## Depolarisation Attenuation

Using orthogonal polarisations, two independent information channels with the same frequency can be transmitted along the same link. While in theory these two orthogonally polarised channels are completely isolated from each other, in reality a certain level of interference inevitably arises between them, due to the fact that the polarisation characteristics of the antennas are not perfect and to the depolarisation effects along the propagation path. Absorption and diffusion by hydrome-teors...

## Hf 1 CTf jVdz428

Where is the group refractive index, while t is the time required for an impulse to propagate forth and back between the origin and the reflection level in the ionosphere. When a radio waves penetrates inside the ionosphere, the presence in this medium of charged particles such as ions and electrons, combined with the influence of the magnetic field, causes modifications in the characteristics of this wave. These effects shall be successively reviewed hereafter. The wave is refracted, that is,...

## Electromagnetic Waves and Propagation Characteristics

3.1 Basic Properties of Electromagnetic Waves 3.1.1 Electromagnetic Parameters characterising Wave Propagation The propagation of an electromagnetic wave is described through different parameters the electric and magnetic fields E and H, the electric flux density D and the magnetic induction B (Jouguet 1978). Only vectors E and B generate effects allowing the determination of the electromagnetic field. The vectors D and B are linked to vectors E and H through the following linear relations

## Building Penetration Loss

The building penetration loss is the power attenuation that an electromagnetic wave undergoes as it propagates from outside a building towards one or several places inside this building. This parameter is generally calculated by comparing the external field and the field present in different parts of the building where the receiver is located. The value of the building penetration loss is influenced by a number of different physical parameters, whose effects intermingle most of the time. Among...

## CSELT Models

These models were developed at the CSELT for the study of UMTS systems, and may consist either of 6 or 12 paths. The distinction between indoor building environments and external environments is not taken into account. A criterion between line-of-sight situations and non line-of-sight situations results in the definition of two different propagation scenarios. These models were constructed from measurements carried out either in microcell environment or inside open space buildings. The...

## Ray Launching Model

The ray launching technique is a deterministic method which seems particularly promising. This method, based on very accurate geographical databases and on a physical theory, is particularly well suited to urban environments and provides results with rich information, for instance impulse responses. As a consequence, a number of models using this method have been developed in the last recent years (Kurner 1993 Lawton 1994 Liang 1998). Fig. 7.14. Principles of a ray launching modelling (RAYON...

## D E31

The and coefficients depend on the nature of the medium where the electromagnetic wave propagates. In the case of homogeneous, isotropic media, and are constants, whereas inside vacuum, these coefficients, respectively referred to as the permittivity and magnetic permeability of the medium, assume the following values 0 10-9 36 n 8.842 10-12 Faradper metre 3.3 o 4 n 10-7 Henry per metre . 3.4 For any material medium, these coefficients can be deduced from the previous values using the following...

## 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...

## 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

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...

## 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...