Adaptation of frame length, frequency and bandwidth with automatic HF communications

An automatic system for HF radiocommunications is described. Measurements of channel stability are presented the result of which favour an automatic link set-up process according to a prediction calculation combined with passive channel analysis rather than with channel sounding. The automatic link maintenance procedure embedded in the packet radio data transmission protocol RSX.25 comprises the adaptation of frame length, frequency and bandwidth. Channel analysis during data transmission is done by the control of the repetition rate. Depending on the defined thresholds, the aforementioned adaptation of system parameters is initiated. The results of field trials over good, medium and poor channels and the accompanying system behaviour are presented. Only in the case of severe interference the throughput drops below the mean value of 1800 bit/s. A comparison by computer simulation was done between the RSX.25 protocol and the packet radio protocol, which shows that both protocols may be improved by implementing the other´s benefits