Trends and design considerations in automated high speed HF data systems

The emerging generation of HF data systems provide transmission of error-free data at unprecedented rates and in severe channel conditions. Messages, digitized audio, facsimiles, and images can be sent automatically between nodes. Operational requirements such as precedence, preemption, and automatic failure recovery are accommodated by design. The new generation systems accomplish these tasks using capabilities developed over the past decade to automate the process of data transmission. They include automatic link establishment (ALE), high speed HF modem, advanced HF data link protocols (DLPs) and off-the-shelf computer networking systems. The purpose of these functions is shown. A typical system will provide facilities for an operator to create, edit, and import messages. The operator will then command the system to send the message to a programmed address. The system will automatically link with the destination (or a relay node) using some form of ALE, pass the data using a protocol optimized for the HF modem in use, and terminate the link. The data can then be sent to a particular computer or destination over a local area network (LAN) or wide area network (WAN). The message is resent at a later time if the message is not delivered over the HF path immediately. The design considerations for the various functions of automated systems are discussed in the paragraphs that follow