A communications pipeline enables warfighters to do more with less

By DAVID AXE, Special Correspondent

The airspace over western Iraq was crowded with coalition aircraft when Marine All-Weather Fighter-Attack Squadron 224, the “Bengals,” arrived at Al Asad airbase in January 2005 for a seven-month stint supporting ground forces. According to squadron commander Lt. Col. Wilbert Thomas, the Link 16 tactical datalinks in the squadron’s F/A-18D fighters were critical to making sense of this environment.

“[Link 16] provided the ground commander with seamless air support as new sections of … aircraft checked in to relieve off-going sections. Battle handovers were streamlined as aircrew could now see altitudes, loads and sensor designations of the oncoming aircraft,” he said.

Link 16 is an Ultra High Frequency waveform, or data format, employed by a wide range of air, sea and ground platforms of the U.S. military to exchange information within line-of-sight, according to Navy Capt. Joseph C. Adan, deputy program manager for command and control systems at Space and Naval Warfare Systems Command (SPAWAR), the service’s space warfare office.

In development for more than a decade, the Link 16 tactical datalink is advancing the Navy’s ability to dominate the battlespace with a shrinking arsenal of networked platforms. However, there are limitations to its performance due in part to the incompatibility of messaging formats between services — and even between different warfare communities within a single service. Many in the Navy and other services have grand visions of a truly interoperable network easily accessible by all elements of the U.S. forces and their coalition partners. But its realization remains in the future.

An evolution of the NATO air-defense datalinks of the 1950s, Link 16 is finally coming into widespread service. Platforms equipped for Link 16 include the Navy’s E-2 surveillance planes, its F/A-18E/F fighters, upgraded MH-60 helicopters, Flight IIA Arleigh Burke-class destroyers, cruisers and most submarines; the Marines’ F/A-18D fighters; the Air Force’s E-3, RC-135 and E-8 surveillance aircraft, and its newest F-16 and F-15 fighters and B-2 bombers; Army Patriot missile batteries; and ground stations across the services. Foreign users include many NATO nations and Japan.

Recently, the Navy and Marine Corps hosted exercises intended to test Link 16 employment.

Meanwhile, SPAWAR and other Navy offices are working to expand the system’s utility from a tactical datalink supporting only specialized message exchange between platforms equipped to handle similar formats — and within a narrow, pre-assigned bandwidth — to a more flexible system accommodating ad-hoc networks. At present, for example, a B-2 and a destroyer sharing the same battlespace might both be equipped with Link 16 terminals, but if their message formats are different, they may not be able to communicate using the datalink.

The goal, Adan said, is to develop Link 16 equipment capable of supporting a universal joint message format intended for a wide range of air and surface assets, including ground troops, to allow for greater interoperability. Another improvement being sought is the capability for Link 16 data to hop around the available bandwidth to make it more accessible and easier to send and receive. The end result, he said, would be a faster, more flexible system.

In addition, this evolution will bridge the gap to the next generation of battlefield networks, Adan said.

Link 16-capable platforms communicate in several ways. The most common — and most useful for large-scale operations — requires a single platform, usually an airborne command-and-control asset such as an E-2 or E-3, or a surface asset such as a cruiser, to establish a baseline Network Time Reference (NTR). This is the foundation on which the network is built.

The NTR platform identifies the other platforms with which it wants to communicate. These might include fighters, patrol planes, electronic warfare aircraft, warships, air-defense missile batteries and ground stations.

The Link 16 terminal aboard the original, or NTR, platform sends out Initial Entry Messages (IEM) to the other platforms, whose own Link 16 terminals at this point are set to receive only. Having received the IEM, a receiving platform replies with a Round Trip Timing message that serves to synchronize the receiving platform, or “entering terminal,” with the NTR terminal. Now the entering terminal can send and receive data. With several entering terminals synchronized with the NTR, and data flowing among all platforms, a network is up and running.

Netted platforms can share a variety of data culled from the full range of active and passive sensors, from radars to targeting pods to Radar Warning Receivers. Basically, if one platform on the network can see a target, so can the other platforms on the network capable of reading the same message formats.

There are several generations of Link 16 terminals in use, but the most modern, such as those on upgraded Air Force F-16s and Navy F/A-18E/Fs, feature full-color displays that allow color-coding of targets to distinguish good guys from bad. Paired with helmet-mounted sights and AIM-9X missiles, Link 16 substantially increases situational awareness in these jets and enables them to perform as fearsome dogfighters.

For fighter jets, widespread support of Link 16 represents a leap in capability analogous to that provided by the proliferation of miniaturized radars 50 years ago, said Air Force Capt. Tyler Niebuhr.

Compared to forthcoming netcentric technologies such as the Warfighter Information Network-Terrestrial ground network and the multiservice Joint Tactical Radio System, Link 16 is old — but it has the advantage of being in widespread use.

Accordingly, Link 16 development remains a priority across the military services. Recent advancements have expanded its utility.

“Functionally, Link-16 is maturing from predominantly surveillance and air-to-air applications to included sensor networking, missile defense and air-to-ground engagements,” Adan said.

Link 16, however, is far from perfect. Among its problem areas:

• The network’s finite capacity means that NTRs broadcast information only every 12 seconds, meaning a networked platform’s situational awareness, while more complete than ever, comes at the price of being up to 12 seconds old.
• Link 16’s message formatting capability is another major limitation. The waveforms that evolved into Link 16 were intended just to connect interceptor aircraft to ground control stations. As a result, these waveforms supported only highly specialized message formats adapted to particular relationships between particular platforms.

Consequently, while many platforms are capable of sending and receiving messages using Link 16 terminals, most can read only messages specifically formatted for them and similar platforms. Adan said specialized message formats have dangerous consequences.

“Recall that during Operation Iraqi Freedom, without common Link 16 capability, we had Patriot batteries targeting F-16s and F/A-18s,” he said.

• Link 16’s “data throughput” also is a concern, said Lt. Cmdr. Jacqueline McElhannon, deputy director of the Navy’s Forcenet Execution Center, which runs exercises for the service’s Network Warfare Command. In other words, even with all the requisite platforms and terminals in place, it’s a challenge getting useful quantities of data across the network.

Part of the problem is that Link 16 is a line-of-sight system, so dispersed networks with elements over the horizon require relay services courtesy of high-demand specially equipped platforms such as the Air Force’s RC-135 Rivet Joint aircraft. While there are hundreds of Link 16-capable fighters in the U.S. inventory, there are only a few dozen relay platforms.

• Finally, Link 16’s effectiveness hinges on a lot of technologies. Link 16 is designed to leverage the capabilities of a relatively small number of platforms. But single-point failures with terminals, displays or Global Positioning Satellite service can drop platforms from the network.

• All these limitations mean Link 16 is essentially a compromise system. Ideal future networks would employ Internet Protocols (IP), or sets of rules networks use to specify data format and transmission parameters, to enable true plug-and-play capability at much higher data rates. But getting to there from here will take years and require all the services and the Department of Defense to commit to standard equipment and waveforms.

In the meantime, the services are working hard to refine Link 16 tactics to squeeze every ounce of utility out of the dated but potent system.

In December, the Marine Corps hosted exercise Agile Lion at Yuma, Ariz., specifically to test Link 16 employment using an F/A-18D, an AH-1W attack helicopter, a KC-130J tanker and ground forces. Lately, the Navy’s annual Triton Warrior and JFEX exercises also have emphasized Link 16 development.

Navy Cmdr. Rick Strickland from Network Warfare Command said that these days, “datalinks are one of those things you’re going to do in the course of any exercise.”

Datalink aspects of November’s Trident Warrior exercise focused on testing the joint message format, according to McElhannon. In that exercise, Link 16-equipped F/A-18E/Fs swapped imagery and data from their Litening AT targeting pods and Active Electronically Scanned Array radars to enable time-sensitive targeting.

“We take the results of experimentation and pass them to the warfighter,” Strickland said.

One notable result of Link 16 experimentation has been the creation of the Joint Interface Control Officer (JIFC) qualification. These specialists are deployed to headquarters to manage battlefield networks.

“They monitor the network … look at performance characteristics and make changes to the architecture,” Strickland said of JIFCs. “If you have some F-16s in your battlegroup and an Aegis cruiser … and then you bring in an [E-8] or a coalition force, a Canadian corvette or something, you would have to make changes to the architecture. [The JIFC is] also the guy who makes sure we lose nothing in the translation between various kinds of datalinks. He facilitates the extended range of Link 16 using relay platforms.”

The JIFC qualification was “developed because of the complex nature of datalinks and networks,” Strickland said. “Only recently did we put a label to it.”

Even with refinements to Link 16 equipment and employment as a result of Trident Warrior and other exercises, “we [still] need to go through the IP transition,” McElhannon said.

But Adan stresses that any forthcoming network based on Internet Protocols must be compatible with Link 16.

“IP-based waveforms could be the ultimate future solution, but with thousands (and growing) of fielded Link 16 platforms, any platform using a new airborne networking waveform must be able to interoperate with Link 16.”