Measured wideband HF mid-latitude channel characteristics

The authors present the results of HF ionospheric channel measurements on a 2000-km midlatitude path between Florida and Massachusetts performed during September 1988 and February/March 1989 using a 1-MHz bandwidth direct-sequence-pseudonoise (DSPN) probing signal. The channel impulse response is extracted by correlating the received probe signal with a local DSPN reference. Doppler information is obtained by Fourier-transforming a succession of these impulse responses. The channel is characterized in terms of its time, its Doppler spread, and the autocorrelation and distribution functions of the received power. The data indicate that this particular channel can operate within 2 dB of the ideal matched-filter signal-to-noise ratio given (1) a decision-directed Rake modem without Doppler correction and (2) a low-overhead backlink for infrequent (a few times, a minute at most) and small (1- or 2-dB increments) transmit power adjustments