Single-frequency Differential GPS Accuracy Improvement via Local Area Ionospheric Time Delay Model Development

Abstract

Ionospheric time delay is one of the main error sources for single-frequency DGPS applications, including time transfer and Wide Area Differential GPS (WADGPS). When ionosphere activity is peak in the year 2000 and also if the Selective Availability (SA) is turned off in the near future, ionospheric time delay will be the biggest error source. Currently, there are many attempts to develop real-time ionospheric time delay estimation techniques to reduce positioning error due to the ionospheric time delay. Klobuchar model is now widely used for ionospheric time delay calculation for single-frequency users. It uses flat surface at night time and cosine surface at daytime. However, the model was developed for worldwide ionosphere fit, it is not adequate for local area single-frequency users who want to estimate ionospheric time delay accurately. Therefore, there are needs to develop a new ionospheric time delay model which covers local region in view from one reference station with dual-frequency receiver, and send the parameters of the model to DGPS users. Since the coverage of one DGPS reference station is limited mainly by ionosphere spatial decorrelation, this basic idea also can be used to extend the coverage of DGPS. In this paper, we developed a new and practical ionospheric time delay model, which is simple to be used and does not have any singular points and divergence problem in ionospheric time delay estimation. We also developed a new SNUDGPS (Seoul National University DGPS) algorithm which minimizes the effect of the ionosphere spatial decorrelation by sending ionosphere parameters to the DGPS users. Experimental results show that the mean of SNUDGPS three-dimensional positioning error is reduced to at least half of DGPS and therefore the coverage of SNUDGPS is expected to be extended more than twice of DGPS.