B-VHF - Broadband VHF - Aeronautical Communications System Based on MC-CDMA
Overview
Background & policy context:
Air transport has been identified as a dominant factor for sustainable economic growth of the European Union. The 'Vision 2020' clearly points out the cornerstones of a future air transport system and the Advisory Council for ATM Research in Europe (ACARE) elaborates these requirements in depth in their 'Strategic Research Agenda'.
The key element for achieving an Air Transport System that is capable of meeting future demands is A/G communication. Today, DSB-AM is used for aircraft separation and guidance, a VHF communications technology that was introduced in the '40s and utilises the available spectrum in a highly inefficient manner.
Eurocontrol's Communications Strategy indicates the need of alternative communications systems as the saturation point of the current system is reached around 2015 even with full VDL Mode 2 and 8,33 kHz deployment.
The B-VHF project conducts bottom up research on multi-carrier technology (MC) for aeronautical communications in the VHF band for a future MC broadband VHF (B-VHF) system. The baseline technology is MC-CDMA, a highly innovative, high capacity communications technology also discussed for fourth generation (4G) mobile communications systems.
MC-CDMA has the potential to exploit the mobile aeronautical channel better than any currently discussed VHF communication alternatives. It increases voice and data capacity and addresses security and safety issues with a service level unknown to the aeronautics user today. Moreover, MC-CDMA has the potential to preserve the excellent cost performance of the VHF band as it may be applied as an overlay system and co-exist with the existing VHF infrastructure, thus providing smooth transition and rollout scenarios.
The B-VHF project aims at identifying MC-CDMA as the still missing European approach for the future ATM VHF communication system that supports Single European Sky and the Free Flight concept and leads far beyond 2015 into Vision 2020.
Objectives:
The main objectives of the B-VHF project were:
Proof of suitability of multi-carrier technology for aeronautical communications
The B-VHF project identified and resolved the most significant technological challenges of the MC-CDMA technology when applied to aeronautical communications. A real-time test-bed for the B-VHF forward and reverse link has been implemented to assess the suitability of the proposed multi-carrier technology.
Proof of increased communications performance and service flexibility
The B-VHF system has been designed to support within the same VHF spectrum an increased number of users than the current legacy systems while providing higher aggregate channel throughput. It supports a mixture of communications services with varying Quality of Service (QoS) expectations and is easily configurable, following changing user needs in each deployment phase.
Proof of increased security
Laboratory measurements conduced with the B-VHF forward- and reverse link test-bed have demonstrated the robustness of the adopted multi-carrier OFDM physical layer to narrowband interference. The system design allows the integration of end-to-end security applications. However, such applications need a mature end-to-end security concept accompanied by a threat analysis. Developing such concepts was not an aim of the B-VHF project.
Proof of operational feasibility of deployment concept
The project produced a set of scenarios for an initial system deployment in the VHF band or in other frequency ranges, both with voluntary and mandatory equipage, and with smooth transition towards the final system deployment. The proposed scenarios are well aligned with operational concepts for the introductory phase and for a time period ten years after an initial introduction.
Proof of feasibility of overlay concept in the VHF band
With an overlay concept, the B-VHF system locally re-uses spectral resources in the VHF COM range allocated to the narrowband systems that continue operating within the broadband B-VHF channel. The project results have confirmed the feasibility of the B-VHF overlay concept if the two systems remain separated by some protection distance. However, considerable additional efforts must be taken to reduce side-lobes of the transmitted B-VHF signal and, in particular, to mitigate the interference from legacy VHF systems at the B-VHF receiver.
Methodology:
The tasks required to achieve these objectives have been encapsulated into four separate stages:
- 'Project Management and Quality Assurance' comprised activities that are essential to all work-packages. It covered all management activities within the consortium and in particular the liaison with the European Commission.
- 'B-VHF System Aspects' produced high-level requirements for the B-VHF system, described the reference aeronautical environment used in simulations of the B-VHF system, as well as the B-VHF Operational Concept. WP 1 was closed after producing the B-VHF Deployment Scenario document. It addressed technological, operational and institutional issues of the B-VHF initial deployment, transition and operational usage.
- 'VHF Band Compatibility Aspects' addressed theoretical and practical assessment of the probably most critical aspect of the future B-VHF broadband system: its capability to be installed and operated 'interleaved' with a number of legacy narrowband systems, sharing the same part of the VHF spectrum, but remaining robust against interference coming from such legacy narrowband VHF systems.
- 'B-VHF Design and Evaluation' covered B-VHF system detailed design tasks, starting with developing the model of the broadband VHF channel and proceeding with the development of the SW representing the physical B-VHF layer, DLL layer, higher protocol layers and representative aeronautical applications for the subsequent performance simulations.
- 'B-VHF Testbed' covered the baseband implementation and evaluation of a testbed for both the forward- and reverse B-VHF link. The implementation is restricted to the physical layer, which is the most critical part in the B-VHF system.
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