Precise pseudoranges obtained from combining code and dual carrier measurements in Global Positioning System receivers

Abstract

The Global Positioning System (GPS), which was declared operational in December 1993, has provided continuous worldwide navigational capabilities in all types of weather. GPS has a minimum of 24 satellites in its constellation with additional fully functional spare satellites, which vary about 30 in total number. This navigational service has provided three-dimensional position within 30 meters and time within 100 ns to the civil community, which typically uses the coarse acquisition (C/A) code. The military GPS user has improved position accuracy within 6 meters using the dual GPS frequencies that carry the precise (P) code. The coarse resolution of a code measurement is about 1/10 of the smallest bit length of either code, which is about 29 m on C/A or 2.9 m with P code. Also, the GPS phase measurements can be determined well within 1/100 of a cycle by both civil and military receivers, so that the equivalent wavelength portion will be less than 0.19 cm and 0.24 cm. Recent GPS technology has improved civil navigation close to the military precision limits. To improve the precision by at least a hundred-fold, this dissertation considers a new exact linear navigation algorithm compared to the standard iterative GPS solution and also considers a new method of measurement by combining both carrier and phase measurements to improve pseudoranges within a centimeter tolerance. The GPS signal design is described in detail, and the novel techniques are derived explicitly. A simulation illustrating the novel exact solution demonstrates the greater versatility over the standard GPS iterative method, which, in some special cases, converges prematurely. Also, the GPS navigation solution is computed using both methods with actual GPS data against surveyed benchmarks. In conclusion, this dissertation: (1) derives a new exact linear GPS navigation algorithm as an alternative to the standard iterative GPS method, (2) demonstrates the standard iterative GPS navigation solution may stall prematurely in many small regions, which are dependent on the satellite configuration, before getting to the receiver’s actual location, and (3) illustrates a new method that combines carrier phases with pseudorange data to obtain subcentimeter precision in the GPS pseudoranges plus improved navigation with the exact GPS algorithm.