Robust HF data communications at high latitudes

It is well known that the ionosphere can be highly disturbed in the auroral and polar cap regions. However, efforts to quantify ionospheric effects on high-frequency communications have concentrated mainly on lower-latitude regions. The Doppler and multipath sounding network (DAMSON) has been used in an extensive campaign to measure the channel characteristics on four paths in the auroral region of northern Scandinavia. The conditions observed indicate that robust data modems, used when less-robust, higher-rate modems fail, are required up to 90%, of the time. A detailed analysis of the propagation parameters indicates that these modems, designed to operate in these regions, should be able to operate when the Doppler spread exceeds 40 Hz and the multipath spread is greater than 11.5 ms. Multiple propagation modes are common, especially between the lowest and maximum usable frequencies. The distribution of the received signal power in these cases is examined, and it is concluded that laboratory simulations used for robust-modem evaluation should include channel models with dominant modes