THREE BASIC PROPAGATION MECHANISMS IN WIRELESS COMMUNICATION

PROPAGATION:

                                  We know that electromagnetic waves travel with the speed of light in free space or in air as the medium . The speed will be 3*10^8 m/sec .

But while travelling it suffers from three basic mechanisms which decreases its strength while travelling in space . 

                                 Those are the listed below..... 

1) Reflection 

2) Diffraction 

3) Scattering 

REFLECTION:

                                "Reflection occurs when a propagating electromagnetic wave impinges upon an object whose dimension is large , compared to wave length of travelling electromagnetic wave ".

So reflection can be seen on any object whose dimensions are greater as compared to the wavelength of electromagnetic wave which will be hitting that object.

Example: It can occur on the surface of "earth" , buildings and walls etc.

HOW IT HAPPENS:

                                          When the wave propagating in one medium impinges upon another medium having different electrical properties, Then the wave will be partially reflected and partially transmitted . Again reflection depends on the type of second medium that is if the medium is perfect "Dielectric" then a part of incident energy will be transmitted into the second medium and part of that will be reflected back to the first medium. Suppose if the second medium is the "conductor" then the incident wave will be completely reflected back to the first medium.In case of perfect conductor there is no absorption of energy .

                                          "Fresnel reflection coefficient " gives the information regarding the electric field intensity between the transmitted and reflected waves. The reflection coefficient is the function of material properties. and in general depends on "wave polarization, angel of incidence and also on frequency " of transmitted wave.

"Reflection"

DIFFRACTION :

                                    "Diffraction occurs when the path between the transmitter and receiver is obstructed by surfaces with sharp irregularities (sharp edges)".

So diffraction occurs due to the objects with sharp irregularities on them . 

Due to diffraction  there will be production of secondary waves which are present in space and they are also present "behind obstacles" Gives rise to the phenomena called as "Bending of waves" around the obstacle, even if there is no line of sight communication present .

                                                                       

                                                     At higher frequencies just like reflection the , diffraction also depends on geometry of object and also on amplitude , phase , polarization of the incident waves.

"Diffraction"

SCATTERING :

                                  " Scattering occurs when the medium through which electromagnetic wave travels contain's objects with dimensions lesser than wavelength of propagating wave".

                                         Consider a wave with wavelength 1mm is propagating in the medium then scattering only occurs if the objects which are present in medium are having the dimensions lesser than 1mm (wavelength < 1mm). And "number of obstacles per unit volume should be large" .

                              The scattered waves can be produced by rough surfaces, small objects , other irregularities present in transmission channel.

                               

"scattering"