Recent Evolution of ITU Method for Prediction of Multipath Fading on Terrestrial Microwave Links Basile L. Agba1 , Olfa Ben-Sik-Ali1 , Robert Morin2 , and Germain Bergeron2 1
Institut de Recherche d’Hydro-Qu´bec, 1800 Lionel-Boulet, Varennes, Qu´bec, Canada e e 2 Hydro-Qu´bec, 15000 University, Montreal, Qu´bec, Canada e e
Abstract— Three methods are commonly used to predict multipath fading on terrestrial lineof-sight (LOS) links namely Barnett-Vigants and Morita methods used respectively in North America and Japan, and the worldwide ITU method. This later gains in importance even in North America and in Japan, due to the regular updates proposed by Study Group 3 of the ITU Radiocommunications sector. The ITU recommendation, ITU-R P.530 provides guidelines based on fading measurements of 251 links in various geoclimatic regions. Since 1978, thirteen revisions were proposed. The paper reviews the evolution of ITU-R P.530 from 1997 to 2009 with focus on the diﬀerence between the last two revisions (Rev. 12 versus Rev. 13). These diﬀerences concern mainly the geoclimatic factor, which depends on the refractivity gradient and the terrain roughness, and the multipath fade occurrence factor that aﬀects worst month outage probability. The paper also presents parametric studies carried out using our prediction tool, Microwave link simulator, to determine the critical parameters aﬀecting link performance. In our studies, 20 links located in Quebec, Canada, are designed based on real-world parameters. The detailed link proﬁles are known and refractivity gradients are extracted from ITU database according to ITU-R P.453-9. Climatic conditions are also taken into account using local rain database. The results of this work show that three climatic parameters, namely rain intensity, refractivity gradient and annual mean temperature are critical. Likewise for equipments, radio signature and antenna cross-polarization discrimination highly reduce the overall performance in terms of link availability. Finally, two year measurements data of ﬁve links are analysed. The results show a good agreement with ITU-R P.530-13. 1. INTRODUCTION
Microwave prediction methods used in links design are intensively investigated since many years. Nevertheless, the unpredictable variation of waves propagation remained a challenging issue, that Scientiﬁcs try to handle by proposing prediction methods (such as Barnett-Vigants  in North America, Morita in Japon . . . ) that take into account several climatic and environmental parameters. The Study Group 3 of ITU has proposed and maintained actively a microwave prediction method deﬁned in the ITU-R P.530 recommendation. This method gains in importance even in North America and in Japan, due to its regular updates. ITU-R P.530 provides guidelines based on fading measurements of 251 links in various geoclimatic regions. Since 1978, thirteen revisions were proposed. This paper addresses the recent evolution of this method and presents some experimental validation examples. Section 2 of this paper reviews the evolution of ITU-R P.530 from 1997 to 2009 with focus on the diﬀerence between the last two revisions (Rev. 12  versus Rev. 13 ). Section 3 presents parametric studies carried out using our prediction tool, Microwave link simulator, to determine the critical parameters aﬀecting link performance. This section also provides comparison between some experimental measurements and the predicted values. 2. EVOLUTION OF ITU-R P.530
It is interesting to look at the signiﬁcant changes in the evolution of diﬀerent versions since the 1978 original one. For practical reasons, we will limit ourselves to versions from version 7 (1997) to version 13 (2009, currently in use). Note that there are only minor diﬀerences between versions 7 and 8 and also between versions 11 and 12. • From versions 7/8 to...