p J
The polarisation here is circular the phase difference between Ex and Ey is equal to n 2 , and Ez 0. In the ordinary mode, i.e. in left-hand polarisation where the wave travels away from the observer, the index sr is equal to zero if Xq 1 YL gt , while in the extraordinary mode, i.e. in right-hand polarisation where the wave travels towards the observer, the index is equal to zero if Xq 1 - Yl. Assuming that the two modes ordinary and extraordinary are in phase when they penetrate inside a...
R 0o pRcos 0o340
where p is the surface reflection coefficient, while Ri represents the incident power, and 0, is the observation angle. Phong Model. The reflection pattern is adequately represented with the Lambert model for a number of different rough surfaces. An exception however is the region of space in the vicinity of specular reflection here the diagram presents an important component which is not allowed for by the Lambert model. In the Phong model, the reflection diagram is considered as the sum of...
f
where belongs to the interval -fd, fd . The Doppler spectra deduced from experimental measurements Gollreiter 1994 Codit 1994 Dersch 1994 reveal a clear asymmetry in the spatial frequency domain. This asymmetry points to the existence of privileged directions of arrival, especially in line-of-light situations. The reverse of the width of the Doppler spectrum, or Doppler dispersion, is referred to as the coherence time. It is defined as the time during which function T fo,t can be regarded as...
Main Propagation Mechanisms
The first researches on interferences confirmed that seven main mechanisms of propagation are to be considered in the prediction procedures of these interferences ITU-R P.452 . These propagation mechanisms can be classified into two categories - long-term mechanisms or normal propagation mechanisms line-of-sight propagation, propagation by diffraction and tropospheric scatter. - short-term mechanisms or abnormal propagation mechanisms tropospheric radio duct, reflection and or refraction at...
References
Bean BR, Dutton EJ 1966 Radio Meteorology, US. Department of Commerce National Bureau of Standards Monograph Bertel L 1994 Introduction aux Radiocommunications. Premi re partie. Cours de DEA Universit de Rennes 1 Blanchard L 1999 Contribution l' tude des propagations longues distances en UHF M canismes, mesures de champ et brouillage. Ph.D. thesis, Universit de Rennes Blanchard L, Sizun H 1997a Refractivity over France - First results of the ARGOS experiment. COST 255, Prague, Czech Republic...
A23 The Magnetic Fields of Sunspots
The existence of intense magnetic fields inside sunspots was discovered as early as 1908 by G.E. Hale by applying the principle of Zeeman splitting to the study of the solar spectrum. The amplitude of these fields varies from a few hundreds Gauss for small spots to 3000 Gauss approximately for the largest ones. Inside a given sunspot, the amplitude of the magnetic field reaches its maximum at the centre of the umbra, where the field is approximately vertical. The amplitude of the field then...
CAPADOCE Model
This model can be applied to the study of the propagation of waves at frequencies ranging from 30 MHz to 30 GHz in flat, undulating and mountainous terrains, in rural and in moderately urbanised areas. It takes into account the physical parameters of the actual environment as represented by geographical databases digital terrain model DTM , the land use, the relative permittivity and conductivity of the ground, the refractive index, the roughness, which is a reduction factor of the reflection...
References Bgu
Barbot JP, Levy AJ, Bic JC 1992 Estimation of fast fading distribution functions. Com. URSI Commission F Open Symposium Bic JC, Charbonnier A, Duponteil D, Ruelle D, Tabbane S, Taisant JP 1995 Radiocommunications et mobilit . Annales des T l communications, 50, 1 114-141 Berg JE 1995 A recursive method for street microcell path loss calculations. PIMRC95, Toronto, Canada, pp 140-143 Bertoni HL, Honcharenko W, Maciel LR, Xia HH 1994 UHF propagation prediction for wireless personal...
COSTCNET Model
The integration of a profile mode and different multiple diffraction algorithms over a succession of edges significantly improves statistical models for small suburban and urban cells. These methods, which have already been tested for the prediction of the field strength in rural environments, offer the advantage of taking into account the influence of the land use and the topography through the use of geographical databases with a more or less high degree of precision. The best known such...
Ray Models
Ray models are deterministic models which rely on an accurate knowledge of the actual propagation environment and therefore require the use of such geographical databases as baseline databases or indoor databases. For more detail on geographical databases, the reader is referred to Appendix N. These models can be used for the prediction of the different propagation paths in a given configuration. Further, by performing an adjustment to the frequency band under consideration, these models allow...
Experimental Results
Fig. 5.22. Example of a phenomenon of tropospheric scatter at the 468 MHz, 915 MHz and 2208 MHz frequencies Fig. 5.23. Example of a recording showing a signal enhancement by tropospheric duct at the 468 MHz, 915 MHz and 2208 MHz frequencies Fig. 5.23. Example of a recording showing a signal enhancement by tropospheric duct at the 468 MHz, 915 MHz and 2208 MHz frequencies The phenomenon of tropospheric scatter is associated with the fluctuations of the refractive index. The received signal is...
Introduction to the Propagation of Radio Waves
One of the prerequisites for the development of telecommunication services is the understanding of the propagation of the waves, either acoustic, electromagnetic, radio or light waves, which are used for the transmission of information. In this work, we shall limit ourselves to the study of radio waves this term apply to the electromagnetic waves used in radio communications. Their frequency spectrum is very broad, and is divided into the following frequency bands ELF waves f lt 3 kHz , VLF...
Hydrometeor Attenuation
The transmission attenuation due to hydrometeors like clouds, snow, fog or rain is caused by two factors the energy absorption by Joule effect by hydrometeors and the wave diffusion induced by the particles. 6.5.1 Attenuation due to Clouds and Fog Attenuation due to clouds and fog is determined on the basis of the total water content per volume unit. At frequencies around 100 GHz and at higher frequencies, fog attenuation may reach significant levels. The liquid water concentration is typically...
dh
where dM dh is the vertical gradient of the modified refractive index and Ah is the thickness of the duct, corresponding to the height above the emission antenna of the upper boundary layer of the duct. The maximal trapping angle increases rapidly as the refractive index gradients falls below - 157 N units km or when the thickness of the duct increases. Recommendation ITU-R P.834 presents curves giving the maximum trapping angle depending on the refractive index and on the thickness of the duct...
UHF Model
This model, developed by France Telecom R amp D, is valid for distances ranging from 200 metres to 50 kilometres and at the 400, 900 and 1800 MHz frequencies. It is based on geographical mesh databases representing the relief and the land use, and takes into account the following parameters - multiple edge diffraction, using the Deygout method, - corrective terms of additional attenuation in order to account for such parameters as the effective height of the antennas, the value of the...
Effects of Vegetation
An empirical model for representing the shadowing effect induced by trees along roads has been made available for the 2-30 GHz frequency range by the ITU-R ITU-R P.681 4.1 . In this model, the influence of the trees is represented by the percentage of optical shadowing resulting from their presence for a 45 degree elevation angle along the direction of the source of the signal. In the case where the environment is known with an adequate level of precision for example, if geographical base...
Attenuation by Atmospheric Gases
The transmission attenuation caused by atmospheric gases results from the molecular resonance of oxygen and water vapour. An oxygen molecule has a single permanent magnetic moment. At certain frequencies, its coupling with the magnetic field of an incident electromagnetic wave causes resonance absorption. In particular, at frequencies around 60 GHz a coupling occurs between the intrinsic moment of the electron, its spin, and the rotational energy of the molecule, generating a series of...
Building Penetration Loss Models
The building penetration loss is defined as the power loss that an electromagnetic wave undergoes as it propagates from outside a building towards one or several places inside this building. This parameter is determined from the comparison between the external field and the field present in different parts of the building where the receiver is located. Penetration loss models, being integrated into the coverage prediction tools, must take into account the environment around the buildings which...
Modelling of the Cumulative Distributions of the Refractivity Gradient
The model presented in Recommendation ITU-R P.453-6 allows determining the cumulative distribution of the refractive index from a point of this distribution, which may be either the median or the 3o coefficient ITU-R P.453 1997 . This model is composed from two submodels connected to each other by the median of the gradient of the refractive index. Chart for the percentage of time thai dn gt 100 N km Chart for the percentage of time thai dn gt 100 N km Fig. 5.13. Cartography of the f...
Path Loss Models COST 207 or GSM Models
The principle of path loss models is far from being new and was initially defined in the context of the COST 207 European cooperation on digital land mobile radio communications. These models are based on the representation of the impulse response in the form of a limited number of discrete paths for different propagation environments, in rural area RA , typical urban TU bad urban BU and hilly terrain HT profiles respectively. Each path is defined by an amplitude, a delay and a Doppler spectrum...
Influence of Rain on Propagation
The emergence of new telecommunication needs, associated with the increasing congestion of the radio spectrum, have led radio system designers to become interested in increasingly high frequencies and more specifically to frequencies in the millimetre wavelength range, ranging from 30 to 300 GHz. Given the bandwidth available in this frequency band, considerably increased data transmission rates exceeding some hundreds of Mbits s can be obtained. At these frequencies however, atmospheric...
Acknowledgements
I would like first to express my most sincere gratitude to the Profs. Jean Mevel and Louis Bertel from the Radioelectricity Laboratory of the University of Rennes, who introduced me to research, and to Mr. Jacques Papet-L pine, who welcomed me at France Telecom Research amp Development, formerly known as the Centre National d'Etudes des T l communications, within the Ionospheric and Radioelectric Measurement Department. I would also link to thank those under which I had the opportunity of...