The effects of channel variability on high data rate HF communications

Research continues to explore mechanisms to increase data throughput over HF circuits. Several of these techniques rely on the use of multiple 3 kHz channels to increase the overall bandwidth and therefore the data capacity available to the user. Depending on the particulars of the technique, some may be sensitive to the variability of HF channel conditions across the set of utilized channels. This paper reports on recent testing performed to characterize the degree of variability across a set of propagating HF frequencies. Results are presented for two different HF radio links. The importance of these measurements in the design of higher throughput multiple frequency systems is discussed.