By FELIX DEFENCE
The 2020-21 Defence budget signalled a significant increase in, “…long-range capabilities to hold adversary forces and infrastructure at risk, further from Australia, including longer-range strike weapons, offensive cyber capabilities and area denial capabilities”, as well as investing, “…in capabilities to give Australia better awareness of our region and to support regional engagement”.
A key enabler for this capability will be secure tactical data links which can operate beyond line of sight (BLOS).
As described in earlier editions of ADBR, Link 16 is the pre-eminent tactical data link (TDL). However, there are others which provide the broader range of capabilities necessary to support the establishment of an agile and redundant data link network. One of those TDLs is Link 22, introduced into the ADF recently to replace older Link 11 functionality, and provide BLOS data link capability.
Link 22 has been a long time coming. As far back as the late 1980s eight nations (US, UK, Canada, France, Germany, Italy, Netherlands, and Spain) agreed a memoranda of understanding (MOU) to improve Link 11. This MOU morphed over time, but those eight nations established the NATO Improved Link Eleven (NILE) project.
Fast forward to 2020, and much has changed. Australia is a third party sales (3PS) nation and, while the term NILE is still used, it is arguably a legacy term as many non-NATO nations can – if sponsored by one of the eight NILE nations – become a 3PS nation and gain access to the technology. NILE is now only used to describe specific components of the wider Link 22 system under the umbrella term ‘NILE Communications Equipment (NCE)’.
WHAT IS LINK 22?
Link 22 provides a secure, electronic countermeasures-resistant capability for air, surface, subsurface, and ground-based systems to exchange tactical data utilising both high frequency (HF) and ultra-high frequency (UHF) media paths.
The ability to use HF provides a BLOS advantage over Link 16. Furthermore, it has been designed with a data exchange message set that works seamlessly with Link 16. These messages are known as F and FJ-Series. While F-Series messages are newly defined for Link 22, FJ-Series are in simple terms a ‘cut and paste’ of a Link 16 J-Series message.
Link 22 is primarily (but not limited to) a maritime capability to support BLOS operations. It enables deployed assets to perform a variety of Information Exchange Requirements (IERs) without the need for satellites. Those IERs involve the exchange of situational awareness (SA).
The use and connectivity of deployed assets utilising the HF media path is vulnerable to change. To combat this, Link 22 has more robust waveforms whereby in poor radio frequency (RF) conditions improved coding and modulation is used to maintain connectivity at the expense of throughput.
Like many TDLs, there is always a trade-off. If RF conditions become too bad, this will undoubtedly affect the operational capacity and, as a consequence, impact the warfighter’s ability to achieve their mission.
SYSTEM NETWORK CONTROLLER (SNC)
Jointly-developed and mandated for use by the eight NILE nations, SNC is the software that manages the Link 22 system, networks, and architecture.
While many diagrams that illustrate the Link 22 system show the SNC as a separate box, it will most likely reside within the data link processor itself. Often described as the brains of Link 22, each Link 22 unit is equipped with the SNC software to undertake two main functions – communications transport and management.
EFFICIENCY IS KEY
We already know that Link 16 is the primary capability for many nations which need to operate with the US, and therefore we can unquestionably describe it as the key enabler to connect the joint force.
But as good as Link 16 is, it is inefficient when it comes to actual data throughput. Link 16 offers far more bits per second than Link 22, but it is inefficient with the bandwidth it has available. This lack of efficiency is just one area where the NILE nations have learnt many lessons from the use of both Link 11 & 16, and made Link 22 far more efficient with the bandwidth it has available to use.
Firstly, many of the newly defined F-Series messages have been defined based solely on efficiency, and support improved transmission rules over Link 16. For example, to perform the reporting of own unit position and many situational awareness messages, Link 22 performs far better.
Secondly, for every message sent over Link 22 it provides several quality of service features ranging from priority and level of reliability through to perishability and the use of different addressing techniques. Finally, each unit’s SNC will calculate if relay is needed for each individual message dependent upon its own connectivity with other units.
NETWORKS AND CONNECTIVITY
Within Link 22 there are a variety of networks, but the main two are the Super Network (SN) and NILE Network (NN), aka Link 22 network.
A Link 22 SN exists as soon as at least two units are exchanging data within a single NN, with the most complex SN being 125 unit’s exchanging data across 8 NN. A unit, dependent upon its Link 22 capabilities, could operate in up to four of those NNs at any one time – it really is conditional on the number of data radios a unit has at its disposal.
When it comes to connectivity, a feature known as ‘link reception quality’ recognises how well a unit is receiving data from another unit – the connection between two units. This data is sent in Time Slots (TS).
The transmission capacity for each NN network is divided into TS which are subsequently divided into mini slots. There are two types of TS – assignment and interrupt. Assignment slots are assigned to individual units and the addition of these TS within a NN form the Network Cycle Time (NCT). Consequently, dependent upon the number of units and how many TS they are assigned, is just one of the factors that determines the NCT. Another factor is the media path – when operating over HF the mini slot duration is 112.5ms, whereas for UHF it is 48ms.
After that, it can become complicated when deciding how to build Link 22 networks and provide each unit enough capacity to meet their IERs versus access delay. For any tactical situation we would not want to afford a unit sufficient time in the NCT for it then to suffer from not being able to update their data in a timely manner.
IS LINK 22 ALREADY REDUNDANT?
A question many ask is, “Why should a platform integrate Link 22?”
Six of the eight NILE nations are investing significantly in Link 22, although the US – despite being a committed Link 22 nation – appears to be moving slower with its integration effort. There are a number of possible reasons including the investigation by the US Air Force Research Laboratory (AFRL) Space Vehicles XVI programme to provide 24-hour BLOS Link 16 coverage through the utilisation of low orbit satellites.
There are also other technologies able to provide SA BLOS, and many without the need for satellites. For example, the use of Joint Range Extension (JRE) for reach-back and/or reach-forward is generally transmitted over satellite using primarily TCP/IP. But in the event of a satellite denied environment, JRE could easily be switched and sent over HF. After all, they are just data packets and, as long as the media path can be managed there shouldn’t be a problem. Indeed, there are a number of vendors who claim to manage a HF connection in a manner similar to Link 22.
Ultimately, every program manager responsible for a weapon system or platform must firstly consider the mission aim and the subsequent IERs. This is something that, regrettably, is often overseen, and the procurement of what some perceive as the latest and greatest technology does nothing to support the warfighter in meeting their operational outcomes.