One giant step for resilient tactical satellite communications

A lot of information is imparted during a voice conversation, beyond the spoken words. You can tell if a person you're talking to is frustrated, confused, angry, tired or all of the above. For that reason, it's important for warfighters to have clear voice communication channels.

Following the rapid integration of extant Australian technology over the last year, a team comprising DSTG and Australian academic and industry partners, supported by the SmartSat CRC, recently demonstrated an advanced 'push to talk' voice over satellite system.

Defence uses tactical satellite communication (SATCOM) systems to talk to warfighters out in the field. At the moment, Defence systems are based on ultra-high frequency (UHF) technology which has not advanced significantly from what was developed in the 1970s. Communications broadcast across wide areas from geo-stationary satellites are vulnerable to intentional interference and use a UHF spectrum that is limited and highly oversubscribed.

Defence scientist Mr Luis Lorenzin leads DSTG's investigation of future SATCOM technologies. He says this project has demonstrated the viability of providing tactical SATCOM to high-mobility users using a nano-satellite. New systems like this use low-Earth orbit satellites which reduce the coverage footprint and hence are less-susceptible to intentional interference.

All-Australian achievement

Mr Lorenzin says the voice relay from a nano-satellite that this project demonstrated is probably a world-first achievement. The team is particularly proud that every aspect of the recent demonstration relied on sovereign Australian technology.

During the demonstration the team transmitted to a reconfigured Fleet Space Technologies nano-satellite in low-Earth orbit, using a small user terminal developed by DSTG and a modified software-defined radio waveform originally developed for search and rescue applications by the company Safety From Space. The satellite then transmitted to a remote University of South Australia user terminal which relayed the signal back to team members.

'All of this project work was done in less than a year, making use of technology that was already available and in place,' reports Mr Lorenzin. 'The Fleet Space Technologies satellite had been launched well before the project was even conceived; the fact that we were able to reconfigure an existing space asset for a purpose for which it wasn't intended is a tremendous technical accomplishment.'

According to Fleet Space, its Centauri satellites are reprogrammable by design, and in this case the new voice capabilities were enabled via a software update. The company says the demonstration validated the ability of highly-adaptable microsatellite constellations to rapidly deliver purpose-built, high-quality SATCOM capabilities.

Space command over the moon

Mr Lorenzin reports that Defence representatives were pleased with the clarity of the voices received over the satellite system during the trial.

Further resilient satellite communication system research and development will use higher frequency bands, offering greater bandwidth and the opportunity to make communication more secure with smaller antennas and narrower beamwidths.

According to Mr Lorenzin there is a lot of improvement possible now that satellites can have "regenerative payloads" that do intensive on-board signal processing. 'Noise can be removed from a received signal before regenerating it and transmitting it back down. Using techniques like beamforming, advanced signal processing and advanced coding techniques we can create resilient and secure communication systems that will hopefully one day augment or possibly replace Defence's UHF tactical satellite communications.'

'Our next challenge is demonstrating data transmission over the link. Data is less forgiving to outages than voice communication. The ultimate goal is to be able to provide voice and data services to multiple high-mobility users over X-Band frequencies.'

'A further technical challenge will be to develop a system that can communicate reliably at a low elevation angle to the satellite, in order to increase each satellite's transmission footprint and minimise the number of satellites required in a satellite constellation to provide persistent coverage.'

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