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There are three common mobile positioning technologies in GSM: COO, E-OTD and A-GPS.
COO（CellOfOrigin）
Origin cell location (COO) is the simplest location method. It determines the user's location according to the cell ID of the mobile station. After the mobile station registers in the current cell, it will have the corresponding cell ID number in the system database. As long as the system can broadcast the center location (in the local map) and the coverage radius of the cell to all mobile stations within the cell, these mobile stations can know where they are and obtain the location information by querying the database. The origin cell technology is a network-based location scheme, which has the advantages of no need to modify the network and mobile phone, and short response time. However, the resulting disadvantage is poor accuracy.
E-OTD
E-OTD positioning method is developed from the measurement time difference (OTD). OTD refers to the amount of time measured, and E-OTD refers to the measurement method. The mobile phone can get the measurement result without any additional hardware. For the synchronous network, the mobile phone measures the relative arrival time of several BTS signals; for the asynchronous network, the signal also needs to be received by an LMU whose location is known. If the signal transmission time from BTS to mobile phone is determined, the geometric distance between BTS and mobile phone can be determined, and then the location of mobile phone can be determined according to the distance.
The mobile phone receives the signals from each base station and gets toa parameters; the LMU gets RTD parameters; the mobile phone transmits TOA and RTD parameters to the GSM network. OTD measurement requires synchronous, standard and analog pulses. When the frames sent by BTS are not synchronized, the network needs to measure the RTD between BTS. In order to carry out accurate triangulation, both OTD measurement and RTD measurement (asynchronous BTS) need three BTS. After obtaining the OTD parameters, the location of the mobile phone can be calculated not only in the network, but also in the terminal (the mobile phone is required to have all kinds of necessary information). The former is called mobile phone assisted mode, and the latter is called mobile phone autonomous mode. Through the location calculation function module of mobile phone or network, the location calculation is realized.
A-GPS（AssistGPS）
A-GPS（AssistedGPS）。 A-GPS is the same as GPS solution, it also needs to add GPS receiver module in the mobile phone, and transform the mobile phone antenna, but the mobile phone itself does not calculate the location information, but transmits the GPS location information data to the mobile communication network, which is calculated by the positioning server of the network. At the same time, the mobile network generates auxiliary data according to the reference network of GPS, such as differential correction data , satellite operation status, etc. are transmitted to the mobile phone, and the approximate location of the mobile phone and the location information of the community are found out from the database and transmitted to the mobile phone. At this time, the mobile phone can quickly capture the GPS signal, and the first acquisition time will be greatly reduced, generally only a few seconds. Unlike GPS, the first acquisition time may take 2? 3 minutes. And the accuracy is only a few meters, higher than that of GPS.
GpsOne of Qualcomm adopts A-GPS scheme.
There are two ways: mobile phone assisted and mobile phone autonomous: (1) mobile phone assisted GPS positioning. This solution is to transfer most functions of traditional GPS receiver to network processor. This method needs antenna, RF unit and data processor. GSM network sends a series of very short auxiliary information to mobile phone, including time, visual satellite list, Doppler parameters of satellite signal and code phase search window. These parameters help the built-in GPS module to reduce the GPS signal acquisition time. The auxiliary data comes from the pseudo range data processed by GPS module of mobile phone, and can last for several minutes. After receiving the pseudo range data, the corresponding network processor or location server can roughly estimate the location of the mobile phone. After adding necessary correction to GSM network, the positioning accuracy can be improved. (2) Mobile phone independent GPS positioning mode. The mobile phone contains a full-featured GPS receiver, which has all the functions of the mobile phone in (1) mode, plus the satellite position and mobile phone position calculation functions. At the beginning of the operation, more data is needed than mobile phone assisted mode. These data can last more than 4 hours or be updated as needed, usually including time, reference position, satellite ephemeris and time verification parameters. If higher accuracy is needed in some applications, differential GPS (DGPS) signals must be sent to mobile phones continuously (with an interval of about 30s). DGPS signal is effective in a very wide area, and a reference receiver can serve a wide area. The final location information is calculated by the mobile phone itself. If necessary, the location information can be sent to any other application.
