A LONG-TERM INVESTIGATION OF THE HF COMMUNICATION CHANNEL OVER MIDDLE-LATITUDE AND HIGH-LATITUDE PATHS

A study of HF communication link and network availability has been car ried out using frequency modulated continuous wave (FMCW) swept-freque ncy sounders operating in an oblique-incidence configuration. The soun der deployment enabled 28 middle- and high-latitude paths to be evalua ted; the time period of the study was from December 1994 until the sum mer of 1996. Propagation conditions including ionospheric mode informa tion, maximum observable frequencies, signal-to-noise ratios, and chan nel availabilities for digital data communication were derived and arc hived. The objective of the study was to ascertain the efficacy of HF data link communication for a proposed aeronautical-mobile service. Da ta were used to simulate the propagation environment which would be ex perienced in actual operation and to evaluate the value of path and fr equency diversity in overcoming various propagation effects. It has be en concluded that path and frequency diversity will lead to channel av ailabilities approaching nearly 100% and that a practical engineering solution was possible. These positive results are achievable if and on ly if dynamic frequency management methods are invoked. The paper outl ines the nature of a real-time system, which is based upon a terrestri al FMCW swept-frequency sounder constellation and by which communicati on nowcasts and short-term forecasts are developed to drive a dynamic frequency management system.