The Characteristics of the HF Radio Channel and Its Influence on Modern HF Data Communication System Design

Abstract : A basic requirement for the design and realization of modern HF data communication systems is the detailed analysis and modelling of the transmission medium. The paper describes, how this analysis and modelling of the HF radio channel influences the design of such data communication systems. The first part of the paper is concerned with a description of the characteristics of the HF radio channel by parameters like multipath and Doppler spread and its variation with time, short and long term statistics, variation of useful frequencies with time and it gives a short introduction into modelling. The second part then shows, in which way a modern system design can cope with the unwanted characteristics of the transmission medium. As an example a system is presented, which is realized according to the open systems interconnection architecture proposed by ISO and in which the protocols of layers 1 to 3 are adapted to the medium HF radio. The third part describes details of an adaptive frequency management system with its operational requirements, the basic functions and the position within the communications system. The frequency management system is implemented as a functional model of a radio link processor, which is a part of the data communication system. The frequency management system comprises the following features: long term prediction and analysis; short term analysis with link statistics; and channel monitoring with measurement of noise and interference.