1、 Rec. ITU-R F.1571 1 RECOMMENDATION ITU-R F.1571*Mitigation techniques for use in reducing the potential for interference between airborne stations in the radionavigation service and stations in the fixed service in the band 31.8-33.4 GHz (Question ITU-R 224/9) (2002) The ITU Radiocommunication Asse
2、mbly, considering a) that the band 31.8-33.4 GHz is allocated to the fixed service (FS) on a primary basis in all three ITU Regions; b) that footnote No. 5.547 of the Radio Regulations (RR) identifies the 31.8-33.4 GHz band as available for applications in the high-density fixed service (HDFS); c) t
3、hat the band 31.8-33.4 GHz is also allocated to the radionavigation service (RNS) on a primary basis in all three ITU Regions; d) that, the World Radiocommunication Conference (Istanbul, 2000) (WRC-2000) agreed RR footnote No. 5.547A, stating that administrations should take practical measures to mi
4、nimize potential interference between stations in the FS and airborne stations in the RNS in the band 31.8-33.4 GHz, taking into account the operational needs of the airborne RNS (see Note 1); e) that Recommendation ITU-R F.1097 contains details of mitigation techniques for unwanted emissions from t
5、he radiodetermination service, which could be used to minimize the potential for interference between airborne stations in the RNS and stations in the FS; f) that radio-frequency arrangements including frequency block arrangements, in consultation with organizations developing standards for radio sy
6、stems, have been developed (see Recommendation ITU-R F.1520) in order to make the most effective use of the spectrum available; g) that the RNS is used for weather avoidance and, in some cases, e.g. where the local air traffic control (ATC) services are not available, for takeoff and landing (see RR
7、 No. 4.10). The existing systems are also used for aerial delivery of cargo and personnel in support of international humanitarian operations; h) that the band 31.8-33.4 GHz provides 1 600 MHz of contiguous spectrum, which is suitable for use in supporting FS applications such as access to the end u
8、ser and the provision of infrastructure for mobile networks, i.e. IMT-2000, _ *This Recommendation should be brought to the attention of Radiocommunication Study Group 8 (Working Party 8B). 2 Rec. ITU-R F.1571 noting a) that one administration has implemented a limited number of airborne stations in
9、 the RNS in the entire 31.8-33.4 GHz band, operated worldwide (see Note 1); b) that the band 31.8-33.4 GHz is not shared with the fixed-satellite service/mobile-satellite service, recommends 1 that appropriate mitigation techniques be used, where possible or practical, in order to significantly redu
10、ce the potential for interference between stations in the FS and airborne stations in the radionavigation service (see Note 2). These may include measures such as: 1.1 for stations operating in the FS: automatic transmitter power control (ATPC), forward error correction (FEC) coding, bit interleavin
11、g technique (BIT), robust access/modulation techniques, receiver blocking filter, robust synchronization and high performance antennas (see Note 3); 1.2 for stations operating in the RNS: frequency agile systems, RF filter installation in the radar transmitter and pulse coding in future systems; 2 t
12、hat in addition to the appropriate mitigation techniques, some operational restrictions on both services may be necessary where practical or possible. These may include amongst others the following considerations: 2.1 airborne stations in the RNS are encouraged to avoid low operational altitudes and
13、 low down tilt antenna angles in the vicinity of urban areas (zero tilt angle corresponds to directions towards the horizon). These operational conditions do not apply to takeoff and landing; 2.2 systems in the FS are encouraged to avoid the use of high elevation angles; 2.3 stations in the RNS are
14、encouraged, in the vicinity of urban areas, to use the centre gap of the FS RF arrangements in Recommendation ITU-R F.1520. NOTE 1 Annex 1 provides a summary of the conducted sharing studies. Annex 2 provides charac-teristics of existing airborne systems operating in the RNS in the frequency band 31
15、.8-33.4 GHz. Characteristics of systems in the FS operating in the frequency band 31.8-33.4 GHz are contained in Recommendation ITU-R F.758. NOTE 2 Annex 3 outlines potential mitigation techniques and operational measures applicable to systems in the FS as well as airborne systems in the RNS. NOTE 3
16、 ATPC is efficient in reducing the interference from systems in the FS to systems in the RNS, but may make FS receivers more susceptible to interference from systems in the RNS. Rec. ITU-R F.1571 3 ANNEX 1 Summary of sharing studies between stations in the FS and airborne stations in the RNS 1 Backg
17、round Resolution 126 (WRC-97) resolved to conduct, as a matter of urgency, the appropriate studies in time for WRC-2000 to determine what criteria would be necessary for sharing between stations in the fixed service and stations in the other services to which the frequency band 31.8-33.4 GHz is allo
18、cated. In response to this Resolution, ITU-R adopted Question ITU-R 224/9 (1997) addressing sharing criteria between stations in the FS and RNS in this band. The conducted sharing studies are summarized below. 2 Interference to the FS from the RNS Calculation of separation distance is based on a pro
19、babilistic approach as well as on a deterministic approach (worst-case based on minimum coupling loss (MCL). In principle, the studies show that if the required minimum separation distance between systems in the two services to preclude interference cannot be assured, then appropriate measures, incl
20、uding mitigation techniques and/or some restrictions on operational conditions, will be needed to facilitate sharing. Further, the studies indicate that the concept of geographical coordination may be difficult to apply for the mobile radar systems. The pulsed nature of the interfering radar signal
21、allows for shorter separation distances compared to a non-pulsed interfering source. This has been taken into account in the relevant sharing studies as well as the impact of short duration pulsed, extremely high-power interference of the airborne radar system into the FS receiver. The studies indic
22、ate that, without some operational restrictions and appropriate mitigation techniques, severe interference events may occur during exceptional main beam coupling between the antennas of the radar system and the fixed system. Various combinations of aircraft altitudes, radar tilt angle and fixed syst
23、em antenna elevation angle can generate such events. However, the probability of such events is expected to be low. Further, the events will be short in duration due to the narrow radar antenna beam and the antenna rotation. The studies outlined necessary criteria, in terms of required mitigation te
24、chniques (see Annex 3) for the FS and primarily some limitations on radar operational altitude and/or tilt angle in particular in the vicinity of urban areas. In particular, the studies indicate that the fixed system antenna elevation angle and the radar tilt angle are crucial. In cases where suitab
25、le mitigation techniques and/or restrictions on operational conditions are not applicable, appropriate and agreed operational procedures should be applied. 4 Rec. ITU-R F.1571 3 Interference to the RNS from the FS Considering traditional point-to-point (P-P) systems with a low density of terminals,
26、assuming worst-case scenarios and operational altitudes of the RNS above approximately 4 000 m and some limitations on the tilt angle, the sharing studies show that required unavailability criterion of the airborne radar system will be met. Considering high-density point-to-multipoint (P-MP) applica
27、tions, assuming densities of 1 000 1terminal stations/km2and 0.3 central stations/km2, respectively,the sharing studies, using practical assumptions, show that the performance of the airborne radionavigation radar will be acceptable over urban areas. This conclusion is reached assuming that the airc
28、raft operate at altitudes above roughly 6 000 m and with antenna down tilt angles of more than 20. In addition, the antenna elevation angles of HDFS stations, oriented toward the aircraft, are encouraged not to exceed approximately 5. HDFS systems may require higher elevation angles than 5 in dense
29、urban areas. For these cases appropriate mitigation techniques should be taken into account in order to reduce the possible interference to the airborne radar system. Required criteria, in terms of required mitigation techniques and operational restrictions, are established in the conducted sharing
30、studies. Used propagation models cover the most recent versions of Recommendations ITU-R P.452 and ITU-R P.676. The antenna radiation patterns are modelled by the most recent versions of Recommendations ITU-R F.699, ITU-R F.1245 and ITU-R F.1336. Technical characteristics for the considered P-P and
31、P-MP systems in the FS are based on inputs from Recommendation ITU-R F.758. Since the airborne radar operates throughout all phases of aircraft flight, it is not apparent that interference, without countermeasures, can be avoided in all cases. Mitigation techniques such as high-performance antennas,
32、 ATPC, etc. implemented in future P-MP applications, will ensure that the availability criteria of the airborne radar system may be met. Concerning mitigation techniques for the radar system, frequency agile systems and pulse-coded systems have high potential with respect to the increase in the resi
33、stance to interference (see Annex 3 for more details). 4 Summary The sharing studies show that high-density systems in the fixed service can coexist with the currently limited deployment of airborne systems in the RNS in the band 31.8-33.4 GHz. This conclusion is reached with the assumption of some
34、limitations on both services. Based on the above, WRC-2000 suppressed Resolution 126 (WRC-97) and in footnote RR No. 5.547A stated that administrations should take practical measures to minimize the potential interference between stations in the FS and airborne stations in the RNS in the 31.8-33.4 G
35、Hz band, taking into account the operational needs of the airborne radar systems. _ 1The number of simultaneously active terminals is significantly lower than this figure. Rec. ITU-R F.1571 5 ANNEX 2 Characteristics of radionavigation systems in the 31.8-33.4 GHz band 1 Operational conditions Radion
36、avigation systems identified to operate in the band 31.8-33.4 GHz are onboard aircraft. The system operates worldwide mostly continuously during flight. This encompasses an altitude range of from just off the ground to approximately 30 000 ft (or 9 000 m). Flight times can be up to six hours, and ty
37、pically the majority of the time is spent en route, but some longer time at either the departure or destination points is expected. Information from one administration indicates that it operates a limited number of aircraft worldwide with radionavigation systems in this frequency band. Up to 18 airc
38、raft operating these radionavigation systems can be active in a small geographic area (i.e. separated by less than a kilometre from each other), though most often only 1 to 3 aircraft will be operating simultaneously together. The term radionavigation throughout this Recommendation refers to an airb
39、orne radar system operating in the 31.8-33.4 GHz band. One administration has reported worldwide use of this band for the RNS in terms of a limited number of airborne radar systems. The actual radar system is used for ground mapping, weather avoidance and navigation, but not primarily for functions
40、such as airport approaching and landing. Future replacement of some of the fixed frequency systems with the frequency agile system is envisaged. 2 Technical characteristics Two radar systems are implemented: one system using fixed frequency (of 80% of aircraft stations) and one system (of 20% of air
41、craft stations) with the option to use frequency agility (nine channels in the band 32.2-33 GHz). The technical characteristics of systems operating in the RNS are given in Table 1. From the Table, it can be concluded that the concept of pulse compression technique using coded pulses (with error det
42、ection capability) is not implemented in the considered radar systems. Furthermore, the large bandwidth of 37 and 17 MHz respectively in comparison to the band-width 1.2/0.2 = 6 MHz (0.2 s pulse width), indicates that digital signal processing is not utilized. From the Table, the radar term 106/(pul
43、se repetition frequency (prf) pulse width )s( is determined to 2 500 (System 1) and 3 125 (System 2). This factor is essential in determining protection criteria for stations in the FS interfered with radar systems. It should be noted that the antenna rotation is mechanically, i.e. the antenna beam
44、is not electronically controlled. 6 Rec. ITU-R F.1571 TABLE 1 Technical characteristics of systems in the RNS operating in the band 31.8-33.4 GHz ANNEX 3 Mitigation techniques and operational measures 1 Technical and operational measures RR footnote No. 5.547A states that administrations should take
45、 practical measures to reduce the potential interference between airborne stations in the RNS and stations in the FS in the band 31.8-33.4 GHz, taking into account the operational needs of the RNS. This Annex provides guidance on technical and operational measures that may reduce the potential inter
46、ference. Parameter System 1 System 2 Tuning type Fixed frequency; tunes continuously across 31.8-33.4 GHz Fixed frequency or frequency hopping; operates in either mode on one of nine discrete channels spaced 100 MHz apart (32.2-33 GHz) Emission type Unmodulated pulses Unmodulated pulses RF emission
47、bandwidth (MHz) 37 17 (instantaneous) 117 (hopping) Pulse width (s) 0.2 0.2 prf (pps) 2 000 1 600 Peak transmitter power (kW) 60 39 Receiver IF bandwidth (20 dB) (MHz) 40 17 Receiver noise figure 11 11 Antenna type Parabolic reflector Parabolic reflector Antenna main beam gain (dBi) 44 41.1 Antenna
48、scan Elevation: 30 to +10, manual Azimuth: 360 at 7, 12, or 21 rpm Elevation: 30 to +10, manual Azimuth: 360 at 12 or 45 rpm Rec. ITU-R F.1571 7 2 Measures FS Enhancements to future FS systems in terms of ATPC and robust error correcting coding should be easy and relatively inexpensive to implement.
49、 In particular, in combination with bit interleaving (see Recommendation ITU-R F.1097), FEC has shown to be efficient with respect to particularly short duration burst errors. In order to further reduce the potential for interference, certain access/modulation techniques less susceptible to pulsed energy, robust synchronization schemes and RF-blocking filter are available to the FS. Furthermore, improved antennas combined with modest limitations on elevation angle will reduce the potential for interference between both systems.
