UAV Communications

By Jonathan Ray | March 1, 2013
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Unmanned aircraft systems (UAS) programs are evolving rapidly with a wide range of application requirements in both military/government and civilian applications. At the same time, the market has seen recent advancements in SwiftBroadband service and hardware including smaller, lighter avionics that don’t compromise on performance or data capacity. These satcom datalinks can provide worldwide coverage for a range of operations.

On a recent Avionics Magazine Webcast, “Beyond Line of Sight: Using Satcom Datalinks to Enhance UAV Operations,” terminal manufacturer Cobham Satcom (formerly Thrane & Thrane), service provider Inmarsat and systems integrator Cahon Systems presented their perspectives and insights on how to select the right terminal, service and configuration to meet the needs of a beyond-line-of-sight solution for UAV applications.

Andy Beers, director of Aeronautical Sales for Americas at Cobham Satcom

I don’t think there’s a week that goes by now without some story in the news about an unmanned system. … It’s a very prevalent part of what’s going on out there in the aerospace industry these days.

We can obviously see all the benefits that we’re seeing from the likes of very high-profile platforms such as the Predator and the Global Hawk. But, there’s much more that’s going on out there right now that’s really starting to drive a pent-up demand for UAVs in the civilian market. So, UAVs certainly have great potential for use in a wide variety of applications. And, certainly, when they have the capacity for an over-the-horizon type view, it gives them even more of an application across all platforms.

What is beyond line of sight? We’re talking about satcom. We’re talking about satellite communications. Line of sight type links microwave and VHF, UHF radio type applications certainly have their limitations due to range and weather interference. Satcom has historically been perceived as an expensive, too big of an option for anything other than the high-altitude and medium-altitude unmanned aerial vehicles. But, line-of-sight data links certainly have played a role in UAV applications to date.

Satcom has historically been perceived as an expensive, too big of an option for anything other than the high-altitude and medium-altitude unmanned aerial vehicles. But, line-of-sight data links certainly have played a role in UAV applications to date.

Andy Beers, director of Aeronautical Sales for Americas at Cobham Satcom

There’s been new advancements on the satcom side, particularly with Inmarsat and SwiftBroadband. These new advances in service and terminals are changing the landscape dramatically. Inmarsat’s new SwiftBroadband and I-4 satellites have ushered in an era of new smaller, lighter, less expensive terminals that can bring a beyond-line-of-sight data link capability to more UAV types and to more applications…. Not every UAV is going to need a beyond-line-of-sight application. Others are going to need multiple links and, certainly, Inmarsat can provide both the large pipe, if you will, as well as the critical safety services and other type applications that will be moving in more and more and needed with UAVs with the L-band products….

From the hardware perspective, (with regards to growth in certain geographic areas) we’re talking to every major country that is a NATO country about some form of a UAV platform at this point. It is actually so hard to keep track of how quickly all these things are happening because, again, these are programs that on one hand could employ more simpler technologies in terms of the actual airframe itself, but yet the payloads and the things that they’re carrying could be much more complex. So, there’s so many different configurations of UAVs right now, from jet propulsion to turbo propulsion to helicopter type configurations. It’s just happening so rapidly.

But, I think where we’re going to see continued growth will continue to be here, primarily U.S. DoD. The NATO countries. But, we are seeing a lot of inquiries from Asia now, as well. So, I think that we’re really looking at what the future of aviation will be like for the next 10, 15, 20 years. It’s quite astounding.

Jack Deasy, director of Aeronautical and AISR Programs at Inmarsat Government

The whole UAV sector is an exciting one for us, and it’s something that Inmarsat has supported for a while. But, with SwiftBroadband and the ability to provide higher data rates to smaller terminals, our relevance to UAV platforms has become increasingly important.

In our current mobile world, people tend to assume that there will be a data and voice network available for whichever devices they’re using. One of our main purposes at Inmarsat is to make sure that’s actually the case. We own and operate a worldwide constellation of satellites that provides high-speed voice and data basically anywhere in the world between 70 degrees north and 70 degrees south, which means that using our geostationary satellites, satellites that sit in one place over the earth on the equator, we can see and support services pretty much anywhere in the world, except the extreme polar regions.

In 2005, with the launch of our fourth-generation satellites, the I-4 satellites, we entered a dramatically different world, an ability to provide both a voice and a broadband data service over these satellites.

The big innovation of the I-4s is the ability to support a global service. In providing that kind of service, Inmarsat is able to support UAVs in flight, as well as the ground control stations that manage them to the extent that those stations need to be mobile or ready to move at any given time. The basic architecture would be that a signal from the UAV, a voice or an IP data stream, leaves the UAV, communicates with the Inmarsat-4 satellite, and is landed at one of our satellite access stations. For U.S. users, that station is in Hawaii, and, from there, it can be put into, depending on the nature of the communication, either the IP cloud or into the public switch network and landed like any other internet or telephony product at a computer or on a phone anywhere in the world.

For the ground control stations, a separate architecture can be used, whereby the communication at the ground control station can also be an Inmarsat satellite service a Broadband Global Area Network (BGAN) service, which is the counterpart to the aero service of SwiftBroadband. If you do that, the communication basically bounces from the UAV to the satellite, down to the earth station, back up to the satellite, and to a ground control station, which allows that station to be located anywhere under the footprint of the satellite and allows it to be hooked up very quickly. Inmarsat BGAN terminals can access a satellite within two or three minutes of being located at a site, which means that for users that move quickly or go to places without a lot of advance planning, this allows them to have a primary or a secondary communications network access to their control station.

Because Inmarsat SwiftBroadband is basically providing an internet connection between a mobile user and their destination, Inmarsat can support a wide range of traditional legacy, as well as IP encryptors used by particularly government users, without any modifications to the Inmarsat network itself or anything added to the Inmarsat ground station to support it. This makes it very user-friendly for people who need added security.

For Inmarsat’s part, we continue to innovate as well. We are adding over the next year capabilities to get higher data rates through existing SwiftBroadband terminals. We’ll be adding safety services to SwiftBroadband to bring it in line with the safety services traditionally offered by Inmarsat for aeronautical vehicles. And then, in addition, we’ve got a major program underway with Global Xpress which will offer, in addition to our L-band service, Ka-band broadband service. Those satellites will start to be launched in 2013, at which point Inmarsat will be operating both an L-band service and Ka-band service, which will allow us to provide the benefits of the resilience and high mobility support that L-band gives you along with very, very high data rates with the Global Xpress service…

Global Xpress, which will operate in the Ka-band, will be providing much wider bandwidth to the platforms.

In a lot of respects, if you think of a UAV like a manned aircraft, there are cockpit communication requirements and cabin communication requirements. And, L-band today is mostly providing the cockpit communications requirements, largely because of the resiliency of the system.

Global Xpress will allow us to support all these sensors that you hear about all the time, with the growing demand for ISR data coming off of UAVs. Today, those platforms generally use Ku-band satellite to provide that service, and Global Xpress will provide a variation on that service at higher bandwidth and with a truly mobile, worldwide system, like the Inmarsat L-band system only at higher bandwidths.

So, the size of the terminals being developed for the aero world right now, we have an exclusive arrangement with a provider to develop a commercial solution, and we’re talking to a number of other terminal manufacturers, for particularly the government space, where one size generally does not fit all for terminal requirements.

So, that’s something, with specific requirements, we’d certainly be interested in talking about customers, but I think it’s fair to say that we’re looking … everyone is aware of the fact that, for platforms that today use Ku-band satellite communications, one of the big obstacles to any sort of improvement in capability with a new service is not having to change out the physical radome or the bolt holes in the fuselage. And, so, our intention is to have terminals on the commercial basis that would be similarly sized to the existing ones.

Barry Jackson, president and founder of Cahon Systems

Back in 2009, we wanted to supply an Inmarsat I-4-based system for our major UAV manufacturer. We won that contract for a number of reasons. There were some innovative technologies and, since then, we’ve been building these systems. We’ve got double-digit numbers supplied in field now.

Primarily, we don’t use most of the facilities that the Thrane & Thrane modem offers us, because it didn’t fit into the requirements. We’re an IP-centric device. We concentrate all the channels, including the data, the video and the voice into one IP stream. We add extra encryption to it, because that’s a requirement of the system. That encryption at the moment is 256 AES [advanced encryption standard], but the system is built such that we can add other government-approved encryptors into the program if desired.

There are two elements to the system the airborne elements and the ground element. The ground element has two modes of operation. It can either be a direct Ethernet link through the gateway sat, or it can be via a satellite link if there is no Ethernet capability where the ground station is deployed.

So, if we go through the satellites to control and talk to the aircraft we call it a Double Hawk mode because we go through the satellite twice and, currently, the latency is down to less than two seconds.

One of the things about the voice system we use is that if you’re not speaking, it doesn’t cost you any time over the satellite, and the bandwidth is dynamically controlled by the software/firmware package that we’ve put together with another one of our subcontractors.

The system we use includes three elements the modem itself in the air which is the Thrane & Thrane Aviator 350. We use only the IP interface on that. Because the Aviator 350 does not meet the full military specification, we condition that so it can survive the -40C to +70C requirements. And, then, we’ve got our own communications electronics and interfaces that are based on our protobus system where we concentrate all the data. Currently, we have two voice channels. We have in-band signaling, such that you’ve got “push to talk” to open up the transmitters on board the aircraft and the “squelch” opens up the receive path as one would expect.

Through the template system in the Thrane & Thrane box, we have various streams that we can now put data on 32-, 64-, 128-, or 256-kilobits, and the customer can select those depending on the mission profile and what they wish to do. And, we have a set of standard templates that are pretty much used all the while.

The system has actually flown an aircraft on a number of occasions with everything else switched off. So, Inmarsat was the only thing controlling the aircraft, because we’ve got telemetry and command-and-control links on there, as well. So, it’s been proven as a secondary backup through the Ku-band system that also flies on the aircraft and other modes that they use to control the aircraft.

From our perspective, the future has a number of things going. We’re in the process of reducing size to get onto smaller UAVs, plus the fact reducing the size allows us to increase the number of modems for the future on the large UAVs, in particular integrating Inmarsat’s Global Xpress into the system so we can switch between LNS band for the safety of flight services. We’re working and looking at DO-178 certification of all the equipment and software, too, as part of the safety of services, and the RTCA Committee’s report is working on that. And, they’re the main focuses. We’re also looking at extra interfaces, ARINC 429 and Mil-Std-1553, both of which we see as possible requirements in the future.

An archived version of this free Webcast is available at 

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