1、HTTP:/WWW.ITU.INT/DMS_PUB/ITU-R/OPB/QUE/R-QUE-SG03.205-1-1995-MSW-E.DOC 16.10.03 14.07.10QUESTION ITU-R 205-1/3Propagation data and prediction methods required for trans-horizon systems(1990-1993-1995)Q. ITU-R 205/3The ITU Radiocommunication Assembly,consideringa) that, in the planning of a digital
2、communication network, it is necessary to define theoverall system performance and availability achieved for a given percentage of the time;b) that designers of radio systems in the VHF (metric), UHF (decimetric) and SHF(centimetric) bands require to know, from the viewpoint of sustained satisfactor
3、y operation, thetropospheric propagation characteristics and the resulting transmission loss that is not exceeded fora large percentage of the time for each particular frequency band, over the distance corresponding tothe service range, which may extend from about 100 km to more than 500 km;c) that
4、the planning of systems requires a knowledge of the distribution curves, as functions oftime, of the transmission loss for the most unfavourable month of the climatic zone underconsideration;d) that the bandwidth of the system may be limited by the nature of the mode of propagationemployed,decides t
5、hat the following Question should be studied1 What is the distribution in time of the basic transmission loss (seeRecommendation ITU-R P.341), in the VHF (metric), UHF (decimetric) and SHF (centimetric)bands, for each month of the year (the value of the path antenna gain being specified). Therecordi
6、ng should be performed with an instrument having a time constant of 1 s (other timeconstants may be used, should it appear desirable, but in all cases the time constant used should bespecified) and special importance should be attached to the quasi-maximum and quasi-minimumvalues of the transmission
7、 loss or field strength?2 For given levels, what are the percentages of time corresponding to the worst month andcorresponding to the whole year?3 What are the hours of the day for which the greatest transmission loss may usually beexpected?4 What is the dependence of the distributions on the climat
8、ic zone in which the path underconsideration is located, and which distinct climatic zones should be taken into consideration (inview of the paucity of data relating to propagation in climates other than temperate, administrationsare urged to give special attention to the collection of data relating
9、 to other types of climate)?5 What is the dependence of the distributions on the frequency, on the distance between thestations, on the angle of elevation of the antennas at each terminal and on the nature of the terrainover which the path passes?6 What are the limitations imposed on the bandwidth o
10、f the system by the propagationprocess (diffraction, partial reflection, scattering, etc.)?7 What models can be used, in particular:- 2 -3/1-EHTTP:/WWW.ITU.INT/DMS_PUB/ITU-R/OPB/QUE/R-QUE-SG03.205-1-1995-MSW-E.DOC 16.10.03 14.07.10 to describe the dispersive behaviour of the transmission channel par
11、ticularly for digitalsystems; for the prediction of system performance and availability degradation?8 What is the degree of correlation of fading on different radio channels on the same path anddifferent paths in a multi-hop link?9 What is the improvement to be gained using diversity (space, angle, frequency andpolarization)?NOTE 1 Priority will be given to studies relating to 7._
