Toward real-time precise point positioning: Differential GPS based on IGS ultra rapid product

In this paper, the problem of GPS precise point positioning (PPP) using single frequency data is investigated. Traditionally, GPS PPP can only be achieved by using the P code signal or using dual-frequency, where the former is only accessible to authorized personnel and the later is usually done in a post-processing manner. In view of this, there is still a need for a real-time publicly accessible PPP service. In this paper, we present a differential GPS algorithm that is capable of providing real-time near PPP service. In the proposed method, IGS ultra-rapid product is used to calculate vector differential GPS correction, therefore it is capable of providing wide-area DGPS service. By transforming the vector into a scalar correction, we show that a conventional GPS receiver may also utilize the correction to yield a real-time precise point positioning.