Introduction
Long-range, beyond line-of-sight (BLOS) communications can be provided by a number of means. Some, such as cable and microwave radio-relay, require significant infrastructure. Other BLOS means use radio-frequency (RF) channels with no intervening infrastructure other than a single repeating platform, if one is necessary. Such options include high-frequency (HF) sky-wave transmission, troposcatter, airborne platforms and satellite-based systems. Of these, satellite communications systems are preferred because they can provide long-range communications with a much greater channel capacity than the other options—the capacity of a communications channel is the maximum bit rate over that channel that will result in negligible errors.
Yet, despite their almost ubiquitous use for long-range communications, satellite communications systems are very vulnerable to the space environment and to space warfare. Consequently, it would be extremely unwise to rely heavily on satellite communications systems unless space superiority can be guaranteed. The vulnerabilities of satellite systems mean that a number of militaries have recognized for some time that reliance solely on these services is simply no longer wise.1 In that regard, Australia’s 2016 Defence White Paper recognized that the ADF and its partners are reliant on space-based systems to communicate and fight, and noted that a number of countries are developing capabilities to destroy or degrade satellite capabilities.2
This article provides a brief overview of the options available for BLOS communication in a satellite-denied/degraded environment. It begins by describing in outline the various communications mechanisms, focusing on the four broad options suitable for BLOS communications: HF sky wave, troposcatter, airborne platforms and satellite-based systems. An explanation is then provided as to why satellite communications are almost universally used by military forces for long-range BLOS communications.
Consideration is then given to the vulnerability of satellite communications and the likelihood of the need to communicate in a satellite-denied environment. On the assumption that satellite-based communications systems may not be available, suitable back-up systems are recommended. Finally, comment is made on the need to support the transition from satellite communications to a back-up system, should satellite communications be degraded/denied.