WAW Location-based Service Positioning

Coordinated positioning operations require the user to be aware, not only, of his own position but also of the positions of the other elements on his team. Its deployment can be supported in WAW (“Where Are We?”) location-based services, where the position of each user is made available to the rest of the group. This paper presents a method for the estimation of a user’s position based on measurements from a group of Global Positioning System (GPS) receivers. None of the GPS receiver positions, used in the estimation process, is considered to be known. The proposed approach leads to an improvement on the accuracy of the position estimates, when compared with those computed on an autonomous way, and has a direct application in the development of enhanced services in WAW location-based services. The positioning estimator takes advantage from the fact that, in this type of location-based service, GPS measurements are available from several receivers. Instead of estimating the user’s position based only on the measurements of his own GPS receiver, the proposed approach uses the measurements from all the GPS receivers in the group. The paper presents details of the positioning model and estimator used to achieve the accuracy improvements. Simulation results are presented based on real GPS satellite ephemeris, collected at the University campus.