Analysis of the System Performance of LADGPS and WADGPS Services in Europe

As the achievable accuracy for single point positioning with GPS is insufficient for many applications, DGPS services have been established all over the world. They can be distinguished into so-called Local Area DGPS services (LADGPS) for small areas such as a country and Wide Area DGPS services (WADGPS) for larger areas such as a whole continent or even worldwide. All of them have in common that for the DGPS services, distinct methods for generating differential GPS corrections have been developed. However, the main disadvantage of LADGPS Services is that position accuracy of a user degrades as the reference-to-user separation increases. The spatial decorrelation of the error sources, i.e., the atmospheric propagation and satellite orbit errors, are the main causes for the degradation of position accuracy. The combination of the measurements of several reference stations can be used to model these error components separately. Starting from the discussion of the mathematical connections and the illustration of the main error sources on pseudo range measurements, this paper will concentrate on the essential features and differences of LADGPS and WADGPS services. For that purpose, also the characteristics of existing correction data services in Europe of each of these groups are analysed. The focus of these analyses will lie on the error modelling and the estimation of correction data in connection with the achievable accuracies. In the following, possibilities for embedding the common solution strategies of WADGPS concepts in LADGPS are discussed. Finally, practical studies of one of these possibilities, the virtual reference stations concept, using data of a test network in Germany will be presented.