1、QUESTION ITU-R 204-4/3Propagation data and prediction methods requiredfor terrestrial line-of-sight systems(1990-1993-1995-1997-2000-2009)The ITU Radiocommunication Assembly,consideringa) that a better knowledge of the characteristics of propagation contributes greatly to thedesign of economic line-
2、of-sight systems and to the improvement of system performance and inparticular: that the design of digital systems is largely controlled by the performance and theavailability required (as related to propagation) and that periods of adverse propagation aresignificant to the design of digital systems
3、; that amplitude and group-delay distortions across a microwave radio channel have aprofound effect on the bit error ratio of digital systems,decides that the following Questions should be studied1 What is the distribution of the value of transmission loss additional to free space resultingfrom mult
4、ipath propagation, diffraction, precipitation and absorption, etc., for frequency bandsabove about 300 MHz for each month of the year, including its diurnal variation averaged over eachmonth?2 What propagation data may be used for station site selection and for determining the heightof antennas and
5、their radiation characteristics, including the distribution of refractive-index gradientor k-factor during subrefractive conditions averaged over a specified path length?3 What data may be obtained on clear-air propagation effects (both fading andenhancements), in particular: the number of atmospher
6、ic and ground reflected rays during multipath propagation, and thestatistical distribution of their relative amplitudes and delays; statistics of single-frequency fading, flat fading, selective fading (including minimum andnon-minimum phase fading, in-band power differences (IBPD), in-band amplitude
7、dispersions (IBAD) and notch depths) and composite fading (flat plus selective), anddiffraction fading; conditional probabilities of flat fading, selective fading, delays and notch depth todetermine the inter-dependence of the principal multipath parameters;- 2 - the dependence of all the items abov
8、e on: path and terrain characteristics, frequency, antenna patterns and geoclimatic factors; diversity (angle, space and in-band and cross-band frequency); degree of correlation of multipath fading on different channels on the same path anddifferent paths in a multi-hop link?4 What models of the tro
9、pospheric channel transfer function can be used for the computationof system performance?5 What data may be obtained on precipitation effects, in particular: concurrent long-term statistical distributions of rainfall attenuation and rainfall intensity,especially in tropical regions; the influence of
10、 sleet and wet snow; long-term number of precipitation attenuation events of duration shorter than 10 s and 10 sor longer for various attenuation levels, and the mean duration of precipitation eventsof duration 10 s or longer in combination with long-term statistical distributions ofprecipitation at
11、tenuation exceedances; the degree of correlation of precipitation effects on different paths of the same link?6 What precipitation parameters, in addition to rainfall intensity, can be applied toprecipitation-related prediction methods to take account of different climates?7 What refractivity parame
12、ters, in addition to, or instead of, refractivity gradient statistics inthe first 100 m of the atmosphere, can be applied to clear-air prediction methods to take accountof different climates?8 What is the variation, due to clear-air propagation effects, precipitation or any other cause,of the isolat
13、ion between two orthogonal polarizations, including systems using diversity?9 What is the set of conditions that must be met to identify the period of non-fadedpropagation?10 What is the frequency of occurrence and duration of fades exceeding specified values andthe rate of change of received signal
14、 in these fades, noting that the time resolution of measurementsto obtain these statistics must be adequate to describe the rate of variation of the propagationeffects. The duration statistics should also be apportioned between events shorter than 10 s andthose 10 s or longer?11 What is the improvem
15、ent to be gained using diversity systems in the presence of rain ormultipath?12 What are the cumulative effects of all propagation factors, on the overall systemperformance of multi-hop links (including one or more satellite hops), and the dependence of thesefactors on hop characteristics?13 How can
16、 the contributions from the various propagation effects be apportioned toperformance and availability?- 3 -14 What are the relevant short-term propagation considerations for bringing a system intoservice?15 How to simulate realistic time-series data for system testing taking into account all types ofpropagation effects?further decides1 that the available information should be prepared as new Recommendations, or as revisionsto existing Recommendations;NOTE 1 Priority will be given to studies relating to 5, 7, 11 and 13.Category: S2
