 available without any additional effort. The CI method in WCDMA networks operates in the same way, using the cell identity of the serving cell to estimate the location of the MS. The 3G CI method can be enhanced with the Round Trip Time (RTT) feature. The RTT is also an existing feature of WCDMA networks. The accuracy of a cell-based method depends on the size of the cell coverage area; the smaller the cell size, the higher is the accuracy. An example of GSM network architecture for location positioning methods is presented in Figure C.2. The necessary new network elements are Gateway Mobile Location Cen- ter (GMLC), Serving Mobile Location Center (SMLC) and Location Measurement Unit (LMU). The location-based services' applications communicate with the GMLC, SO the first task for the GMLC is to receive a request to locate a mobile phone. The GLMC initiates the positioning procedure in the network, by routing the request to the appropriate SMLC. The actual location estimate is calculated in the SMLC, which also handles the coordination of resources needed in the positioning procedure. The SMLC can either be integrated with a BSC or be an independent network element. The LMU unit, which works under control of the SMLC, is shown in Figure B.2 to be connected to the BTS, but alternatively it could be Application Figure C.2 GSM network architecture for LBS ACCURACY connected to a BSC. Some of the location positioning methods require supportive measure- ments carried out by the LMUs. The GMLC finishes the positioning procedure by sending the estimated location to the external application. C.4 ACCURACY The accuracy of location positioning methods varies, as does the required accuracy for various location-based services. There is no existing system that is highly accurate yet at the same time inexpensive and technically not complex. Generally the GPS-based services are more accurate than network-based methods, as can be seen from Figure C.3. With A-GPS it is possible to reach 3-metre accuracy, while with network-based m