1、 Rec. ITU-R RS. 1416 1 RECOMMENDATION ITU-R RS.1416*, *SHARING BETWEEN SPACEBORNE PASSIVE SENSORS AND THE INTER-SATELLITE SERVICE OPERATING NEAR 118 AND 183 GHz (Question ITU-R 228/7) (1999) Rec. ITU-R RS. 1416 The ITU Radiocommunication Assembly, considering a) that Resolution 723 (WRC-97) resolves
2、 to address the allocations of frequency bands above 71 GHz to passive services; b) that Recommendation ITU-R RS.515 indicates that the band 115-122 GHz is necessary for spaceborne passive sensing to obtain vertical temperature profiles; c) that Recommendation ITU-R RS.515 indicates that the band 17
3、5-192 GHz is necessary for spaceborne passive sensing to obtain vertical water vapour profiles; d) that weather forecasting is an important tool essential to all human economic activities, and also plays a predominant role in early identification and warnings of potentially dangerous phenomena; e) t
4、hat atmospheric temperature and water vapour profiles are essential data needed for weather forecasting on a global basis; f) that the oxygen absorption band around 118 GHz and the water vapour absorption band around 183 GHz represent a unique natural resource for remote temperature and water vapour
5、 profile sensing in the atmosphere; g) that these passive measurements are extremely vulnerable to interference because the natural variability of the atmosphere makes it impossible to recognize and to filter measurements contaminated by interference; h) that contaminated passive sensor measurements
6、 can have a dramatic, adverse impact on climate studies and the quality of weather predictions, recognizing a) that the bands 116-126 GHz, 174.5-182 GHz, and 185-190 GHz are currently allocated to the inter-satellite service (ISS); b) that Recommendation ITU-R RS.1029 provides interference criteria
7、for the passive sensors in the bands 115-122 GHz and 175-192 GHz; c) that studies conducted in the bands 116-122 GHz, 174.5-182 GHz and 185-190 GHz have shown that the inter-satellite links (ISLs) in a non-geostationary (non-GSO) satellite system can cause interference to the passive sensors well in
8、 excess of these protection criteria (see Annex 1); d) that studies conducted in these bands have shown that ISLs in GSO satellite systems can share the band with passive sensors with suitable restrictions on the power flux-density (pfd) produced by GSO satellites at the sensor orbital altitude (see
9、 Annex 1); e) that No. S9.7 of the Radio Regulations of the specifies that satellite stations using the geostationary-satellite orbit must consider and coordinate with other space radiocommunication systems, recommends 1 that, in view of recognizing b) and c), passive sensors and ISLs of non-GSO sat
10、ellite systems should not operate on a co-frequency basis in the bands 116-122 GHz, 174.5-182 GHz and 185-190 GHz; _ *This Recommendation should be brought to the attention of Radicommunication Study Group 4. *Radiocommunication Study Group 7 made editorial amendments to this Recommendation. 2 Rec.
11、ITU-R RS. 1416 2 that, in view of recognizing d), passive sensors and ISLs of GSO satellite systems can share the 116-122 GHz band provided that the single-entry pfd at all altitudes from 0 to 1 000 km above the Earths surface and in the vicinity of all geostationary orbital positions occupied by pa
12、ssive sensors, produced by a station in ISS, for all conditions and for all methods of modulation, does not exceed 148 dB(W/(m2 200 MHz) for all angles of arrival; 3 that, in view of recognizing d) and e), passive sensors and ISLs of GSO satellite systems can share the 174.5-182 GHz and 185-190 GHz
13、bands provided that the single-entry pfd at all altitudes from 0 to 1 000 km above the Earths surface and in the vicinity of all geostationary orbital positions occupied by passive sensors, produced by a station in the ISS, for all conditions and for all methods of modulation, does not exceed 144 dB
14、(W/(m2 200 MHz) for all angles of arrival. ANNEX 1 Feasibility of sharing between the Earth exploration-satellite service (EESS) (spaceborne passive sensors) and the ISS operating near 118 and 183 GHz 1 Introduction The frequency bands near 118 and 183 GHz are allocated to the EESS on a primary basi
15、s for passive sensors as shown in Table 1. The allocation near 118 GHz is shared with other services. Near 183 GHz, the passive services have an exclusively allocated band. A need has been identified in this band to expand the frequency range over which passive measurements can be made, and therefor
16、e the passive sensors may have to share with active services in adjacent bands. It is important that frequency sharing be examined: to determine if currently allocated sharing at 118 GHz adequately protects the passive sensors; and to determine if the expansion of the range over which passive sensor
17、s operate near 183 GHz would create potential sharing problem with other services. TABLE 1 EESS allocations at 116-126 GHz and near 183 GHz Frequency band (GHz) Allocation to services (all worldwide) 116-126 EESS (PASSIVE) FIXED INTER-SATELLITE MOBILE SPACE RESEARCH (PASSIVE) 174.5-176.5 EESS (PASSI
18、VE) FIXED INTER-SATELLITE MOBILE SPACE RESEARCH (PASSIVE) 176.5-182 FIXED INTER-SATELLITE MOBILE 182-185 EESS (PASSIVE) RADIO ASTRONOMY SPACE RESEARCH (PASSIVE) 185-190 FIXED INTER-SATELLITE MOBILE Rec. ITU-R RS. 1416 3 2 Equipment characteristics 2.1 Passive sensors 2.1.1 Low-Earth orbiting (LEO) s
19、canning sensors The LEO passive sensor used in this analysis is modelled from the advanced microwave sensing unit (AMSU). The AMSU-B is already deployed at 183 GHz and represents the current technology in microwave sensors. The operation of the sensor is highly dependent upon a mechanically scanned
20、antenna. The reflector moves within a cylindrical shroud. The cylinder has an opened area that allows the antenna to receive radiation across about 50 of the Earths surface and into the night sky up to about 85 from nadir. The antenna scans the Earth, moves to the sky for a cold calibration measurem
21、ent, and then moves inside the shroud for a warm calibration measurement. The angle at which the antenna takes the cold measurement is constrained by the Earth limb and the area of the shroud needed to cover the antenna for a warm measurement. The calibration measurements are used to measure the rec
22、eiving system gain. The AMSU scanning scheme has the advantage over other schemes that all receiving components remain the same between atmospheric and calibration measurements. This scanning and calibration method is used on LEO sensors. Because the orbit is sun-synchronous, the sensor can always m
23、ake a cold measurement at the same location relative to the spacecraft. Most other arrangements would risk having the calibration antenna point toward the sun and not produce a cold measurement. 2.1.2 Geostationary orbiting sensors Sensors have been proposed to operate in the geostationary orbit. A
24、scanning type of antenna similar to the AMSU would sweep the visible portion of the Earth to about 8 from the spacecrafts nadir. If this sensor uses cold space for calibration it could either point its scanning antenna away from the Earth similarly to the AMSU or have a separate antenna for calibrat
25、ion pointed at any convenient location. The cold calibration antenna must not only avoid the Earth but also the sun and preferably the moon. The AMSU sensor in sun-synchronous orbit can calibrate at the same location relative to the spacecraft and always avoid pointing toward the sun. If the geostat
26、ionary satellite points anywhere within its orbital plane, it is likely to point at some time toward the sun or the moon and corrupt the cold measurement. It is therefore assumed that the geostationary satellite would point the cold calibration antenna in some direction that does not cause the anten
27、na to aim near the sun, Earth or moon. Most isolation for the calibration antenna would occur if pointed normal to the equatorial plane. This points the calibration antenna at least 67 from the ecliptic where the directional gain would be relatively low. 2.1.3 Push-broom sensors At this time no push
28、-broom sensors are in operation and no calibration method has been strictly defined. The push-broom sensor operates true to the analogy by having a series of small antenna beams across the spacecrafts track. Like bristles in the broom, the multiple beams sweep along the track. This system is not mec
29、hanical: each antenna beam is fixed. Therefore the Earth pointed beams cannot be used for cold calibration. If a separate antenna is used, it is not as constrained as the AMSU antenna in gain or calibration angle. The single constraint is that it must point toward cold space. If sun-synchronous orbi
30、ts are used, the best direction is away from the sun, which is where the AMSU points. However the push-broom can use angles above the 85 limit imposed by the AMSU shroud. 2.1.4 Limb sounding sensors Limb sounding sensors would have characteristics that differ from the AMSU-B, but are not addressed i
31、n this analysis. 2.1.5 Sensor characteristics Sensor characteristics are given in Table 2 for the AMSU and GSO sensors. Two modes of operation for the sensor are considered in this analysis: the scanning mode; and the calibration mode. 4 Rec. ITU-R RS. 1416 The pointing angles for these two modes ar
32、e given in Table 2. TABLE 2 Passive sensor characteristics The practical operational range for sensors in LEOs is between about 500 and 1 000 km. Operational or planned sensor systems in this band orbit at a nominal altitude of 833 km. However, orbits achieved by currently operating systems vary in
33、altitude by as much as 20 km. 2.2 Inter-satellite systems 2.2.1 Modelled systems The characteristics of an inter-satellite system modelled in this analysis are listed in Table 3. It is assumed to be a broadband digital system with a data rate of 200 Mbit/s, chosen to match the reference bandwidth of
34、 the sensor. This analysis is also applicable to broader band systems that have proportionally higher power. TABLE 3 ISL parameters The link performance is chosen as a C/N of 12 dB. This includes an Eb/N0of 10 dB for QPSK modulation and a 2 dB implementation loss. The system noise temperature is der
35、ived from the system design of ISLs in lower bands and the receivers built for the AMSU-B. A range of antenna gains between 45 and 60 dBi are examined. Generally, the 45 dBi antenna is chosen for low altitude links and the higher 55 or 60 dBi-antenna gain for higher altitudes and longer links. The a
36、ntenna side-lobe patterns are modelled using the single feed circular beam antenna pattern from Recommen-dation ITU-R S.672. Parameter AMSU-B GSO Antenna main-beam gain (dBi) 45 66 Antenna back-lobe gain (dBi) 14 14 Antenna beamwidth at half power points (degrees) 1.15 0.102 Sensor altitude range (k
37、m) 500 to 1 000 850 (nominal) 35 786 Interference criteria per bandwidth (dB(W/200 MHz) 160 160 Antenna measurement scan angles (from nadir) (degrees) 50 8 Cold calibration angle (from orbital plane) (degrees) 90 4 90 Cold calibration angle range (from nadir) (degrees) 65 to 85 83 (nominal) 90 (nomi
38、nal) Parameter Value Antenna mainbeam gain (dBi) 45, 50, 55 or 60 Antenna back-lobe gain (dBi) 10 System noise temperature (K) 2 000 at 118 GHz and 3 000 at 183 GHz Performance criterion of link, C/N (dB) 12 Rec. ITU-R RS. 1416 5 The analysis was limited to scanning sensors and inter-satellite syste
39、ms in circular orbits. ISLs are limited to a network of satellites with the same orbital altitude. 2.2.2 Operational systems in other bands No known inter-satellite systems currently operate in the bands addressed in this analysis. In the ITU records Belarus, Malaysia, and the United States of Ameri
40、ca have advanced filed their intentions to operate space-to-space systems in the 116 to 126 GHz band. No advanced filings appeared for ISLs near 183 GHz. Of those that operate in other bands, most are either at the GSO or at LEOs nominally 700 to 800 km. A few operate above the sensor at orbits that
41、 range from 1 000 to 10 350 km. These systems use multiple satellite constellations to achieve full Earth coverage. Table 4 lists several operating or proposed non-GSO ISL satellite constellations. The geocentric angles subtended by the links are listed for each constellation. TABLE 4 Example non-GS
42、O satellite constellations Existing or planned GSO satellite systems operating in other bands do not have, in general, evenly spaced satellites. For example, a look at one system shows five links with varying geocentric angles: 149, 31, 85, 85 and 125. Table 5 shows the maximum longitudinal spacing
43、for ten GSO constellations along with their antenna gains. TABLE 5 Parameters of example GSO inter-satellite systems System Number of orbits Number of satellites per orbit Separation within the orbit(degrees) Separation between orbits (degrees) Orbital altitude (km) System A 6 11 32.7 60 780 System
44、B 3 4 90 120 10 350 System C 8 6 60 45 1 414 System D 4 8 45 90 775 System E 21 40 9 17.1 700 System F 6 8 45 60 950 System G 4 6 60 90 800 System H 2 5 72 180 500 System I 6 4 90 60 1 000 System 1 2 3 4 5 6 7 8 9 10 Antenna gain (dBi) 58.5 59 58 46 55.5 60.3 53 50.3 49.1 55.7 Maximum longitudinal s
45、pacing (degrees) 162.6 162.6 78.6 10.1 67.3 162.6 53.9 111.1 77.4 136.4 6 Rec. ITU-R RS. 1416 3 Approach This analysis considers a broad range of parameters for ISL constellations and determines what restrictions on these parameters would permit co-channel sharing. Sharing is considered to be feasib
46、le only if the restrictions on the ISL parameters permit the development of systems similar to systems that are planned for other bands. Unacceptable interference to the Earth-exploration satellite (passive) service is determined by two criteria. First is an interference threshold of 160 dB(W/200 MH
47、z). Interference above this level is considered to be unacceptable. This power level corresponds to 20% of the sensitivity (Recommendation ITU-R RS.1029) of the sensor. Interference received above this level will increase the temperature reading that the satellite is making and corrupt long-term tem
48、perature averages. Another 3 dB will be added to the sensitivity to account for sharing with between space and terrestrial services. The second criterion is temporal and is applied when the first criterion, threshold level, is exceeded. The interference should not exceed the threshold for more than
49、0.01% of the time. This percentage is given in recommends 4 of Recommendation ITU-R RS.1029. 3.1 Analysis organization The analysis is presented in two investigations. The first is interference to LEO sensors from ISLs in orbits from close to the Earth to the geostationary orbit. The second investigation is interference into sensors in the geostationary orbit from both GSO and non-GSO ISLs. Each of these investigations starts with a static analysis that identifies the circumstances under which interference can occur. These circums
