Smart antenna system design for airborne GSM base-stations

A great interest has arisen in the international community for the employ of Unmanned Aeronautical Vehicles High-Altitude Very-Long-Endurance (UAV-HAVE) platforms as a new technology for the development of telecommunication services and remote sensing applications. We consider the use of a stratospheric, solar powered, UAV-HAVE platform, named HELIPLAT, that is currently being designed at the Politecnico di Torino, as a base station for the GSM mobile communication system. We present a study on the on-board smart antenna system, considering the constraints imposed to the payload by the GSM standard, and by the platform technology. The smart antenna system is realized by a direction of arrival (DOA) estimator, based on the PRIME algorithm, whose output is used by an optimum combiner to shape a suitable radiation pattern of the equivalent antenna; so that the interference due to co-channel users and background noise can be reduced and the transmitted power can be directed just towards the users' location. Computer simulations have been performed in order to evaluate the average error in both azimuth and elevation angles estimation. The analysis of the results yield to the conclusion that a frequency reuse factor of 3 can be achieved.