Testing of Wideband Small Satellite Receivers in Complex Radio Frequency Environments Using Synthetic Spectrum Generation Techniques

Testing of Wideband Small Satellite Receivers in Complex Radio Frequency Environments Using Synthetic Spectrum Generation Techniques

Utah State University, Logan, UT

As spacecraft technology improves, smaller cost-effective spacecraft become capable of increasingly sophisticated Earth observation missions, including wideband Radio Frequency (RF) sensing. Current methods available for validating the RF payloads on-board these missions, such as on-orbit payload validation using a pathfinder mission, are expensive, time consuming, and difficult. The challenge of modelling the RF environment of an orbital receiver is increased by path characteristics that become nontrivial at orbital velocities and distances, as well as unique modelling challenges such as ionospheric delay and multiple transmitters. A fast, inexpensive method for validating RF sensing payloads on the ground is presented in this paper. This method makes use of custom-made synthetic spectrum generation software, where the transmitter-receiver system is modelled in high fidelity and digital signal processing tools are used to simulate the RF environment at the orbital receiver. This modelling is performed using a set of modules to simulate factors affecting signals received by the spacecraft. Path loss, Doppler shift, and other channel-effect modules are used to create a realistic RF environment at the receiver. Representative networks of transmitters are simulated in this system, with nodes adhering to rules defined in network modules. Modules can be added to alter the overall transmitter network, receiver, and path models as required. To perform end-to-end payload testing, a Software Defined Radio transmitter generates representative RF spectrum, which is injected into the payload under test either over the air or via cable. Testing components along the RF chain is accomplished by modelling components up the chain, then injecting synthetic RF spectrum at the component of interest. The test system presented in this paper can also simulate the data output of Software Defined Radio payload receivers, such that data analysis methods and software processes can be validated without requiring access to physical payload components. End users of orbital RE spectrum can simulate scenarios to determine what data will be most useful to them, and modelling the RF stages up to the analog-to-digital converter ensures representative inputs for signal processing validation. The ability to accurately, quickly and cost-effectively test RF payloads at the component level or end-to-end makes this system a powerful tool for small satellite developers.