Error correction models and their effects on GPS precise point positioning

Along with improvements in International GPS Services (IGS) products with regard to GPS satellite orbit and clock errors, the Precise Point Positioning (PPP) technique has been developed in recent years. Compared with conventional GPS relative positioning mode, the PPP technique does not require the presence of a nearby reference station, which makes it more attractive than other techniques for some applications. However, to achieve centimetre-level positioning accuracy, all GPS errors have to be modelled carefully and removed from measurements. Some errors that have not been seriously considered in a relative positioning mode have to be treated now. This paper analyses the effects of the earth tide, satellite antenna offset, and phase wind-up corrections on the accuracy of the PPP technique. Similar to relative positioning mode, we can also combine measurements from different satellites and different epochs to reduce errors in measurement in the PPP data processing. The positioning accuracies with different combinations of GPS phase observables are also presented in the paper.