1、 Recommendation ITU-R M.2059-0(02/2014)M SeriesMobile, radiodetermination, amateurand related satellite servicesii Rec. ITU-R M.2059-0 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the radio-frequency spectrum by all radiocom
2、munication services, including satellite services, and carry out studies without limit of frequency range on the basis of which Recommendations are adopted. The regulatory and policy functions of the Radiocommunication Sector are performed by World and Regional Radiocommunication Conferences and Rad
3、iocommunication Assemblies supported by Study Groups. Policy on Intellectual Property Right (IPR) ITU-R policy on IPR is described in the Common Patent Policy for ITU-T/ITU-R/ISO/IEC referenced in Annex 1 of Resolution ITU-R 1. Forms to be used for the submission of patent statements and licensing d
4、eclarations by patent holders are available from http:/www.itu.int/ITU-R/go/patents/en where the Guidelines for Implementation of the Common Patent Policy for ITU-T/ITU-R/ISO/IEC and the ITU-R patent information database can also be found. Series of ITU-R Recommendations (Also available online at ht
5、tp:/www.itu.int/publ/R-REC/en) Series Title BO Satellite delivery BR Recording for production, archival and play-out; film for television BS Broadcasting service (sound) BT Broadcasting service (television) F Fixed service M Mobile, radiodetermination, amateur and related satellite services P Radiow
6、ave propagation RA Radio astronomy RS Remote sensing systems S Fixed-satellite service SA Space applications and meteorology SF Frequency sharing and coordination between fixed-satellite and fixed service systems SM Spectrum management SNG Satellite news gathering TF Time signals and frequency stand
7、ards emissions V Vocabulary and related subjects Note: This ITU-R Recommendation was approved in English under the procedure detailed in Resolution ITU-R 1. Electronic Publication Geneva, 2014 ITU 2014 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, witho
8、ut written permission of ITU. Rec. ITU-R M.2059-0 1 RECOMMENDATION ITU-R M.2059-0 Operational and technical characteristics and protection criteria of radio altimeters utilizing the band 4 200-4 400 MHz (2014) Scope This Recommendation describes the technical and operational characteristics, and pro
9、tection criteria of radio altimeters used in the aeronautical radionavigation service. The ITU Radiocommunication Assembly, considering a) that radio altimeters are an essential component of aeronautical safety-of-life systems, including precision approach, landing, ground proximity and collision av
10、oidance systems; b) that radio altimeter systems operate in the aeronautical radionavigation service; c) that radio altimeters have been fitted for decades to all types of aircraft; d) that radio altimeters are operational during and must operate without harmful interference for the entire flight; e
11、) that a radio altimeter system on a single aircraft consists of up to three identical radio altimeters; f) that there is a need to document the spectrum usage characteristics and deployment of radio altimeter systems on a worldwide basis; g) that coexistence between radio altimeters located on the
12、same aircraft is achieved by technical and operational mitigation methods, recognizing a) that the aeronautical radionavigation service is a safety service; b) that radio altimeter systems operate in the frequency band 4 200-4 400 MHz on a worldwide basis; c) that representative technical and operat
13、ional characteristics and protection criteria of radio altimeter systems are required for spectrum management and deployment planning; d) that the airworthiness certification of radio altimeters is a lengthy and costly process; e) that radio altimeters require a bandwidth of 196 MHz, noting a) that,
14、 in accordance with RR No. 4.10, the safety aspects of radionavigation and other safety services require special measures to ensure their freedom from harmful interference; b) that regulatory requirements for radio altimeters are specified by the International Civil Aviation Organization (ICAO); c)
15、that Recommendation ITU-R M.1461 is used as a guideline in analysing the compatibility between radars (including radio altimeters) operating in the radiodetermination service with systems in other services, 2 Rec. ITU-R M.2059-0 recommends 1 that operational and technical characteristics of the radi
16、o altimeters described in Annex 1 and Annex 2 should be considered representative of those systems operating in the frequency band 4 200-4 400 MHz and should be used when conducting compatibility studies; 2 that the protection criteria provided in Annex 3 should be used for protection of radio altim
17、eters operation. Annex 1 Operational characteristics 1 Introduction The band 4 200-4 400 MHz is currently allocated to the aeronautical radionavigation service (ARNS) and is reserved exclusively for radio altimeters installed onboard aircraft and for the associated transponders on the ground by Radi
18、o Regulations footnote No. 5.438. The basic function of a radio altimeter is to provide accurate height measurements above the Earth surface with a high degree of accuracy and integrity during the approach, landing, and climb phases of aircraft operation representing a wide variety of reflectivity.
19、Such information is used for many purposes and the high degree of accuracy and integrity of those measurements must be achieved regardless of the Earth surface, such as during final approach and flare guidance in the last stages of automated approach to land. It is also used to determine the particu
20、lar altitude in which the aircraft can safely land and as an input to the terrain awareness warning system (TAWS), which gives a “pull up” warning at a predetermined altitude and closure rate; and as an input to the collision avoidance equipment and weather radar (predictive wind shear system), auto
21、throttle (navigation), and flight controls (autopilot). Radio altimeter systems are designed to operate for the entire life of the aircraft in which they are installed. The installed life can exceed 30 years, resulting in a wide range of equipment age, performance and tolerance. 2 Altimeters There
22、are two types of radio altimeters in use today. One type utilizes Frequency Modulated Continuous Wave (FMCW) modulation, the second utilizes pulsed modulation. The following sections provide information regarding these types of radio altimeters. 2.1 Frequency Modulated Carrier Wave Altimeters 2.1.1
23、Operational description The purpose of a radio altimeter is to provide the aircraft with an accurate, independent and absolute measurement of the minimum distance to the Earth surface below that aircraft. Typically, radio altimeters have a measurement range from 6 metres to 6 000 metres (20 feet to
24、19 685 feet). However, there are exceptions where some altimeters have a measurement range greater than 15 000 metres (49 213 feet). Radio altimeters are an essential component of aeronautical Rec. ITU-R M.2059-0 3 safety-of-life systems, including precision approach, landing, ground proximity and c
25、ollision avoidance systems. Radio altimeters are essential for landing on autopilot and in low-visibility conditions. Additionally, radio altimeters are employed when landing manually to help alert a pilot when to or automatically engage in a manoeuvre known as a “flare”, which is performed just bef
26、ore touchdown to lessen the force upon landing with the ground. A radio altimeter also functions as part of an aircrafts terrain avoidance warning system providing predictive forward-looking capability on the flight deck, and if necessary a warning, when an aircraft descends beneath a certain altitu
27、de or too close to the ground. Because of the importance of radio altimeters to the safe operation of an aircraft, they are included in the minimum equipment list on aircraft certified for passenger service. Furthermore, they must be certified at a safety criticality rating or Design Assurance Level
28、 (DAL) of “A”, “Where a software/hardware failure would cause and/or contribute to a catastrophic failure of the aircraft flight control systems” for all transport aircraft and a DAL of “B”, “Where a software/hardware failure would cause and/or contribute to a hazardous/severe failure condition in t
29、he flight control systems” for business and regional aircraft. Design assurance level is a safety criticality rating from level A to E, with level A/B being the most critical and requiring the most stringent certification process. Radio altimeter systems on a single aircraft consist of up to three i
30、dentical radio altimeter transceiver (Tx/Rx) units with their associated equipment. All Tx/Rx units operate simultaneously and independently from one another. The radio altitude is computed from the time interval a signal, originating from the aircraft, is reflected from the ground. Radio altimeters
31、 designed for use in automated landing systems are required to achieve an accuracy of 0.9 metres (3 feet). Several methods utilized either individually or in combination are used to avoid altimeter to altimeter mutual interference. First, the centre frequency of each altimeter can be offset. Second,
32、 transmissions can be offset in time. Third, transmissions can be offset by frequency bandwidth and/or modulation period. Using one or a combination of these options will cause the occupied bandwidth on a single aircraft to be greater than the required bandwidth of any single radio altimeter. Figure
33、 1 shows the location and direction of transmissions of the radio altimeter signal. FIGURE 1 M.2059-01H0Hi2.1.2 Principles of operation FMCW radio altimeters operate by a Tx/Rx working in conjunction with separate transmit/receive antennas. Operation requires a signal from the transmit antenna to be
34、 directed to the ground. When the signal hits the ground it is reflected back to the receive antenna. The system then performs a time calculation to determine the distance between the aircraft and ground, as the altitude of the aircraft is proportional to the time required for the transmitted signal
35、 to make the round trip. 4 Rec. ITU-R M.2059-0 The frequency modulated (FM) signal produced by the Tx/Rx is not tunable from the flight deck. The calculation is based upon the stipulation that a signal transmitted in the 4 200-4 400 MHz band will return at the same frequency. However, during the tim
36、e it takes for the signal to travel to the ground and return, the transmitter frequency has changed. The difference between the transmit and receive frequencies (f) is directly proportional to the height of the aircraft above the ground and depends on the exact slope of the FMCW modulation (span vs.
37、 period) as shown in Fig. 2. As illustrated by Fig. 2, an altitude is calculated by determining the difference between the frequency f1of the reflected signal and the frequency f2of the signal being transmitted at the instant t2the reflected signal is received. This difference frequency f is directl
38、y proportional to the time t required for the reflected signal to traverse the distance from the aircraft to the terrain and back to the aircraft. FIGURE 2 Typical frequency modulated carrier wave radio altimeter transmitted and received signals M.2059-02t1tt2ff1f2fmaxfminTransmitsignalReceivesignal
39、TimeFrequencyThe period of the triangle FMCW waveform could be variable depending upon the altitude. At every instant, a beat signal is obtained by mixing the transmitted wave (with frequency f2) and the received wave (with frequency f1). The frequency f of this signal is equal to: f = f2 f1(1) Know
40、ing either t or f, the height above terrain can be calculated using the following formula: )/(220dtdffctcH= (2) where: H0: height above the terrain (m) c: speed of light (m/s) t: measured time difference (s) f: measured difference in frequency (Hz) df/dt: transmitters frequency shift per unit time (
41、Hz/s). Rec. ITU-R M.2059-0 5 2.2 Pulsed altimeters 2.2.1 Operational description Similar to FMCW, pulsed altimeters provide the aircraft with accurate, independent and absolute measurement of the minimum distance to the Earth surface below that aircraft. Typical pulsed radio altimeters have a range
42、of reported altitude from 6 metres to 2 500 metres (20 feet to 8 200 feet) and an operational altitude of 12 km (39 360 feet). Any analysis of the aggregate effects of potential interferers must be computed at the Operational Altitude, where the altimeters continue to search for the ground and are v
43、ulnerable to interference that may result in a false altitude track. Functions of pulsed radio altimeters also include precision approach, landing, ground proximity and collision avoidance systems that are essential for landing on autopilot, and in low-visibility conditions, function as part of an a
44、ircrafts terrain avoidance warning system providing predictive forward-looking capability on the flight deck, and if necessary a warning, when an aircraft descends beneath a certain altitude or too close to the ground. 2.2.2 Pulsed altimeter principles of operation The pulsed-type radio altimeter us
45、es a pulse of radio-frequency energy transmitted towards the earth to measure the absolute height above the terrain immediately underneath the aircraft. The time difference between the transmitted pulse and the received pulse is measured. Where the velocity of propagations of electrometric energy is
46、 known and is a constant, the time is proportional to the height of the aircraft. The function of the pulsed radar altimeter is to provide terrain clearance or altitude between the ground and the bottom of the aircraft. The pulsed altimeter may also provide vertical rate of climb or descent and sele
47、ctable low altitude warning. Performance characteristics are designed to match particular applications where altitude tracking at high vertical rates may be necessary. Pulsed radar altimeters are also designed to support automatic landing and also auto-hover function on helicopters. 2.3 Application
48、Radio altimeters designed for use in automated landing systems are required to achieve an accuracy of 0.9 metres (3 feet) or more. Such elevation readings are transmitted to a pilots visual display and to several automatic safety components. Radio altimeters provide an essential informational compon
49、ent of the automatic flight control system1for approach and landing, ground proximity warning system2, terrain awareness and warning system3, flight management guidance computer, flight control systems, electronic centralized aircraft monitoring4and engine-indicating and 1A system which includes all equipment to control automatically the flight of an aircraft to a path or altitude described by references internal or external to the aircraft. 2This system alerts the flight crew when certain thresholds are exceeded, such as excessive descent rate, between 50 and 2 450 f
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