Mobile station emergency locating in GSM

The positioning of a mobile station (MS) will become mandatory in the US in the near future to support enhanced emergency calls (E911). Also a lot of other applications are foreseen for the location service, when implemented. In the US a five-year, three-phase implementation of the E911 services is the most likely scenario. The authors study the feasibility of the Global System for Mobile Communications (GSM) for the MS emergency locating in each of the three phases. The results are relevant to all GSM based systems, i.e., to DCS 1800 and to PCS 1900. The TDMA based GSM offers some inherent means of calculating the location of the MS. The serving cell is already known by the mobile switching centre (MSC) and if wanted also by the operation and maintenance center (OMC). A set of measurement functions is already implemented in the MS that can be used to locate it more accurately. We investigate the use of timing advance (TA) and observed timing difference (OTD). By using the existing measurement functions the complexity of the handsets and the network does not increase much and additional costs remain moderate.