Performance Assessment of GNSS Signals in Terms of Time to First Fix for Cold, Warm and Hot Start

Abstract

The objective of this paper is to cope with the complex problem of the estimation of the so called Time to First Fix (TTFF). The TTFF is the measure of the time interval covering the acquisition of visible satellite signals, the demodulation of the navigation data and the calculation of the first position fix, starting from the moment the receiver is switched on. In the first part of the paper the theoretical fundamentals for the computation of the TTFF are given. The definition of TTFF in different receiver starting conditions is presented. Later the different contributions are discussed, and particular attention is devoted to the acquisition time and the data read time, that represent the most significant terms in the computation of the TTFF. In the second part of the paper the TTFF is computed under various conditions for different Galileo and GPS open service signals. Many simulation results are presented for the TTFF also for different signal to noise ratio conditions. Moreover estimations of the minimum required signal to noise ratio values to reach some TTFF performance requirements are also given. The paper is closed with a critical review of the obtained results.