coverage
issue is satisfied. Although sensor s 1 is allowed to enter the sleep mode
by CCP, it will be requested to stay active to connect with its neighbors to
form a communication backbone according to SPAN. Note that the resulting
network may remain k-covered but less than k-connected.
Ref. [15] discusses the coverage-connectivity-combined issue by adopting
a probability-based coverage model and the concept of connected
dominating set (CDS). The coverage of any location depends not only on
the sensing ranges of sensors but also on its distances from these sensors.
This probability model is similar to the models discussed in Section 1.2.2.
To compute the coverage of the network, the sensing field is divided into
grids. For each grid point, we compute its detection probability contributed
by nearby sensors. Then, each sensor decides if it should stay active by
observing the redundancy degrees of grid points within its sensing area.
The redundancy degree of a sensor at a grid point is the end result of
comparing the detection probability contributed by this sensor with it by