1. EE 6331, Spring, 2009 Advanced Telecommunication Zhu Han Department of Electrical and Computer Engineering Class 6 Feb. 5 th, 2009

2. ECE6331 Spring 2009 Outline Review –Channel capacity revisit –Free Space Propagation Model –Reflection –Diffraction –Scattering Stochastic large scale models: –Log-distance path loss model –log-normal shadowing Outdoor propagation models Indoor propagation models Homework due next Tuesday

3. ECE6331 Spring 2009 Large-scale small-scale propagation

4. ECE6331 Spring 2009 Free space propagation model Assumes far-field (Fraunhofer region) –d >> D and d >>, where u D is the largest linear dimension of antenna u is the carrier wavelength No interference, no obstructions Black board 4.1 Effective isotropic radiated power Effective radiated power Path loss Fraunhofer region/far field In log scale Example 4.1 and 4.2

5. ECE6331 Spring 2009 Radio Propagation Mechanisms Refraction –Conductors & Dielectric materials (refraction) –Propagation wave impinges on an object which is large as compared to wavelength - e.g., the surface of the Earth, buildings, walls, etc. Diffraction –Fresnel zones –Radio path between transmitter and receiver obstructed by surface with sharp irregular edges –Waves bend around the obstacle, even when LOS (line of sight) does not exist Scattering –Objects smaller than the wavelength of the propagation wave - e.g. foliage, street signs, lamp posts –“Clutter” is small relative to wavelength

6. ECE6331 Spring 2009 Classical 2-ray ground bounce model One line of sight and one ground bound

7. ECE6331 Spring 2009 Propagation Models Large scale models predict behavior averaged over distances >> –Function of distance & significant environmental features, roughly frequency independent –Breaks down as distance decreases –Useful for modeling the range of a radio system and rough capacity planning, –Experimental rather than the theoretical for previous three models –Path loss models, Outdoor models, Indoor models Small scale (fading) models describe signal variability on a scale of –Multipath effects (phase cancellation) dominate, path attenuation considered constant –Frequency and bandwidth dependent –Focus is on modeling “Fading”: rapid change in signal over a short distance or length of time.

8. ECE6331 Spring 2009 Free Space Path Loss Path Loss is a measure of attenuation based only on the distance to the transmitter Free space model only valid in far-field; –Path loss models typically define a “close-in” point d 0 and reference other points from there: Log-distance generalizes path loss to account for other environmental factors –Choose a d 0 in the far field. –Measure PL(d 0 ) or calculate Free Space Path Loss. –Take measurements and derive  empirically.

9. ECE6331 Spring 2009 Typical large-scale path loss

10. ECE6331 Spring 2009 Log-Normal Shadowing Model Shadowing occurs when objects block LOS between transmitter and receiver A simple statistical model can account for unpredictable “shadowing” –PL(d)(dB)=PL(d)+X0, –Add a 0-mean Gaussian RV to Log-Distance PLAdd –Variance  is usually from 3 to 12. –Reason for Gaussian

11. ECE6331 Spring 2009 Measured large-scale path loss Determine n and  by mean and variance Equ. 4.70 Equ. 4.72 Basic of Gaussian distribution

12. ECE6331 Spring 2009 Area versus Distance coverage model with shadowing model Percentage for SNR larger than a threshold Equ. 4.79 Exam. 4.9

13. ECE6331 Spring 2009 Longley-Rice Model Point-to-point from 40MHZ to 100GHz. irregular terrain model (ITS). Predicts median transmission loss, Takes terrain into account, Uses path geometry, Calculates diffraction losses Inputs: –Frequency –Path length –Polarization and antenna heights –Surface refractivity –Effective radius of earth –Ground conductivity –Ground dielectric constant –Climate Disadvantages –Does not take into account details of terrain near the receiver –Does not consider Buildings, Foliage, Multipath Original model modified by Okamura for urban terrain

14. ECE6331 Spring 2009 Longley-Rice Model, OPNET implementation

15. ECE6331 Spring 2009 Durkin’s Model It is a computer simulator for predicting field strength contours over irregular terrain. Adopted in UK Line of sight or non-LOS Edge diffractions using Fresnel zone The disadvantage are that it can not adequately predict propagation effects due to foliage, building, and it cannot account for multipath propagation.

16. ECE6331 Spring 2009 2-D Propagation Raster data Digital elevation models (DEM) United States Geological Survey (USGS)

17. ECE6331 Spring 2009 Algorithm for line of sight (LOS) Line of sight (LOS) or not

18. ECE6331 Spring 2009 Multiple diffraction computation

19. ECE6331 Spring 2009 Okumura Model It is one of the most widely used models for signal prediction in urban areas, and it is applicable for frequencies in the range 150 MHz to 1920 MHz Based totally on measurements (not analytical calculations) Applicable in the range: 150MHz to ~ 2000MHz, 1km to 100km T-R separation, Antenna heights of 30m to 100m

20. ECE6331 Spring 2009 Okumura Model The major disadvantage with the model is its low response to rapid changes in terrain, therefore the model is fairly good in urban areas, but not as good in rural areas. Common standard deviations between predicted and measured path loss values are around 10 to 14 dB. G(hre) ：

21. ECE6331 Spring 2009 Okumura and Hata’s model Example 4.10

22. ECE6331 Spring 2009 Hata Model Empirical formulation of the graphical data in the Okamura model. Valid 150MHz to 1500MHz, Used for cellular systems The following classification was used by Hata: ■ Urban area ■ Suburban area ■ Open area

23. ECE6331 Spring 2009 PCS Extension of Hata Model COST-231 Hata Model, European standard Higher frequencies: up to 2GHz Smaller cell sizes Lower antenna heights f >1500MHz Metropolitan centers Medium sized city and suburban areas

24. ECE6331 Spring 2009 Walfisch and Bertoni Model Path loss (1) Free space path loss : (1)(2)(3) (2) Roof-top-to-street diffraction and scatter loss term : (3) Multiscreen diffraction loss :

25. ECE6331 Spring 2009 Walfisch and Bertoni’s model

26. ECE6331 Spring 2009 Wideband PCS Microcell Model A 2-ray ground reflection model is a good estimate for path loss in LOS microcells, Low antenna heights A simple log-distance path loss model holds well for obstructed microcells, Urban clutter d f represents the distance at which the first Fresnel zone just becomes obstructed by the ground

27. ECE6331 Spring 2009 Measured data from San Francisco

28. ECE6331 Spring 2009 Indoor Propagation Models The distances covered are much smaller The variability of the environment is much greater Key variables: layout of the building, construction materials, building type, where the antenna mounted, …etc. In general, indoor channels may be classified either as LOS or OBS with varying degree of clutter The losses between floors of a building are determined by the external dimensions and materials of the building, as well as the type of construction used to create the floors and the external surroundings. Floor attenuation factor (FAF)

29. ECE6331 Spring 2009 Partition losses

30. ECE6331 Spring 2009 Partition losses

31. ECE6331 Spring 2009 Partition losses between floors

32. ECE6331 Spring 2009 Partition losses between floors

33. ECE6331 Spring 2009 Log-distance Path Loss Model The exponent n depends on the surroundings and building type –X  is the variable in dB having a standard deviation .

34. ECE6331 Spring 2009 Ericsson Multiple Breakpoint Model

35. ECE6331 Spring 2009 Attenuation Factor Model FAF represents a floor attenuation factor for a specified number of building floors. PAF represents the partition attenuation factor for a specific obstruction encountered by a ray drawn between the transmitter and receiver in 3-D  is the attenuation constant for the channel with units of dB per meter.

36. ECE6331 Spring 2009 Measured indoor path loss

37. ECE6331 Spring 2009 Measured indoor path loss

38. ECE6331 Spring 2009 Measured indoor path loss

39. ECE6331 Spring 2009 Devasirvatham’s model

40. ECE6331 Spring 2009 Signal Penetration into Buildings RF penetration has been found to be a function of frequency as well as height within the building. Signal strength received inside a building increases with height, and penetration loss decreases with increasing frequency. Walker’s work shows that building penetration loss decrease at a rate of 1.9 dB per floor from the ground level up to the 15 th floor and then began increasing above the 15 th floor. The increase in penetration loss at higher floors was attributed to shadowing effects of adjacent buildings. Some devices to conduct the signals into the buildings

41. ECE6331 Spring 2009 Ray Tracing and Site Specific Modeling Site specific propagation model and graphical information system. Ray tracing. Deterministic model. Data base for buildings, trees, etc. SitePlanner

42. ECE6331 Spring 2009 Questions?