Frequency and Spectrum Management
Directorate of Airspace Policy
Aviation is a global industry that lies at the heart of modern, globalized economies. It has to take into account the interests of all airspace users – whether commercial, leisure or government – in a manner that maintains the safety and integrity of the airspace in which these diverse activities operate.
An economic study carried out in 2009 estimated that, in 2007, commercial aviation carried a total of 2.5 billion passengers and approximately 50 million tonnes of freight, directly employing more than 5.5 million workers, had a turnover of more than USD 1 trillion and generated USD 425 billion of gross domestic product (GDP) – indeed, if commercial aviation were a country it would rank 21st in terms of GDP. Taking into account other industries that depend on air transport would make these figures even more impressive. For example, just including air transport’s contribution to tourism increases the number of jobs to more than 33 million jobs and GDP to USD 1.5 trillion.
For the aviation industry to continue to thrive and expand, the safety and integrity of the airspace must be maintained. This is becoming increasingly complex because of capacity demand, diversity of aircraft types and environmental constraints. A key element in ensuring the safety and integrity of the airspace is the maintenance of minimum separation standards through accurate navigation and the provision of air traffic control. Radio spectrum is the only available means of supporting communication and navigation (including surveillance) systems can use to enable aircraft to navigate and obtain air traffic information. Spectrum allocations that are appropriately protected are therefore critical to the industry.
Agenda item 1.3 of the World Radiocommunication Conference (WRC-12) addresses the spectrum needs, both terrestrial and satellite, for safety critical non-payload communication requirements (such as command and control, and the relaying of air traffic control messages). These communication links will effectively replace the wiring in the cabin between the pilot and the various systems required to fly an aircraft. Given the safety critical nature of such links, it is essential to ensure that the spectrum they will operate in is appropriately identified and protected.
The evolution of unmanned aircraft from little more than model aircraft to sophisticated remote-sensing platforms has resulted from advances in the fields of sensing, and command and control. Current applications include environmental monitoring, border patrolling, and fire-fighting. The command and control elements could eventually find their way onto commercial aircraft, reducing the number of pilots required on an aircraft.
As the number and capabilities (in terms of size, endurance and payload capacity) of these unmanned aircraft have increased, so the demand to share airspace with manned aircraft has also increased. For unmanned aircraft to be allowed access to airspace where manned aircraft operate, the unmanned aircraft will have to demonstrate that they can operate in that airspace and interact, where necessary with air traffic control, in a manner that is comparable to that of manned aircraft.
Current proposals would suggest that there is sufficient satellite spectrum to meet the needs of unmanned aircraft for non-payload communications. It should be noted that other so-called payload communications that are associated with the commercial purpose of the flight rather than its safety (for example, sensor data for environmental monitoring, or radio relay for a communications platform) are not part of agenda item 1.3 and have not been assessed, but may need to be studied in the future. As far as the terrestrial component is concerned, studies have centred around the bands used by existing aeronautical systems, namely the 5 and 15 GHz bands currently allocated to aeronautical radionavigation services.
Having spectrum allocated and ensuring the appropriate level of protection for the systems that will operate in those bands are two different problems. How the conference resolves those problems will be the crux of the discussions under agenda item 1.3, and will involve having to weigh up commercial demands against safety requirements.
Aviation by its nature is a conservative industry, preferring to use tried and tested technology over the more advanced emerging technologies favoured by industries such as mobile communications. Nevertheless, the aviation industry is currently reviewing various worldwide programmes to enhance air traffic control communication systems through the introduction of a number of datalink services. These systems will enhance aeronautical communications capability and – in conjunction with more precise navigational capabilities – allow flight routing to be more efficient. If this can be achieved, then it will result in fewer delays, shorter flight times on average, lower fuel costs and reduced CO2 emissions.
Agenda item 1.4 is the vehicle by which the aviation industry is seeking to finalize the work, started in preparation for WRC-07, to ensure that the necessary spectrum is available to allow for the introduction of these systems in a timely manner. The agenda item addresses three frequency bands (112-117.975 MHz, 960-1 164 MHz and 5 000-5 030 MHz) that are currently allocated on a worldwide basis to the aeronautical radionavigation service, and in the case of the first two bands were “provisionally” allocated to the aeronautical mobile (route) service by WRC-07.
Two problems have to be considered in regard to the frequency band 112-117.975 MHz, namely compatibility with in-band aeronautical radionavigation systems and compatibility with adjacent band broadcasting services. Analysis has shown that if the aeronautical mobile systems are built in accordance with International Civil Aviation Organization (ICAO) standards and limited to operating above 112 MHz, then compatibility with broadcast systems is guaranteed. Compatibility with aeronautical radionavigation systems operating in the same frequency band is ICAO’s concern, because any interference will be with ICAO’s own standardized systems. This is therefore not of concern to ITU.
Matters are a little more complex in the frequency band 960-1 164 MHz. Consideration has to be given not only to compatibility with existing aeronautical radionavigation systems (both ICAO and non-ICAO standardized) operating within the frequency band, but also to adjacent band satellite navigation systems, such as GPS and Galileo, that operate above 1 164 MHz. As with the frequency band 112-117.975 MHz, it is proposed that compatibility with existing ICAO systems is a matter for ICAO to address and therefore not of concern to ITU. It is further proposed to assure compatibility with other aeronautical radionavigation systems operating in the band, and with satellite navigation services operating above 1 164 MHz, through mandatory technical provisions included in a WRC Resolution and possibly in an associated ITU-R Recommendation that is incorporated by reference. Compatibility with adjacent band mobile systems was addressed by WRC-07.
In the frequency band 5 000-5 030 MHz, technical compatibility can be shown between the proposed airport surface aeronautical mobile systems and existing services in the frequency band 5 000-5 010 MHz, and adjacent band radio astronomy systems. No conclusions could be drawn with regard to the remaining part of the frequency band because of the uncertainty around a number of the operational and technical parameters. The main area of uncertainty is whether or not an additional allocation to the aeronautical mobile (route) service for airport surface communications is required.
Agenda item 1.7 addresses aviation’s long-term access to spectrum allocated to the aeronautical mobile-satellite (route) service in the frequency bands 1 525-1 559 MHz and 1 626.5-1 660.5 MHz, as allowed for by footnote 5.357A in Article 5 of the Radio Regulations. This item has been debated by WRCs ever since the allocation was made generic at the 1997 conference.
As the aviation industry has expanded and aircraft have flown further, the need for and capacity of mobile communication links that can operate over the horizon have increased. The capacity and reliability of existing high-frequency communication links are no longer capable of supporting the traffic requirements of a modern air traffic control system. As a result, greater use of satellite networks is planned, especially over remote areas such as oceans. Improved communications allow aircraft to fly optimal routes that reduce flight time, fuel burn and hence CO2 emissions.
If aviation cannot have access to appropriate satellite spectrum, then further advances in beyond line of sight communication systems – as foreseen in projects such as the European Union Single Sky initiative – are unlikely. The question that needs to be answered through the processes that are established as a result of agenda item 1.7 is how to allow aviation access to aeronautical mobile satellite (route) spectrum, as called for in footnote 5.357A, without unduly constraining current mobile satellite operations. The prescribed processes will have to be robust enough to ensure that all aeronautical requirements are justified. This will avoid any perception that requirements are being inflated or that the spectrum will not be used as efficiently as it could be, taking into account the various constraints.
Mobile communication is vital to aviation for ensuring that the airspace above our heads is kept safe. It can also act as an enabler to allow aviation to optimize the way in which the airspace is used, keeping flight times to a minimum, reducing fuel burn and CO2 emissions. Discussions under WRC-12 agenda items 1.3, 1.4 and 1.7 will all be important in ensuring that the communication systems used by aviation preserve the integrity of the airspace and deliver efficiencies in use.