Development of a multi-antenna GPS/beidou receiver for troposphere/ ionosphere monitoring

In addition to providing accurate PVT service, GNSS signals have also been utilized in science research for probing the earth and atmosphere. Some researchers are investigating the strong earthquakes precursor by variations of the ionospheric total electron content (TEC) observed with GPS signal. In addition, in the Taiwan/US joint science mission FORMOSAT-3/COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate), six satellites are equipped with GPS receiver for Radio Occultation (RO) experiment. This mission has successfully provided a significant amount of RO data for weather forecasting. Several such kind of GPS signal applications are developing for more accurate weather or disaster prediction, especially for weather anomaly. With the emerging of other satellite navigation system, such as Galileo, GLONASS and Compass, more GPS-like signals are available and provide more observation on the above researches. The high availability of Beidou signals in Taiwan may lead to more GNSS-based observations. Indeed, the geometric relationship between Taiwan and Beidou satellites also provides nice opportunity to observe the severe ionospheric anomaly at low latitude region. This paper describes the development of a GPS L1/Beidou B1 signals receiver. The goal is to receive signals from all satellites for RO application. As a single antenna cannot track the satellite over a wide range of azimuths, antenna array and digital beam forming approach are adopted in the GPS/Beidou receiver to cope with weak signal of low elevation or occultation environment. This multi-antenna receiver collects the signals by 4 identical multi-band GNSS antennas. The captured RF signals are downconverted and digitized to be IF signals with I/Q components. The IF signals are then weighted and summed in the digital beamforming approach according to the reception pattern control algorithm. This research employs convex optimization-based beamforming algorithm to mitigate the mismatches in the desired signal steering vector. The validation of this proposed multi-antenna receiver is conducted by receiving real GPS/Beidou signals. The discussion compares the performance of one antenna only and antenna array with beamforming to understand the benefit of the proposed approached on GPS signal and the Beidou signal. The research result can provide more opportunities on troposphere/ionosphere monitoring and provide ground based RO and weather forecast observation data.