1. Wireless communication lectureset: 8

2. 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 theoretical
Path loss models, Outdoor models, Indoor models
Small scale (fading) models describe signal variations on a scale of 
Multipath effects (phase cancellation) dominate, path attenuation considered constant
Frequency (and bandwidth) dependent
Focused on modeling of “Fading”: rapid change in signal over a short distance or length of time. 2

3. Free Space Path Loss
Path Loss is a measure of attenuation based only on the distance to the transmitter : P(L)=Pt / Pr
Free space model valid only in far-field;
Path loss models typically define a “close-in” point d0 and reference other points from there: eq 4.8
Log-distance generalizes path loss to account for other environmental factors
Choose a d0 in the far field.
Measure PL(d0) or calculate Free Space Path Loss.
Take measurements and derive  empirically. 3

4. Typical large-scale path loss4

5. 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)+ X , eq 4.69
Add a 0-mean Gaussian RV (with standard deviation  ) to Log-Distance PL
Variance  is usually 3 to 12.
Reason for Gaussian 5

6. Measured large-scale path loss
Determine n and  by mean and variance
Read Q and erf
functions
Equ. 4.70
Equ. 4.72
Read basic of
Gaussian
distribution 6

7. Area versus Distance coverage model with shadowing model
Percentage for
SNR larger than
a threshold
Equ. 4.79
Example 4.9 7

8. Models for analysis Review
Propagation mechanism: too theoretical for practice use. concept
Reflection
Diffraction
Scattering
Log-distance path loss model and log-normal shadowing: too simple
Tradeoff between simplicity and accuracy
Outdoor propagation models
Indoor propagation models

9. 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 9

10. Longley-Rice Model, OPNET implementation10

11. 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. 11

12. 2-D Propagation Raster data
Digital elevation models (DEM) United States Geological Survey (USGS) 12

13. Algorithm for line of sight (LOS)
Line of sight (LOS) or not 13

14. Multiple diffraction computation14

15. 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 15

16. 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)： 16

17. Okumura and Hata’s model
Example 4.10 17

18. 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 18

19. 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 19

20. Walfisch and Bertoni Model
Path loss
(1)
(2)
(3)
(1) Free space path loss :
(2) Roof-top-to-street diffraction and scatter loss term :
(3) Multiscreen diffraction loss : 20

21. Walfisch and Bertoni’s model21

22. 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
df represents the distance at which the first Fresnel zone just becomes obstructed by the ground 22

23. Measured data from San Francisco23

24. 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)
Partition losses 24

25. 25

26. Partition
losses 26

27. Partition losses between floors27

28. Partition losses between floors28

29. Log-distance Path Loss Model
Equation 4.93
The exponent n depends on the surroundings and building type
X is the variable in dB having a standard deviation . 29

30. Ericsson Multiple Breakpoint Model30

31. 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. 31

32. Measured indoor path loss32

33. Measured indoor path loss33

34. Measured indoor path loss34

35. Devasirvatham’s model
Eq 4.96 35

36. 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 15th floor and then began increasing above the 15th 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 36

37. 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 37

38. Assignments
4.9
4.15
4.16
4.19
4.25
4.30
4.34 38