Signal Tracking Performance Improvement of Spaceborne GNSS Receiver, GPS-12

A satellite depends entirely on a GNSS receiver to acquire current time and to synchronize each sub-system. To generate stable current time information and synchronization signal such as PPS(Pulse Per Second), it is very important to maintain a 3D fix during the mission. This paper describes the performance degradation phenomenon of navigation signal tracking of the GNSS receiver(GPS-12) developed by the SI(Satrec Initiative) and suggest how to handle the issue. The performance degradation was caused by both a distortion of a radiation pattern and the attitude maneuvering of a satellite which operated in LEO(Low Earth Orbit). The antennas of the GNSS receiver need to be isolated electrically that's because the radiation pattern of the antenna will be transformed when the other equipment affect the receiver antenna electrically. However, there is a practical difficulty to isolate the antenna electrically considering the limited size of a small satellite. In this reason, the other equipment is likely to affect the radiation pattern and the radiation pattern of the antenna needs to be verified after installing the receiver antenna to check if the electrical affects are adequately limited. In addition, an attitude maneuvering of a satellite which has GNSS receiver cause fast relocation of the GNSS satellites in the FOV(Field of View). Moreover, the wide carrier search area of spaceborne GNSS receiver considering the LEO satellite's velocity takes more time to acquire the navigation signal. That's why the attitude maneuver degrades the 3D fix performance. SI has been developing the single-band GNSS receiver and trying to improve its signal tracking performance in both sides the stable uniform radiation pattern and the signal tracking speed. At the result, average acquisition number of navigation signal has been increased from 7.35 to 10.6 and the 3D fix fails ratio at the eclipse scenario mode which does the attitude maneuvering up to 100° has mostly disappeared (67 %->0 %).