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All digital wireless networks have measurements, such as signal strength or signal-to-interference ratio, built into reporting protocols in the air interface standards in the form of call processing messages used to make handover decisions. WLS uses a pattern matching approach to capitalize on this reporting structure that is inherent in all wireless air interfaces. As a phone measures signal strengths and time delays from nearby cells, it compiles a list of these measurements and reports them back to the serving base station, with the reporting procedure varying from protocol to protocol. These measurements can be correlated against a database of radio environment maps, where the best match indicates the most likely position of the handset.
