A radio mobile-position system operates by measuring, processing, and storing physical quantities related to radio signals travelling between a mobile terminal and a set of transceivers, for example, satellites or Base Stations (BSs). Positioning techniques in cellular networks are of great importance for supporting emerging services that require a sufficient, precise estimation of the position of the mobile terminal (MT) associated with a number of given base stations. The ability to support position location within wireless networks provides network operators with valuable services, as well as users with a host of new applications. This includes navigation, location-based services, network management, and security applications. Nowadays in GSM networks, there is no specific algorithm included in the software to locate subscribers. The only possibility to locate a subscriber is accomplished by using GPS technology or special firmware. An innovative development should be the design and implementation of certain location positioning techniques, as Time of Arrival (ToA) and Angle of Arrival (AoA), over the existing GSM network. Although there are already next generation networks in use nowadays (UMTS, GPRS, WLAN), and there also is extensive research towards the fourth generation cellular networks, GSM seems to be the most popular network so far. GPRS network is a data network over GSM platform and it exists only with GSM architecture. The reason is that GPRS uses the GSM air interface (Radio Network Part) and it only diverts in the core network where it transmits the data packets towards a different switch. UMTS, on the other hand, is a unique network supporting cellular and voice-data applications, and is the evolution of GSM towards IP applications. Although it could be implemented separately from GSM, most of the operators preferred to implement it in a GSM convergence mode towards the core network for eliminating the investment. As a result, in most countries GSM is the major network with full geographical coverage and network location positioning techniques are most implemented in a network environment with a satisfactory number of Base Stations.
In 1991, European Telecommunication and Standardization Institute (ETSI) accepted the standards for a new upcoming mobile, fully digital, and cellular communication network (Figure 1).
The purpose of positioning the mobile is to provide location-based services (LBS), including wireless emergency services (Porretta, Nepa, Manara, Giannetti, Dohler, Ben, & Aghvami, 2004). The handset based positioning techniques require that the existing handsets have to be redesigned in order to meet new requirements, while the network based positioning techniques need adjustments only at the Base Stations (BSs) or switching centers. Furthermore, with the first approach, the MT utilizes transmitted signals from the BSs to estimate its own position while with the second approach the BSs measure the transmitted signals from the MT and relay them to a central site for processing.
Key Terms in this Chapter
Transceiver: The hardware element of the Base Station that produces the electromagnetic coverage in a cell.
Idle Mode: The subscriber’s mode when the mobile is activated and it listens to the network.
nLOS: Non Line of Site. The indirect path between the mobile terminal and the antennae due to reflections and scattering.
Mobile Switching Centre: The switch that controls all the mobility management in the core network part.
Picocell: The cell with a coverage area distance of 100m to 1 Km.
Location Area Code: The code that specifies uniquely a cell in a large geographical area.
Line Of Site (LOS): The direct physical path between the mobile terminal and the antennae of the Base Station.
Base Station: The module that produces the cellular coverage through electromagnetic radiation.
Busy Mode: The subscriber’s mode when the mobile is activated and a dedicated traffic channel is reserved and used for the transmission of voice data.
Microcell: The cell with a coverage area distance of 1Km to 5 Km.
Base Station Controller: The switch that controls all the Radio resource management in the core network part.
Subscriber Identity Module (SIM): The portable database that is carries inside the mobile station.
Cell: The geographical area covered by electromagnetic radiation from a transmitter in the GSM frequency band.