Cell Identity (Cell-ID or CI) is the cell identifier of a base station in GSM networks. The CI number is composed of the Location Area Identity( LAI) and a part that refers directly to the corresponding radio cell. This identification number can be used to uniquely identify the coverage area. The Cell Identity is also referred to as Cell of Origin( COO) and is a unique identification of a radio cell.
The Cell ID method is not suitable for more precise location, since the radio cell radius can be several kilometers depending on the coverage area. The positioning accuracy, which is determined via the CEP value, Circular Error Probable (CEP), ranges from about 100 m for picocells and microcells to 20 km for large macrocells.
Higher positioning accuracies are achieved by subdividing the radio cell using cell sector( CS) and hybrid methods. In these methods, the radio cell identification is combined with a field strength measurement: Cell-ID in combination with Received Signal Strength( RSS) or Cell-ID in combination with Reception Level( RXLEV). This doubles the location accuracy. The Cell-ID method can also be combined with a distance-dependent timing signal, with Timing Advance( TA). Another significant improvement in positioning accuracy is achieved with Enhanced Observed Time Difference( E-OTD).