1 introduction to fading channels, part 1 dr. essam sourour alexandria university, faculty of...
TRANSCRIPT
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Introduction to
Fading Channels, part 1
Dr. Essam SourourAlexandria University, Faculty of Engineering, Dept. Of Electrical
Engineering
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• Characterization of Fading Channels
• Large Scale Fading
• Short Scale Fading
• Fading Counter Measures
Section Overview
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• Two main effects:– Large Scale– Small Scale
• Large Scale Fading– Depends on environment and topology– Path Loss, Shadowing
• Small Scale Fading– Faster Changes– Depends on signal parameters
Characterization
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Small Scale and Large Scale Fading
Distance
ReceivedPower
dBDistance
effect
Shadowingeffect
Small ScaleFading
Characterization, cont.
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• For Open Areas use Line of Sight (LOS):
• Path Loss L (in dB) in far field:
Loss(dB) 20 log d• Loss with distance follows 20 dB/Octave
0
220
2 24t r
r t d
G G dP d P P
dd
Line of Sight (LOS)
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Loss(dB) 40 log d• Loss with distance follows 40 dB/Octave• In General, with many rays
Loss(dB) 10 log d• The loss exponent depends on environment
Cell phone
2 2
4t r t r
r t
G G h hP d P
d
2~3Obstructed in factories3 ~ 5Shadowed Urban
4~6Obstructed in building2.7~3.5Urban
1.6~1.8In-building LOS2Free Space
EnvironmentEnvironment
Path Loss with Distance
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• Most famous model: Okumura-Hata
• Okumura made extensive measurements• Hata transformed Okumura’s plots to an
empirical model• Valid for 150-1500 MHz • Model takes the effect of
– Transmitter height hb in m
– receiver height hm in m
– frequency fc in MHz
– Distance d in km– different environments
Hata Propagation Model
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log
( ) log
log
A B d Urban
L dB A B d C Suburban
A B d D open
2
2
69.55 26.16log 13.82log
44.9 6.55log
5.4 2 log 28
40.94 4.78 log 19.33 log
c b m
b
c
c c
A f h a h
B h
C f
D f f
2
2
1.1 log 0.7 1.56 log 0.8
8.28 log 1.54 1.1 400 ,
3.2 log 11.75 4.97 400 ,
c m c
m m c
m c
f h f Medium or small city
a h h f Mhz large city
h f Mhz large city
Hata’s Model
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COST 231 Extension to Hata
• The European Cooperative for Scientific and Technical Research (COST) extended Hata model to 2GHz
9
46.3 33.9 log 13.82log
44.9 6.55log log
c b m
b
L dB f h a h
h d C
0 mediumcityor suburb
3 metropolitan area
dBC
dB
• Valid for 1.5 Ghz<fc<2 GHz, 30 m<hb<200 m
and 1 m<hm<10 m
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Indoor Propagation Loss (ITU-R P1238-1
• Simple ITU model for WPAN:
L(dB) = 20 log(f ) + N log(d) + Lf (n) − 28
• N =Distance Power Loss Coefficient
• f =Frequency (MHz)
• d =Distance (m) between nodes (d > 1)
• Lf =Floor Penetration Loss Factor (dB)
• n =Number of Floors Penetrated (n > 0)
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Indoor Model Parameters
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• In addition, indoor obstacles add more losses
• Extensive measurements made. Tables available in literature
• For example:– Concrete wall, 8 to 15 dB– Concrete floor, 10 dB– Foil insulation, 3.9 dB
Indoor Effects
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• Surrounding Environment varies, even at same distance from Tx
• Path Loss is random, with an average that depends on distance and frequency
• Distribution, in dB, found to be Gaussian
• Denoted by Log-Normal Shadowing
• Over and above loss due to distance
Shadowing Loss
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• L(dB)|d = L(dB)|do + 10 log (d/do) + X
• X is Gaussian with zero mean and standard deviation
• depends on environment, increases with more variations
• Outdoor: = 5 ~ 12 dB, typical 8 dB
• Hence, L(dB) is Gaussian with mean given by any of the distance-based relations, and standard deviation
Shadowing Loss, Cont.
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Indoor Shadowing
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Indoor shadowing standard deviation for ITU-R P.1238-1 model
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Total Effect
• In all previous models the received power at distance
• Where
• The value of , K and Kdo depends on frequency and environment
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10 log
10 logo
rec t
t
t d o
P dB P dB L dB
P dB K dB d X
P dB K dB d d X
10 logod oK dB K dB d
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Cell Coverage Area
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• Coverage may be defined as the percentage of the area of the cell that receive power > Pmin
• C=covered area inside cell / cell area
• C 1
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Coverage calculation, 1
• Received power Prec(x) at any distance r is Gaussian, with:– Mean dB (r) which depends on r, given by any of the
previous relations (LOS, two paths, Hata, or COST-231)– Standard deviation that depends on location
• Define F(r) as the probability Prec(x) exceeds Pmin
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min
min min1
2 2
rec
P
dB dB
F r P x dx
P r P rerfc Q
10 logodB t d or P dB K dB r d
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Coverage calculation, 2
• On the average, the part of the area dA with received power > Pmin is : F (r) dA
• The total area (yellow part) in the cell with received power > Pmin is :
• Hence, the coverage C is given by:
19
A
F r dA
2
2 20 0 0
1
1 2
A
R R
C F r dAA
F r r d dr r F r drR R
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Coverage calculation, 3
• F(r) can be written as:
• Using integral (2.58) in textbook, we get
20
lnr
F r Q a bR
min 10 log
10 log
ot d oP P K R da
eb
2
2 2 2exp
ab abC Q a Q
b b
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Coverage calculation, 4
• Note that, without shadowing, the received power at cell border is given by:
• If we transmit enough power Pt such that Prec(at R)=Pmin , then a=0 and Q(a)=0.5
• In this case:
• Also, if there is no shadowing, =0, b= and C=1
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10 logorec t d oP at R P K R d
2
1 2 2exp
2C Q
b b
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Homework
• Please solve the following problems from Chapter 2 of the textbook:
• Problems: 1, 13, 14, 15, 17, 19, 21, 23, 24, 25
• You may use any of the models in the lecture but specify in your answer which propagation model you are using.
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