3.1 Overview of the Link Establishment Process

High-frequency communication link design and establishment is the subject of Chapter 3. Section 3.2 provides a review of system design trade-off considerations and an overview of propagation and system performance predictions. This is followed by a design example showing how a radio link may be designed. Next, a new tool is introduced that provides automated assistance for HF skywave frequency selection and applications planning.

The communications link design example demonstrates the need for link establishment and frequency management techniques, including the highly desirable feature of automatic connectivity. The latter subject is covered extensively in section 3.3, which gives general design principles and an example of a highly developed system in current use for global communications. Lastly, section 3.4 addresses HF network design issues based on automatic link establishment implementation and operations.

In general, a complete HF link management system includes the following functional elements to some degree ^{[1] , [2]}:

1. Preparatory and/or on-line propagation and performance prediction algorithms and programs

2. A control mechanism, including an "engineering orderwire" function

3. Channel evaluation and/or sounding and noise monitoring

4. Selective calling and a frequency-scanning receiver, if automatic connectivity is required

5. On-line performance monitoring and adaptation

Figure 3.1 represents some of the relationships between these functions in the complete HF link call process, as discussed below. The optimum combination of the five functional elements and the implementation of each is dependent upon the overall...