1、 Rec. ITU-R M.1800 1 RECOMMENDATION ITU-R M.1800 Protection of the fixed, mobile and radiolocation services from MSS feeder links that may operate in the bands 1 390-1 392 MHz (Earth-to-space) and 1 430-1 432 MHz (space-to-Earth)*(2007) Scope This Recommendation provides protection requirements for
2、ground-based receivers of the radiolocation service with respect to MSS feeder links (Earth-to-space) that may operate in the band 1 390-1 392 MHz as well as protection requirements for the fixed and the aeronautical mobile service with respect to MSS feeder links (space-to-Earth) that may operate i
3、n the band 1 430-1 432 MHz. The ITU Radiocommunication Assembly, considering a) that WRC-03 made a provisional allocation on a secondary basis to the FSS for MSS feeder links through RR No. 5.339A in the bands 1 390-1 392 (Earth-to-space) and 1 430-1 432 MHz (space-to-Earth); b) that these allocatio
4、ns are limited to use by feeder links for non-geostationary-satellite networks in the mobile-satellite service with service links below 1 GHz, and Resolution 745 (WRC-03) applies; c) that Resolution 745 (WRC-03) calls for studies, tests and demonstrations to validate the studies on operational and t
5、echnical means to facilitate sharing around 1.4 GHz between existing and currently planned services and FSS feeder links for use by non-GSO satellite systems in the MSS with service links operating below 1 GHz; d) that the band 1 427-1 452 MHz is allocated to the fixed service (FS) and the mobile se
6、rvice (MS) on a primary basis in all Regions; e) that this band is used, amongst others, by low-capacity digital FS links with channel bandwidths as low as 25 kHz; f) that the band 1 429-1 535 MHz is also allocated to the aeronautical mobile service (AMS) on a primary basis exclusively for the purpo
7、ses of aeronautical telemetry within the national territory of countries identified in RR (Radio Regulations) No. 5.342; g) that the protection criteria and typical system characteristics of aeronautical telemetry in the band 1 429-1 535 MHz fully comply with the protection criteria and system chara
8、cteristics presented in Recommendation ITU-R M.1459 for the band 1 452-1 525 MHz; *This Recommendation was jointly prepared by Radiocommunication Study Groups 8 and 9 and any future revision will also be undertaken jointly. 2 Rec. ITU-R M.1800 h) that the band 1 350-1 400 MHz is allocated to the rad
9、iolocation service on a primary basis in all Regions; j) that studies have shown that large separation distances would be required for the protection of ground-based radiolocation systems as shown in Annex 2; k) that Recommendation ITU-R M.1184 provides technical characteristics of mobile-satellite
10、systems in frequency bands below 3 GHz for use in developing criteria for sharing between the MSS and other services, noting a) that studies have shown that sharing would not be feasible with ship-borne and transportable radiolocation systems; b) that studies have shown that sharing would not be fea
11、sible with aeronautical radiolocation systems; c) that the pfd limit recommended for protection of the FS is also adequate for the protection of transportable radio-relay systems which are operated under the MS by some administrations, recommends 1 that, in order to protect FS receivers in the band
12、1 427-1 452 MHz, MSS feeder links operating in the band 1 430-1 432 MHz (space-to-Earth) should not exceed a pfd value of 164 dBW/m2in any 4 kHz in the band 1 427-1 452 MHz (see Annex 1); 2 that, in order to protect AMS receivers in the band 1 429-1 535 MHz, MSS feeder links operating in the band 1
13、430-1 432 MHz (space-to-Earth) should not exceed the following pfd values at any aeronautical mobile receiving station in any 4 kHz in the band 1 429-1 535 MHz: 181 dB(W/m2) 0 4 193 +20 log dB(W/m2) 4 20 213.3 + 35.6 log dB(W/m2) 20 60 150 dB(W/m2) 60 90 where: : angle of arrival (in degrees above t
14、he horizon plane). 3 that the methodology in Annex 2 be taken into account when selecting the location of FSS earth stations in the range 1 390-1 392 MHz, in order to compute separation distances between FSS stations and ground-based radiolocation systems. Annex 1 Protection of the fixed service in
15、the band 1 430-1 432 MHz 1 Derivation of a pfd mask for the protection of FS receivers in the 1.4 GHz band Simulations were conducted to assess the interference generated by one single representative non-GSO MSS constellation with a given pfd limit in a fixed service receiver located on the Earth. S
16、imulation results are expressed in terms of fractional degradation in performance (FDP), described in Recommendation ITU-R F.1108, for azimuths 0 to 180 with a step of 1. Rec. ITU-R M.1800 3 This FDP is then compared to a criterion. If this criterion is exceeded, the pfd limit is tightened, and the
17、simulation is run again until the criterion is respected. 2 MSS system characteristics Several MSS system descriptions of the “little LEO” type can be found in Recommendation ITU-R M.1184. Table 1 shows the MSS systems and relevant characteristics extracted from this Recommendation. In line with rec
18、ent developments and studies within the relevant ITU-R working parties, the number of satellites for the “Q” constellation was reduced from five satellites per plane to four, and the total number of satellites from 32 to 26. The inclination angles were increased from 51 to 66. TABLE 1 Parameters of
19、several non-GSO MSS networks System L M P Q S Number of satellites 48 48 6 26 (32) 6 Altitude (km) 950 825 775 893 1 000 692, 667 Inclination (degrees) 50 45 0 70, 108 99 66 (51) 83 98.04 Orbit planes 8 3 1 2 2 6 2 2 Satellite/plane 6 8 3 4 (5) 1 3 Right ascension of ascending node (degrees) 0, 45,
20、90, 135, 180, 225, 270, 315 0, 120, 240 0 0, 180 9.8 0, 60, 120, 180, 240, 300 0, 90 143.5, 53.5 Channel bandwidth for gateway downlinks (kHz) 60 50 855 175/45 300 Polarization (Tx wave) RHCP LHCP RHCP RHCP 3 FS station characteristics and protection criterion Table 2 hereafter lists the characteris
21、tics of point-to-multipoint links from Recommendation ITU-R F.758. 4 Rec. ITU-R M.1800 TABLE 2 Point-to-multipoint system characteristics Frequency band (GHz) 1.427-1.452/1.492-1.517 Modulation O-QPSK Capacity 60 64 kbit/s Channel spacing (MHz) 3.5 Central station/repeater Out station Antenna gain (
22、maximum) (dBi) 13 16 31 23.5 17 Feeder/multiplexer loss (dB) 4.4 2.5 Antenna type Omni Sectoral 180 Dish (3 m) Dish (1.2 m) Panel Receiver IF bandwidth (MHz) 3.5 3.5 Receiver thermal noise (dBW) 134 134 The FS receiver corresponding to the worst case is a directional central station with a maximum a
23、ntenna gain of 31 dBi, a feeder/multiplexer loss of 4.4 dB, a bandwidth of 3.5 MHz and a 4.5 dB noise figure. A worst-case elevation angle of 5 is also considered. Recommendation ITU-R F.1245 was used to model the antenna pattern of the directional central station. According to Recommendation ITU-R
24、F.1094, the maximum allowable performance degradation should be divided into 89% for the fixed service, 10% for sharing with primary services, and 1% for all other sources of interference, including secondary services and unwanted emissions. In this case, the FDP must therefore stay below the value
25、of 1%, at least on average overall azimuth pointing angles. 4 Simulation results Table 3 gives the results obtained for the MSS constellations given in Table 1. The pfd value taken in the simulation is given in row 3, which leads to the FDP values given in rows 4, 5 and 6. Figures 1 and 2 give as an
26、 example more details on the FDP values obtained for system Q. TABLE 3 Simulation results for several non-GSO MSS networks System Q L M P S Number of satellites 26 48 48 6 6 Altitude (km) 1 000 950 800 900 700 Pfd to comply with an FDP of 1% (dBW/m2in 4 kHz) 163 164 164 156 155 FDP min. (%) 0.27 0.0
27、5 0.40 0.15 0.15 FDP avg. (%) 0.85 0.95 0.86 0.83 0.86 FDP max. (%) 3.08 4.61 2.39 1.80 1.72 Rec. ITU-R M.1800 5 FIGURE 1 FDP for all FS pointing azimuths for MSS system Q FIGURE 2 FDP distribution for all FS pointing azimuths for MSS system Q 6 Rec. ITU-R M.1800 Annex 2 Protection of ground-based r
28、adiolocation receivers operating in the band 1 390-1 392 MHz 1 Technical characteristics of radiolocation receivers Radiolocation receiver characteristics used in this study have been obtained from Recommendation ITU-R M.1463. This Recommendation describes four different systems in the band of 1 215
29、-1 400 MHz. The radars operating in the 1 215-1 400 MHz band use a variety of modulation schemes including continuous wave (CW) pulses, frequency modulated (chirped) pulses and phase coded pulses. Cross-field, linear beam and solid state output devices are used in the final stages of the transmitter
30、s. Typical receiver bandwidths of radars operating in the 1 215-1 400 MHz band range from 0.5 to 6.4 MHz. 2 Protection criteria The desensitizing effect on radiolocation radars from other emissions of a CW or noise-like type modulation is predictably related to its intensity. In any azimuth sectors
31、in which such interference arrives, its power spectral-density can, to within a reasonable approximation, simply be added to the power spectral-density of the radar receiver thermal noise. If power spectral-density of radar-receiver noise in the absence of interference is denoted by N0and that of no
32、ise-like interference by I0, the resultant effective noise power spectral-density becomes simply I0+ N0. An increase of about 1 dB would constitute significant degradation, equivalent to a detection-range reduction of about 6%. Such an increase corresponds to an (I + N)/N ratio of 1.26, or an I/N ra
33、tio of about 6 dB (see recommends 3 of Recommendation ITU-R M.1463). This represents the aggregate effect of multiple interferers, when present; the tolerable I/N ratio for an individual interferer depends on the number of interferers and their geometry, and needs to be assessed in the course of ana
34、lysis of a given scenario. If CW interference were received from most azimuth directions, a lower I/N ratio would need to be maintained. 3 Technical characteristics of MSS feeder-link earth stations The MSS Earth-to-space feeder-link characteristics used for this study are described in Table 4. Feed
35、er-link characteristics are based on Annex 2 of Recommendation ITU-R M.1184. The pattern shown in Fig. 3 illustrates the gain envelope of the MSS earth station antenna. This pattern is taken from Appendix 8, Annex III of the Radio Regulations. Gain values are obtained considering a ratio between the
36、 antenna diameter and the wavelength of D/ 100. Rec. ITU-R M.1800 7 TABLE 4 Earth-to-space feeder-link characteristics Parameter Value Number of earth stations 60 Earth station locations Distributed throughout the world Transmit antenna peak gain 30 dBi 3 dB beamwidth 5 Gain floor 1.5 dBi Antenna pa
37、ttern RR Appendix 8, Annex III Antenna polarization Right hand circular Antenna pointing Tracks nearest satellite at elevations between 5 and 90 Transmit power 10 W per 100 kHz FIGURE 3 MSS earth station receive and transmit antenna pattern 4 Study considerations and assumptions This study assumes a
38、 receiver reference bandwidth of 100 kHz. A transmitting MSS feeder uplink station may cause interference to a receiving ground-based radiolocation system if the separation distance between these systems is not sufficient. This distance is a function of several parameters. The following assumptions
39、have been made in this study: 8 m of effective antenna height over ground for the MSS stations. 10 m of effective antenna height over ground for the radar station. For the MSS feeder uplink station antenna, it has been assumed that the antenna is pointing in the direction of the radiolocation receiv
40、er with a minimum transmission elevation angle of 5. Radio climatic zone A2, propagation over land, has been considered. Propagation paths over the sea will require higher separation distances. Calculations are based on a latitude of 45. 8 Rec. ITU-R M.1800 Regarding percentage of time that such a l
41、evel may be exceeded, 0.1% is considered appropriate. Assuming pointing of the radar antenna main lobe towards the MSS earth station, it is considered that any interference received by the radar receiver will be seen as a target and therefore can be considered as harmful interference. 5 Permissible
42、interference power level for radar systems The first step is to determine the permissible interference power level that radar systems can afford without losses in their performance. This procedure is described in Recommendation ITU-R M.1461-1. Equation (1) allows to determine the interference power
43、level at which the radar receiver performance starts to degrade, IT. IT= I/N + N (1) where: I/N: interference-to-noise ratio at the detector input necessary to maintain acceptable performance criteria, equal to 6 dB in this case N: receiver inherent noise level (dBW) N = 144 dBW + 10 log B (MHz) + N
44、F where: B: receiver bandwidth (MHz) NF: receiver noise figure (dB). Assuming an interference-to-noise ratio 6 dB below its threshold level and a receiver reference bandwidth of 100 kHz, the results for the four radar systems are shown in Table 5. TABLE 5 Permissible interference power level for rad
45、ar systems Radar system (Recommendation ITU-R M.1463) 1 2 3 4 Noise factor NF (dB) 2 2 4.7 3.5 Noise level N (dBW/100 kHz) 152 152 149.3 150.5 Permissible interference IT (dBW/100 kHz) 158 158 155.3 156.5 6 Computation of the separation distance Interference to a radiolocation receiver may arise thr
46、ough a range of propagation mechanisms whose individual dominance depends on climate, radio frequency, time percentage, distance and path topography. The required separation distance is to a major extent a function of the actual transmitter and receiver antenna gains. In addition to the free space l
47、oss, interfering signals are attenuated by path obstacles and diffraction due to the Earths curvature. Besides direct paths and propagation by diffraction, there exist additional propagation mechanisms, such as troposcatter and layer refraction (ducting), which can cause interference to the radioloc
48、ation receivers. Rec. ITU-R M.1800 9 The procedure for the evaluation of microwave interference between stations on the surface of the Earth at frequencies above about 0.7 GHz is considered in Recommendation ITU-R P.452. The underlying mathematical models are quite complex and can only be addressed
49、at high level in this Recommendation. The key equation for the required basic transmission loss is given by: )()( pIGGPpLTrttb+= (dB) (2) where: p: maximum percentage of time for which the permissible interference power may be exceeded Lb(p): minimum required loss (dB) for p% of the time; this value must be exceeded by the predicted path loss for all but p% of the time. This is the basic transmission loss taken as the reference level (0 dB) in the plots of Figs. 5 to 8 Pt: maximum available transmitting power
