Air Power: Data links - Defence’s renewed focus on tactical data links | ADM Mar 2009
Tom Muir
According to the Defence Capability Plan, JP2089 aims to deliver tactical data links to the ADF's legacy platforms and capabilities as well as the infrastructure to support tactical data exchange at the operational level.
The initial focus is on information links comprising Link 16 and the Variable Message Format (VMF).
Consideration is also being given to upgrade legacy Link 11 platforms to Link 22.
Tactical data links (TDLs) covers both Tactical Digital Information Links (TADILs) which process tactical data (such as Link-16) as well as tactical data systems that pass raw or unformatted data.
And now the demand for improved situational awareness and ISR capabilities has seen the advent of newer Common Data Link (CDL) and Tactical Common Data Link (TCDL) technologies introduced to provide secure, digital data links for use with both manned and unmanned airborne reconnaissance platforms.
Rapid growth in the development of TCDLs has tended to focus on ensuring interoperability and thus common standards for TCDL-equipped platforms in US military service.
What is not immediately apparent is where TCDL lies where Coalition interoperability is concerned.
This has now prompted Defence to seek help from the Defence-Industry RPDE organisation for advice on issues arising from the acquisition and implementation of TCDL technologies.
And while the introduction of Link 16 has been somewhat problematic and currently found only on F/A-18 and upgraded FFGs, AP-3Cs have been equipped with TCDL to support their deployed ISR missions.
Link-11
The ADF has considerable experience with Link 11 which exchanges digital information among airborne, land-based, and ship-board tactical data systems.
It is the primary means for the exchange of data such as radar tracking information.
Link-11 can be used on HF or UHF frequencies although the US Army uses only HF.
Operation in the UHF line of sight (LOS) band, provides ship-to-ship ranges of 25nm, ship-to-air up to150nm (depending on aircraft height), and air-to-air 300nm plus.
Operating in the Ground or Skywave band HF coverage is 300nm plus.
While Link-11 lacks the robustness and data exchange capabilities of more modern systems such as Link-16, it does provide a necessary ‘beyond line of sight' (BLOS) capability.
In the maritime domain, RAN vessels equipped with, or to be equipped with Link-11 include the Collins submarines, the LPAs, the LHD and AWD, the FFGs, the MHCs and the ANZAC.
The ADF's Northern, Eastern and Mobile Regional Operations Centres are also equipped with Link 11.
Aircraft fitted with Link-11 include AP-3C and AEWC Wedgetail.
The ADF intends operating Link-11 until at least 2015 when the US Navy also plans to phase out its use.
But before phasing it out the ADF will need to select a replacement that provides a similar BLOS capability.
Alternatives under examination include Link-22 and JREAP (Joint Range Extension Application Protocol) an application protocol that is promising because it allows J series messages to be sent over a variety of communications systems including satellite.
J series is the US messaging format for Link 16 data links.
Link-16
Link-16 will be the ADF's primary tactical data link for command, control, and intelligence, providing critical joint interpretability and situation awareness information.
Link 16 uses TMDA architecture and the J message format standard.
Link-16 broadly follows the information exchange concepts of Link-11 but provides certain technical and operational improvements to existing tactical data link capabilities and provides some data exchange elements, which the other data links lack.
Significant advantages over Link-11 include jam resistance, improved security, greater data rate (throughput), and precise location of participants.
A reduced data terminal size allows installation in fighter and attack aircraft.
Although designed many years ago, it is currently entering a phase of rapid uptake by many platforms in many countries, particularly with the introduction of the Multifunctional Information Distribution System (MIDS) terminal.
MIDS supports key theatre functions such as surveillance, identification, air control, and weapons engagement.
This is resulting in moves to enhance its capability, while maintaining compatibility with the existing system.
MIDS is also designed to be fully interoperable with the Joint Tactical Information Distribution System (JTIDS), an earlier Link-16 system.
The primary use of the US Army's MIDS Low Volume Terminal (LVT) is to provide an interoperable joint and allied Link-16 tactical digital data link with air, ground, surface and subsurface platforms.
Link 16 terminals periodically and automatically broadcast a precise position location and identification (PPLI) message, providing a reliable identification of the platform in which the terminal is installed, and reducing or eliminating the risk of damage from friendly fire.
Furthermore, command and control and/or sensor centres can transmit an identification of those sites within their Link 16 track files, providing an indirect method of combat identification.
Link 16 in Oz
Australian Link-16 candidate platforms include AEW&C Wedgetail; F/A-18 Hornet, F/A-18 Super Hornet; AAR; the CRUs, Upgraded FFG; ANZAC; AWD and LHD.
Australia has been experiencing difficulties in introducing Link-16 into service on naval and air platforms before it has fully developed expertise in their use.
There have been hurdles in establishing the test environments as well as management concepts and processes needed to ensure the integrity of new networks.
And before introducing them into service the prospect of costly further evolutions of the technology must be faced.
The increased use of data links by ground forces also places more demands on Defence systems.
As the Army begins to make greater use of data links, the issue of scalability of the network assumes a higher priority.
In the past, with limited ships and aircraft operating on the same network, this was not a serious issue.
Now however, the Army brings hundreds of tactical nodes to the network, all of which may join and depart as operational needs dictate.
The Defence organisation is faced not only with the further introduction of Link-16 in the aerospace and maritime domains but with the convergence of the following range of tactical information exchange systems in the various domains:
• Maritime: Link-11 to Link-22 or JREAP; Link-16; Combat Net Radio/Variable Message Format (CNR/VMF).
• Aerospace: Link-16; Beyond Line of Sight (BLOS); CNR/VMF.
• Land: CNR/VMF.
• ISR: TCDL/CDL.
Link-16 a bottleneck?
At the recent MILCIS Conference in Canberra, a paper presented by QinetiQ Consulting Pty Ltd*, underscores the need for careful thought in the choice of a Link-16 network structure.
The authors developed a hypothetical communications network on the OPNET? modelling environment involving both static and mobile nodes, data transmission via a geostationary satellite, optical landlines and a tailored and controllable Link 16 network.
The model was developed to test a maritime strike scenario to determine the communication budget for imagery and track files being relayed to an AEW&C platform, and thence to strike aircraft.
The modelling revealed that the major bottleneck with regard to the timely transfer of data was the final link in the communications chain, the Link 16 carrier between the AEW&C and the strike aircraft.
That final link was investigated in some detail and the results indicated that careful thought should be given to the choice of the Link 16 network structure, and the form of data ‘packing' used.
The experiment showed that the standard Link 16 ADF Network 1 limits the rate at which imagery can be delivered to the strike aircraft.
Better rates were achieved using a simple Link 16 network with a free-text (rather than a fixed-format) data packing structure and just two nodes (the AEW&C and the strike aircraft).
This assumed that reduced security, jam resistance, and error detection and control were deemed to be acceptable, consistent with a line-of-sight system being used exclusively to deliver time-critical imagery to an operational strike aircraft.
*J.Wells, C.Williams, B.Mcgrath & D.Steel: Modelling of Future Mobile Communications Concepts, MilCIS 2008, QinetiQ Consulting, Canberra ACT.