1、 STD-ITU-R RECMN F-302-3-ENGL 1997 4855212 053022Y 1q8 D 1 Rec. ITU-R F.302-3 RECOMMENDATION ITU-R F.302-3 LIMITATION OF INTERFERENCE FROM TRANS-HORIZON RADIO-RELAY SYSTEMS (Question ITU-R 103/9) (1959-1982-1990-1997) The IT Radiocommunication Assembly, considering a) extend across national boundari
2、es; that trans-horizon radio-relay systems can cause interference over long distances which in many cases may b) bands and particularly to space communication systems; that trans-horizon radio-relay systems can cause interference to all the systems sharing the same frequency c) that trans-horizon sy
3、stems need some form of diversity to circumvent fading; d) antennas, with or without cross-polarization, that multiple-diversity can be provided without using additional frequencies, e.g. by employing spaced recommends in planning trans-horizon radio-relay systems: 1 that account be taken of the hig
4、h degree of international coordination and planning which will be involved if trans-horizon radio-relay systems of this type are to occupy the same frequency bands in nearby countries without mutual interference, and that the problem would become much more complex if, in addition, they were to occup
5、y the same frequency bands as conventional line-of-sight systems or other services; 2 that the utmost economy in frequency should be observed; 3 frequency spectrum is likely to become congested; that frequency-diversity should be avoided as far as possible, particularly in those parts of the world w
6、here the 4 radiated power, and in particular: that special efforts should be made to operate such radio-relay systems at the lowest practicable level of 4.1 in the case of a frequency band shared with space radiocommunication services (space-to-Earth), due consideration should be given to interferen
7、ce from the trans-horizon radio-relay system to earth stations on the basis of the coordination area for receiving earth stations determined in accordance with Recommendation ITU-R IS.847; 7 4.2 for the range of angles for which the e.i.r.p. of the trans-horizon radio-relay systems is less than +40
8、dBW in a 4 kHz bandwith (see Note i), careful consideration should be exercised, comparable to that required for coordination between line-of-sight radio-relay systems and earth stations. For the range of angles for which the directional e.i.r.p. of the trans-horizon system exceeds +40 dF3W in a 4 k
9、Hz bandwith, more careful consideration is required; 5 that special efforts should be made to reduce radiation in, and reception from, undesired directions; 6 NOTE 1 - This value is the maximum allowable e.i.r.p. transmitted towards the horizon by an earth station sharing the same frequency band wit
10、h the fixed service (see Article 28, No. 2541 of the Radio Regulations (RR) and Article S21, No. S2 1.8 of the RR revised by the World Radiocommunication Conference (Geneva, 1995) (WRC-95). that special efforts should be made to reduce spurious emissions to the lowest practicable level. COPYRIGHT In
11、ternational Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services STD*ITU-R RECMN F-302-3-ENGL 1997 D 4855232 0530225 O84 2 Rec. ITU-R F.302-3 ANNEX 1 Trans-horizon radio-relay systems have interference-producing capabilities and susceptibilities not unlike those
12、encountered in line-of-sight radio-relay systems. Differences are primarily due to the usually higher transmitting powers, narrower antenna beamwidths and more sensitive receivers encountered in trans-horizon systems. This means that siting considerations are very important with trans-horizon system
13、s. To minimize interference from a trans-horizon radio-relay system line-of-sight situations are usually avoided, as are areas where the diffracted signal will be strong. Under some circumstances, it may be impossible to avoid occasional interference from signals due to difiaction, strong layer refl
14、ection, and especially ducting. To estimate expected co-channel interference, it is necessary to calculate transmission loss by subtracting the path antenna gain Gp given in Fig. 1 of Recommendation ITU-R F.1106 from the estimated basic transmission loss. The interfering field depends on the mean lo
15、ng-term loss and any additional fluctuations. At UHF and higher frequencies, the lowest observed values of extra-difiaction transmission loss are the result of atmospheric focusing and ducting, either over sea or over land. Field strength may be combined with antenna gain to yield azimuthal distance
16、-interference patterns for various systems and combinations. In considering non-Co-channel interference, account must also be taken of transmitter spectrum distribution and receiver passband characteristics. For antenna pattern considerations see Recommendation ITU-R F.699. Although it is not possib
17、le to recommend final channel arrangements, there is a need to select frequencies in an orderly manner on a regional basis. In arriving at such agreements between administrations, the guidelines in Report286 (Geneva, 1982) should be observed. Polarization discrimination is also suggested to aid the
18、use of space-diversity and the rejection of interference. It has been general practice to engineer tropospheric-scatter systems on the high propagation attenuations exceeded only during small percentages of the time. It should be realized that under more favourable conditions, prevailing for the res
19、t of the time, transmitter powers and antenna gains so justified can cause increased interference fields. It may be advisable under such conditions to reduce the transmitter power temporarily. Typical power output statistics While automatic power control (APC) is not currently operated on analogue s
20、ystems, successful trials of APC functionality have been carried out. More recent trans-horizon systems employ digital modulation techniques and APC. Maximum power amplifier output is 1.6 kW but actual transmitter power monitored over a period of 12 consecutive months resulted in the following stati
21、stics: - - - It is worth noting the median transmitter power level is approximately 10 dB below the maximum power level of 1 kW. The mitigating effect of automatic power control, when evaluating interference from trans-horizon radio into other services, is therefore significant. power exceeded for 10% time: 1 kW, power exceeded for 50% time: 175 W, power exceeded for 90% time: 6.5 W. COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services
