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Adaptive HF Propagation Path Utilization
Final rept. 11 Jun-30 Sep 1979
SMITHSONIAN ASTROPHYSICAL OBSERVATORY CAMBRIDGE MA
Pagination or Media Count:
Detailed knowledge of the characteristics of HF propagation is an essential requirement to a better utilization of these paths in reliable communications. Recent advances in HF path characterization as well as in communication equipment, coding schemes, and microprocessor technology make it possible to conceive approaches of adaptive utilization of HF propagation that promise a substantial improvement upon present-day HF circuit performance. This recently acquired expertise includes the following advances a better understanding of the multipath spread and Doppler spread characteristics of HF propagation paths in several path configurations midlatitude paths, transequatorial paths, transauroral paths, etc. b availability of frequency- agile HF transmitters and receivers c availability of high-speed sounding techniques, such as the digisonde approach d availability of microprocessor logics for real-time evaluation of channel performance, for making decisions on the required diversity and for carrier frequency selection. e availability of coding schemes, such as the M-ary codes, that maximize the data rate for the selected signalling approach. This report illustrates an adaptive method that makes it possible to transmit a data rate of 24 kilobitssec with an error rate of .0004 therefore suitable for high-quality digital voice in a single-hop ionospheric path established in midlatitude or across the aurora belt.
APPROVED FOR PUBLIC RELEASE