Doc 9718 an/957 Handbook on Radio Frequency Spectrum Requirements for Civil Aviation
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- Chapter 9 INTERFERENCE PROTECTION CONSIDERATIONS 9.1 INTRODUCTION
- 9.2 REGULATORY ASPECTS The basic definitions of interference and harmful interference
- The treatment of harmful interference
- RR 8.1 and RR 8.3
- Permissible interference and accepted interference
- *1.167.1 and 1.168.1
- Multiple interference inputs
- Electromagnetic compatibility (EMC)
8.3 FUTURE SYSTEMS AND STRATEGY EVOLUTION 8.3.1 Growth in air traffic requires new ways of planning and enhanced ground, airborne and satellite infrastructure in order to reduce ATM costs, maintain safety, reduce the environmental impact of each flight and enhance the passenger experience. A process of international discussion and agreement, normally involving a minimum of five years for operational and technical finalization of system parameters followed by an adoption process taking several additional years (as prescribed in the ICAO Convention), is necessary to ensure that any new systems introduced as part of the infrastructure evolution are appropriate and safe. Other aeronautical systems not requiring international agreement to this degree can often be developed and implemented in a shorter timescale, but still require a minimum of several years to reach maturity and acceptance. In all these cases, the actual implementation of these systems requires additional time for implementation (e.g. regional agreement) in aircraft and on the ground, and a positive business case justifying the commitment of adequate financial resources. 8.3.2 In general, the standardization and the introduction of new systems will have to be consistent with the framework laid out in the Global Air Navigation Plan (Doc 9750) and may require updates to one or more of the Technology Roadmaps included in the Plan. This, in turn, may translate into updates to specific elements of the ICAO band-by-band spectrum strategy. 8.3.3 The impact on the ICAO spectrum strategy of the introduction of a new system will depend, inter alia, on which of the three following general categories the system falls into with respect to its spectrum requirements: a) aviation systems that can be accommodated in existing allocations, with necessary footnote modifications, or less commonly, with modification to the allocation status or description; b) aviation systems that require additional spectrum allocations for reasons of compatibility or frequency availability; and c) other systems with multi-service application capability whose aviation requirements can be integrated with the other applications, entailing changes to allocation, modification of band limits or footnotes or, less commonly, a completely new allocation. 8.3.4 In any case, the allocation of spectrum for new services and systems in frequency bands already allocated for aeronautical use will have to be consistent with the high-level ICAO spectrum strategy and will need to take place within the framework set by the relevant ICAO Standards and Recommended Practices (SARPs) for communication, navigation and surveillance systems, as well as other (industry) standards that apply to current operational systems. Note.— Requirements for spectrum for meteorological radar and meteorological satellite systems are addressed by the World Meteorological Organization (WMO). However, specific requirements for airborne weather radar systems are included in the ICAO spectrum policy. 8.4 CHALLENGES 8.4.1 For many years aeronautical radio frequency spectrum has been targeted for use by non-aeronautical services, in particular to satisfy requirements for mobile (terrestrial) and mobile-satellite communications. This has, for example, led to the loss of spectrum that was once allocated exclusively for aeronautical mobile-satellite communications (1.5/1.6 GHz) and to the introduction of non-aeronautical services in bands previously allocated for aeronautical use on an exclusive basis (e.g. the fixed satellite service in the frequency band 5 091–5 250 MHz, the non-safety aeronautical mobile service for telemetry in the frequency band 5 091–5 150 MHz and the radionavigation satellite service in the frequency band 5 000–5 030 MHz). This has created the potential for interference and/or loss of spectrum capacity to satisfy current and future aeronautical requirements for CNS systems. 8.4.2 There is currently pressure to release significant amounts of spectrum to support future commercial mobile communications and broadband wireless applications. Between 500 and 1 200 MHz of bandwidth is being sought, mainly in the range from 300 MHz to 6 GHz. This range includes frequency bands used by a large number of safety-critical aeronautical systems, including instrument landing system (ILS) glide path, distance measuring system (DME), primary and secondary radar, airborne collision avoidance system (ACAS), AMS(R)S, VSAT aeronautical networks and radio altimeters. 8.4.3 Another new element that may affect the future availability of radio frequency spectrum for aviation is the possible introduction of “Spectrum Pricing” which may have a significant economic impact on the aviation industry as a whole. 8.4.4 The ICAO spectrum strategy recognizes the challenges outlined above and provides the framework within which ICAO develops the international civil aviation ICAO Position on issues of interest to international civil aviation to be decided at ITU World Radiocommunication Conferences, which are the fora where these challenges typically face aviation. ______________________ Chapter 9 INTERFERENCE PROTECTION CONSIDERATIONS 9.1 INTRODUCTION The regulation and control of interference is essential to the safe and efficient operation of aeronautical radio services. An agreed framework of rules and preventative measures is thus an essential requirement. This framework is laid down in the Radio Regulations for observance by ITU members when cross-border cases of interference arise. National legislation then provides each State with the regulatory means to effect the discharge of the international obligation within its territory. This chapter describes the elements in this framework and contains the following specific sections: — 9.2 Regulatory aspects — 9.3 Management and control of interference — 9.4 Assessment of protection for aeronautical radio services — 9.5 Some special cases (e.g. VSAT, ISM) — 9.6 General protection limits for aeronautical radio. 9.2 REGULATORY ASPECTS The basic definitions of interference and harmful interference 9.2.1 The international framework of agreements for dealing with interference to radio services is contained in the ITU Radio Regulations. The provisions in these Regulations govern the circumstances and the procedures for seeking clearance action from other ITU administrations when interference occurs. The basic qualification for claiming protection is “conformity with the Radio Regulations” which implies that the radio service which is being interfered with is operating in an agreed frequency band and with characteristics which are specified in the Regulations, including its Appendices. 9.2.2 In the Radio Regulations the basic definition of interference is:
9.2.3 It is to be noted that interference is defined by the way in which the interfered system operation is affected. Thus, any performance degradation, misinterpretation or loss of information which would not occur in its absence constitutes interference. The definition does not imply that it is measurable in a quantitative sense, although it may well be in certain instances, but that there has been an adverse change of some detectable character. The change may be detectable by primary means, either aurally (voice signals) or visually (radar or TV), or by measurement (loss of data, inaccurate information, etc.). In some cases, it may be easier or preferable to instrument and record, or use the changed condition to give warning or to apply corrective measures. It is assumed also that interference in the sense employed in the Radio Regulations arises in all cases from sources outside the receiving system itself. 9.2.4 This basic definition of interference as stated in the Radio Regulations makes no reference to whether it is acceptable, but merely to the condition of its existence and its recognition. It is in the category of interference classed as harmful interference that the concept of unacceptability appears as a qualification or condition. This is clearly stated in the Radio Regulations as follows:
9.2.5 This regulation introduces the concept of unacceptability and defines criteria with which to make the decision. It is notable that the definition has two quite separate elements, one for radionavigation and safety services, and one for all other radio services. The former requires only proof of endangerment of the functioning, but the latter must demonstrate that a serious degradation or disruption has occurred which is at a higher level of disturbance. Again, as in the case of interference above, the means of assessment is not prescribed and could be either subjective or quantitative. It is important to observe that for interference to be considered harmful, it must be to a service that is operating in accordance with the Radio Regulations. In this respect, accordance with the Radio Regulations means the totality of the Radio Regulations, including the Appendices. A service which does not operate in accordance with the Radio Regulations cannot claim protection as a right under the Radio Regulations, although administrations may often respond positively to the best of their ability. It is to be noted that all aviation safety services are operating on frequencies according to allocations to the service concerned, either the aeronautical mobile (R) service, the aeronautical mobile-satellite (R) service or the (aeronautical) radionavigation service, and to agreed characteristics, and are operating in accordance with the Radio Regulations, as normally specified in Annex 10. This framework recognizes that interference, in its general sense, is a condition whereby a parameter of a received signal is affected in some way but not necessarily to the extent of being damaging to the reception. The interfering service must cease the interference when it creates a situation in which the operator of the interfered service decides that the service cannot be used for its intended purpose. The action to be taken is to remove interference which can include the reduction of radiated power or closing of the transmitter. The treatment of harmful interference 9.2.6 Harmful interference is the condition recognized throughout the Radio Regulations as establishing a case for complaint and for the removal of the sources causing the problem. Procedures, obligations and rules related to interference are given detailed attention in Chapter IV of the Radio Regulations. The reporting and clearance of harmful interference to a radio service is one of the rights established by a registration in the MIFR and is a right conferred in general terms in RR 8.1 and RR 8.3. In international terms, it creates an obligation for the country operating the interfering service to take action. The Regulations do not, however, carry mandatory force, and negotiation is the only course of action to resolve difficulties. 9.2.7 Safety services, such as a radionavigation service or an aeronautical mobile (R) service, or in certain cases the aeronautical mobile-satellite (R) service, are safety services as defined in:
9.2.8 Harmful interference to a safety service always requires urgent attention, and this is recognized by all ITU administrations. Safety services include not only the aeronautical services, but also maritime and land mobile services when the messages have safety-of-life content. 9.2.9 Of particular interest to aeronautical services in this context are the provisions mentioned at Section 7-III-3.4 of this handbook. Also, the permission to operate without an identification for the testing of navaids is to be noted as at RR 15.16. These measures provide a framework of regulatory actions which ensure that interference judged as harmful is cleared in an effective and expeditious manner.
The definitions of these two elements are given below.
9.2.12 The understanding of these definitions is completed by the definition of the term “necessary bandwidth”:
9.2.13 With increased congestion in spectrum utilization, this set of interlinking Regulations has become a highly important starting point for dealing with interactions between adjacent services, between services sharing the same frequency band, and in any other situation of frequency use conflict. A depiction of these relationships is in Figure 9-1. 9.2.14 The Regulations in Appendix 3 specify a Table of Maximum Permitted Spurious Emission Power Levels. These refer to the power supplied to the antenna transmission line from the transmitter and are “never to be exceeded values”. It is recognized that more stringent levels may be laid down by Conference agreement or by special agreement between administrations. For system performance reasons, ICAO SARPs often specify more stringent levels, in effect, meeting the spirit of the “special agreement” requirements of the Regulations. Permissible interference and accepted interference 9.2.15 The Regulations specify these two further classes of interference:
Figure 9-1. Unwanted emissions 9.2.16 These definitions have been developed to provide a basis for planning, and they highlight the fact that frequency planning is essentially a process involving the control of interference. 9.2.17 This concept of acceptability, based on quantitative criteria, can only be a conditional one since it cannot negate the freedom to state a complaint of harmful interference by a service suffering harmful interference. It would provide, nevertheless, a basis for review and adjustment of the criteria as a condition for the agreement to continue. In such a situation, it would be assumed that an aeronautical safety service would be permitted to continue to operate, with the prime obligation being on the interfering service to adjust, close down or take other immediate action to resolve the situation. Frequency sharing 9.2.18 Assignment planning within a service is the most notable example of the concept of permissible interference and is the application of an agreed protection criterion to ensure that the strength of the unwanted signal from a like facility, or a similar facility in the same service (e.g. voice and data in the VHF communications band), is the agreed number of decibels below that of the wanted signal. In these cases, the acceptable performance change is normally minimal and quite often is a change in the noise floor or the received signal-to-noise ratio. This is highly important for systems such as VOR or ILS, or navigation systems in general, where the changes to the received signal are not easily detectable by the user. All of these quantitative criteria for in-service planning are developed by ICAO for harmonized worldwide application. 9.2.19 Frequency sharing has recently developed a new context with the addition of services other than aeronautical services to previously exclusive aeronautical bands. The criteria for acceptability in these cases are normally developed by the Study Groups of ITU-R and embodied in their recommendations. Bands where this procedure has already been applied are the aeronautical radionavigation bands at 5 000–5 250 MHz, 9 000–9 500 MHz and 15.4–15.7 GHz. As the spectrum is increasingly exploited and greater demands appear for further uses, the principle of sharing of allocations between two compatible services is likely to become more extensively relied on. In such discussions, the aviation service justifies its protection requirements. Final decisions are made at ITU conferences, sometimes against the best advice from the aviation community. 9.2.20 Sharing an allocation between two services normally places constraints on any future expansion and implementation of both services. This can ultimately be detrimental to aeronautical services whose expansion rate is slower than other, more commercially-based services, in effect resulting in a first-come, first-served situation. As mentioned above, the application of sharing criteria, whether covered by an ITU-R Recommendation or not, cannot negate the right to claim protection from harmful interference. Where the service interfered with has safety-of-life functions, harmful interference would normally require immediate termination or reduction of power of the interfering service until a permanent resolution has been found. Multiple interference inputs 9.2.21 Assessments of interference effects and of acceptable levels tend to be conducted in isolation from one another. In any given practical situation, the net effect of many potentially interfering sources must be considered and due allowance made. An extra margin of between 3 dB is recommended in general, with higher values in particular cases where a number of interference sources are known to exist (for example, see ITU-R Recommendation M.1343). Aviation safety factor 9.2.22 Aeronautical safety applications are required to have continued operation through worst case interference, so all factors which contribute to harmful interference should be considered in analyses involving those applications. An aviation safety margin is included in order to address the risk that some such factors cannot be foreseen (for example impacts of differing modulation schemes). This margin is applied to the system protection criteria to increase the operational assurances to the required level. Traditionally for aviation systems/scenarios an aviation safety margin of 6–10 dB is applied. Until established on the basis of further study on a case-by-case basis, an aviation safety margin of not less than 6 dB should be applied. Electromagnetic compatibility (EMC) 9.2.23 EMC is defined as the ability of a system to function satisfactorily in an electromagnetic environment without introducing intolerable electromagnetic disturbance to any other system in that environment. 9.2.24 Two elements, basically receiver rejection and transmitter unwanted emissions, are fundamental design parameters in the specification and engineering of radio systems to operate in their typical operating environment. They are normally addressed by national legislation, such as FCC Rules in the United States or ETSI Standards in Europe. In many countries, they are a prerequisite to the approval of any equipment that generates radio frequency energy as a main functional source. This includes not only communications and navigation equipment but also computing equipment, industrial equipment, etc. The limiting values chosen are normally selected on the basis of best judgement and on the practical and economic factors applying in particular systems. 9.2.25 A good example of the essential need for EMC is in the case of the multiple radio systems (and, more recently, the digital control systems) used on board aircraft. In a modern transport aircraft, these can amount to systems operating in about 18 different frequency bands, with typically 35 antennas. Great care in the placement of antennas and in the internal cabling, and severe limitation of both output power and spurious products are necessary to maintain all installed systems within performance limits. Provisions addressing this point may be found in the specifications for airborne equipment produced by RTCA/EUROCAE and ARINC. Directory: safety -> acp -> repository acp -> Information paper acp -> Acp wgc6/WP24 aeronautical communications panel (acp) working group c meeting 6 Toulouse, France October 20-24, 2003 acp -> Joint meeting of the acp -> Working paper acp -> Amcp wgm/WP19 19 August 2002 Aeronautical Mobile Communication Panel (amcp) Working Group-m meeting Fifth Meeting Saint Petersburg, Russia, 19 to 23 August 2002 Agenda Item 4: satcom acp -> Acp wgf/16 wp 27 Rev. 1 International Civil Aviation Organization acp -> Working paper acp -> Working paper repository -> Doc 9718 an/957 Handbook on Radio Frequency Spectrum Requirements for Civil Aviation Download 1.54 Mb. Share with your friends:
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