Damson HF channel characterisation-a review

For contemporary HF systems the channel often exhibits low SNR, may well be subject to slow fades and is almost always frequency selective. Until 10 years ago it was common for the high frequency (HF) user to expect low data rates of /spl sim/75 bit/s and low availabilities. However, with the advent of digital signal processing, data rates have increased significantly to 2400 bits/s, 4800 bits/s and beyond in a 3 kHz channel. Such is the progress that commercial digital HF broadcasting is now planned. In order to support these initiatives around 7 years ago the UK, Canada, Norway and Sweden started a programme to characterise the HF channel in a systematic way. This programme is known as DAMSON (Doppler And Multipath Sounding Network). DAMSON experimentation has concentrated on auroral and sub-auroral paths but has also included measurements at mid- and equatorial latitudes. Most of these measurements have concentrated on 3 kHz channels but recently 12 kHz channels, more applicable to digital HF broadcasting applications, have also been assessed. This paper reviews both the system that was developed to make these measurements and the various contributions that have been made to the understanding of the channel and the design of HF modems.