In-orbit Radio Measurements using Software-Defined Radios in Small Satellites

Abstract

Environmental monitoring of the oceans and the Arctic is important to understand the impact of global warming and climate change. The use of different types of assets, such as satellites and autonomous agents, can contribute to this task at different spatio-temporal scales. However, the collection and distribution of scientiĄc data from sensors or robotic agents in these remote places are challenging due to limited infrastructure. Thus, a new communication system is needed to obtain faster and easier access to the data. To design a robust satellite communication system for energy-limited sensors, measurements of the communication channel and the interference environment are necessary. In addition to the mission design activities, the main contribution of this thesis is the analysis and characterisation of the in-orbit interference in two different relevant frequency bands in VHF and UHF for small satellite systems. The Ąrst band is the UHF amateur radio band (430Ű440 MHz), selected due to its common use for small satellite communication. This band was measured with payloads on board the Serpens and the LUME-1 satellites. Another contribution of this work is the design and development of an onboard measurement algorithm for small satellites with limited resources. We built a Software-DeĄned Radio (SDR) testbed similar to the actual satellite setup for testing before uploading the algorithm to LUME-1. In addition, we explored the uplink interference from more than 300 measurement locations all over the world. Band-limited pulsed interference was detected in areas where ground radars are located and wide-band pulsed interference was measured over central Europe. The other frequency band measured was the lower leg of the VHF Data Exchange (VDE)-SAT system (157 MHz band). This band was selected to explore the performance of a new communication system that is currently being demonstrated, the VDE-SAT, which will operate in the Arctic. We analysed the uplink interference environment of this system by analysing recordings from an SDR payload on board the NorSat-2 satellite over the Arctic. Pulsed interference of high power was also detected in this band. The pulse length and period were detected using a second algorithm developed in this thesis. The algorithms and software implemented in this thesis can be used in any frequency band to detect the frequency and time variability of different signals in any satellite with an SDR.