Location trial system for mobile phones

There has been a growing interest in the possibility of locating a mobile phone in a wireless network. This interest is partly driven by safety considerations; i.e. the need for real time location of an emergency call, but it also opens a window for wide variety of new services. A number of techniques can be used to locate a mobile phone in a wireless network, e.g. measure the propagation time of a radio wave. This paper describes a GSM 900 trial system that uses the observed time difference (OTD) method to locate cellular phones. The OTD method belongs to a group of location methods that are based on time-of-arrival measurements.