Localisation in Wireless Sensor Networks

One important issue in WSNs is a localisation system among the sensor nodes. The localisation problem consists in identifying the physical location of the sensor nodes. Most localisation algorithms have two phases. First phase is ranging and second phase is estimation or iteration. It will depend on the ranging method. In range-based, ranging involved estimation of distance, angle and time, while in range free, it only depends on hop counts. The second phase is location estimation, where information form previous phase is used. Estimated location of the sensor node always has error. Therefore some algorithm introduce other phase, which is refinement process. The objective of this phase is to reduce localisation error. Error will grow in presence of irregularity of the RSSI.
Range-based
RSSI – Received Signal Strength Indicator, ToA – Time of Arrival, AoA – Angle of Arrival
Range free
DV Hop

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