An Electromagnetic-Time Delay Method for Determining the Positions and Velocities of Mobile Stations in a Gsm Network - Abstract

Abstract

In this paper we propose a hybrid method to determine the positions and velocities of mobile stations (MSs) in a GSM (Global System for Mobile communication) network. The proposed method can be implemented within the existing GSM standard without any additional hardware changes. The hybrid method operates at two levels. At a lower level, time delay method (TDM) is used to obtain coarse values for distances between a MS and three or more Base Transceivers (BTSs). At a higher level, field strength method (FSM) uses the coarse distances estimates obtained using TDM as initial values to obtain refined values for distances. The accurate position of a MS then can be determined by the refined distance values. Subsequently, the velocity of the MS be can obtained using the FSM estimates of the sequential positions of the MS. Least mean square (LMS) method is used to determine the refined distances in the FSM algorithm and to estimate the actual position of the MS from the refined distance estimates. The proposed method was tested for several cases, including complex MS trajectories and varying speeds along the trajectory. The heights of the BTSs were allowed to vary between 20 m and 60 m. The convergence characteristics were found to be satisfactory. For a SNR of 20 dB, position measurements accuracy in a roughly 4 km² cell is 30 m in a Gaussian channel, 60 m in a Rayleigh channel and 80 m in a Rician channel. The velocity accuracy for a MS traveling at 200 km/h is 15 km/h in a Gaussian channel, 30 km/h in a Rayleigh channel and 50 km/h in a Rician Channel.