mobile communications systems
TRANSCRIPT
Lecture #10
Effects of Mobile Radio Propagation (p1)
Instructor: Dr. Ahmad El-Banna
Dec
em
ber
2014
E-716-A Mobile Communications Systems
Integrated Technical Education Cluster At AlAmeeria
© A
hmad
El-B
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Agenda
Types of waves
Propagation Mechanisms
Path Loss 2
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Speed, Wavelength, Frequency
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
Light speed = Wavelength x Frequency
= 3 x 108 m/s = 300,000 km/s
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Types of Waves
Earth
Sky wave
Space wave
Ground wave
Troposphere
(0 - 12 km)
Stratosphere
(12 - 50 km)
Mesosphere
(50 - 80 km)
Ionosphere
(80 - 720 km)
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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 - 300 kHz
Medium MF 300 kHz - 3 MHz Ground/Sky wave
High HF 3 MHz - 30 MHz Sky wave
Very high VHF 30 MHz - 300 MHz
Space wave
Ultra high UHF 300 MHz - 3 GHz
Super high SHF 3 GHz - 30 GHz
Extremely high EHF 30 GHz - 300 GHz
Tremendously high THF 300 GHz - 3000 GHz
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Propagation Mechanisms
• Reflection
• 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
• Shadowing ! distance
sender
transmission
detection
interference
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Radio Propagation Effects
Transmitter d
Receiver
hb
hm
Diffracted
Signal
Reflected Signal
Direct Signal
Building
reflection scattering diffraction shadowing refraction
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Free-space Propagation
• The received signal power at distance d:
where Pt is transmitting power, Ae is effective area, and Gt is the transmitting antenna gain. Assuming that the radiated power is uniformly distributed over the surface of the sphere.
Transmitter Distance d
Receiver
hb
hm
2r
4P
d
PGA tte
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Antenna Gain
• For a circular reflector antenna
Gain G = ( D / )2
= net efficiency (depends on the electric field distribution over the antenna aperture, losses, ohmic heating , typically 0.55)
D = diameter
thus, G = ( D f /c )2, c = f (c is speed of light)
Example:
• Antenna with diameter = 2 m, frequency = 6 GHz, wavelength = 0.05 m
G = 39.4 dB
• Frequency = 14 GHz, same diameter, wavelength = 0.021 m
G = 46.9 dB
* Higher the frequency, higher the gain for the same size antenna
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Land Propagation
• The received signal power:
where Gr is the receiver antenna gain,
L is the propagation loss in the channel, i.e.,
L = LP LS LF
L
PGGP trt
r
Fast fading
Slow fading
Path loss
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Path Loss (Free-space)
• Definition of path loss LP :
Path Loss in Free-space:
where fc is the carrier frequency.
This shows greater the fc , more is the loss.
,r
tP
P
PL
),(log20)(log2045.32)( 1010 kmdMHzfdBL cPF
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Path Loss (Land Propagation)
• Simplest Formula:
Lp = A d-α
where
A and α: propagation constants
d : distance between transmitter and receiver
α : value of 3 ~ 4 in typical urban area
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Example of Path Loss (Free-space)
Path Loss in Free-space
70
80
90
100
110
120
130
0 5 10 15 20 25 30
Distance d (km)
Path
Loss L
f (d
B) fc=150MHz
fc=200MHz
fc=400MHz
fc=800MHz
fc=1000MHz
fc=1500MHz
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Path Loss (Urban, Suburban and Open areas)
• Urban area:
where
• Suburban area:
• Open area:
)(log)(log55.69.44
)()(log82.13)(log16.2655.69)(
1010
1010
kmdmh
mhmhMHzfdBL
b
mbcPU
citymediumsmallfor
MHzfformh
MHzfformh
cityelforMHzfmhMHzf
mh
cm
cm
cmc
m&,
400,97.4)(75.11log2.3
200,1.1)(54.1log29.8
arg,8.0)(log56.1)(7.0)(log1.1
)(
2
10
2
10
1010
4.528
)(log2)()(
2
10
MHzfdBLdBL c
PUPS
94.40)(log33.18)(log78.4)()( 10
2
10 MHzfMHzfdBLdBL ccPUPO
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Path Loss
• Path loss in decreasing order:
• Urban area (large city)
• Urban area (medium and small city)
• Suburban area
• Open area
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• For more details, refer to:
• Chapter 2, A. Goldsmith, Wireless Communications, 2004.
• The lecture is available online at:
• https://speakerdeck.com/ahmad_elbanna
• For inquires, send to:
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