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ALLAH. Wireless & Mobile Communications. Compiled by : Engr.Muhammad Waseem Assistant Professor , Telecom Eng.Deptt . Sir Syed University of Engineering & Technology, Karachi, Pakistan. Email ID:engrmwaseem@gmail.com Office: CF-02,FFT-10. Mobile Radio Propagation.
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Wireless & Mobile Communications • Compiled by :Engr.MuhammadWaseem • Assistant Professor , Telecom Eng.Deptt. • Sir Syed University of Engineering & Technology, Karachi, Pakistan. • Email ID:engrmwaseem@gmail.com • Office: CF-02,FFT-10
Mobile Radio Propagation • The Mobile Radio Channel places fundamental limitations on the performance of wireless communication System. • The transmission path between the transmitter and the receiver can vary from simple line of sight to one that is severely obstructed by buildings ,mountains and foliage(plants).
Mobile Radio Propagation( Conti…) • Unlike wired channels that are stationary and predictable, radio channels are extremely random and don’t offer easy analysis. • Even the speed of motion affects how rapidly the signal level fades as mobile terminal moves in space. • Modeling the radio channel has historically been one the most difficult parts of mobile radio system design.
Mobile Radio Propagation( Conti…) • And is typically done in a statistical fashion ,based on measurements made specifically for an intended communication system or spectrum allocation.
Introduction to Radio Wave Propagation • The mechanisms behind electromagnetic waves propagation are diverse, but can generally be attributed to reflection, diffraction and scattering. • Most cellular systems operate in urban areas where there is no direct line of sight path between the transmitter and the receiver, and where the presence of high rise buildings causes severe diffraction loss.
Introduction to Radio Wave Propagation • Due to multiple reflections from various objects , the electromagnetic waves travel along different paths of varying lengths. • The interaction between these waves causes multipath fading at specific location, and the strengths of the waves decrease as the distance between the transmitter and receiver increases.
Propagation Models • Propagation models have traditionally focused on predicting the average received signal strength at a given distance from the transmitter, as well as the variability of the signal strength in close spatial proximity ( nearness) to a particular location.
Large Scale Propagation Models • Propagation Models that predicts the mean signal strength for an arbitrary (random, uninformed ) transmitter-receiver(T-R) separation distance are useful in estimating the radio coverage area of a transmitter and are called Large Scale Propagation Models, as they characterize signal strength over large T-R separation distances (Several Hundreds or thousands of meters).
Small Scale Propagation /Fading Models • Propagation Models that characterize the rapid fluctuations of the received signal strength over very short travel distances( a few wavelengths) or short time durations ( on the order of seconds) are called as small scale or fading models. • As a mobile moves over very small distances, the instantaneous received signal strength may fluctuate rapidly giving rise to small scale fading.
The Basic Propagation Mechanisms • Reflection, Diffraction and scattering are the three basic propagation mechanisms which affect propagation in a mobile communication system.
Reflection • It occurs from the surface of the earth and from the buildings and walls. • Reflection can take place when a propagating electromagnetic wave impinges upon an object which has very large dimensions when compared to the wavelength of the propagating wave.
Diffraction • It occurs when the radio path between the transmitter and receiver is obstructed by a surface that has sharp irregularities(edges). • Bending of electromagnetic waves around sharp edges such as, sharp towers or peaks. • At high frequencies diffraction , like reflection,
Diffraction( Conti…..) • Also depends on the geometry of the object , as well as the amplitude , phase and polarization of the incident wave at the point of diffraction.
Scattering • It can take place because of the rough surfaces , small objects or by other irregularities in the channel. • Foliage (plants) ,street signs, and lamp posts induce scattering in a mobile communication system. • When a radio wave impinges on a rough surface, the reflected energy is spread out or diffused in all directions.
