Citation
Abstract
In this article, results of an analytical study of a three-frequency ranging system are presented. In particular, the effects of both receiver noise and the errors introduced by inter-frequency biases on the determination of pseudorange and ionospheric parameters are discussed. It is shown that by properly choosing the three frequencies, the effect of receiver noise can be minimized to a degree that the firstand second-order ionospheric contributions to the signal delay, which vary as the inverse square and inverse cube of the frequency, respectively, can be calibrated for precise pseudorange measurements. Also, one can solve for the tonospheric parameters, obtaining values for the line-of-sight total electron content (TEC) and for the magnitude of Faraday rotation, which, in turn, can be exploited to extract information about the Earth’s magnetic field. Moreover, it is shown that simultaneous measurements of three signal phases can be used to obtain absolute TEC and the geometric range, provided that the phase bias can be calibrated to acceptable levels. In particular, the phase of the Global Positioning System (GPS) L3 signal can be used with the L1 and L2 GPS phases in order to find absolute TEC. Once absolute TEC is obtained at a given instant, its value at later times can be updated by adding to it the relative TEC changes as determined from continuous L1 and L2 phase measurements. The simple procedure outlined here can be implemented in codeless GPS receivers in order to find the ionospheric group delay and the absolute TEC. Public GPS users can also take advantage of this method at times when precise pseudorange observables are not available. Although the case of the GPS L3 signal is used for numerical calculations, the results presented are of a general nature and can be used in designing future three-frequency ranging systems.
Details
- Volume
- 42-103
- Published
- November 15, 1990
- Pages
- 14–20
- File Size
- 312.9 KB