Ref. [26] proposes a prototype navigation system
for autonomous vehicles, which estimates AoA by means of a set of optical
sources and a rotating optical sensor. The system is not suitable for outdoor
sensor networks due to its cost and complexity. Ref. [28] first transforms
TDoA measurements into AoA information, then applies triangulation for location
estimates. It requires three base stations with synchronized rotating
directional antennae.
Range-free Localization
Range-free localization requires no measurement on distance or angle among
nodes. They can be further classified as local techniques and hop-counting
techniques [18].
??? Local Techniques. A simple centroid algorithm is proposed in [3], in which
each sensor estimates its position as the centroid of the locations of the
neighboring beacons. The computation error can be reduced by a density
adaptive algorithm (HEAP) if beacons are well-positioned [4]. However,
this is unfeasible for ad hoc deployment. Later, He et al. proposed the
APIT method [15], which divides the environment into triangular regions
between beacon nodes. Each sensor determines its relative position with
the triangles, and estimates its own location as the center of gravity of the
intersection of all the triangles that the node may reside in. However, APIT
requires long-range beacon stations, which requires expensive high-power
transmitters.
??? Hop-Counting Techniques.
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