WIDEBAND DIGITAL MODULATION AND DETECTION TECHNIQUES FOR TROPOSCATTER.
Final rept. 1 Jul 66-15 Dec 67,
COMMUNICATIONS AND SYSTEMS INC PARAMUS N J
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A new technique was devised and implemented for optimum transmission of digital data rates up to 2.3 megabits over tactical troposcatter paths of 50 to 150 miles in the 5 GHz band. The basic approach, resulting from a study of fading and multipath propagation statistics, is a time-frequency-phase keying pattern designed to resist multipath echoes and maximize performance through coherent detection of four-phase modulation on two frequencies transmitted one at a time. Dual in-band single antenna diversity is provided plus optional space diversity through quadruple predetection combining. Several innovations in digital equivalents of analog circuits were used in the breadboard model which was interfaced with the ECOM experimental Hexagon-Tobyhanna link. Performance calculations predict an increase of 2 to 1 in maximum range for an error probability on the order of 0.00001 compared to orthodox FSK or binary FM using space diversity. Single antenna in-band diversity performance is expected to be superior to FSK with two antennas at the same distance. Laboratory tests with the ECOM troposcatter simulator indicated that the expected reduction in multipath effects is obtained and that the in-band diversity is effective. Author
- Radio Communications