Homework-2, Terminology: Path loss, Shadowing , Fading

1. Homework-2, Terminology: Path loss, Shadowing , Fading by Ikhsan Putra Kurniawan 운영체제특론(Advanced Operating System) - Spring 2012

2. Wired vsWireless 운영체제특론(Advanced Operating System) - Spring 2012

3. 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 freespaceloss, 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

4. 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

5. 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-Hatamodel, • 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

6. Fading & Shadowing To lose freshness, strength, or vitality(dict.). Fadingis 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

7. 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

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

9. 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

10. 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

11. 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

12. 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_interference http://www.radio-electronics.com/info/propagation/path-loss/rf-signal-loss-tutorial.php 운영체제특론(Advanced Operating System) - Spring 2012

13. 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

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

15. 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