Researchers are developing new GNSS receivers and antennas based on an innovative signal-processing scheme to significantly improve GNSS tracking reliability and accuracy under degraded signal conditions. It is based on the principles of synthetic-aperture radar. Like in a multi-antenna phased array receiver, GNSS signals from different spatial locations are combined coherently forming an optimized synthetic antenna-gain pattern. The method is implemented in a real-time PC-based software receiver and works with GPS, GLONASS, and Galileo signals. Multiple frequencies are generally supported. The idea of synthetic-aperture processing is realized as a coherent summation of correlation values of each satellite over the so-called beamforming interval. Each correlation value is multiplied with a phase factor. For example, the phase factor can be chosen to compensate for the relative antenna motion over the beam-forming interval and the resulting sum of the scaled correlation values represents a coherent correlation value maximizing the line of sight signal power.
