In this article, Ioseba Tena, Head of Defence at Sonardyne and Jonathan Davies, Chief Scientist at Sonardyne discuss the trends in allied underwater communication and what collaboration and interoperability really mean for those in charge of naval communications strategy.
Allied navies have different languages, traditions, vessels, and strategies. Yet, if they share the same technology, it is possible for these fleets of divers, autonomous underwater vehicles and submarines to also share intelligence and data.
The subsea communication technology landscape
Over the last 20 years, a bedrock of commercial off the shelf (COTS) technologies has grown to enable subsea communication, navigation and tracking in uniquely hostile and challenging underwater environments, largely driven by non-defence needs in maritime market sectors including oil and gas exploration, marine construction and renewables.
Over a similar timeframe, the Royal Navy and the rest of the world’s navies have become increasingly aware of the growing need for, and importance of secure communication, both above and below water, in delivering military effect and capability, as part of a modernised, more agile, more operationally versatile, and more interoperable maritime force.
Leveraging and adapting non-defence COTS subsea communication technologies to meet specific military needs in terms of performance, security and interoperability remain a very worthwhile challenge. The commercial subsea technology market has responded, in part to defence needs, for example by embracing multi-physics bearers (acoustics/optics/electromagnetics) there is potential for far more sophisticated communication solutions in support of covert assets. There is still a way to go, and some technologies stand head and shoulders above the rest.
International navies need to be able to communicate with each other underwater, as easily as they do terrestrially. Due to the nature of the sea, adversaries easily obscured meaning that detection and safeguarding using technology is critical for intelligence and surveillance missions. In May 2020, NATO’s Communications and Information Agency (NCI) agreed on secure access to satellite communications for maritime operations and for updating cryptographic equipment on ships. This kind of agreement demonstrates that communications collaboration is a top priority. To fully enable this over a variety of vendor platforms and formats, interoperability and open standards are key.
The challenge is exemplified in the RN’s Astute-class submarines, and the potential role of tactical subsea communication technology to deliver enhanced mission effectiveness, across diverse roles, from traditional ‘lone-wolf’ carrier strike group support and special forces operations each with specific tactical and operational requirements, through to new and emerging roles involving greater coordination with, and control of, off-board autonomous sensor and autonomous underwater vehicle (AUV) technologies.
AUVs – the Navy’s needs and current limitations
AUVs themselves are relatively easy to operate, monitor and control, but to communicate in the depths of the underwater environment, above sea technologies like radio and video are rendered useless after just some metres. This puts innovation now firmly in the hands of technologists and physicists to deliver technology solutions involving light and sound, which are still in furious development to take communications to the next level, with security being the number one priority.
To put this into perspective, we should look at the application uses for subsea technology. On a single mission, RN AUVs may need to be out of sight for many hours, sometimes even days. Its operators want to know that everything is working optimally, and they will be relying on continuous monitoring and regular status updates. While an AUV is on a survey, the Navy may wish to assign it a task during this exploratory mission, such as to take pictures of a contact or location and, for this reason, communication to the AUV is of key importance. There are a broad range of underwater assets, from large submarine platforms to very low power autonomous sensors sitting on the seabed. The challenge is that there is a larger range of requirements and drivers in terms of what those various assets can do, what sensors they have and how they communicate. They cannot all physically communicate as they cannot always operate in the same frequency. So how do you get all these disparate naval systems to talk to each other?
JANUS as a first solution
NATO’s JANUS communications system, created in 2017 by its Centre for Maritime Research and Experimentation (CMRE), was a great start, but the jury is still out in terms of its broader role as a tactical acoustic communication solution, due to moderate data rate, lack of underpinning transmission security (TRANSEC) layer, and relatively large overheads associated with JANUS protocols, meaning platforms transmit more energy in the water which collectively elevates counter detection and information exploitation risk. The potential adoption of JANUS as a ‘first contact’ handshake protocol, capable of supporting subsequent hand-off to nation-specific waveforms and protocols is a likely direction of travel. This is to balance basic multi-nation interoperability needs, against broader, nation-specific tactical communication needs. The use of JANUS, of course does not preclude the sharing of sovereign waveforms between allies and partners, as these are developed and proven over time.
Acoustic communication, whilst multifaceted and technically challenging, is both proven and mature, and so the interoperability problem is not just about the underpinning technology, but also how industry-academia-government institutions collaborate at the national and international level to address the specific challenges of military communication in the subsea domain in areas such as transmission security, multi-user networking, and situational awareness.
The need for open standards
Navies are looking at missions where autonomous systems can add value, meaning that technology vendors are playing with concepts and coming up with different robots with all kinds of different abilities. Today, if you want all these robots to work together, customers will need to select a modem from a specific supplier and a specific language from that supplier. But if they want them to be truly effective, they need to come up with a common language which does not lock you down to a specific vendor. Until this happens, navies will not be interoperable with each other through their submarines, divers and AUVs.
Phorcys – The UK’s open and secure acoustic waveform
Considering UK defence future needs for full spectrum tactical subsea acoustic communications, and the limitations of JANUS in delivering against those needs, the UK Defence Science and Technology Laboratory (DSTL) has, in conjunction with UK industry partners and the National Cyber Security Centre (NCSC), been developing a UK government-owned acoustic communication waveform to address the challenges of open secure interoperable tactical acoustic communication.
Phorcys has been developed as an open, secure waveform to enable UK subsea platforms and technologies to communicate effectively and securely. The UK government-owned Phorcys waveform may be shared with other allies and nations to facilitate interoperability.
Phorcys works using cryptographic keys that provide two separate layers of encryption for both the waveforms and the data, making it nigh on impossible to break the code. The Phorcys waveform will allow Phorcys equipment vendors to certify equipment, and so provide truly secure and interoperable acoustic communication.
Solving the range-data rate-size challenge
There is no single operating frequency that meets the many and disparate user requirements for tactical acoustic communication. Acoustic frequency determines range with lower frequencies providing longer ranges and the size of the acoustic transducer used to generate the waveforms scales inversely with frequency. This means that lower frequency systems are larger and heavier. The Phorcys waveform standard spans three frequency bands to provide a trade-off solution space spanning ultralong range, over 15 nautical miles, command and control (C2) i.e. asset ‘paging’, medium-range, up to 15 nautical miles, command control and communication (C3) applications, and short-range, up to 3 nautical miles, C3 applications.
A key consideration in this multi-band approach to subsea acoustic communication is the fact that size, weight and complexity is driven by the acoustic transducer and not the software or hardware responsible for generating and receiving the acoustic signals. Consequently, multi-band tactical acoustic communication can be serviced by a single consolidated software-defined modem (SDM) architecture, separably configurable for each band and transducer, which is hostable on different hardware platforms.
The integration of open secure waveforms and flexible SDM architectures is arguably the key step towards unlocking the future potential of military acoustic communication.
What other technologies are out there?
There are three potential approaches to communicating underwater: acoustics, electromagnetics, and optics. Each technology has benefits and shortfalls, but acoustics is currently the only technology capable of achieving ranges exceeding a kilometre or so, with the potential to exceed many tens of kilometres depending on the operating frequency.
The nature of transmitting sound into water via mechanically resonant devices means that whilst acoustic communication over very long-range is possible, in excess of fifty kilometres, acoustic bandwidths are limited, which limits data rate, and may impact the ability to hide acoustic signals below the background noise floor using spread spectrum signal design techniques.
For covert, manned subsea platforms, the preferred operating posture will invariably be to remain passive, with acoustic transmission brevity key to mitigating detection risk. For AUV platforms operating covertly in forward denied water space, for example augmenting conventional platform sensor capabilities, similar considerations apply, albeit likely outweighed by the tactical picture such distributed sensing assets provide.
Subsea low-frequency electromagnetics occupies a relatively niche and ambivalent position in the subsea acoustic communication technology space. Whilst very low frequency (VLF) radio technology is well established and a key part of submarine C3 infrastructure, subsea EM as a short-range tactical bearer technology is neither widely established nor mature, on account of the relatively limited performance envelope the technology provides.
Subsea electromagnetics affords a short-range, metres to few tens of metres, moderately high data rate, tens of bits per second to several tens of kilobits per second, low latency performance envelope, ultimately limited by the physics of electromagnetic propagation in conductive media. As such, the technology is intrinsically covert but ultimately limited in range.
Comparison of underwater signal transmission methodsComparison-of-underwater-signal-transmission-methods
The future could lie in optical and hybrid optical and acoustic communications, and more specifically in free space optical modems integrated with acoustic communication modems to harness the synergistic benefits of both technologies. Range will be provided by acoustics and optical modems will provide larger bandwidths.
This is now moving beyond the concept stage. With optical communications, the systems emit modulated light to transfer data at around 75% of the speed of light. If the Navy wants to transmit between 10 to 150 metres of the asset (submarine or AUV), it can do so because, at that range, its chances of exposure to the enemy from only that 150-metre distance is limited.
The asset is still not covert, because it is throwing visible light, typically blue and green, everywhere, but by using an optical modem at moderately short range, the risk is minimised. Acoustics provides the means to both localise, establish aspect and remotely communicate with other optical modem systems.
Non-visible ultraviolet light can also be used, which has huge potential to enable covert subsea communication, in conjunction with hybrid acoustic-optical concepts of operations. Defence technology specifiers are watching this space for new AUV concepts.
Open standards are a must
The RN is increasing investment in unmanned systems and looking for more advanced applications which will transmit data covertly at greater ranges. AUVs need a greater capacity to share more refined data for safety, surveillance and international communication. Looking at the limitations of current systems, it has become clear that a secure open standard is required, hence the underwater covert subsea communication market is constantly developing to meet these needs. There will always be a place for proprietary solutions, but only with open standards for better integration of autonomous vehicles will true interoperability underwater will be possible.