A Software Radio Based Satellite Communications Simulator for Small Satellites Using GNU Radio

In this paper, we present the architecture for an open source satellite communication simulator that accurately models communications channels between a ground station and satellite. The simulator is implemented using software defined radio (specifically the GNU Radio framework) which allows for an extremely flexible and customizable system. The simulator provides a low-cost platform for testing satellite communication systems that can be used for multiple different scenarios or use-cases throughout the entire development cycle. Examples include: initial mission planning, satellite and ground systems verification, system research and development, mission training and simulation, and education. It can also be integrated into a larger framework for simulating a mission's command and control structure and/or an entire network of ground stations. The simulator is designed as a module for the GNU Radio framework which allows the end-user to easily customize the toolkit as needed and integrate it into existing frameworks and systems to fit their specific mission objectives. Several flowgraphs are provided that model the communications channel for a satellite in Low Earth Orbit. A simple user interface allows a user to execute these flowgraphs to simulate the pass for a specific satellite. Given the orbital parameters of a satellite, the simulator can model both the uplink and downlink channels for upcoming passes over a specific ground station. The channel flowgraphs themselves model different properties of the communications channel between a satellite and ground station, such as: Doppler shift, path loss, propagation delay, and hardware impairments. Each of these properties is implemented on a per-sample basis within the flowgraph. Different data fitting techniques are used to simulate the channel effect as realistically as possible.