Notwithstanding the current economic climate, air transport is forecast to double by 2025 according to the latest Eurocontrol figures. And it is abundantly clear that current air traffic management (ATM) systems around the world will simply not be able to cope. To address this issue, as well as issues of safety and security, there are a number of strategic government-funded projects currently running, whose remit is to develop the most appropriate and cost-effective new technologies and techniques for the future needs of ATM. Theses include the Next Generation Air Transportation System (NextGen) in the US and Single European Sky ATM Research (SESAR) in the European Union.
The overarching objective of these projects is the more efficient use of available airspace, without compromising on safety. A key enabler of many of the required changes is improved communications between air traffic controllers and pilots. That inevitably will mean increased, and smarter, use of satellite communications.
Communication between controllers and pilots has, for many years, used VHF, or for longer range HF, voice communications. Both have limitations that will only be exacerbated as air traffic volumes increase. HF, for instance, does enable long-range communication, but certainly does not provide the comprehensive global coverage of which satellite communications is capable.
An additional limitation of the existing technology is that as controllers currently use a single frequency, and when a sector is very busy, many pilots will be listening to the same signals, which can, and occasionally does, lead to confusion.
The latter limitation is already being addressed by the introduction of Controller Pilot Data Link Communications (CPDLC). It enables air traffic controllers and pilots to communicate using pro forma data messages, to avoid confusion and save time, though of course the system also allows for free text entry when necessary.
The next generation of ATM technology will be based on Internet technology, the use of both satellite and terrestrial communications, and the interface between them. This is an area in which the European Union is taking a lead, in particular through NEWSKY, an EU-funded research project that has recently come to a conclusion, and in which TriaGnoSys, the expert in satellite-based communications and information transfer, was responsible for the development of the relevant satellite and terrestrial communications solutions, and the handover processes between the two.
As proof of concept of the NEWSKY project, a simulated flight was conducted between Europe and the US at the projects final presentation in October 2009 at the German Aerospace Centre. The three phase simulation over European, oceanic and North American airspace involved testing both voice and data connectivity between pilots and controllers, to deliver continuous, seamless communications throughout the three key phases of the flight. Weather maps and CPDLC-like data messages were also transmitted over the links.
The first phase was in European airspace. Both terrestrial and satellite (Inmarsat BGAN, in this case) radio links were available and either could be selected, based on the programmed link selection rules. The rules are based on a number of factors, including the availability of a specific satellite link, efficiency of the terrestrial radio link which depends on, among other factors, the weather and indeed cost.
The second phase of the flight was over oceanic airspace, where only satellite connectivity was available. The simulation demonstrated the seamless automatic handover from the terrestrial network without loss of session continuity.
The third and final phase was over North American airspace. As with the first phase, the link selection rules governed which link to use, again with automatic handover.
ATM technology is central to the NEWSKY research. The full name is Networking the Sky for Aeronautical Communications, and the concept was the integration of a range of applications, using Internet Protocol version 6 (IPv6) as the basis. In addition to the key air traffic control (ATC) communications, other applications include airline operation communications, airline administrative correspondence, and passenger communications.
One of the key considerations for the use of IP is that is combines high reliability, cost savings, and an optimal alignment with the evolution of communication and security technologies through the use of Commercial-Off-The-Shelf (COTS) solutions. Also, the focus has been on a move away from proprietary software, to allow wide access. In addition, since this system is based on IPv6 for future-proofing, it is backwards compatible with IPv4. In short, every business uses IP, making it the obvious candidate for the next generation of ATM communications.
Cost remains a key factor in the development of air traffic technology, both for the ATMs and the airlines. Of course, it is not as important as reliability, and safety is the overriding consideration but cost/benefit analysis is always part of the decision-making process in both the public and private sectors.
Until now, the benefits of using satellite communications for ATM have been outweighed by the costs. However, Voice Compression and Enhanced Multiplexing (VoCeM), developed by TriaGnoSys, which provides the most efficient satellite use of satellite payload, brings satellite usage costs into line with terrestrial radio links.
VoCeM, as the name suggests, cuts the bandwidth required for voice calls, be they Voice over IP (VoIP), or indeed GSM and for NEWSKY, it is VoIP. To give an idea of the scale of savings provided by VoCeM, VoIP generally consumes 20 kbit/sec, and GSM, which has attracted so much attention, is actually even more inefficient with bit rates up to 30 kbit/sec. Using VoCeM, the requirement for VoIP is only 3.3 kbit/sec, including all overheads. To put it another way, VoCeM enables compression gains of between 500% and 1,000%, and does so through advanced header compression, voice transcoding and channel multiplexing techniques.
The three main elements of the technology are:
- First, the voice payload is transcoded for transmission with a new AMBE2+ codec (Advanced Multi-Band Excitation), providing significant bandwidth efficiencies without compromising quality.
- Secondly, each header is compressed to the minimum (headers are the instruction manuals that enable the receiving servers to reconnect the information in the correct way). VoCeM removes all redundant headers and compresses the useful ones.
- Finally, VoCeM uses multiplexing to bundle a number of voice payloads together, to form a single packet, further reducing the headers required.
Furthermore, quality is not compromised. Telecoms providers use a scale of zero to five to measure Quality of Service (QOS). ISDN telephony typically achieves 4.2 or 4.3 and a full-rate GSM call is about 3.5, and VoIP 3.7. Using VoCeM, we achieve rates of 3.7, even though it demands only a fraction of the bandwidth
Satellite communications will play in increasingly important role in ATM, particularly where terrestrial links are not available. As efficiency and safety demands increase, with it becoming unacceptable for aircraft to be out of touch at any point during the flight, and satellite costs are reduced, ATM services using satellite links are the future.
About the author
Dr. Markus Werner is one of the founders of TriaGnoSys. He received a Dipl.-Ing. Degree from Darmstadt Technical University in 1991 and a Ph.D. degree from Munich Technical University in 2002, both in electrical engineering. Markus received the Best Paper Award of ITG conference Mobile Communications in 1993. He has co-authored more than 120 publications, including two scientific textbooks and numerous scientific journal papers, and teaches satellite communications courses for telecommunications professionals.