1、 Rec. ITU-R F.1607 1 RECOMMENDATION ITU-R F.1607 Interference mitigation techniques for use by high altitude platform stations in the 27.5-28.35 GHz and 31.0-31.3 GHz bands (Question ITU-R 212/9) (2003) The ITU Radiocommunication Assembly, considering a) that new technology utilizing high altitude p
2、latform stations (HAPS) in the stratosphere is being developed; b) that WRC-97 made provisions for operation of HAPS within the fixed service in the bands 47.2-47.5 GHz and 47.9-48.2 GHz; c) that, since the 47 GHz bands are more susceptible to rain attenuation in those countries listed in Nos. 5.537
3、A and 5.543A of the Radio Regulations (RR), the frequency range 18-32 GHz has been studied for possible identification of additional spectrum in ITU-R; d) that WRC-2000 made a provision for the use of HAPS in the fixed service in the bands 27.5-28.35 GHz and 31.0-31.3 GHz in certain countries on a n
4、on-harmful interference, non-protection basis in order to address issues of rain attenuation associated with the 47 GHz bands (RR Nos. 5.537A and 5.543A); e) that Resolution 122 (Rev.WRC-2000) urgently requested studies on technical, sharing and regulatory issues in order to determine criteria for t
5、he operation of HAPS in the bands referred to in considering d) above, recommends 1 that the following general interference mitigation techniques be considered in the development of a system using HAPS in the 27.5-28.35 GHz and 31.0-31.3 GHz bands (Notes 1 and 2): 1) increasing minimum operational e
6、levation angle; 2) improvement of radiation patterns of antennas on board HAPS and their ground stations; 3) shielding effect by HAPS airship envelope; 4) dynamic channel assignment; 5) automatic transmitting power control (ATPC). NOTE 1 Annex 1 describes general principles of the above interference
7、 mitigation techniques and Annex 2 gives a more detailed description of dynamic channel assignment. NOTE 2 Recommendation ITU-R F.1569 should be referred to for the HAPS system using the frequency bands 27.5-28.35 GHz and 31.0-31.3 GHz. 2 Rec. ITU-R F.1607 Annex 1 Interference mitigation techniques
8、proposed for use by HAPS in the 27.5-28.35 GHz and 31.0-31.3 GHz bands 1 Interference situation Figure 1 shows an example of interference situation between HAPS system and other services. This Annex lists the interference mitigation techniques for frequency sharing between the HAPS system with other
9、 services and describes their principle and advantages. 1607-01FIGURE 1Interference situation including HAPS, FSS, FS, EESS, and RAS systemsfor uplink of 31 GHz and downlink of 28 GHzUplink = 31 GHzDownlink = 28 GHzFSS/ES: earth station for FSSHAPS/GS: ground station for HAPS systemFS/GS: ground sta
10、tion for FS (transmitting only at 28 GHz)FS/GS FS/GSHAPS/GSFSS/ESHAPSCommunication linkEarth exploration satelliteInterferenceGSO/non-GSORadio astronomyantennaEESS: Earth exploration-satellite serviceRAS: radio astronomy service2 Interference mitigation techniques Table 1 summarizes the relation bet
11、ween the mitigation technique and its effective interference situation. The technical principle and advantages of each mitigation technique follow Table 1. Rec. ITU-R F.1607 3 TABLE 1 Relation between interference mitigation techniques and interference scenarios 1) Increasing minimum operational ele
12、vation angle Interferences from the FSS earth station to the HAPS ground station, that between FS ground station and HAPS ground station and that from the HAPS ground station to the RAS station could be reduced by increasing minimum operational elevation angle of HAPS ground station so as to increas
13、e antenna separation angle toward ground stations for other services. As a result, required separation distance could be shortened. For example, in the case that the minimum operation angle of the HAPS ground station is increased from 20 to 40, the separation distance is reduced to about half (0.42
14、in precise) as shown below. In the theoretical analysis, radiation pattern of HAPS ground station antenna in that range of off-axis angle is given by the following equation, Recommendation ITU-R F.1245: G() = 39 5 log10(D/) 25 log10() where: : off-axis angle (degrees) D : antenna diameter : waveleng
15、th expressed in the same units FSS (in-band interference) Science service (interference to adjacent band) Systems for sharing and interference scenario Interference mitigation techniques To FSS satellite From FSS/ES To/from FS (in-band) To EESS satellite To RAS station 1) Increasing minimum operatio
16、nal elevation angle 2) Improvement of radiation patterns of antennas on board HAPS and ground station 3) Shielding effect by HAPS airship envelope 4) Dynamic channel assignment HAPS uplink 5) Automatic transmitting power control HAPS downlink : Effective. 4 Rec. ITU-R F.1607 The difference between a
17、ntenna gain for 20 off-axis and that for 40 is calculated to be about 7.5 dB. Therefore, the reduction is calculated by 10/5.710/1 = 0.42, since path loss is proportional to the square of transmission distance. It is noted in the case of minimum elevation angle of 40 that the required number of HAPS
18、 airship needs to be increased so as to keep the total service coverage unchanged. 2) Improvement of radiation patterns of antennas on board HAPS and ground station Interference from the HAPS airship to the satellite space segment could be reduced by pattern shaping of each beam of multibeam antenna
19、 on board HAPS airship, because the pattern shaping improves main-lobe and side-lobe characteristics. As a preliminary study result, radiation power of side lobe and back lobe is expected to be reduced by about 5 dB, by shaping the antenna beam pattern having the worst characteristics with four clus
20、ter beams as depicted in Fig. 2. The improvement is due to the transmission power reduction by gain increase of the antenna for boresight and also due to side-lobe gain reduction. 1607-02FIGURE 2Improvement of radiation pattern by beam shapingFSS satelliteReducedinterference(5 dB)InterferenceHAPSSup
21、pressed side lobe levelHAPS5 dB reductionFSS satelliteImprovement of radiation pattern (gain suppression in the elevation angle smaller than the minimum operational elevation angle in HAPS system) of the antenna in the HAPS ground station is also effective to reduce interference between the HAPS gro
22、und station and stations on the ground in other services (station in FS, FSS earth station and RAS station). Rec. ITU-R F.1607 5 3) Shielding effect by HAPS airship envelope This effect is given from the metal coating of HAPS airship envelope. Interference calculation between HAPS airship and satell
23、ite space segment is reduced by taking into account shielding effect to the side-lobe and back-lobe beam characteristics of the antenna on board the HAPS airship. The expected shielding effect is examined by electromagnetic scattering analysis using the model of 2-D cylindrical conductor with plane
24、wave normal incidence. According to the analysis and its approximation in equation expression, the following shield effect mask could be used for the maximum diameter of HAPS airship body more than 15 m and frequency of signals higher than 20 GHz. 0 dB for 0 90 0.5( 90) dB for 90 1 km and the DCA ma
25、y not be feasible (Fig. 6A a). Signal sensing at HAPS AS could also be very difficult. If the FS system uses TDD or the HAPS system knows one of the pair channels of FS SUB signal in the uplink of the FS system using FDD, the HAPS system can get channel information of FS HUB signal in downlink by se
26、nsing FS SUB signal. Figure 6A b) shows that HAPS GS at Gaand Gccan sense the FS SUB signal, which are almost the same as those giving interference to FS SUB, and that the DCA could be feasible. Almost the same situation takes place in Figure 6B, which shows the result when FS SUB and FS HUB are loc
27、ated at Foand Fa, respectively. HAPS AS may not give interference to both FS HUB and SUB c) in Figs. 6A and B). 1607-06a30252015105002468252015105002468401020304050103020002468FIGURE 6AFS HUB at the location Foand FS SUB at the location Fain Case 1 (Fx= Fa)Raisednoiselevel atHAPSGS/AS(dB)a) Sensing
28、level of FS (Fo) signalDistance d (km)From GaFrom GbFrom GcFrom GdHAPS ASRaisednoiselevel atHAPSGS/AS(dB)b) Sensing level of FS (Fx) signalDistance d (km)From GaFrom GbFrom GcFrom GdHAPS ASI/NatFSstation(dB)c) Interference HAPS GS FS (Fx)Distance d (km)From GaFrom GbFrom GcFrom GdHAPS AS14 Rec. ITU-
29、R F.1607 1607-06b3025201510500246825201510500246820101020304050002468FIGURE 6BFS SUB at the location Foand FS HUB at the location Fain Case 1 (Fx= Fa)Raisednoiselevel atHAPSGS/AS(dB)a) Sensing level of FS (Fo) signalDistance d (km)From GaFrom GbFrom GcFrom GdHAPS ASRaisednoiselevel atHAPSGS/AS(dB)b)
30、 Sensing level of FS (Fx) signalDistance d (km)From GaFrom GbFrom GcFrom GdHAPS ASI/NatFSstation(dB)c) Interference HAPS GS FS (Fx)Distance d (km)From GaFrom GbFrom GcFrom GdHAPS ASb) Case 2 The calculated result in Case 2 is shown in Figs. 7A and 7B when FS SUB or FS HUB is located at Foor Fb. Thes
31、e Figures show the following features: When FS HUB and SUB are located at Foand Fb, respectively (Fig. 7A), FS SUB is interfered by HAPS GS at Gband Gd(Fig. 7A c). However, HAPS GS at Gband Gccan sense the FS SUB signal as long as d 1 km and the DCA may not be feasible (Fig. 7A a). Signal sensing at
32、 HAPS AS could also be very difficult. If the FS system uses TDD or the HAPS system knows one of the pair channels of FS SUB signal in uplink of the FS system using FDD, the HAPS system can get channel information of FS HUB signal in downlink by sensing FS SUB signal. Figure 7A b) shows that HAPS GS
33、 at Gbcan sense the FS SUB signal and also HAPS GS at Gdcan sense it when d 2 km, the off-axis transmitting antenna gain of HAPS GS needs to be reduced by at least about 15 dB or the carrier sensing threshold at HAPS GS needs to be decreased to about 0.3 dB to make DCA available. When FS HUB and SUB
34、 are located at Fband Fo, respectively (Fig. 7B), only HAPS GS at Gbinterferes FS HUB and HAPS GS at Gbcan sense both FS HUB signal and SUB signal. Therefore the DCA could be feasible. HAPS AS may not give interference to both FS HUB and SUB in Figs. 7A c) and B c). 1607-07a3025201510500246815105002
35、46830101020304050002468FIGURE 7AFS HUB at the location Foand FS SUB at the location Fbin Case 2 (Fx= Fb)Raisednoiselevel atHAPSGS/AS(dB)a) Sensing level of FS (Fo) signalDistance d (km)From GaFrom GbFrom GcFrom GdHAPS ASRaisednoiselevel atHAPSGS/AS(dB)b) Sensing level of FS (Fx) signalDistance d (km
36、)From GaFrom GbFrom GcFrom GdHAPS ASI/NatFSstation(dB)c) Interference HAPS GS FS (Fx)Distance d (km)From GaFrom GbFrom GcFrom GdHAPS AS16 Rec. ITU-R F.1607 1607-07b30252015105002468 0246814128642010024681010203040500FIGURE 7BFS SUB at the location Foand FS HUB at the location Fbin Case 2 (Fx= Fb)Rai
37、sednoiselevel atHAPSGS/AS(dB)a) Sensing level of FS (Fo) signalDistance d (km)From GaFrom GbFrom GcFrom GdHAPS ASRaisednoiselevel atHAPSGS/AS(dB)b) Sensing level of FS (Fx) signalDistance d (km)From GaFrom GbFrom GcFrom GdHAPS ASI/NatFSstation(dB)c) Interference HAPS GS FS (Fx)Distance d (km)From Ga
38、From GbFrom GcFrom GdHAPS ASc) Case 3 The calculated result in Case 3 is shown in Figs. 8A and 8B when FS SUB or FS HUB is located at Foor Fc. These Figures show the following features: When the FS SUB and FS HUB are located at Fcand Fo, respectively (Fig. 8A), the FS SUB seriously receives interfer
39、ence from HAPS GS at Gaand Gc(Fig. 8A c). However, only the HAPS GS at Gccan sense the FS HUB signal as long as d 1 km and the DCA may not be feasible (Fig. 8A a). Signal sensing at HAPS AS could also be very difficult. If the FS system uses TDD or the HAPS system knows one of the pair channels of F
40、S SUB signal in uplink of the FS system using FDD, the HAPS system can get channel information of FS HUB signal in downlink by sensing FS SUB signal. Fig. 8A b) shows that HAPS GS Rec. ITU-R F.1607 17 at Gaand Gccan sense the FS SUB signal when d 2 km. Therefore, DCA is feasible when d 2 km, the off
41、-axis transmitting antenna gain of HAPS GS needs to be reduced by at least about 15 dB or the carrier sensing threshold at HAPS GS needs to be decreased to about 0.3 dB to make DCA available. When FS HUB and SUB are located at Fcand Fo, respectively (Fig. 8B), HAPS GS at Gb, Gcand Gdinterfere FS HUB
42、 and HAPS GS at any location can sense both FS HUB signal. Therefore the DCA could be feasible. HAPS AS may not give interference to both FS HUB and SUB in Figs. 8A c) and B c). 1807-08a3525201510503002468151050024682010102030405001502468FIGURE 8AFS HUB at the location Foand FS SUB at the location F
43、cin Case 3 (Fx= Fc)Raisednoiselevel atHAPSGS/AS(dB)a) Sensing level of FS (Fo) signalDistance d (km)From GaFrom GbFrom GcFrom GdHAPS ASRaisednoiselevel atHAPSGS/AS(dB)b) Sensing level of FS (Fx) signalDistance d (km)From GaFrom GbFrom GcFrom GdHAPS ASI/NatFSstation(dB)c) Interference HAPS GS FS (Fx)
44、Distance d (km)From GaFrom GbFrom GcFrom GdHAPS AS18 Rec. ITU-R F.1607 1607-08b40252015105030350246814104012862024681030355202510150502468FIGURE 8BFS SUB at the location Foand FS HUB at the location Fcin Case 3 (Fx= Fc)Raisednoiselevel atHAPSGS/AS(dB)a) Sensing level of FS (Fo) signalDistance d (km)
45、From GaFrom GbFrom GcFrom GdHAPS ASRaisednoiselevel atHAPSGS/AS(dB)b) Sensing level of FS (Fx) signalDistance d (km)From GaFrom GbFrom GcFrom GdHAPS ASI/NatFSstation(dB)c) Interference HAPS GS FS (Fx)Distance d (km)From GaFrom GbFrom GcFrom GdHAPS AS5 Summary The DCA technique to avoid interference
46、from HAPS GS to FS stations in the 31 GHz band could be feasible in most of the patterns of station location in HAPS and FS systems, if HAPS GS have a function of carrier sensing in use by the FS system. The antenna and receiver for carrier sensing in HAPS GS may be shared with those for HAPS commun
47、ication link. It was found that carrier sensing at HAPS AS is not practical when HAPS GS could interfere FS stations. It was also found that there are some cases that HAPS GS cannot sense the FS signal and it interferes to the receiver in FS station. The interference could be avoided by using improv
48、ed antenna pattern in HAPS GS with low side and back lobes by at least 15 dB or by decreasing the carrier sensing threshold to about 0.3 dB. This carrier sensing threshold could be increased and relaxed if the side and back lobes of the antenna pattern in HAPS GS is raised by several dB. HAPS AS may not give serious interference to both FS HUB and SUB in any location scenario, so that sharing is feasible between them without special techniques.
