Ionospheric time delay estimation algorithm for GPS applications

Abstract

The global positioning system (GPS) signal transit time delay in ionosphere comprised of ionized plasma is a major error source in GPS range measurements. As the density of the ionized plasma varies, the velocity of the radio waves differs from the velocity of light. Due to this, the GPS signals experience group delay or phase advance. Hence, the GPS signal transit time measurement is affected, and this time delay directly propagates into pseudorange measurements when scaled by the velocity of light. The delay depends on elevation angle of the satellite since the signal takes the longer propagation path when transmitted by the satellites tracked at lower elevation angle. The delay also depends on the solar activity conditions since the ionized plasma is a result of solar radiation. To achieve the precise navigation solution, the delay in ionosphere is estimated using conventional method where the total electron content (TEC) is modeled and pseudorange measurements of Link1 (L1) and Link2 (L2) frequencies are used. In this method, the TEC is an additional parameter to be calculated and the accurate range measurements determine the accuracy of the TEC. To overcome this, an eigenvector algorithm is proposed in this paper. The algorithm decomposes the pseudorange and carrier phase measurement coefficient matrix. The ionospheric time delay estimates of the proposed algorithm and conventional method are presented in this paper. The delays are estimated for the typical data collected on April 7, 2015, from dual frequency (DF) GPS receiver located in a typical geographic location over Bay of Bengal (Lat: 17.73° N/Long: 83.319° E). The proposed algorithm can be implemented for military and civil aircraft navigation and also in precise surveying applications.