Since sensors just listen passively to beacon signals, no extra communication
overhead is introduced. With only local measurements, TPS and iTPS retain
the fine-grained computation of range-based schemes, but exclude the necessity
of time synchronization among beacon nodes. As the location detection
algorithm involves only some simple algebraic operations, the computation
overhead is also low.
TPSS retains all the above nice features of TPS and iTPS, but requires
no powerful long-range beacons to cover the entire network. With only a
few short-range beacons deployed, sensors can compute their positions easily.
TPSS can be applied to large-scale sensor networks where the deployment of
powerful long-range beacons are too expensive or not practical.
3 Network Model
In this chapter, we consider a sensor network deployed over a two-dimensional
monitored area. Actually, our TPSS scheme can be easily extended to higherdimensional
space. In this model, each sensor has limited resources (battery,
CPU, etc.), and is equipped with an omni-directional antenna. Some sensors,
called beacons, have the ability to position themselves. They are deployed
together with typical sensors whose positions are to be computed with the
TPSS. An example scenario is plotted in Figure 1. The beacon nodes will
broadcast beacon signals periodically to assist other sensors with location
discovery. Note that the only di?®erence between a beacon and a sensor is
whether the location is known.
Pages:
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308