1. EELE 5490, Fall, 2009 Wireless Communications
                                                           
Ali S. Afana
Department of Electrical Engineering
Class 5
Dec. 4th, 2009 1

2. Speed, Wavelength, Frequency
Light speed = Wavelength x Frequency
= 3 x 108 m/s = 300,000 km/s
System
Frequency
Wavelength
AC current
60 Hz
5,000 km
FM radio
100 MHz
3 m
Cellular
800 MHz
37.5 cm
Ka band satellite
20 GHz
15 mm
Ultraviolet light
1015 Hz
10-7 m

3. Type of waves

4. Radio Frequency Bands Classification Band Initials Frequency Range
Characteristics
Extremely low
ELF
< 300 Hz
Ground wave
Infra low
ILF
300 Hz - 3 kHz
Very low
VLF
3 kHz - 30 kHz
Low LF
30 kHz kHz
Medium MF
300 kHz - 3 MHz
Ground/Sky wave
High HF
3 MHz - 30 MHz
Sky wave
Very high
VHF
30 MHz MHz
Space wave
Ultra high
UHF
300 MHz - 3 GHz
Super high
SHF
3 GHz - 30 GHz
Extremely high
EHF
30 GHz GHz
Tremendously high
THF
300 GHz GHz

5. Large-scale small-scale propagation

6. Models are Specialized
Different scales
Large scale (averaged over meters)
Small scale (order of wavelength)
Different environmental characteristics
Outdoor, indoor, land, sea, space, etc.
Different application areas
macrocell (2km), microcell(500m), picocell

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

8. Friis Transmission Equation
No 2
No 1
G1, A1
G2, A2
From previous section
If antenna 1 were isotropic then power density at distance d is
W0 = Pt / 4πd2
As antenna 1 is directive then this will be increased by Gt so that
W0 = PtG1 / 4πd2
The power transferred to the load of antenna 2 is
Pr = W0A2 = PtG1A2 / 4πd2

9. Pr / Pt =G1G2 ( λ / 4πd )2 No 2 No 1 G1, A1 G2, A2 Now we know that
So that
Pr / Pt = G1A2 / 4πd2
=G1G2 ( λ2 / 4π 4πd2 )
Pr / Pt =G1G2 ( λ / 4πd )2

10. 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
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

11. Refraction Perfect conductors reflect with no attenuation
Like light to the mirror
Dielectrics reflect a fraction of incident energy
“Grazing angles” reflect max*
Steep angles transmit max*
Like light to the water
Reflection induces 180 phase shift
Why? See yourself in the mirror q qr qt

12. Reflection from smooth surface

13. Typical electromagnetic properties

14. Classical 2-ray ground bounce model
One line of sight and one ground bound

15. Method of image

16. Simplified model
Far field simplified model
Example 4.6

17. Questions?