1、 Rep. ITU-R M.2121 1 REPORT ITU-R M.2121 Guidelines for AM(R)S sharing studies in the 960-1 164 MHz band (2007) 1 Introduction Current aviation communication bands are severely congested and further pressured by the introduction of new aviation applications and security requirements. In addition, re
2、cent experience has shown that evolving technology for navigation and surveillance may necessitate allocations that are more encompassing than simply aeronautical radionavigation service (ARNS). Based on available studies, two distinct categories of AM(R)S spectrum are required. The first for surfac
3、e applications at airports including data links is distinguished by a high data throughput, however only moderate transmission distances and it is expected that single frequency resources can be shared at multiple geographic locations. The second category, like the current very high frequency (VHF)
4、AM(R)S, will require longer propagation distances (e.g. out to radio line-of-sight), moderate bandwidth, and a number of distinct channels to allow for sector-to-sector assignments. This report deals with the latter category, and initial estimates of potential spectrum requirements have been determi
5、ned taking into account evolving aeronautical applications, and integration of a new system on an aircraft. For the 960-1 164 MHz band, that estimate is that approximately 60 MHz will be required. The 960-1 164 MHz band is allocated to ARNS in all Regions on a primary basis. Even though overall in t
6、he band 960-1 164 MHz the usage is generally high, in the sub-bands 960-977 and 1 143-1 164 MHz usage by International Civil Aviation Organization (ICAO) Standard systems is relatively low. The band 960-1 164 MHz is also occupied by different systems that are either operated on a nationally coordina
7、ted or on a non-interference basis. Compatibility with existing or planned aeronautical systems operating in accordance with international aeronautical standards will be ensured by ICAO. In some countries in Region 1, the frequency band 960-1 164 MHz is also used by systems in aeronautical radionavi
8、gation service for which no ICAO Standards and Recommended Practices (SARPs) have been developed. Studies regarding compatibility between AM(R)S and these systems need to be undertaken in the ITU-R. This document presents status on ongoing studies within national administrations, ICAO and ITU-R aime
9、d at: a) defining the assumptions and key characteristics for an aeronautical future communication system (FCS) operating in the considered AM(R)S spectrum allocation in the band 960-1 164 MHz. b) considering the topic of the FCS compatibility with services (as defined in the ITU-R radio regulations
10、) operating in the adjacent bands below 960 and above 1 164 MHz. c) supporting the WRC CPM draft resolution text aiming at adding an AM(R)S allocation in the band 960-1 164 MHz, without constraining in any way the operations and the development of systems operating under ARNS in accordance with ICAO
11、 standards and recommended practices. 2 Rep. ITU-R M.2121 2 Current use of the band The 960-1 215 MHz band is an ARNS band that is reserved and protected for aeronautical navigation services. This band is already used by many civil aeronautical systems: DME, SSR, GNSS signals etc. There is also the
12、universal access transceiver (UAT) datalink system that will operate in the future on the 978 MHz frequency. Other systems also operate within this band on a nationally-coordinated basis. Distance measuring equipment (DME) The DME system is an ICAO standardized pulse-ranging system for aircrafts. It
13、 allows for the determination of the slant range between an aircraft and known ground locations. A DME ground station may be combined with a collocated VOR, ILS or MLS system to form a single facility. When this is done, the DME frequency is paired with the VOR, ILS or MLS frequency according to ICA
14、O provisions. The DME onboard interrogator obtains a distance measurement by transmitting pulse pairs and waiting for pulse pairs replies from the ground beacon. Each pulse pair is returned by the transponder after a fixed delay. Based on the measured propagation delay, the aircraft interrogator equ
15、ipment calculates the distance (slant range) from the transponder to its current location. Pulses have a half-amplitude duration of 3.5 s and pulse pair spacing depends on the mode. There are four DME modes (X, Y, W and Z) but currently modes W and Z are not used. DME frequencies are spaced in 1 MHz
16、 increments throughout the 962 to 1 213 MHz band. Interrogation frequencies are contained within the band 1 025 to 1 150 MHz, and reply frequencies from the beacon are on paired channels located either 63 MHz below or above the corresponding interrogation frequency. Figure 1 depicts the standard DME
17、/TACAN channel plan. Note that secondary surveillance radar (SSR) and ACAS operate on the frequencies 1 030 and 1 090 MHz, so DME channels lying near those frequencies, and the corresponding ground reply frequencies are not used. Note this frequency plan is also valid for the TACAN system that is de
18、scribed below. FIGURE 1 Standard DME/TACAN Channel Plan Secondary surveillance radars (SSR) ATC secondary surveillance systems (SSR) Mode A, Mode C, and Mode S are cooperative radars that operate by interrogating transponders onboard suitably equipped aircrafts. Ground stations interrogate on a freq
19、uency of 1 030 MHz and aircraft respond on 1 090 MHz. Because of the aircraft active response, SSRs typically operate at much lower power levels, a few Rep. ITU-R M.2121 3 hundreds of watts, compared to primary radars, several thousand of watts. Mode S equipped SSRs interrogate aircraft individually
20、 using differential phase shift keying (DPSK). The airborne collision avoidance system (ACAS) interrogates SSR transponders onboard nearby aircraft on 1030 MHz. Then, this system processes replies transmitted at 1090 MHz to provide the collision avoidance function. Universal access transceiver (UAT)
21、 The ICAO standard UAT system supports automatic dependent surveillance broadcast (ADS-B) data transmission as well as ground uplink services such as traffic information service broadcast (TIS-B) and flight information service broadcast (FIS-B). UAT employs TDMA technique on a single wideband channe
22、l of 1 MHz at a frequency of transmission of 978 MHz. Transmissions from individual aircrafts are composed of a single short burst, of duration 276 s (basic message) or 420 s (long message), that is transmitted each second. Ground uplink transmissions occur also once per second and lasts 4452 s. The
23、 modulation employed is a binary continuous phase frequency shift keying (CPFSK) at a 1.042 Mbit/s rate and modulation index is not less than 0.6. 1 090 extended squitter (1090ES) 1 090 MHz extended squitter transmissions from Mode S transponders or other non-transponder devices are used to broadcas
24、t information relating to position of aircraft, aerodrome surface vehicles, fixed obstacles and/or other related information. The broadcast can be received by airborne or ground based receivers and can contain ADS-B and/or TIS-B messages. GNSS Global Navigation Satellite System (GNSS) signals will b
25、e transmitted in the coming years within the 1 164-1 215 MHz RNSS frequency band that is included in the 960-1 215 MHz ARNS band. Examples include the Galileo E5 signal, that is composed of both the Galileo E5a signal transmitted at 1 176.45 MHz and the Galileo E5b signal broadcast at 1 207.14 MHz,
26、the GPS L5 signal also transmitted at 1 176.45 MHz, and GLONASS also transmitting an L5 signal at several nominal frequencies in the band 1 197,648 - 1 213,875 MHz. These signals are expected to be used by Civil Aviation for Safety-of-Life applications. ICAO is undertaking standardization of those s
27、ignals and preliminary susceptibility levels have been proposed. DME operations are protected from GNSS by Resolution 609 (WRC-03) procedures and agreements. National systems (NS) One example of a nationally-coordinated system operating in portions of the 960-1 215 MHz band is an advanced radio syst
28、em that provides information distribution, position location and identification capabilities in an integrated form. This system is not ARNS, therefore it operates under constraints that are set on national basis to avoid interference with existing air traffic control equipment that operate within th
29、e same frequency band. Non ICAO-standard ARNS systems The Tactical Air Navigation (TACAN) system was designed primarily for military use. A TACAN transponder consists of a DME transponder and an associated bearing antenna. This antenna rotates or scans, enabling an aircraft to estimate its bearing w
30、ith respect to the transponder. Ranging information is also estimated by the airborne TACAN receiver thanks to the DME transponder. This system operates on the same frequencies and with the same channel separations than those of DME. In addition, in a number of countries the band 960-1 164 MHz is us
31、ed by other non ICAO-standard systems operating in the aeronautical radionavigation service. These systems are used to support navigation (e.g., radio systems of short range navigation (RSBN) and air traffic control functions 4 Rep. ITU-R M.2121 2.1 Interference scenarios to consider To perform the
32、compatibility analysis, one can use the classic “source-path-receiver” methodology. This requires collecting information on the following three elements: Potential interference sources (location, antenna characteristics, transmitted power, operating frequency, waveform type etc.). In our study, the
33、potential interference source is the FCS. Interference-victim receiver encounter scenario (distance between interference and victim receiver antenna, victim receiver antenna characteristics etc.). Receiver performance in presence of interference (susceptibility values depending on the interference t
34、ype). Once that information is available, link analyses can be performed. There are multiple potential outcomes of these analyses, e.g. the maximum allowable unwanted emissions by a potential interference source or the minimum separation distances between the interference source and the victim recei
35、ver. The compatibility scenarios that must be analyzed include those listed below. For each of them, the “source-path-receiver “methodology may be applied. Co-site compatibility. FCS transmissions from an aircraft will be sensed by aeronautical receivers onboard the same aircraft. Co-site compatibil
36、ity is likely to be one of the driving compatibilities given the close spatial proximity of equipments and the close frequency proximity of systems. Air-to-ground compatibility. FCS transmissions from aircraft will be sensed by aeronautical ground stations. In a worst-case approach, minimum separati
37、on distances between the aircraft and ground-based stations must be assumed. These minimum distances depend on the current phase of flight of the aircraft. Ground-to-ground compatibility. Uplink transmissions from FCS ground stations will be sensed by ground stations. One of the outcomes of this ite
38、m will be the minimum separation distance between the involved ground stations. Ground-to-air compatibility. Uplink transmissions from FCS ground stations will be sensed by airborne receivers. Same comments than for the air-to-ground compatibility. Air-to-air compatibility. FCS transmissions from ai
39、rcraft will be sensed by aeronautical receivers onboard a nearby aircraft. For this case, minimum separation distances are given by applicable ATC standards. 2.2 Analysis Temporally speaking, one has to distinguish between continuous and bursted-type communication signals, e.g. TDMA structure. Then,
40、 from a frequency standpoint, narrow band and wideband signals must be considered separately. Wideband signals are assumed to be signals whose spectrum is flat over the victim receiver passband. The emissions of the FCS in adjacent bands will consist of out-of-band emissions and spurious emissions s
41、uch as intermodulation products. Note the FCS cannot generate any harmonics within the 960-1 215 MHz frequency band given the small frequency separation between the involved systems. Assuming the FCS equipment transmit on multiple frequencies, intermodulation products will have to be considered. Con
42、tinuous signal If FCS equipment broadcast continuous signals, then out-of-band emissions will likely result in an increase of wideband background noise in passbands of victim receivers. Rep. ITU-R M.2121 5 Regarding co-channel compatibility, if the spectrum of the FCS is large as compared to the vic
43、tim receiver passband then continuous wideband susceptibilities may be applicable. In any case dedicated study through simulations or experiments may be required. Bursted-type signal If the FCS employs a TDMA structure, victim receivers may consequently receive burst-type interfering signals. For ad
44、jacent-band compatibility, out-of-band emissions will likely appear as bursts of background noise within the receiver passband. Typical bursts durations could range from about hundreds of microseconds to a few milliseconds depending on the signal bandwidth and the amount of data to be transmitted. M
45、oreover, because of the rise and fall times of bursts, time-domain transient peaks are expected within the victim receivers passbands. Those transient peaks must be accounted for as they may be harmful to receivers. For instance they could lead to early RF component saturation. 2.3 Interference redu
46、ction There are multiple ways to reduce the impact of the future aeronautical communication system on other systems. Some possible examples to be considered are listed below: Signal spectrum design The spectrum of the signal can be carefully selected so as to limit the occupied bandwidth to the most
47、 efficient value as well as to limit the level of the components emitted in the outer parts of the spectrum, i.e. unwanted emissions. To do so, compliance with Recommendation ITU-R SM.329-9 is advised. For instance, nulls of the spectrum may be chosen on the UAT and DME equipment frequencies. An int
48、eresting modulation is the binary continuous phase frequency shift keying (CPFSK). This CPFSK modulation reduces the level of side lobes as well as constraining the passband. Emission filter The emission filter should also be chosen carefully to limit the amplitudes of spectrum components present in
49、 outer parts of the spectrum. Regarding spurious emissions, Recommendation ITU-R SM.329-9 should be applied. State-of-the-art in technology, and economic constraints should also be accounted for when selecting the emission filter. Signal polarization The signal polarization may be chosen to include, if possible, polarization losses at the other (victim) systems. Antenna isolation The on-board isolation between the FCS and other systems antennas should be carefully studied as it will allow reduction of unwanted emission levels in victim receivers passbands. One ty
