Multiple Antenna GNSS Receiver Design on Spin-Stabilized Rockets

Global Navigation Satellite Systems (GNSS) are used to determine position, altitude and speed of objects. This is possible thanks to a network of satellites and the advent of low cost GNSS receivers. Application include but are not limited to surveying, navigational aid and weather monitoring. Spin-stabilised sounding rockets are one such vehicle that use GNSS for navigation. GNSS receivers must be able to acquire and track signals in high dynamic situations taking into account Doppler shifts, multi-path interference and high acceleration. Traditionally antennas are mounted within the nosecone of rockets but this is not always possible. One approach is to use an array of antennas mounted on the side of the rocket but due to rotation and high dynamics, modification to the radio frequency (RF) front end or receiver architecture is required. This project compares and characterises a summing front end, time-domain multiplexing front end and a smart correlation-based receiver design (diversity architecture). GNSS signals were generated using Orolia's Skydel, taking inputs from real world rocket data and tracking was done using the open source FGI-GSRx receiver in MATLAB. The summing and multiplexing front end resulted in correlation results depicting oscillations and phase reversals at a rate not consistent with the spinning of the rocket. An algorithm measuring the gradient and zero crossing detection was able to recover some navigational data in scenarios with high received signal power. The implemented diversity architecture yielded good recovery of navigational data with a small periodic loss of data during RF stream transitions. Analysis of the results suggest that the recovered navigational data is dictated by the architecture of the tracking loop how it deals with multiple tones/RF streams.