A technical solution to fadings in tactical satellite digital transmissions

Tactical satellite communication systems may provide service to high performance aircrafts employing antennas with relatively wide beamwidths. Unfortunately, the fading and multipath phenomena could strongly influence the capability of point to point data transmission. In order to overcome the problem of the design of a coding/mo-demodulation structure, and to determine the actual link margin, an analysis and a simulation of a multipath channel has been performed. The performance gains that are achieved with the use of a suitably wide bandwidth modulation and with three different theoretical fading models are shown. The problem of the bandwidth spreading has been related to the aircraft height and to the geometry of the multipath model. A solution to the problem of multiplexing of several wideband signals, over a repeater bandwidth, proposed and the performances of a receiver, based on a FFT spectra analyzer, are illustrated. The simulation to the problem of multiplexing of several wideband signals, over a repeater bandwidth, was proposed and the performance of a receiver, based on a FFT spectra analyzer, are illustrated. The simulation results confirm that, the FFT based receiver allows the soft decision demodulation of one or several simultaneous channels, with performances that are very close to the ones given by the optimal receiver for orthogonal codewords; moreover, the FFT solves, elegantly, the problem of Doppler shifts even in presence of fadings and with the capability to track the satellite signal even for maneuvering aircraft.