Several multi-aperture multiple beam antenna (MA-MBA) designs have been proposed for future military communications satellites to satisfy demands for increased nulling resolution against jammers. However, overall network performance can be severely degraded because of spurious nulls that are associated with MA-MBA antennas. In this paper, we propose and analyze a nulling algorithm that improves overall network performance by reducing potential performance degradation caused by MA-MBA antenna spurious nulls while providing high jamming resolution. This algorithm also provides wide area coverage for network users near a jamner in support of tactical scenarios. We show that optimized beam weights are a function of individual user optimum beam weights along with proper phase rotation for each beam. Computer simulated results are then provided illustrating p e r j o m c e of this proposed technique versus another nulling algorithm developed for Defense Satellite Communication System (DSCS) Super High Frequency (SHF) satellites.
The upcoming GNSS Galileo, with its new satellite geometry and frequency plan, will not only bring many benefits for navigation and positioning but also help to improve ionosphere delay estimation. This paper investigates ionosphere estimation with Galileo and compares it with the results from GPS-only and combined GPS-Galileo. The standard deviation of the Vertical Total Electron Content (VTEC) at a certain location can improve significantly by 40 per cent. Various Galileo configurations are considered to assess the differences in frequency plan and signals to be used. The IGS network, which is involved in producing the current IGS Global Ionosphere Map (GIM) is used in the simulation for more realistic results. A more accurate GIM will in its turn improve navigation and positioning performance.
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