Performance of Precise Point Positioning (PPP) Based on Uncombined Dual-Frequency GPS Observables
A new PPP algorithm based on uncombined dual-frequency GPS code and phase observables is presented. The algorithms different from traditional ones in which the ionosphere-free code and phase observables are formed. The Line Of Sight (LOS) ionospheric delays are taken as estimate parameters by introducing the constraints of between-epoch temporal behaviour of ionosphere. This alternative approach has the advantage of avoiding adverse effect of amplified multipath and measurement errors existing in the combined observations. A further study of the performance of the proposed algorithm was conducted by comparing with the traditional ones in different case studies. The results show that kinematic positioning accuracy of several centimetres to decimetres is achieved, with an improvement of 6%-30% compared to traditional PPP algorithms, especially in the upper component; the accuracy of receive clock corrections and ZTDs estimation can be better improved to ∼ 0.1ns and ∼4mm respectively, which demonstrates the feasibility and effectiveness of this new algorithm.