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Advanced Operating System HomeWork2

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					  Homework-2, Terminology:
Path loss, Shadowing , Fading
                         by Ikhsan Putra Kurniawan




운영체제특론(Advanced Operating System) - Spring 2012
                                Wired vs Wireless
                Wired                                   Wireless
Each cable is a different channel          One media (cable) shared by all
No interference                            High interference
                                           Noise;
                                           co-channel interference;
                                           adjacent channel interference




     운영체제특론(Advanced Operating System) - Spring 2012
                                                     Path loss
Path loss (or path attenuation) is the reduction in
 power density (attenuation) of an
 electromagnetic wave as it propagates through
 space.
  • Path loss is a major component in the analysis and design
    of the link budget of a telecommunication system.
Path loss may be due to many effects, such as
 freespace loss, refraction, diffraction, reflection,
 aperture-medium coupling loss, and absorption.
  • Path loss is also influenced by terrain contours,
    environment (urban or rural, vegetation and foliage),
    propagation medium (dry or moist air), the distance
    between the transmitter and the receiver, and the height
    and location of antennas.

   운영체제특론(Advanced Operating System) - Spring 2012
                                   Cause of Path loss
 Free space loss:   the signal travels through space without any other
    effects attenuating the signal it will still diminish as it spreads out. 
   Absorption losses:   if the radio signal passes into a medium which is not
    totally transparent to radio signals. 
   Diffraction:   Diffraction losses occur when an object appears in the path.
   Multipath:   In a real terrestrial environment, signals will be reflected
    and they will reach the receiver via a number of different paths. 
   Terrain:   The terrain over which signals travel will have a significant
    effect on the signal.
   Buildings and vegetation:   For mobile applications, buildings and other
    obstructions including vegetation have a marked effect.
   Atmosphere:   The atmosphere can affect radio signal paths. At lower
    frequencies, especially below 30 - 50MHz, the ionosphere has a
    significant effect, reflecting (or more correctly refracting) them back to
    Earth. At frequencies above 50 MHz and more the troposphere has a
    major effect, refracting the signals back to earth as a result of changing
    refractive index. For UHF broadcast this can extend coverage to
    approximately a third beyond the horizon.



      운영체제특론(Advanced Operating System) - Spring 2012
                                 Predicting Path loss
                                   (path loss model)
free space path loss basic

irregular terrain
  • Sea path, dry sandy terrain.
pathloss matrix (start node, end node and time,
 mobility)
two ray
Okumura-Hata model,
  • the most widely used radio frequency propagation model
    for predicting the behaviour of cellular transmissions in
    built up areas.
  • reflection and scattering caused by city structures


   운영체제특론(Advanced Operating System) - Spring 2012
                        Fading & Shadowing
To lose freshness, strength, or vitality(dict.).
Fading is deviation of the attenuation that a
 signal experiences over certain
 propagation media.
The fading may vary with time,
 geographical position or radio frequency,
 and is often modelled as a random process.
Fading may either be due to multipath
 propagation, referred to as multipath
 induced fading, or due to shadowing from
 obstacles affecting the wave propagation,
 sometimes referred to as shadow fading.
   운영체제특론(Advanced Operating System) - Spring 2012
   Wireless Multipath Channel




Channel varies at two spatial scales:
  • Large scale fading: path loss, shadowing
  • Small scale fading: Multi-path fading, Doppler

   운영체제특론(Advanced Operating System) - Spring 2012
Path Loss, Shadowing, Fading
Variable decay of signal due to
 environment, multipaths, mobility.




  운영체제특론(Advanced Operating System) - Spring 2012
                                                  Shadowing
The received signal is shadowed by
 obstructions such as hills, buildings,
 caves.
This results in variation in the local mean
 received signal power.
Implications:
  • Nonuniform coverage
  • Increases the required transmit power


     운영체제특론(Advanced Operating System) - Spring
                                           2012
                                          Fading Jargon
Flat fading: No multipath ISI effects
  • Narrowband, indoors.
Frequency-selective fading: multipath
 ISI effects
  • Broadband, outdoor.
Slow fading: no doppler effects.
  • Indoor Wi-fi home networking.
Fast fading: doppler effects, time
 selective channel.
  • Cellular, vehicular.

  운영체제특론(Advanced Operating System) - Spring 2012
                                   Multipath fading
Due to constructive and destructive
 interference of the transmitted waves.
Multipath propagation: a wireless signal
 from a transmitter reaches the receiver
 via many different paths, in different
 times.




  운영체제특론(Advanced Operating System) - Spring 2012
                                                     References
Basic Principles of Wireless Networks (I),
 Chalmers University of Technology slide
 presentations.
http://en.wikipedia.org/wiki/Path_loss
http://en.wikipedia.org/wiki/Fading
http://en.wikipedia.org/wiki/Rayleigh_fading
http://www.merriam-
 webster.com/dictionary/fade
http://en.wikipedia.org/wiki/Intersymbol_interf
 erence
http://www.radio-
 electronics.com/info/propagation/path-loss/rf-
 signal-loss-tutorial.php

   운영체제특론(Advanced Operating System) - Spring 2012
Explain the difference between path loss
 and shadowing?
What is the impact of shadowing on cell
 design?
What is flat fading?
How exactly does multi-path fading lead to
 frequency-selectivity and ISI in a
 broadband channel?
How exactly does mobility lead to time-
 selectivity in the channel?

  운영체제특론(Advanced Operating System) - Spring 2012
                                                     Summary
pathloss                  : the reduction of signal
fading                    : the deviation/variation of signal
shadowing                 : shadow fading -> because of
 obstacles
pathloss model                     : okumura hatta n others.
fading model                       : rayleigh, ricean.
shadowing model                    :
pathloss: free space, absorption, diffraction,
 multipath, terrain, building & vegetation,
 atmosphere.

   운영체제특론(Advanced Operating System) - Spring 2012
                                                 Fading type
Rayleigh
  • a model when there are many objects in the environment that
    scatter the radio signal before it arrives at the receiver. The
    central limit theorem holds that, if there is sufficiently much
    scatter, the channel impulse response will be well-modelled as
    a Gaussian process irrespective of the distribution of the
    individual components. If there is no dominant component to
    the scatter, then such a process will have zero mean and phase
    evenly distributed between 0 and 2π radians.
Ricean
  • a stochastic model for radio propagation anomaly caused by
    partial cancellation of a radio signal by itself — the signal
    arrives at the receiver by several different paths (hence
    exhibiting multipath interference), and at least one of the paths
    is changing (lengthening or shortening). Rician fading occurs
    when one of the paths, typically a line of sight signal, is much
    stronger than the others.

   운영체제특론(Advanced Operating System) - Spring 2012

				
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