asurements are needed for at least three distinct pairs of geographically dispersed BTSs. Based on the measured E-OTD values the location of the terminal can be calculated either in the network or in the terminal itself, if all the needed information is available in the mobile station. The accuracy of E-OTD positioning method can differ from 50 to 150 m [36,37]. OTDOA: Observed Time Difference Of Arrival (OTDOA) operates only in UMTS networks. It can be considered as the UMTS version of E-OTD and its performance and weaknesses are similar to those of EOTD. In UMTS networks the handset's ability to use multiple Node B stations is limited. The use of the idle-period down link (IPDL) to compensate for this problem is being considered, but IPDL has not been SO successful. Although UMTS networks are synchronized, resolution on the order of tens of microseconds is inadequate for the resolution required for OTDOA. Thus, additional R&D and investment is required to make OTDOA a good position method [35]. IMS, Services and Applications U-TDOA: The U-TDOA (Uplink Time Difference of Arrival) positioning method is based on network measurements of the Time of Arrival (TOA) of a known signal sent from the mobile and received at three or more LMUs. The known signal is the normal bursts generated by a mobile while in the dedicated mode; either on the SDCCH (Stand alone dedicated control channel) or TCH (traffic channel). The method requires LMUs in the geographic vicinity of the mobile to be positioned to accurately measure the TOA of the bursts. Since the geographical coordinates of the measurement units are known, the mobile position can be calculated via hyperbolic tri-alteration. This method will work with existing mobiles without any modification [39]. GNSS: Global Navigation Satellite System (GNSS) refers to satellite systems that are set up for positioning purposes. A-GNSS refers to a concept which supports several global navigation satellite systems and their different navigation signals. Systems belonging to this catego