TROPO-SCATTER MULTI CHANNEL DIGITAL SYSTEMS STUDY.

Abstract : This report studies a panorama of digital communication techniques in order to determine efficient digital communication systems for medium and long distance troposcatter links. The various techniques are rated both with respect to power and bandwidth utilization efficiency so that one may readily assess the trade-offs that exist between various combinations of techniques. After the initial rating of techniques, three classes of time division multiplex system are selected for detailed comparative performance evaluation. The selective fading properties of the troposcatter channel are modeled using the general approach of Bello and Nelin, with the basic defining parameters in this model determined by the physics of scatter propagation and the troposcatter link parameters such as antenna size, path length, etc. As a result of the study it is concluded that a certain class of systems employing pre-detection maximal ratio combining, time gating, coherent detection, matched filtering, and adaptive biases provides the best tradeoffs between utilization of signal power and maximization of data rate within the bandwidth and power constraints of troposcatter links. The signaling technique associated with this class of systems is the time-division-multiplex and single-side-band transmission of M'ary frequency shift keying with superposed phase shift keying employing no more than four phases. (Author)