1、348 Rec. ITU-R F.698-2 RECOMMENDATION ITU-R F.698-2 PREFERRED FREQUENCY BANDS FOR TRANS-HORIZON RADIO-RELAY SYSTEBIS (Question IT-R 1039) (1990- 1992-1993) The Ini Radiocommunication Assembly, considering a that the World Administrative Radio Conference (Geneva, 1979) (WARC-79). in its Recommendatio
2、n No. 100 asked the ex-CCIR to prepare a Recommendation concerning the specific frequency bands found preferable for trans- horizon radio-relay systems, taking into account allocations to other services, particularly allocations to space services; b) that the WARC-79 and the World Administrative Rad
3、io Conference for Dealing with Frequency Allocations in Certain Parts of the Spectrum (Malaga-Torremolinos, 1992) (WARC-92) made additional allocations of frequency bands for the space services in view of their increasing development; c) that Recommendation No. 100 of the WARC-79 notes that the prol
4、iferation of trans-horizon systems in all frequency bands, and particularly in those shared with the space systems, is bound to aggravate an already difficult situation; d) and intermodulation noise due to propagation, depending on the distance of links; that there are optimum frequency ranges for t
5、rans-horizon radio-relay systems from the viewpoint of thermal e) that the power limits specified in Article 27 of the Radio Regulations (RR) are applicable to transmitters of trans-horizon radio-relay systems, sharing the frequency bands with space radiocommunication services (Earth-to-space) excep
6、t for certain frequency bands, recommends 1. into account from the viewpoint of the total noise including thermal and intermodulation noises due to propagation: that in selecting frequency bands for trans-horizon radio-relay systems, the following factors should be taken 1.1 on links of approximatel
7、y 400 to 700 km relatively low frequencies below about 1 GHz with large antennas are optimum to provide adequate performance including low intermodulation noise. The transmission capacity will normally be small. Operation above 1 GHz may result in poor performance except for very favourably sited te
8、rminals and for very favourable propagation conditions; 1.2 on links of approximately 200 to 400 km the transmission capacity may be somewhat greater. Multipath intermodulation noise may be a major factor; frequencies around 2 GHz may be preferable to lower frequencies in order to reduce intermodula
9、tion noise; 1.3 for shorter links (approximately 100 to 200 km) operation at frequencies up to about 5 GHz is possible, resulting in low multipath intermoduIation noise even with relatively small antennas. Frequencies between about 2 GHz and 3 GHz may be optimum for high transmission capacities on s
10、uch links; 2. which are not shared with space radiocommunication services; that in selecting frequency bands for trans-horizon radio-relay systems, priority should be given to bands 3. be used for trans-horizon radio-relay systems (see Note I); that, in general, frequency bands shared with space rad
11、iocommunication services (Earth-to-space) should not 4. that frequency bands shared with space radiocommunication services (space-to-Earth) may be used for trans- horizon radio-relay systems, provided that due consideration is given, on the basis of Recommendation ITU-R IS.847, to avoiding interfere
12、nce from trans-horizon radio-relay systems to earth station receivers in space radiocommunication services (see Notes 2 and 3); COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesRec. ITU-R F.698-2 349 5. that in selecting frequency bands
13、 for trans-horizon radio-relay systems, due consideration should be given to avoiding interferences to line-of-sight radio-relay systems in accordance with Recommendation ITU-R F.302 (see Note 4); 6. that the additional information given in Annex 1 should be referred to for the application of this R
14、ecommendation: 7. Note 1 - Trans-horizon radio-relay systems cannot generally operate under the power limits applicable to all systems in the fixed service shared with space radiocommunication services (Earth-to-space), as specified in RR Article 27 (see also that thz following Notes should be treat
15、ed as part of this Recommendation. 3.1 of Annex I). Note 2 - When frequency bands shared with space radiocommunication services (space-to-Earth) are used for trans- horizon radio-relay systems, it should be confirmed that space stations in space radiocommunication services complying with Recommendat
16、ion ITU-R SF.358 (or, with RR Article 28 for I 525-3 500 MHz bands) do not cause unacceptable interference into trans-horizon systems. It should be taken into account that the space stations may be in geostationary or non-geostationary-satellite orbits. Note 3 - Further study is required concerning
17、frequency sharing between trans-horizon radio-relay systems and receiving earth stations in the broadcasting-satellite service. Note 4 - It should be also confirmed that interference into trans-horizon radio-relay systems caused by line-of-sight radio-relay systems is within acceptable limits. ANNEX
18、 1 Factors affecting the choice of frequency bands for trans-horizon radio-relay systems 1. Introduction This Annex identifies various factors affecting the choice of frequency bands for trans-horizon radio-relay systems. At first the optimum frequency range of a trans-horizon radio-relay link syste
19、m is determined from propagation considerations, taking into account the antenna diameter and the transmitting power. Then, interference problems relating to frequency sharing with other systems, including line-of-sight radio-relay systems and space radiocommunication systems, are discussed. 2. Opti
20、mum frequency range of a trans-horizon system 2. I AS a function of received level considering thermal noise onlj) Existing trans-horizon radio-relay systems normally use transmitter powers which are of the same order of magnitude for different frequency ranges. The sensitivity of modern receivers i
21、s, to a large extent, independent of the frequency band used. Long-term variations in received power levels, as a function of carrier frequency, depend essentially on three phenomena: - the loss between isotropic antennas; it is usually assumed that this loss is proportional to the cube of the frequ
22、ency; the free-space gain of the antennas used; for an antenna of a given diameter this gain is proportional to the square of the frequency; the drop in antenna gain; for an antenna of a given diameter this drop depends on the frequency and can be calculated from Fig. I of Recommendation ITU-R F. 11
23、06. - - COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services ITU-R RECMN*F. 698-2 94 U 4855232 0523562 793 m 350 Rec. ITU-R F.698-2 The effect of variations of all these three parameters, as a function of the frequency for antenna diameter
24、s between 4 and 40 m, is shown in Fig. 1. Figure 1 represents the relative loss between the terminals of two antennas of the same diameter, located at the two ends of a trans-horizon radio-relay system; the reference loss (O dB) is taken as that which exists under the same conditions between two ant
25、ennas 10 m in diameter at 1 O00 MHz. As regards the length of the connection, the validity of Fig. 1 is the same as that giving the loss in antenna gain, Le. the link under consideration is assumed to be between about i50 and 500 km in length. RGURE 1 Relative los between antennas of a given diamete
26、r - 20 - 10 + 10 + 16 I 2 IO2 5 io4 . .DO1 , Frequency (MHz) It can be seen that, for an antenna of given diameter, the relative loss passes through a minimum at a particular frequency and increases on either side; at the lower frequencies, because the relative dimensions of the antenna measured in
27、wavelengths decrease (with a consequent decrease in free-space gain) and at the upper frequencies, because the drop in antenna gain increases as the free-space gain increases. The optimum operating frequency lies between 200 MHz for an antenna with a diameter of 40 m and 2 GHz for an antenna 4 m in
28、diameter. However, the minimum is very flat and a frequency departure on either side in the ratio of 2/1 is possible without substantially increasing the relative loss. 2.2 As a function of total noise (including thermal and intermodulation) for analogue systems The reduction of intermodulation nois
29、e due to propagation may demand higher antenna gains than would be strictly necessary for the reduction of thermal noise. For a given antenna gain, the dimensions of the antennas are obviously smaller at high frequencies. The choice of frequency does not depend essentially on the intermodulation noi
30、se if the antenna gain is fixed, but this is not true if the antenna diameter is fixed. Regarding intermodulation noise, theoretical considerations have shown that intermodulation noise increases in proportion to the fourth power of multipath delay in the radio path. The multipath delay on the path
31、is proportional to the beamwidths of the antennas employed, and the antenna beamwidth is inversely proportional to the radio frequency, therefore the intermodulation noise decreases in inverse- proportion to the fourth power of the radio frequency when the antenna diameter employed is constant. An e
32、stimate of the intermodulation noise for each radio-frequency band and channel capacity is shown in Fig. 2 for a path length of 200 km and an antenna diameter of 10 m. COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesITU-R RECMN*F= 698-
33、2 7Lt 4855212 05215b3 b2T 80 h 70 v O .3 Y e B 8 60 t) .3 -0 5 3 +I 9 50 O dz a % !7 40 .- i% E ;a O Y 30 CA 20 FIGURE 2 Signal to mean psophometncaiiy weighted noise themal and intermodulation noise) ratio I -1 2 1 o2 Rec. ITU-R F.698-2 l i 5 Frequency (MHz) Curves A: 24 channels B: 60channels C: i
34、 20 channels D: 300 channels Link length: 200 km Antenna diameter: 10 m Output power: 1 kW 35 1 I o4 As shown in Fig. 2, no conspicuous differences appear in total noise in the 900 MHz, 2 GHz and 2.6 GHz bands for the transmission capacity of 24 channels. These bands have more advantages over bands
35、higher than 3 GHz. It appears that when the transmission capacity is increased to 300 channels, frequency bands of about 2 GHz are more suitable than other bands. An example of how path intermodulation noise or thermal noise can determine the minimum antenna size is the first group of curves (which
36、decrease from left to right) show antenna size versus frequency for a signal-to-path intermodulation noise ratio of 60 dB. Each curve corresponds to given values of path length and channel capacity; the second group of curves (which dip to a minimum value) show antenna size versus frequency for a si
37、gnal-to-thermal noise ratio of 50 dB (assuming a received signai level of 20 dB above threshold and a signal-to-thermal noise ratio of 30 dB at threshold). Each curve corresponds to given values of transmitter power and distance. shown in Fig. 3. There are two groups of curves as follows: - - COPYRI
38、GHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services ITU-R RECHN*F* 678-2 74 = 4855232 O523564 5bb 352 Rec. ITU-R F.698-2 The two groups of curves must be used together to determine the limiting parameter on antenna size (or frequency). For exam
39、ple, with a transmitter power of 1 kW, a frequency of 1 GHz and a distance of 200 km, the minimum antenna diameter would be about 8 m for 24 telephone channels (due to thermal noise), 13 m for 120 telephone channels and 24 m for 300 telephone channels (the last two being due to path intermodulation
40、noise). The power levels shown in Fig. 3 cover the range of transmitter powers actually available. For practical reasons, the maximum transmitter power considered is 10 kW, but lower powers are desirable to achieve system economy and practical maintainability. Using a large aperture antenna is prefe
41、rable to using large transmit power, but the cost of the antenna and support tower increases significantly, and therefore, for large capacities, lower frequency bands are less economical. FIGURE 3 Required minimum antenna diameter for frequency bands 24 20 h E 8 s v 16 8 2 3 -0 12 2 e: Y F: cd .- =I
42、 8 4 1 oz . I 100 km -.-.-.-.-.- 200 km 300 km 400 km - CH: channels 10 kW Ti 10 kW 300 km- T c 1 o4 COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services ITU-R RECMNxF- 698-2 94 = 4855232 05215b5 4T2 m Rec. ITU-R F.698-2 353 2.3 Summary Co
43、nsidering all the relevant factors, including the mechanical aspects, the maximum useful physical diameter of antennas is approximately 40/fm (wherefis in GHz) for frequencies above 1 GHz. This corresponds to a plane wave gain of about 50 dB and an antenna-to-medium coupling loss of about 15 dB for
44、two identical antennas. The higher antenna-to-medium coupling loss and higher thermal noise may be partially offset by an increase in deviation; for example, thermal and intermodulation noise contributions could be approximately equal. 3. Frequency sharing with space radiocommunication systems 3.1 F
45、requency bands shared with space services (Earth-to-space) Recommendation ITU-R SF.406 specifies the maximum e.i.r.p. of radio-relay system transmitters operating in frequency bands shared with the fixed-satellite service. On the other hand. RR Article 27 gives the power limits for a station in the
46、fixed or mobile service sharing frequency bands with any space radiocommunication services. It is noted that Recommendation ITU-R SF.406 and RR Article 27 are applicable not only to line-of-sight radio-relay systems but also to trans-horizon radio-relay systems. The most important provisions of the
47、RR are No. 2503, which stipulates that the maximum e.i.r.p. of a station in the fixed or mobile service shall not exceed i-55 dBW, and No. 2507 which stipulates that the power delivered by a transmitter to the antenna of a station in the fixed or mobile service in frequency bands between 1 GHz and 1
48、0 GHz shall not exceed +13 dBW. Most trans-horizon radio-relay systems exceed both of these limits, and therefore cannot generally operate in the frequency bands shared with space services (Earth-to-space). According to No. 2509 of RR Article 27, such frequency bands used for both fixed service and
49、up links of space services below 5 GHz are as follows: 1610-1 645.5 MHz (for certain countries) 1 646.5-1 660 MHz (for certain countries) 1 675-1 690 MHz (for Region 2) 1 690-1 700 MHz (for certain Countries) 1700-1 710 MHz (for Region 2) 1970-1 980 MHz (for Region 2) 1 980-2 O1 O MHz 2 025-2 1 10 MHz 2 200-2 290 MHz 2 655-2 670 MHz (for Regions 2 and 3) 2 670-2 690 MHz However, No. 2509A of RR Article 27 recognizes that trans-horizon systems in the 1700-1 710MHz, 1970-2010 MHz, 2025-2 110 MHz and 2200-2290 MHz bands may exceed the e.i.r.p. limit of RR No. 2505 (+55dBW)
