INTEGRATED GPS GLONASS NAVIGATION - ALGORITHMS AND RESULTS

The presence of selective availability (SA) on GPS has led to a variet y of proposals for mitigation of its effects, for example combining GP S with other sensors or by identifying and removing the SA using redun dant information in the position solution. A further method for reduci ng the impact of SA is the combination of GPS and GLONASS measurements . GLONASS does not have any deliberate degradation. This paper describ es several algorithms for combining GPS and GLONASS measurements in re al time on a single receiver. There are two least squares solutions us ing the code phase measurements alone: one with the measurements from both systems weighted equally, and one with the measurements weighted by the covariance of the measurements. Kalman filters with no SA model , and first- and second-order models, using both the code and carrier phase to estimate user position and velocity, are also implemented. Tw o different adaptive schemes are compared which attempt to identify SA model parameters in real time. The algorithms are compared in terms o f their positioning accuracy, computational overhead and robustness. A ten-channel GPS/GLONASS receiver developed at The University of Leeds is used to provide satellite data for the evaluation of the different methods.