SUMMARY With this information paper, we would like to inform the meeting about an European aeronautical communications project within the 6th Framework Program of the European Commission (EC). The project with provisional starting date of 1st January 2004 is termed “Broadband VHF” (B-VHF) and deals with the design, investigation, and evaluation of a broadband overlay communications system based on multi-carrier technology for ATC/ATM communications in the VHF band.
B-VHF Project Within the 6th Framework Program of EC
It is expected that the current aeronautical communications systems will reach their saturation point in Europe around 2015 even with full VDL Mode 2 and 8,33 kHz deployment. Thus, potential technologies for future aeronautical communications have to be discussed which preferably show the following characteristics:
Fulfill increasing capacity demand for both voice and data traffic beyond 2015
As simple as possible deployment scenario
As far as possible reuse of existing technologies
The multi-carrier technology is identified as the most promising broadband technology for the next generation mobile communications systems – the so-called “Fourth Generation” (4G) systems. Currently, several European research projects within the 6th Framework Program of the European Commission are dealing with multi-carrier communications for 4G systems and it is expected that the multi-carrier technology will be standardized as air interface for 4G around 2010-2015.
Considering the current situation of aeronautical communications on the one hand side and the development of multi-carrier systems for 4G on the other hand side, it becomes clear that multi-carrier communications is one interesting potential technology for future aeronautical communications. First, the multi-carrier technology is highly bandwidth efficient as already proven in the terrestrial broadcast standards DAB (Digital Audio Broadcasting) and DVB-T (Digital Video Broadcasting - Terrestrial) and, therefore, suitable to fulfill the increasing capacity demand of future aeronautical communications. Second, the multi-carrier technology enables an in-band deployment scenario. A new broadband aeronautical communications system based on multi-carrier technology can be deployed as an overlay system in the VHF band, co-existing with the legacy VHF systems. Third, besides the already available COTS components for DAB and DVB-T it is expected that additional components will be developed for 4G systems. Thus, future aeronautical communications systems based on multi-carrier technology can profit from hardware and software developments made for terrestrial communications. Taking into account these three aspects, the multi-carrier technology might have some striking advantages over other potential technologies for future aeronautical communications.
With this in mind, Frequentis and DLR have established a consortium to investigate the potential of multi-carrier communications for future aeronautical communications and proposed to the European Commission within the 6th Framework Program the so-called “Broadband VHF” (B-VHF) project. The provisional starting date of the project is the 1st January 2004, the duration will be 30 month. In the following, the basic B-VHF system concept (air interface) is described and some information about the consortium and the project itself is given.
Basic B-VHF Concept
Broadband communications systems can be realized in a highly efficient way by applying multi-carrier technology. An interesting advantage of multi-carrier communications is its flexibility and adjustability to certain spectrum restrictions which comes from the fact that multi-carrier systems are designed in the frequency domain. With multi-carrier technology it is even possible to realize transmission systems which do not need a contiguous transmission band. Certain frequency areas can be left unused by simply turning off the respective carriers in this area. Thus, multi-carrier technology enables the realization of an overlay broadband system if the legacy narrowband systems applied in the considered frequency band do not use the whole frequency band at the whole time, but leave some frequency gaps. Since multi-carrier systems are very flexible and can be easily reconfigured for each transmission symbol, the adjustment to current frequency gaps can be made in an adaptive manner.
Considering the different ATC sectors, it is expected that at least certain sectors show frequency gaps in their VHF band usage, especially, lower airspace sectors or sectors on ground due to their limited radio horizon. Thus, it is possible to establish a multi-carrier overlay system (B-VHF) in the VHF band starting in certain sectors and successively deploying this system in all sectors, since usage of the VHF legacy systems can be reduced due to the additional transmission capacity provided by B-VHF. Figure 1 gives a schematic view, how the B-VHF system could be established within the VHF band as an overlay broadband system to the existing VHF legacy narrowband systems by excluding active “near” narrowband channels (black) and reusing (grey) both currently inactive near channels and active, but distant channels.
Figure 1: B-VHF as an overlay system in the VHF band. A main goal of the B-VHF project is to prove the feasibility of establishing an overlay broadband system in the VHF band based on multi-carrier technology.
The B-VHF consortium is led by Frequentis Nachrichtentechnik Ges.m.b.H., Austria. Altogether, the B-VHF consortium consists of eleven partners from five different European countries:
Frequentis Nachrichtentechnik Ges.m.b.H., Austria
German Aerospace Center (DLR), Germany
National Air Traffic Services (En Route) Ltd (NATS), United Kingdom
Within the B-VHF project there are four work-packages (WP 1, WP 2, WP 3, WP 4) defined. In the following a short overview of the work-packages is given:
WP 1 “B-VHF System Aspects”
B-VHF Operational Concept: Definition of the B-VHF system functional requirements and the communications architecture as well as description how the system will be operated in a specific European aeronautical environment at the 2010+ time frame.
Reference Environment: Description of the specific European aeronautical environment (e.g. airspace, systems, procedures, air traffic) to be used as a reference for conducting B-VHF analysis, interference modeling as well as for developing air traffic scenarios for B-VHF performance simulation.
B-VHF Deployment Scenario: Description of the options for the operational deployment of the future B-VHF broadband communications system in a 2010+ time frame.
WP 2 “VHF Band Compatibility Aspects”
Theoretical VHF Band Compatibility Study: Determination of the conditions and requirements under which the B-VHF system can be established as an overlay system in the VHF band without degrading the performance of existing VHF legacy systems (DSB-AM, ACARS, VDL).
VHF Channel Occupancy Measurements: Determination of current VHF channel occupancy by measuring the aeronautical VHF spectrum (118-137 MHz). The measurements are performed both on ground at large airports, e.g. London or Frankfurt, and at different flight levels in areas with high aircraft density.
Interference Modeling: Determination of an interference model for performance simulations which takes into account the influence of existing VHF legacy systems on the B-VHF system.
WP 3 “B-VHF Design and Evaluation”
VHF Channel Modeling: Development and software implementation of broadband VHF channel models that can be used for physical layer simulations of the B-VHF system.
Physical Layer Design: Development and software implementation of the physical layer for the B-VHF overlay system for both the forward- and reverse-link. The physical layer design takes into account that the communications medium has to be shared with existing VHF legacy systems and that mutual interference between the B-VHF overlay system and existing VHF systems has to be avoided by proper design of the B-VHF system.
Data Link Layer Design: Development and software implementation of a data link layer scheme that uses the services of the physical layer to transmit data over the B-VHF link and responds to service requests of the upper layer protocol.
Protocol Design: Development and software implementation of higher layer protocols and application interfaces according to the required level of detail to fulfill the communication requirements of foreseen ATM/ATC applications.
B-VHF Evaluation: Investigation and evaluation of the B-VHF performance and co-existence with VHF legacy systems using software simulations.
WP 4 “B-VHF Testbed”
Baseband Implementation: Baseband implementation of a B-VHF testbed for the forward- and the reverse-link in DSP technology. One transmitter/receiver pair is implemented enabling either a forward- or a reverse-link transmission.
VHF Frontend Development: Development of VHF frontends for both the B-VHF transmitter and the B-VHF receiver. One transmitter/receiver pair of VHF frontends are designed and implemented which are adjusted to the parameters of the B-VHF baseband implementation.
B-VHF Testbed Evaluation: Hardware based evaluation of the B-VHF physical layer using the B-VHF testbed. The testbed evaluation is performed in the baseband as well as in the VHF band. The baseband evaluation applies a channel and interference model whereas the VHF band evaluation is performed using actual VHF legacy systems as interference sources and victim receivers, respectively.