1、Rec. ITU-R F.1246 1RECOMMENDATION ITU-R F.1246*REFERENCE BANDWIDTH OF RECEIVING STATIONS IN THE FIXED SERVICETO BE USED IN COORDINATION OF FREQUENCY ASSIGNMENTS WITHTRANSMITTING SPACE STATIONS IN THE MOBILE-SATELLITESERVICE IN THE 1-3 GHz RANGE(Questions ITU-R 201/8 and ITU-R 118/9)(1997)Rec. ITU-R
2、F.1246The ITU Radiocommunication Assembly,consideringa) that several frequency bands in the 1-3 GHz range are shared between the mobile-satellite (space-to-Earth)service and the fixed service (FS);b) that networks in the mobile-satellite service (MSS) will generally use digital modulation and freque
3、ncydivision multiple access (FDMA), time division multiple access (TDMA) or code division multiple access (CDMA)access techniques, which will result in relatively uniform spectral shape in the allocated bandwidth of the MSS carrier;c) that most MSS networks, according to Radio Regulation (RR) Append
4、ix 4 data, use narrow-band modulationtechniques such that several channels in these networks could be encompassed in a 1 MHz reference bandwidth forsystems in the FS and that these channels are also usually subject to voice activated channel loading and active powercontrol in order to reduce the eff
5、ective power resource requirements on the MSS satellite;d) that in order to accommodate the worst potential case for interference to the FS, coordination threshold levelsof power flux-density have been specified in Recommendations ITU-R IS.1141 (Geneva, 1995) and ITU-R IS.1142(Geneva, 1995) for 4 kH
6、z reference bandwidth;e) that use of a relatively large reference bandwidth for receivers in the FS enables consideration of the actualtypes of digital modulation and access schemes used for space-to-Earth transmissions from space stations in the MSS,which can reduce the effective level of expected
7、interference;f) that digital systems should generally be used as the reference model for interference calculations in the1-3 GHz range,recommends1 that a 1 MHz reference bandwidth should be used for analogue and digital systems in the FS for coordinationthresholds of power flux-density and fractiona
8、l degradation in performance of MSS systems in the MSS space-to-Earthallocations in the 1-3 GHz range (see Notes 1, 2, 3 and 4);2 that a 4 kHz reference bandwidth should be also used for analogue FDM-FM systems in the FS forcoordination thresholds of power flux-density for MSS systems in the MSS spa
9、ce-to-Earth allocations in the 1-3 GHzrange (see Notes 1, 3 and 4).NOTE 1 The reference bandwidths in 1 and 2 form a basis of the coordination threshold values of powerflux-density and fractional degradation in performance recommended in Recommendations ITU-R M.1141 andITU-R M.1142.NOTE 2 Use of a 1
10、 MHz reference bandwidth is consistent with the protection of digital systems (see Annex 1)._*This Recommendation was developed jointly by Radiocommunication Study Groups 8 and 9, and any future revision will also beundertaken jointly.2 Rec. ITU-R F.1246NOTE 3 In cases where MSS carrier spectrum is
11、uniform across its occupied bandwidth and is not highly concentratedin any narrow spectral range within the reference bandwidth, use of a 1 MHz reference bandwidth is generally consistentwith protection of analogue systems (see Annex 1).NOTE 4 Use of both a 1 MHz and 4 kHz reference bandwidth would
12、be consistent with the protection of analogueFDM-FM systems, since the use of the 4 kHz reference bandwidth limits the peak power spectral density of narrow-bandinterfering MSS carriers.If the coordination threshold applicable to a 1 MHz reference bandwidth is X dB(W/m2), the additional coordination
13、threshold appropriate for a 4 kHz reference bandwidth is X 18 dB(W/m2) (see Annex 1). For analogue systems inthe FS carrying television, it is not necessary to apply the coordination threshold employing a 4 kHz referencebandwidth.This new approach of employing both 1 MHz and 4 kHz reference bandwidt
14、hs in specifying coordination thresholdlevels is applicable only to the frequency bands in the 1-3 GHz range shared by the MSS and the FS. This result is basedon the fact that the analogue systems in the FS in these bands are generally used for low to medium capacity of960 channels or less. This new
15、 approach is not appropriate for other frequency bands where high-capacity analogueradio-relay systems are employed. (The power flux-density limit for the fixed-satellite service in the 6 825-7 075 MHzband also adopts both 1 MHz and 4 kHz reference bandwidths (see RR Table S21-4), but it was decided
16、 on the basis of areason which is outside the scope of this Recommendation.)NOTE 5 Annex 2 contains information on the characteristics of digital narrow-band MSS carriers and the benefits theuse of a 1 MHz reference bandwidth would have in the coordination of MSS satellite networks with fixed networ
17、ks.Detailed information concerning the spectral characteristics of MSS carriers operating in the space-to-Earth direction inthe 1-3 GHz range can be found in RR Appendix 3 data filed with the Radiocommunication Bureau for planned MSSnetworks.ANNEX 1Reference bandwidth for systems in the fixed servic
18、e in frequencysharing with the mobile-satellite service1 IntroductionRecommendations ITU-R M.1141 and ITU-R M.1142 contain coordination thresholds for systems in the fixed service infrequency sharing with the MSS. The World Radiocommunication conference (Geneva, 1995) (WRC-95) incorporatedthese coor
19、dination thresholds into the revised RR.This Annex provides some comments on the reference bandwidth adopted in the above ITU-R Recommendations.2 Reference bandwidth for digital systems in the FSRecommendation ITU-R IS.1141 (Geneva, 1995) adopts a 1 MHz reference bandwidth for defining fractionaldeg
20、radation in performance (FDP) of digital systems in the FS with respect to frequency sharing with non-geostationary-satellite orbit (GSO)/MSS space stations (except for the band 2 483.5-2 500 MHz). However, Recommen-dation ITU-R IS.1142 (Geneva, 1995) adopts a 4 kHz reference bandwidth for defining
21、the coordination thresholds, interms of power flux-density, for digital systems in the FS with respect to frequency sharing with GSO/MSS spacestations.The above inconsistency should be resolved. In general, it seems adequate to adopt the 1 MHz reference bandwidth toprotect digital FS systems.Rec. IT
22、U-R F.1246 3In some applications, digital FS systems may employ a relatively small bandwidth and such systems may prefer asmaller reference bandwidth. But attention should be drawn to the fact that MSS systems generally operate in digitalmodulation (e.g. QPSK) in which spectra are uniform over a cer
23、tain bandwidth. Therefore, even if a 1 MHz referencebandwidth is adopted, there is little danger in protecting digital FS systems with a smaller bandwidth.3 Reference bandwidth for analogue systems in the FS3.1 Interference assessment in case of two interference entriesTraditionally, a 4 kHz referen
24、ce bandwidth has been adopted for specifying sharing criteria for analogue FS systems. Itis particularly appropriate in specifying sharing criteria for high-capacity analogue radio-relay systems. However, in the1-3 GHz range, analogue FS systems are generally of medium or low capacity. In such case,
25、 the effect of interference isless than that in case of high-capacity systems, because a greater energy dispersion effect through the FM demodulationprocess can be expected at a lower capacity.In order to estimate such effect, calculations were made for a FS radio-relay system carrying 960 channel t
26、elephony(baseband: 60-4 028 kHz). The 960 channel capacity was chosen for the calculations because it is the highest capacitygenerally used in the 1-3 GHz range, thus representing a worst case analysis. The interference was assumed to be asshown in Fig. 1, that is, two interference signals (each wit
27、h bandwidth of BI) appear with the centre frequenciesfc+ fhand fc fhwhere fcis the radio carrier frequency and fhis the highest baseband frequency. The calculation methodis presented in Appendix 1 to Annex 1.1246-01BIfc fhBIfc+ fhfcFIGURE 1Interference situationfc: carrier frequency of the FS system
28、fh: highest baseband frequency of the FS systemBI: bandwidth of the interference signalFIGURE 1-1246.D1246-01 = 3 CMThe results are shown in Fig. 2. BI= 8 MHz corresponds to the case of an interfering signal of very wide bandwidth(similar to thermal noise). The baseband interference level at fh(= 4
29、028 kHz) for BI= 8 MHz is taken as 0 dB. Thebaseband interference in the range of 2-4 MHz is almost constant due to pre-emphasis effect.4 Rec. ITU-R F.12461246-0250 5 10 15 200123 4BI(MHz) = 8 4 2 1 0.5 0.25FIGURE 2Baseband interference distribution for interference signals of various bandwidth(960
30、channel analogue radio-relay system)Interferenceatbaseband (dB)Baseband frequency (MHz)FIGURE 2-1246.D1246-02 = 3 CMCalculations were made for BI= 8, 4, 2, 1, 0.5 and 0.25 MHz. The interference level at fhbecomes lower at smaller BI.This is because of dispersion effect of the analogue radio-relay sy
31、stem. If there is no such dispersion effect, the basebandinterference level should be as follows: no interference for the band from 0 to fh BI/2; almost 0 dB interference for the band from fh BI /2 to fh.This situation will apply only to high-capacity radio-relay systems employing a very small modul
32、ation index. However,in the case of 960 channel systems, the situation is different.For example, in case of BI= 500 kHz, the interference level at fhis 2.5 dB.In some sense, the situation in Fig. 1 is of a worst case. This is because it is assumed that two interfering signals appearsymmetrically in
33、two sides of the FS carrier frequency. If the interfering signal in one side disappears, the basebandinterference level will be 3 dB lower.Rec. ITU-R F.1246 5Interpretation of the calculation results in Fig. 2 is not simple. However, at least, the following may be concluded: the reference bandwidth
34、of 4 kHz is too small. A larger bandwidth may reasonably be chosen; even if the reference bandwidth of 1 MHz was chosen, the actual risk may be negligible, because in case ofBI= 500 kHz, the baseband interference is 2.5 dB (for two sided interference signals) or 5.5 dB (for one sidedinterference sig
35、nal). If this is converted to a spectral density in 1 MHz, the interfering signal is only 0.5 dB higheror still 2.5 dB lower than a uniform interfering signal over a wide bandwidth (i.e. BI= 8 MHz).The above statement may imply that the reference bandwidth of 1 MHz may be adopted without risk in the
36、 frequencyrange of 1 to 3 GHz.This conclusion could be acceptable when the nature of the interfering signal is known (see Annex 2).It is assumed that radio signals emitted from MSS space stations have a uniform spectrum over a certain bandwidth. Insuch case, the 1 MHz reference bandwidth is generall
37、y acceptable.3.2 Interference assessment in case of multiple interference entriesIn order to examine the effects of interfering power concentration on analogue radio-relay systems, calculations weremade under the condition that, as shown in Fig. 3, there exist many interfering carriers with uniform
38、spectral densityover bandwidth BIand with a uniform frequency spacing F.1246-03fc fhBIfc+ fhfcFFIGURE 3Interference situation in case of multiple interference entriesFIGURE 3-1246.D1246-03 = 3 CMBaseband interference is calculated for different values of BIunder the condition that the total power of
39、 each interferingcarrier is constant, that is, the power flux-density increase, PFD (dB), of the interfering carrier is given by:PFD = 10 log (F / BI )The case of BI= F is taken as a reference. In this case, the interfering power spectrum is uniform over a wideband, likethermal noise.When BIbecomes
40、smaller, the baseband interference concentrates at certain frequencies. Figure 4 shows a fine structureof the baseband interference variation for an example of F = 500 kHz and PFD = 4 or 6 dB. The maximum values ofbaseband interference increase have been calculated for various cases. The results are
41、 shown in Table 1 for a960 channel analogue radio-relay system (r.m.s. frequency deviation is 200 kHz per channel) and F = 1 MHz, 500 kHz,200 kHz and 100 kHz.Table 1 shows that, due to energy dispersion effect of the analogue radio-relay system, the baseband interferenceincrease is much smaller than
42、 the value of PFD. The dependence of the baseband interference increase on F andPFD is complicated, but generally speaking it seems that PFD of up to 6 dB is acceptable.6 Rec. ITU-R F.12461246-04FIGURE 4Baseband interference distribution (fine structure) for multipleinterference entries (F = 500 kHz
43、, PFD = 4 or 6 dB)(960 channel analogue radio-relay system)Basebandinterferenceincrease(dB)3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.021.510.50 0.5 1Baseband frequency (MHz)PFD = 4 dBPFD = 6 dB FIGURE 4-1246.D04 = 3 CMTABLE 1Maximum values of baseband interference increase (dB) for various values of F and PFD(9
44、60 channel analogue radio-relay system)It may be also noted that the above calculations assume that there exist many interfering signals with the same frequencyspacing and the same spectral density. This is a kind of worst case assumption.A similar calculation was carried out to evaluate the impacts
45、 of interfering carrier power concentration on the basebandinterference noise of a 960 channel FDM-FM analogue radio-relay system. The spectrum shape for the 960 channelFDM-FM carrier was taken from Recommendation ITU-R SF.766. The interfering MSS carrier with a 25 kHzbandwidth had been characterize
46、d as a (sin X /X )2function.F(kHz)PFD(dB)02 4 6 8101 000 0 1.0 1.8 2.5 3.0 3.9500 0 0.5 1.0 1.6 2.0 3.0200 0 0.4 0.6 1.1 2.0 3.1100 0 0.4 0.8 1.4 2.2 3.3Rec. ITU-R F.1246 7 A numerical convolution technique has been used in the calculations to evaluate the baseband interference. After convolving the
47、 desired and the interfering power spectra, the baseband interference noise power into any baseband channel of the desired radio-relay system for the various frequency offsets was obtained through the following expression: Np= 100.1(87.5-B-C /I )where: B : interference reduction factor (dB) Np: weig
48、hted interference power (pW0p) C/I : carrier-to-interference ratio (dB) due to a single interfering carrier. From the analysis it was found that a baseband channel near the highest baseband frequency receives the worst interference noise for a carrier separation of 4 000 kHz. Then, the effect of mul
49、tiple interfering carriers was evaluated by assuming 40, 20, 10 and 5 interfering carriers at spacing of 25 kHz, 50 kHz, 100 kHz and 200 kHz, respectively. The power of each carrier was adjusted so that the total power in 1 MHz bandwidth was kept constant. From the analysis, it was found that the baseband effect of 40 contiguously placed interfering carriers with an inter-ference power level of X dBW per carrier and placed 4 MHz away from the centre frequency of the radio-relay carrier into the most vulnerable baseband
