Robust Navigation with GPS/INS and Adaptive Beamforming

Abstract: This report can be divided into two parts, the Integration of Inertial Navigation System (INS) and GPS and Adaptive beamforming for a GPS antenna array. GPS and INS have complemen-tary properties. Therefore integration results in enhanced performance and robustness compared to each of the two systems alone. In the first part a tightly coupled navigation filter, based on code pseudorange measurements and an IMU with Litton LN 200 performance has been derived. The filter is used in a com-parison of a stand-alone receiver and differential GPS (two receivers). The navigation filter is a complementary extended Kalman estimator, where combinations of GPS pseudoranges and pseudoranges predicted by the INS are used as observations. Systematic errors in the inertial sensors are estimated and compensated for, which gives an improved navigation performance also during periods without GPS aiding. Results are given as simulations where the different integration methods have been tested using partial satellite outages, different flight paths and atmospheric disturbances. The second part of the report shows how the GPS/INS based navigation system can be made even more robust by using an adaptively beamforming antenna. The received GPS signals are extremely weak and therefore vulnerable to interfering signals. The robustness and performance of the beamforming algorithm LCMV is tested in static simulation scenarios, with multiple jam-mers and different numbers of array elements. Also, navigation performance is tested for a flying vehicle using the tightly coupled navigation filter in a dynamic scenario with severe jamming from airborne jammers. Using the most effective algorithm, multiple outputs LCMV, increases the equivalent C/N0 with more than 40 dB, in the dynamic scenario.