Overview

The wireless networks that are discussed in this chapter have several notable characteristics that are significant from the point of view of wireless positioning. They all operate using low power over relatively short distances, generally no greater than 100 meters. Consequently, for time of arrival methods, time of flight is short, and for useful accuracies, time resolution should be around 10 nanoseconds, equivalent to three meters range. Also, all of the networks are used basically indoors, subjecting wireless signals to non line of sight and severe multipath conditions. These systems all operate on the so called unlicensed bands, and therefore are susceptible to interference from a wide range of signal types. Mobile terminals are small and must have very low current consumption to extend battery life. They also serve many consumer applications and are designed for low cost. Technologies for incorporating location services in these networks must take into account all of the characteristics mentioned above.

The positioning methods mostly used for the short-range wireless networks are TOA, RSS and fingerprinting. GPS is also used but will not be discussed here. Proximity detection for location is also popular but this can be considered a form of RSS. RSS may be more accurate for short distance position estimations since propagation more closely follows a deterministic rule. TOA is inherently a more accurate estimate of the distance between two terminals than RSS. In a multipath environment, the deviation of the distance estimate from the true value depends directly on the length...