SALAMANDRE: HF with wideband capability

HF has been an effective way of communicating over long distances for decades and is still widely used for maritime operations today. Perfectly suited to voice and telegraphy, it is now attracting renewed interest as a way to meet the growing demand for data and support new applications that offer real operational benefits on maritime missions.

Despite the development of satellite communications, HF remains invaluable for shipping and aviation, particularly for secure over-ocean radiocommunications. It is also important for military traffic and for fixed and mobile communications in regions with no infrastructure, or when infrastructure has been damaged in a natural disaster.

Important as it is for communications at sea, HF technology is nonetheless limited in terms of bandwidth — yet naval operators must be able to transmit files and data to perform their missions effectively today. The purpose of the SALAMANDRE advanced study programme, awarded to Thales by the French defence procurement agency (DGA)(1), is to develop new HF communication capabilities by transitioning to Wide Band HF. Also known as HF XL, Wide Band HF supports higher data rates and improves service quality.

Robust communications

France has adopted a different approach to the United States, which has increased the bandwidth of the relevant radio channels by a factor of eight, creating radio superhighways able to absorb the growth in traffic. However, the channels allocated to individual nations under international regulations(2) cannot be extended so easily, at least not without reaching new international agreements and reassigning the frequency spectrum used for operational missions. The DGA and Thales have thus adopted a different approach, which involves using eight standard channels in parallel, though not necessarily adjacent channels, to increase voice and data capacity. If necessary, this can be increased to 16 channels.

As well as a significant increase in bandwidth, this approach overcomes the inherent variability of HF links, resulting in a much more robust solution. Maximum bandwidth is 150 kbit/s, compared to 19.2 kbit/s under optimum conditions today, with typical speeds of 60–100 kbit/s by direct sea wave propagation (up to 100 nautical miles, or 200 km) or indirectly by reflection in the ionosphere (several thousand kilometres). If one of the channels is unusable, the other seven available channels allow transmission as normal and a substitute eighth channel can also be added, making the link highly resilient. This is important, because the HF band is sensitive to outside factors. It works well for direct transmission over relatively short distances, up to 200 km, because the ocean surface is conducive to radio wave propagation. However, the situation is more complicated over longer distances (in the order
of thousands of kilometres) because the radio waves are reflected (actually refracted) by successive layers of the ionosphere. The right frequency must therefore be chosen, depending on location, time and conditions. This is exactly what the Thales solution does: the system automatically selects the most suitable radio channel in real time, based on the actual propagation conditions encountered.

Operational benefits

The solution offers clear advantages in a wide range of situations. Imagine a submarine dispatched ahead of a naval task force to scout for intelligence. Thanks to the high-data-rate capacity of its HF link, it could transmit this information back to the aircraft carrier much faster, thereby minimising time at periscope depth, when it is visible and vulnerable. Or take the example of two naval groups working together. To communicate, they need to share a satellite resource, which is not always easy when two separate nations are involved.By using the HF link, no authorisations are needed and both groups benefit from a fast and reliable link.

In certain cases, HF is the only way to transmit over very long distances, particularly in the polar regions, for example, where coverage via the main communication satellites is poor, since they are positioned over the equator. Lastly, for small vessels, HF remains the spectrum of choice for operators, not least because it is free, unlike satellite frequencies.

The first full-scale tests with the SALAMANDRE demonstrator were conducted in France in September 2016 and were highly conclusive. A video of these tests can be viewed at the Thales stand.

With the experimental phase now complete, this high-data-rate capability will be incorporated into Thales’s wideband-ready MSN 8200 naval radio system between now and 2019. It will also be incorporated into the next version of the Thales TRC 3800 tactical radio.