1、 Rec. ITU-R RS.1259 1 RECOMMENDATION ITU-R RS.1259*FEASIBILITY OF SHARING BETWEEN SPACEBORNE PASSIVE SENSORS*AND THE FIXED SERVICE FROM 50 TO 60 GHz (Question ITU-R 216/7) (1997) Rec. ITU-R RS.1259 The ITU Radiocommunication Assembly, considering a) that unique atmospheric oxygen bands are located a
2、round 50 to 65 GHz allowing “all weather” monitoring of the Earths atmosphere on a worldwide scale; b) that measurements of temperature at different heights in the atmosphere using spaceborne passive sensors are vital for weather forecasts and climate studies (such as “global change”); c) that a sma
3、ll number of undetected interference events can have an extremely detrimental effect on numerical weather prediction; d) that measurements of sufficient accuracy can only be obtained in precise frequency sub-bands from around 50 to 60 GHz dictated by the physical processes of oxygen spectroscopy; e)
4、 that the World Radiocommunication Conference (Geneva, 1997) (WRC-97) Agenda item 1.9.4.3 concerns existing frequency allocations near 60 GHz and, if necessary, their re-allocation to protect Earth exploration-satellite service (EESS) (passive) systems; f) that around 55 GHz, temperature “sounding”
5、is highly sensitive to interference from terrestrial sources; g) that the frequency bands 50.2-50.4 GHz and 54.25-58.2 GHz are shared on a co-primary basis between spaceborne passive sensors and the fixed service; h) that the preferred frequencies and necessary bandwidths for satellite passive sensi
6、ng are contained in Recommendation ITU-R RS.515; j) that extensive sharing studies have been carried out as summarized in Annex 1; k) that restrictions would be required on the operation of fixed links in the band 55.2-55.78 GHz, as detailed in Annex 1; l) that due to the high vulnerability of passi
7、ve temperature soundings to interference, the strict compliance of the restrictions in the band 55.2-55.78 GHz on a worldwide basis would be vital for adequate protection of passive sensors; m) that the enforcement on a worldwide basis of a strict compliance with the required restrictions would not
8、be practicable, recommends 1 that sharing between spaceborne passive sensors and the fixed service is feasible between 55.78 GHz and 60 GHz; 2 that sharing between spaceborne passive sensors and the fixed service is not practicable between 50 GHz and 55.78 GHz and that spaceborne passive sensors and
9、 the fixed service not operate in the same frequency band within this range. _ *Radiocommunication Study Group 7 made editorial amendments to this Recommendation. *Throughout this Recommendation, “spaceborne passive sensors” includes sensors on board satellites operating in the Earth exploration-sat
10、ellite (passive) and space research (passive) services, since the characteristics of these two services are essentially identical throughout the frequency bands under consideration. 2 Rec. ITU-R RS.1259 ANNEX 1 Sharing between the fixed service and passive remote sensors in the range 50.2-58.2 GHz 1
11、 Introduction The fixed service and the Earth exploration-satellite (EES) passive and space research (passive) services have co-primary allocations in the bands 50.2-50.4 GHz and 54.25-58.2 GHz. The purpose of this Annex is to review the suitability of these allocations and, where necessary, to deve
12、lop limitations to be applied to the fixed service to ensure adequate protection of passive remote sensors. The oxygen absorption in the frequency ranges of interest varies considerably, with a large number of absorption lines, around 60 GHz. The level of absorption used in the sharing studies has b
13、een calculated from Recommenda-tion ITU-R P.676. It will be shown that the level of absorption has an important effect on the feasibility of sharing. Figure 1 shows the total absorption on a vertical path from Earth-to-space. The absorption on the ground-space path is reduced as the height of ground
14、 above sea level is increased. Fixed link transmitters could operate from locations at a range of altitudes. Throughout this Annex, as a conservative estimate, it is assumed that fixed service transmitters are at 1 000 m above sea level. At the relatively high frequencies of interest here, indirect
15、propagation effects can be a significant propagation mechanism. As a worst case representative of indirect propagation mechanisms, the studies have considered reflection from building roof tops. 2 Fixed links In some countries, fixed links have been operated in the bands 50.2-50.4 GHz and 57.2-58.2
16、GHz. The maximum transmitter power currently achievable is around 17 dBW. The sharing parameters of the fixed service have been derived from details of those systems in current use. To allow for future advances in microwave technology, a transmitter power higher than that currently achievable has be
17、en assumed. In the initial sharing analysis, the following parameters in Table 1 of fixed links have been used. TABLE 1 Fixed service sharing parameters 3 Passive sensors 3.1 Current and future systems Several organizations are currently operating or developing passive sensors which operate in the b
18、ands around 55 GHz. These sensors use a mechanically scanning design. The next generation of passive sensor are likely to utilize a pushbroom scanning concept which allows improved radiometric and spatial resolution. The pushbroom type sensor is not expected to be used before 2005. Transmitter power
19、 (dBW) 10 Minimum bandwidth (MHz) 14 Feeder loss (dB) 0 Antenna gain (dBi) : boresight 41 90off boresight 10 Antenna elevation angle (degrees) 0 Antenna height above sea level (m) 1 000 Rec. ITU-R RS.1259 3 1259-0150525456586062646668700 km510 150 km 510 15202030020010050 20 105 2 1 0.50.20.1FIGURE
20、1Zenithoxygenabsorptionfor someinitial heightsFrequency,f(GHz)Z e n i t h at te n u at io n (d B )FIGURE 1259-01 = 20 CM PAGE PLEINE 4 Rec. ITU-R RS.1259 3.2 Sharing parameters The pushbroom type of sensor will be more susceptible to interference than the mechanically scanning type used on current s
21、ensors. Therefore, a hypothetical pushbroom sensor has been assumed in the studies. The parameters are given in Table 2. TABLE 2 Passive sensor sharing parameters 3.3 Interference criterion Recommendation ITU-R RS.1029 describes the interference criteria for satellite passive remote sensors. For pus
22、hbroom sensors operating in the range 50 to 66 GHz, the permissible interference level is 166 dBW in a reference bandwidth of 100 MHz. Because of the significant effect of any interference for the users of the data obtained in these bands, the sharing studies below are on the basis of the limit bein
23、g exceeded in no measurement cells. 4 Sharing analysis 4.1 Preliminary analysis If one assumes that fixed links will operate with an antenna elevation angle of around 0, the worst case direct interference path is the zenith path from fixed link-to-satellite, as shown in Fig. 2. 1259-02FIGURE 2Worst
24、case direct interference pathFIGURE 1259-02 = 8 CM Antenna diameter (cm) 45 3 dB beamwidth (degrees) 1.1 Scanning limits (degrees) 50 (cross track) Antenna gain (dBi) 45 Radiometric resolution (K) 0.1 Swath width (km) 2 300 Pixel size (nadir) (km) 16 diameter Number of pixels/line 90 Orbit altitude
25、(circular) (km) 850 Orbit inclination (sun-synchronous) (degrees) 98.8 Rec. ITU-R RS.1259 5 The oxygen absorption on the zenith path, from an initial height of 1 000 m, varies from 1.3 dB at 50.2 GHz to more than 100 dB at 58.2 GHz. The bands considered in this paper are divided into a number of slo
26、ts (as shown in Table 3), defined by the limits of the shared frequency bands and the peaks in the zenith absorption. In each slot, the minimum atmospheric absorption is used to determine the maximum vertically radiated power from the Earth, and hence the maximum number of co-channel interferers. TA
27、BLE 3 Maximum number of co-channel transmitters To determine the feasibility of sharing, one must consider the likelihood of the number of co-channel fixed link transmitters within any 16 km diameter pixel, and within a 15 MHz bandwidth, exceeding the figures given in Table 3. In slots 1 and 2, a hi
28、gh level of interference could be caused by a single transmitter. Thus, sharing appears to be unfeasible. In slot 3, only a few co-channel transmitters would be required to exceed the interference threshold and thus sharing appears to be unfeasible. In slot 4, a reasonable number of fixed links coul
29、d operate, especially if lower transmitter powers were used. In slots 5-8, extremely large numbers of fixed links could operate and thus sharing appears to be feasible. Slot No. 1 2 3 4 5 6 7 8 Frequency range (GHz) 50.2-50.4 54.25-54.67 54.67-55.22 55.22-55.78 55.78-56.26 56.26-56.36 56.36-56.96 56
30、.96-57.20Fixed link maximum transmitter power (dBW) 10 10 10 10 10 10 10 10 Fixed link antenna gain (zenith) (dBi) 10 10 10 10 10 10 10 10 Fixed link maximum e.i.r.p. to zenith (dBW) 20 20 20 20 20 20 20 20 Frequency of absorption minimum (GHz) 50.2 54.25 54.74 55.31 55.89 56.29 56.57 57.19 Satellit
31、e altitude (km) 850 850 850 850 850 850 850 850 Free space loss (dB) 185.0 185.7 185.8 185.9 186.0 186.0 186.1 186.2 O2absorption from 1 000 m (dB) 1.3 12.8 20.3 32.2 50.5 79.3 71.1 86 Sensor antenna gain (dBi) 45 45 45 45 45 45 45 45 Sensor channel bandwidth (MHz) 15 15 15 15 15 15 15 15 Interferen
32、ce threshold in 100 MHz 166.0 166.0 166.0 166.0 166.0 166.0 166.0 166.0 Threshold density (dB(W/15 MHz) 174.2 174.2 174.2 174.2 174.2 174.2 174.2 174.2 Maximum e.i.r.p. from ground (dB(W/15 MHz/pixel) 32.9 20.7 13.1 1.2 17.2 46.1 37.9 52.9 Transmitted vertical e.i.r.p. per fixed link (dB(W/15 MHz) 1
33、9.7 19.7 19.7 19.7 19.7 19.7 19.7 19.7 Margin (dB) 13.2 1.0 6.6 18.5 36.9 65.8 57.6 72.6 Maximum fixed links per sensor channel per pixel 0 0 4 71 4 940 3 801 943 581 186 18 356 2226 Rec. ITU-R RS.1259 To more accurately determine the feasibility of sharing in the band 55.22-55.78 GHz, a more detail
34、ed sharing study is presented in 4.2. 4.2 Detailed sharing analysis in the band 55.2-55.78 GHz This section provides more detailed consideration on the transmitter power of fixed links, the maximum achievable density of links, indirect propagation effects and the effect of the fixed link antenna ele
35、vation angle above 0. The band can be considered as 55.20-55.78 GHz since the zenith absorption minimum is the same for the band 55.22-55.78 GHz. 4.2.1 Maximum fixed link power The existing fixed link channel plan for this band given in Recommendation ITU-R F.1100 covers 54.25-57.2 GHz, so a revised
36、 theoretical plan was used. This was based on 55.2-57.2 GHz with a 68.5 MHz lower guard band, a 70 MHz centre gap and a duplex spacing of 966 MHz. Fixed link bands are arranged in two halves, so that a “go” channel in the lower half is always associated with a “return” channel in the upper half. Lin
37、k budget calculations based on typical equipment parameters show that a power level of _10 dBW results in an upper limit of 2 km on link length, due to the high level of attenuation in the upper half of the band. The transmitter power required to cover this distance in the lower half of the band is
38、23.2 dBW (if 3 dB is allowed for feeder losses at each end), due to the reduced attenuation. Figure 3 shows the required transmitter power for various link lengths. 1259-0301234FIGURE 3Transmitter power against link lengthLink length (km)0.5 1.5 2.5 3.5Transmitter power(dBW)Low channelHigh channel 5
39、0.0 40.0 30.0 20.0 10.00.010.020.0FIGURE 1259-03 = 11.5 CM 4.2.2 Maximum fixed link density A simulation has been performed to determine the theoretical maximum number of fixed links that could be accommodated in a 16 km diameter pixel. The only criteria used were based on interference to and from n
40、eighbouring fixed links. This modelled the situation where users might install links without regard to any imposed density limits. Rec. ITU-R RS.1259 7 4.2.2.1 Simulation methodology The positions, lengths and directions of the links were chosen at random but bound by a maximum link length of 2 km.
41、The simulation used a free space path loss propagation model. The interference threshold for a single interferer was an I/N ratio of 10 dB. The simulation placed links in the test area, each time checking the interference to and from every other link, assigning the new link when the interference lev
42、els were below the threshold, and failing the link when the interference levels were above the threshold. This continued until a predetermined number of consecutive assignment failures occurred. At this point it was considered that the practical maximum link density for the test area had been reache
43、d as far as link-to-link interference is concerned. The allowed number of failures was set to 20 and the simulation was run several times. In each case the number of fixed links allocated in the test area was between about 100 and 120 successful assignments. Figure 4 is a graphical representation of
44、 how one run of the simulation successfully assigned one hundred links in the test area. 1259-04088 8 8FIGURE 4100 links randomly allocated in test area Low channel transmissionHigh channel transmissionFIGURE 1259-04 = 13.5 CM A band in which 20 out of 21 attempted assignments failed would be regard
45、ed as full. Thus an estimated figure of around 150 would appear as the maximum theoretical link density for bidirectional links of this type in the test area. This estimation is supported by Fig. 4 which shows that there is hardly any room in the test area for many more in-band transmitters once 100
46、 have already been assigned. In practice, even this figure would be very difficult to achieve in a real world assignment situation. Links tend to cluster around town centres, hence congestion limits would be reached here while other areas of the pixel were relatively empty. Further reductions in the
47、oretical density would come from: co-channel links outside the pixel, adjacent channel links, nodal deployment of links. 8 Rec. ITU-R RS.1259 4.2.2.2 Derivation of limits One can consider 150 to be a conservative estimate of the maximum density of co-channel fixed links. The maximum e.i.r.p. from th
48、e ground is 1.2 dB(W/15 MHz/pixel) (from Table 3). Dividing this figure by 150 and scaling to various bandwidths gives the limits in Table 4. TABLE 4 Maximum vertical e.i.r.p. By applying this vertical e.i.r.p. limit to each fixed link transmitter in the band 55.2-55.78 GHz, and bearing in mind the
49、maximum conceivable number of co-channel transmitters is 150, one can be sure that such a limit would ensure that interference by direct propagation would not exceed the sensor threshold, and would allow unhindered operation of fixed links. 4.2.3 Indirect propagation effects As a representative worst case indirect propagation effect, a rooftop reflection as illustrated in Fig. 5 is considered. The roof is assumed to have an elevation of 45 and the normal of the roof and the inc
