Precise Point Positioning with Single-Frequency Mass Market Receivers

Precise Point Positioning (PPP) has become an important issue in a wide range of land-based and airborne applications requiring advanced navigation accuracy. It is common practice for Real Time Kinematic (RTK) techniques to deploy expensive dual-frequency receivers for rover and base stations in order to achieve a sub-meter positioning accuracy. The two frequencies are used to mitigate the ionospheric signal delay which is the most limiting factor for precise ranging to navigation satellites. But in the last few years, the installation and advancement of several Satellite Based Augmentation Systems (SBAS) allow single frequency users to correct the ionospheric error to a great extent. Thus, the utilization of SBAS in combination with an enhanced pseudorange smoothing algorithm attracts notice to widely spread single frequency receivers to be used for various PPP applications in farming, guidance, sports and leisure activities. In our study, the continuous carrier phase and pseudorange data are combined to obtain smoothed pseudoranges introduced as observations for positioning into the Kalman filter. In addition, the fast and long-term corrections from SBAS are applied to the measured pseudoranges and computed satellite positions, respectively. Especially the large error due to ionospheric refraction can be corrected more reliable using SBAS by about 70-80% which is a significant advancement compared to the standard ionospheric model of Klobuchar with less than 50% (Somieski et al., 2007). To validate the improvement in positioning accuracy we carried out static long-term tests as well as kinematic pedestrian and vehicle road tests. In order to compare the North AmericanWide Area Augmentation System (WAAS) and the European Geostationary Navigation Overlay Service (EGNOS), static tests are performed in the United States and Switzerland simultaneously. The comparison reveals a remarkable quality advantage of WAAS resulting in higher positioning accuracy. A statistical analysis of several static tests over 24 hours shows an excellent positioning accuracy of about 0.6m (horizontal) and 1.1m (3D), respectively, for 95% Circular Error Probable (CEP). Considering the common use of miniature GPS receivers for personal navigation, pedestrian tests are carried out within changing environment. The performance of the real time PPP algorithm is analyzed by means of differential GPS data retrieved from post-processing using a co-located GPS base station. For dynamic road tests a vehicle equipped with two geodetic GPS receivers, a high precision Inertial Navigation System (INS) and a Distance Measurement Indicator (DMI) is deployed providing a reference trajectory with a positioning accuracy of up to several centimeters. A comparison of both tracks retrieved from DGPS/INS/DMI and PPP single frequency receiver allows for a qualitative analysis of the real time positioning performance at higher dynamics. The concluding comparison results point out the innovation as well as the limitation of a PPP mass market receiver and they show what may be expected under different dynamics and constraints.