Troposcatter Multi-Mode FSK/PSK Modem.

Abstract : The document describes the design, development laboratory evaluation, and field testing of an experimental model of a non-space-diversity high speed digital modem for troposcatter links. The modem has several operational modes employing combined FSK and PSK modulation coupled with nearly optimum coherent demodulation. Acceptance specifications for this modem included the agreement between laboratory measured performance over a hardware troposcatter simulator and theoretical performance. Such specifications have never been imposed before and were met in this program. Moreover, the field performance over the 168 mile path of the RADC troposcatter test bed was substantially in agreement with that predicted. Thus, validation has occurred not only for the near optimum modem performance but also for the theoretical model of troposcatter links used (due to Bello) and the hardware troposcatter simulator. Since the modulation approach used provides the highest data rate packing (bits/sec per Hz bandwidth occupancy) of any high performance high speed digital troposcatter modem, it is recommended that a quadruple space diversity modem be constructed using the same design concept but with modulation parameters tailored to military bandwidth and data rate requirements. (Author)