1、 Recommendation ITU-R P.678-3 (07/2015) Characterization of the variability of propagation phenomena and estimation of the risk associated with propagation margin P Series Radiowave propagation ii Rec. ITU-R P.678-3 Foreword The role of the Radiocommunication Sector is to ensure the rational, equita
2、ble, efficient and economical use of the radio-frequency spectrum by all radiocommunication services, including satellite services, and carry out studies without limit of frequency range on the basis of which Recommendations are adopted. The regulatory and policy functions of the Radiocommunication
3、Sector are performed by World and Regional Radiocommunication Conferences and Radiocommunication Assemblies supported by Study Groups. Policy on Intellectual Property Right (IPR) ITU-R policy on IPR is described in the Common Patent Policy for ITU-T/ITU-R/ISO/IEC referenced in Annex 1 of Resolution
4、ITU-R 1. Forms to be used for the submission of patent statements and licensing declarations by patent holders are available from http:/www.itu.int/ITU-R/go/patents/en where the Guidelines for Implementation of the Common Patent Policy for ITU-T/ITU-R/ISO/IEC and the ITU-R patent information databas
5、e can also be found. Series of ITU-R Recommendations (Also available online at http:/www.itu.int/publ/R-REC/en) Series Title BO Satellite delivery BR Recording for production, archival and play-out; film for television BS Broadcasting service (sound) BT Broadcasting service (television) F Fixed serv
6、ice M Mobile, radiodetermination, amateur and related satellite services P Radiowave propagation RA Radio astronomy RS Remote sensing systems S Fixed-satellite service SA Space applications and meteorology SF Frequency sharing and coordination between fixed-satellite and fixed service systems SM Spe
7、ctrum management SNG Satellite news gathering TF Time signals and frequency standards emissions V Vocabulary and related subjects Note: This ITU-R Recommendation was approved in English under the procedure detailed in Resolution ITU-R 1. Electronic Publication Geneva, 2015 ITU 2015 All rights reserv
8、ed. No part of this publication may be reproduced, by any means whatsoever, without written permission of ITU. Rec. ITU-R P.678-3 1 RECOMMENDATION ITU-R P.678-3 Characterization of the variability of propagation phenomena and estimation of the risk associated with propagation margin (1990-1992-2013-
9、2015) Scope This Recommendation provides three prediction methods of: the expected year-to-year variation of the worst-month time fraction of excess; the inter-annual variability of rainfall rate and rain attenuation statistics; risk parameters associated with the variation of rain attenuation stati
10、stics. The ITU Radiocommunication Assembly, considering a) that knowledge of the variability of propagation phenomena is required to allow proper cost and performance trade-offs to be made in the analysis of system reliability, availability and quality; b) that a prediction procedure to estimate ris
11、k parameters associated with the variation of propagation statistics is required for the formulation of performance criteria of radiocommunication system; c) that a prediction procedure exists for the estimation of the statistics of the year-to-year variations in the annual worst-month time fraction
12、 of excess as defined in Recommendation ITU-R P.581, recommends 1 that Fig. 1 of Annex 1 be used for the estimation of the expected year-to-year variation of the annual worst-month time fraction of excess; 2 that the expected variation about a long-term average predicted value be reported as a funct
13、ion of return period; 3 that the inter-annual variability of rainfall rate and rain attenuation statistics around a long-term average statistics be computed from Annex 2; 4 that the risk parameters associated with the variation of propagation statistics be computed from Annex 3. NOTE 1 The return pe
14、riod is the average time interval between two consecutive occurrences of a defined stochastic event. For a long series of observation, the value of the return period is 1/P (times the average interval between all pairs of consecutive events) where P is the probability of occurrence of the event. For
15、 example, the median value of a long series of annual worst-month time fraction of excess values would have a two-year return period. NOTE 2 The risk is defined as the probability that the yearly guaranteed availability is not fulfilled. 2 Rec. ITU-R P.678-3 Annex 1 Estimation of the expected year-t
16、o-year variation of the annual worst-month time fraction of excess FIGURE 1 Dependance of WR/PW on Q for several value of the return period R (years) P .06 78 -013Q4 5 6 7 8 9 10 11 120123468101520W/PRW1 . 2 5 251020R = 5 0PWRQWR: a v e ra g e a n n u a l w o rs t -m o n t h t i m e fra c t i o n o
17、f e x c e s s: a n n u a l w o rs t -m o n t h t i m e fra c t i o n o f e x c e s s a s s o c i a t e dw i t h a re t u rn p e ri o d o f y e a rs: w o rs t -m o n t h q u o t i e n t , a p ro p a g a t i o n c l i m a t i c fa c t o r(s e e R e c o m m e n d a t i o n IT U -R P . 8 4 1 )Note 1 PW,
18、 WR, Q should be referred to the same pre-selected threshold value. Rec. ITU-R P.678-3 3 Annex 2 Inter-annual variability of rainfall rate and rain attenuation statistics For a desired location, the inter-annual fluctuations of rainfall rate and rain attenuation statistics around the long-term Compl
19、ementary Cumulative Distribution Function (CCDF) p are normally distributed with mean p and yearly variance so that: )()()( 222 ppp EC (1) where: 2E : is the variance of estimation 2C : is the inter-annual climatic variance. The following prediction method provides a step-by-step procedure to comput
20、e )(2 p associated with the probability of exceedance p. The following parameters are required: p: probability of exceedance (0 p 1) rc: climatic ratio. The values of rc, the climatic ratio, are an integral part of this Recommendation and are available in the form of digital maps provided in the fil
21、e CLIMATIC_RATIO.ZIP. C LIM AT IC _RAT IO .ZIP These maps were derived from 50 years of Global Precipitation Climatology Centre (GPCC) data over land and from 34 years of Global Precipitation Climatology Project (GPCP) data over the ocean. Step 1: For the desired probability of exceedance, p, comput
22、e: 11 ),(NNi U pticC(2) where: )e x p (),(60525960bU tiaptictN (3) with: 286.00.03960265.0)ln(21121bbsabpbb(4) Step 2: The variance of estimation 2E is computed from: 4 Rec. ITU-R P.678-3 CN pppE )1()(2 (5) Step 3: Extract the variable rc for the four points closest in latitude (Lat) and longitude (
23、Lon) to the geographical coordinates of the desired location. Step 4: From the values of rc at the four grid points, obtain the value rc(Lat, Lon) at the desired location by performing a bi-linear interpolation, as described in Recommendation ITU-R P.1144. Step 5: The inter-annual climatic variance
24、2C is computed such that: 22 ),()( pL o nL a trp cC (6) If a predicted, rather than an experimental, CCDF is used, the predicted CCDF will not exactly match the actual rainfall rate or rain attenuation (e.g. measured CCDF of rain attenuation will not exactly match the CCDF of rain attenuation predic
25、ted by Recommendation ITU-R P.618). In this case, an additional error, )(2 pM , must be considered in which case equation (1) becomes: )()()()( 2222 pppp MEC (7) where )(2 pM is the error in the predicted CCDF. To assess the impact of the variance )(2 p , it is convenient to refer to the 68% confide
26、nce interval )(),( pppp that corresponds to plus or minus one standard deviation around the probability for a normally distributed quantity. The procedure is applicable for time percentages of exceedance from 2% to 0.01% (i.e. 0.0001 p 0.02) and for the frequency range from 12 to 50 GHz. Annex 3 Est
27、imation of the risk associated with propagation margin Given a fixed rain attenuation Ar exceeded for a given probability p ( 10 p ) such as pAAP r )( , the risk (meaning the probability) that the yearly probability p ( 10 p ) is exceeded satisfies: )( p ppQ(8) or equivalently: pe r f cppQpp )2()(2)()( 11 (9) where )(p can be computed from Annex 2 and where (see Recommendation ITU-R P.1057): Rec. ITU-R P.678-3 5 xt txQ de21 22 Importantly, note that p =p in equation (8) leads, as expected, to =0.5.
