Positioning in Cellular Networks

Cellular networks are primarily designed to provide communication to mobile users. Besides the main application, determining location of mobile users (stations) within the cellular networks like Global System for Mobile Communications (GSM) and Universal Mobile Telecommunications System (UMTS) became an interesting additional feature. To provide the location based services (LBS), radio communication parameters already available in the network are preferably used, while some methods require investment in additional hardware to improve precision of the positioning. Positioning methods applied in cellular networks are characterized by tradeoff between the positioning precision and the requirements for additional hardware. The idea to determine user location in cellular networks originated in the USA to support 911 service for emergency calls. The Federal Communications Commission (FCC) in 1996 initiated a program in which mobile operators are required to provide automatic location determination with specified accuracy for the users that make emergency calls. The new service is named Enhanced 911 (E-911). Similar service was initiated in Europe somewhat later, and it is called E-112. Besides the security related applications, availability of the user location information in cellular networks opened significant commercial opportunities to mobile operators. In this chapter, methods to determine the mobile station position according to the radio communication parameters are presented. Position related radio communication parameters and their modeling are discussed, and algorithms to process collected data in order to determine the mobile station position are presented. Finally, standardized positioning methods are briefly reviewed.