Whether in the field of battle, search-and-rescue or humanitarian aid efforts, the ability to share real-time, networked information between ground, sea and airborne forces is rapidly becoming the defining factor in a mission’s success.
The Royal Australian Air Force (RAAF) and Rockwell Collins have successfully demonstrated of the first wideband high-frequency (WBHF) communications transfer from a ground to air. As part of the WBHF transmission demonstration, the ground station team located in Geelong, Australia, transmitted a wide range of data, including real-time chat, streaming video, file transfers and digital voice audio, to a static C-17A Globemaster III aircraft.
High frequency communications have been used since the 1930s as a means to communicate beyond line of sight. It uses the ionosphere to bounce signals from one point to another. HF Frequencies range from ~1.8 MHz – 30MHz. HF’s single greatest value is its ability to provide reliable short AND longrange Beyond Line Of Sight (BLOS) communications. It can support Point-Point and P-Multipoint data rates up to ~10kbps w/o relays . HF is generally available, rapidly and readily deployable – requires very little infrastructure and can be made extremely reliable.
Broden said it is mostly seen as a back-up system in today’s aircraft as most pilots use satellite links. Legacy systems use three kilohertz wide channels, while the wideband system goes up to 48. Wideband high frequency channels offer users four to seven times more capacity than the legacy high frequency channels, Ron Broden, account manager for high frequency systems at Rockwell Collins, said in an interview.
“Whether it’s a real time conversation, streamed live video or the rapid transfer of large data files between an aviation platform, and support or command and control elements for a broad range of missions, this technology has the ability to deliver a true sovereign beyond line of sight communications capability for defence, and one that complements and hardens existing networks.”
Recent advances in HF radio and Digital Signal Processing (DSP) technology, along with new U.S. and international regulatory flexibility in spectrum allocation policies, have ushered in a new era for terrestrial-based, long-range communications capabilities. As a result, HF radio is now no longer limited to agonizingly slow 9,600 bps data transfer rates – slower than dial-up modems of the early 1990s. Today, modernized Wideband HF (WBHF) can deliver rates up to 240 kpbs on a 48 kHz wide channel.
Rockwell Collins’ modernized HF capabilities, coupled with the inherent anti-jam nature of the widely dispersed nodes in Automatic Link Establishment (ALE) based HF networks, create an ideal alternative to narrow-band SATCOM in Anti-Access/Area Denial (A2/AD) battlefield environments. “Being able to transfer secure data via the WBHF radio could provide greater operational resilience to the Australian Defence Force in the future, especially in satellite denied environments,” said Air Force’s Director of Plan Jericho Group Captain Carl Newman.
Rockwell Collins Asia-Pacific vice-president and managing director Jim Walker said: “WBHF technology is the only modernised HF solution that will deliver net-centric, high-speed communications at costs that are in line with today’s tighter military budgets.”
Since the ionosphere changes conditions, much like Earth’s weather, there are good days and bad days for using it as a means of communications. The experiment took place on average days — not the worst that a radio operator could encounter but not the best, either, he said.
In addition, brand new ALE capability, known as 4G ALE, makes HF linking easier, faster and more reliable than ever before, while taking full advantage of wider channels. Its 4G ALE adds the spectral sensing parameter, as well as other signal enhancing characteristics, to create a new protocol that not only automatically determines the optimal bandwidth but also links much faster than legacy 2G or 3G ALE. Spectral sensing ensures that the established link not only has the best signal, but also the maximum available bandwidth. And it does it all without any operator intervention.
New HF Wideband Technology
Eric E. Johnson Klipsch School of Electrical and Computer Engineering New Mexico State University discusses a few example applications in which the higher data rate of the wider-bandwidth waveforms could offer a qualitative improvement in mission performance.
Currently, most UAV video is sent via satellite or lineof-sight radio channels. WBHF offers the intriguing possibility of beyond line-of-sight communications to and from a UAV via HF radio. Of course, powering an HF transmitter and mounting an HF antenna on a UAV pose challenges. A link is established as soon as the aircraft comes within extended line of sight. At this extreme range, the path loss may be as much as 100 dB greater than when the aircraft passes near the ground transmitter, so the data rate must adapt to the varying SNR during the link.
A somewhat less challenging opportunity for delivering video over WBHF arises with ground forces in mountainous or dense urban terrain, where near-vertical incidence skywave (NVIS) is used to overcome the lack of line-of-sight between a video source and its users.
For our third example application, consider the one-tomany communication involved in maintaining a common operating picture (COP) among vessels in a naval battle group. Propagation is via the (relatively benign) surface wave channel, but nodes in this HF LAN must share the channel. Often, a token passing channel access protocol is used.