A Cell ID (CID) is a generally unique number used to identify each Base transceiver station (BTS) or sector of a BTS within a Location area code (LAC) if not within a GSM network.
Cell-ID operates in most types of cellular networks, including GSM, GPRS, and UMTS/HSDPA networks. It is the simplest way to describe the general location of a handset. It requires the network to identify the Base Transceiver Station (BTS; essentially the cell tower to which the device is connected at the time) to which the cell phone is communicating and the location of that BTS. If this information is available, the Location Server identifies the device location as being the location of the base station and passes this information on to the location service application.
Since the MS can be anywhere in the cell, the accuracy of this method depends on the cell size and can be very poor in many cases, because the typical GSM cell is anywhere from 2km to 20km in diameter. Thus Cell ID positioning is generally more accurate in urban areas with a dense network of smaller cells than in rural areas where there are fewer base stations. Ultimately, the diversity in cell-site size, density and operational characteristics across a network makes the accuracy of this technology inconsistent.
