Spatial Filtering for Interference Mitigation in High-Altitude Spaceborne GNSS Receivers

Since the antennas of high-altitude spaceborne global navigation satellite system (GNSS) receivers are installed in the satellite nadir direction, interference from Earth poses a potential threat. For interference mitigation in high-altitude spaceborne GNSS receivers, a spatial filtering algorithm is proposed with the constrained minimum spatial mean interference power (CMSMIP) as its metric. Specifically, a spatial mean interference power matrix is conceived based on the spatial probability distribution of the interference sources. The optimization problem for spatial filtering is formulated to minimize the spatial mean interference power expressed by the introduced matrix subject to constraints on the desired signal-to-noise ratio gain. To solve this optimization problem, mathematical properties of the spatial mean interference power matrix are derived, based on which the optimal weight vector is found. The performance of the proposed algorithm is evaluated by simulation with respect to power inversion (PI) as well as minimum variance distortionless response, showing an improved performance at typical interference-to-noise ratios. The proposed algorithm is adaptive to a large number of interference signals and consistent in the performance under different levels of interference power. Furthermore, it can be implemented by retrieving a lookup table of precalculated optimal weight vectors for different GNSS signal directions of arrival, which requires less than 10 MB of memory, instead of requiring frequent snapshots and matrix inversion operations as in conventional spatial filters.