Evaluering av HF-modemer og flerfrekvenssystemer basert på kanalmålinger på høye breddegrader
The high latitude HF channel has been measured and characterised in terms of Doppler spread, delay spread and signal-to-noise ratio. This is done by the Doppler And Multipath Sounding Network developed(DAMSON) by DERA in conjunction with CRC, FOA and FFI. The performance of data modems compliant with STANAG 4285 (2400 bps mode, non-robust) and STANAG 4415 (75 bps mode, robust) has been determined over a comprehensive range of simulated channel conditions. A comparision is made between the channel measurements and the modem characterisations, and modem availabilities during the measured channel conditions are determined . The robust modem shows 50-70 % higher availability than the non-robust modem on the measured paths. The most important factor contributing to modem failure is low signal-to-noise ratio. This report also addresses the number of frequencies required for a HF circuit to achieve maximum communications availability. Results from all DAMSON paths show that STANAG 4285 requires 6-8 frequencies whereas the STANAG 4415 modem reaches maximum availability with 2-3 frequencies.