Such special sensors
can be the perimeter nodes [31], whose distance (hops) to the other nodes can
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be estimated through flooding. Each non-perimeter node determines its location
through an iterative procedure and periodically updates its coordinates
as the average of its neighbors??™ coordinates. A more e?±cient position estimation
algorithm is proposed in [13], which uses deployment points to provide
reference for location estimation. Sensors are divided into groups. A group
of sensors are dropped at the same deployment point. Relying on the prior
knowledge about the probability distribution of the sensors??™ resident positions
within each group, a sensor can estimate its location by observing the group
memberships of its neighbors. This method requires only one-hop broadcasting,
thus involves light communication overhead. However, such a scheme has
a strict demand on a priori knowledge of the deployment distribution, which
is usually not possible in many applications.
2.2 Range-based and Range-free Localization Schemes
Range-based Localization
Strength-
Indicator (RSSI), and Angle-of-Arrival (AOA), etc. The range-based localization
may produce fine-grained resolution, but have strict requirements on
signal measurements and time synchronization.
ToA measures the signal arrival times and calculates distances based on
transmission times and speeds. GPS [39] is the most popular ToA-based localization
system.
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