Applying cognitive radio concepts to HF communications

The concept of cognitive radio, originally proposed in 1998, has since then inspired growing interest and research activity. While the proper definition of the term "cognitive radio" remains debated, the concepts commonly offered as examples of cognitive radio all seem to involve ways in which a radio system can sense relevant features of its environment such as location, spectrum utilization, and spectrum availability, and intelligently adapt its behaviour and resource usage in light of regulatory constraints, equipment state, and other factors, so as to best meet the communication needs of the user. While the automatic link establishment techniques widely used in HF radio systems are frequently offered as an example of an early, limited form of cognitive radio, most of the research attention in this area has been given to communications bands well above the 30 MHz upper limit of HF. In this paper, we first provide a concise overview of the variety of techniques that have been proposed as applications of the cognitive radio concept, and consider the applicability of these techniques to HF communications, in light of the distinctive characteristics of the HF communications medium and its typical uses. We then consider whether there might be distinctive cognitive techniques having promise to improve the effectiveness of HF communications, in spite of their having received little or no attention in other domains, and discuss potential challenges and critical success factors impacting the prospects for successful application of cognitive techniques to HF communications.