Optimal orbit selection and design for airborne relay communications

This paper presents a force-level planning approach to optimally select and design the orbit of an airborne relay. The objective is to maximize the aggregate performance of communication subscribers served by the airborne relay. The performance is measured as either the duty cycle in terms of signal-to-noise-ratio or the throughput achieved by communication subscribers. Both measures are computed with realistic channel, terrain, antenna and aircraft characteristics for ground-to-air and air-to-ground communications. Different methods to generate an airborne relay orbit are discussed with their parameters to optimize. Results are specialized to optimization of elliptical orbit parameters. First, an elliptical orbit is optimally selected with the best center and radius (in X and Y-directions) as orbit parameters subject to the specified altitude and speed of the aircraft. Both exhaustive search and gradient search with reduced complexity are considered to find the best set of orbit parameters. This elliptical orbit is then converted to an operational orbit by optimally selecting orbit waypoints and locating smooth turning points while minimizing the fuel consumption of the airborne relay. A software with interactive GUI is designed and implemented for force-level planning that allows the planner to select different properties of airborne relay and communication subscribers, and returns the optimal orbit for the airborne relay.