Linearization technique for measurement of GPS user position

Global Positioning System (GPS) is a satellite based navigation system designed to provide instantaneous Position, Velocity and Time (PVT) information almost anywhere on the globe at any time and in all weather conditions. Using the GPS one can determine his exact location (latitude, longitude, altitude) in ECEF coordinates accurate to within a range of 20m to approx. 1mm. User can also determine the time accurately to within a range of 60ns to approx. 5ns.

The user estimates an apparent or pseudo range to each SV (Satellite Vehicle) by measuring the transit time of the signal. The pseudo range ‘ρ’, is a biased and noisy measurement of the true range. The signal coming from a GPS satellite will be contaminated by various errors like ephemeris error, propagation error in the form of ionospheric and tropospheric delays, satellite and receiver clock biases with respect to GPS Time (GPST), multipath error etc. The accuracy with which we can measure the true range ‘r’ depends upon our ability to compensate for the biases and errors. This paper describes methods of determining various errors such as ionospheric delay, troposheric delay and the satellite clock bias to determine the true range from each satellite and finally the receiver position (xu, yu. zu) is obtained by using linearization technique. The results compared with the exact values measured by the receiver are found to be accurate.