The GNSS receiver subsystem is an important part of the MSS-1 satellite, it provides position, speed and time information for the satellite. The GNSS subsystem can also perform the ionospheric sounding at low latitudes, it provides excellent conditions for studying ionospheric anomaly and scintillation. The GNSS receiver subsystem receives the ionospheric occultation signals of GPS and BD satellites, generates 50Hz occultation scientific data, and transmits it to the data transmission subsystem through the synchronous serial port.

The GNSS subsystem is composed of a SOC-based GNSS receiver, a GNSS preamplifier, an occultation preamplifier, an occultation antenna, and three RF cables. The GNSS receiver is the core instrument of the GNSS subsystem, it can receive the GNSS occultation signals output by the preamplifier, obtain 50Hz raw observation data, and perform positioning and orbit determination. The occultation antenna receives the ionospheric refracted signals broadcast by GPS and BD navigation systems, and outputs the signals to the occultation signal preamplifier. The GNSS preamplifier and the occultation preamplifier receive the signals from the navigation antenna and the occultation antenna respectively, filter the received signals and amplify them with low noise, and send the amplified signals to the GNSS receiver.

The GNSS scintillation receiver is used to obtain the ionospheric electron density and total electron content at low latitudes, as well as the ionospheric scintillation S4 index and other products. The receiver outputs the amplitude and phase data of the occultation signals with a sampling frequency of 50Hz.