Transcript EL675 UHF Propagation(B)

V. Propagation Effects Observed
Indoors
•
•
•
•
July 2003
Multipath fading for narrowband signals
Wall loss and range dependence
Spatial fading of pulsed signals
Delay spread and coherence bandwidth
1
© 2003 by H. L. Bertoni
Multipath Fading for CW Signals
• Fading at both ends of symmetric links
• Fast fading statistics
July 2003
2
© 2003 by H. L. Bertoni
Summary of Fading at Both Ends of the
Link to an Elevated Base Station
xM
xBS
l/2
July 2003
Mobile in Clutter
Signal
Signal
Elevated Base Station
xBS
l/2
3
xM
© 2003 by H. L. Bertoni
Fading When Both Ends of Link in Clutter
xR
xT
xT2 xT1
July 2003
Receiver in Clutter
Signal
Signal
Transmitter in Clutter
xT
4
l/2
xT2
xT1
xR
© 2003 by H. L. Bertoni
Measuring Fading on a Circular Path
Antenna on a
rotating arm
RF Signal
Spectrum
Generator
Analyzer
GPIB/PCMCIA
Interface
Small area average is obtained in confined
space by rotating the antenna in a circle with
circumference ~ 20l
July 2003
5
© 2003 by H. L. Bertoni
Fast Fading on a Non-LOS Indoor Link
- Tx rotated around a circle of radius  1 m
- One complete revolution corresponds to 300 samples of received signal
f = 900 MHz
W. Honcharenko, H. L. Bertoni, J. Dailing, "Bi-Lateral Averaging Over Receiving and Transmitting
Areas for Accurate Measurements of Sector Average Signal Strength Inside Buildings," IEEE Trans.
on Ant. and Prop., AP-43, pp. 508-512, 1995.
July 2003
6
© 2003 by H. L. Bertoni
Single and Double Ended Averages
- Averages obtained rotating Tx only versus rotating both Tx and Rx around
circles inside a building. Tx and Rx locate one floor apart in hallways
- Resulting averages are plotted versus horizontal offset of the centers of the
Tx and Rx circles. F = 879.99 MHz
R.A. Valenzuela, 0. Landron
and D.L. Jacobs, "Estimating
Local Mean Signal Strength of
Indoor Multipath Propagation,"
IEEE Trans. on Veh. Tech., vol.
VT-46, pp. 203-212, 1997.
July 2003
7
© 2003 by H. L. Bertoni
Averaging at One or Both Ends of Link
 Tn
Tx
 Rn
Rx
rR
r T
Unfolded path length = Ln0
Received power for a summation of ray cont ribut ions
Pr, f     an am exp jk Ln  Lm 

n1 m1
an  An e j n = com plex ray amplitude,
Ln = ray path lenth
For small displacements r
T
at t he T x end and r
  
R
at t he Rx end of link


Pr, f     an am e  jkLn0 Lm0  exp  jk  rT   Tn   Tm   rR   Rn   Rm
n1 m1

where  Tn ,  Rn are in the direct ions of ray propagation at t heRx
T x,ends
July 2003
8
© 2003 by H. L. Bertoni
Averaging at One End of Link
T he single end space average is
P
R



  an am e  j( c )Ln 0 L m0  exp  jk r   Tn   Tm 
T
n1 m1
 1
 
AR
 exp jk r
R
area

  
R
n
R
m


dAR 

R
R   R  1 k  r
For rays that are different at t he receiving end
and
n
m
1
AR
 exp jk r
R


  Rn   Rm dAR  n,m
area
However, some rays t hat are different at the t ransmitt ingwill
endbe
nearly parallel at the receiving end and will not satisfy t he condition
    1 k  r
R
n
July 2003
R
m
R
9
© 2003 by H. L. Bertoni
Averaging at Both Ends of Link
T he double ended space average is
P
R
  an a e

m
 j( c ) Ln0 L m0 
n1 m1
 1

AT
 exp jk r
T

  
area
 1
 
AR
 exp jk r
R
T
n

R

  
R
n
area
Rays will either satisfy Rn   Rm 1 k  r
T
m

dAT 

R
m


dAR 

at t he receiving endor
 Tn   Tm 1 k  rT at t he transmit ting end. T hus
 1

AT




T
T T
exp

jk
r


dA

T 
n
m
area

 1
 
AR
July 2003
 exp jk r
area
10
R

  
R
n
R
m


dAR   nm

© 2003 by H. L. Bertoni
Double Ended and Frequency Averages
T hus t he double ended space average P   an
2
is t he sum of t he
n
ray powers
Since k   c the frequency average of t he power is
P r, f     an am
1
exp j( c)Ln  Lm d

  

n1 m 1
If   c Ln  Lm  for all rays,t hen
1

 exp j( c)L
n
 Lm d  nm

and again P   an
2
n
For smaller values of , combining averaging at one end wit h
frequency averaging will result in summ ing ray powers
July 2003
11
© 2003 by H. L. Bertoni
Fading on LOS and Non-LOS Indoor Links
f = 5.2 GHz
Received Power (dBm)
Rx rotated around a circle
of 0.4 m diameter in 1 min
600 samples taken of the
received power
H.K. Chung and H.L. Bertoni, "Indoor
Propagation Characteristics at 5.2 GHz in
Home and Office Environments," Journal
of Communication and Networks; Vol. 4;
No. 3; pp. 176-188, 2002.
Sample number around a 22l circle
July 2003
12
© 2003 by H. L. Bertoni
CDF of Fading for LOS and Non-LOS Links
f = 5.2 GHz
H.K. Chung and H.L. Bertoni, "Indoor
Propagation Characteristics at 5.2 GHz in
Home and Office Environments," Journal
of Communication and Networks; Vol. 4;
No. 3; pp. 176-188, 2002.
Normalized Power (dB to mean)
July 2003
13
© 2003 by H. L. Bertoni
Frequency Dependent Fading at 5.2 GHz
H.K. Chung and H.L. Bertoni, "Indoor Propagation Characteristics
at 5.2 GHz in Home and Office Environments," Journal of
Communication and Networks; Vol. 4; No. 3; pp. 176-188, 2002.
10 - 15 dB fades on LOS links
15 - 20 dB fades on N-LOS links
Fade separation ~ 25 MHz corresponds to path length differences Li - Lj ~ 12
m
July 2003
14
© 2003 by H. L. Bertoni
Summary of Fading Characteristics for
In-Building Links
• Symmetric links experience fading at both ends
• Motion at one end effects the spatial average at the other end
• Double ended averaging is required to measure properties
from one small area to another small area
• Averaging over frequency is equivalent to a double ended
average over space
• Indoor spatial fading has Rayleigh, even for LOS links
• Deep frequency fading with separation ~ 25 MHz
July 2003
15
© 2003 by H. L. Bertoni
Amplitude Dependence of Indoor
Signals
• Wall and floor loss
• Range dependence
• Blockage by people
July 2003
16
© 2003 by H. L. Bertoni
Approximate Measure of Wall Loss
Receiving antenna on rotor is placed in
Living Room and transmitting antenna
placed at locations throughout building.
The received power is averaged (in watts)
over the rotor circle.
Excess path loss is obtained by subtracting
(in dB) the calibrated free space path loss
Calibrated free space loss is that measured
with the antennas outdoors and adjusted to
the actual antenna separation using 1/r2
distance dependence
H.K. Chung and H.L. Bertoni, "Indoor Propagation
Characteristics at 5.2 GHz in Home and Office
Environments," Journal of Communication and
Networks; Vol. 4; No. 3; pp. 176-188, 2002.
July 2003
17
© 2003 by H. L. Bertoni
Excess Path Loss Measured at 5.2 GHz
One interior wall between Tx,Rx
Two interior walls between Tx, Rx
Through floor loss
July 2003
Exterior and filled closed loss
18
© 2003 by H. L. Bertoni
Summary of Excess Wall Loss at 5.2 GHz
H.K. Chung and H.L. Bertoni, "Indoor Propagation
Characteristics at 5.2 GHz in Home and Office
Environments," Journal of Communication and
Networks; Vol. 4; No. 3; pp. 176-188, 2002.
July 2003
19
© 2003 by H. L. Bertoni
Wall Loss at 2.45 GHz
July 2003
20
© 2003 by H. L. Bertoni
Wall Loss at 900 - 1800 MHz
• COST Action 231 (ISBN 92-828-5416-7) for 900 - 1800 MHz:
– Light wall loss = 3.4 dB
– Concrete or brick wall loss = 6.9 dB
– Floor penetration loss = 18.3 dB
• D. Pena, et al, “…Losses in Brick and Concrete Walls for 900MHz..”, IEEE Trans, AP-51, p.31.
– Brick wall loss ~ 5.6 dB
– Reinforced concrete wall ~ 15 dB
• Lafortune and M. Lecours, “… Losses in a Building at 900
MHz,” IEEE Trans, VT 39, p. 101.
– Light concrete wall loss ~ 5 dB
– Reinforce concrete floor loss ~ 25 dB
July 2003
21
© 2003 by H. L. Bertoni
Floor Plan of an Academic Building
J. Lafortune and M. Lecours, “Measurement and Modeling of Propagation Losses in a Building at 900
MHz,” IEEE Trans. on Veh. Tech., vol 39, pp. 101-108, 1990.
July 2003
22
© 2003 by H. L. Bertoni
Path Loss Over Floor of Academic Building
July 2003
23
© 2003 by H. L. Bertoni
Distance Dependence of Average Signal
Inside Large Building at 850 MHz
Excess Loss
at 100 m is
~ 45 dB
so that
45

 0.45
100
Devastravatham, et al., Proc. IEEE ICC’90, p. 1334
July 2003
24
© 2003 by H. L. Bertoni
Estimating Average Path Loss by Accounting
for Wall Transmission Only
l 
2
PG  
T
n
4 R  
n
If t he average wall separat ion is S,
we define  (dB/ m) from relation
2
-1
2
- S /10
Tn = 10
or  =
10log Tn
S
2
R

S

 l  R/10
 l 
10
or PGdB  20log
 20log R  R
4R 
4 
At 850 MHz,wall loss ~ 2 dB, and if S  5 m , t hen   0.4 dB / m
2
Now PG 
July 2003
25
© 2003 by H. L. Bertoni
WalkAbouts Inside a Building
For propagation over one floor
:
 l  R /10
PG 
10
 3.2  1015
4 R 
Rearanging t he inequality
2
 l 
1
12
R  10


0.8810
4   3.2 1015
Solve by trial and error assuming
  0.45:
2
2
R /10
forR  165 m
R /10
R  10
2
 0.72 10
12
Maximum horizontal size of many buildings
< 75 m
July 2003
26
© 2003 by H. L. Bertoni
Path Loss Between Floors
2.62 m
9.20 m
TX

1.3 m
1.3 m

RX
2.1 m
7.50 m
Number of floors separating Tx and Rx
Other paths that go outside of the building will dominate the path gain when
floor loss becomes large.
July 2003
27
© 2003 by H. L. Bertoni
~ 20 dB Fades Due to People Blocking Path
Time in seconds
Time in seconds
Belt mounted Tx as wearer rotates
while standing in same location
Person crossing the path between
Tx and Rx 70 cm in front of Tx
July 2003
28
© 2003 by H. L. Bertoni
Summary of Amplitude Dependence Indoors
• Wall and floor loss increase somewhat with frequency
– Plaster board walls ~ 3 - 6 dB, wood floors ~ 9 dB
– Concrete walls ~ 7 dB, concrete floors ~ 10 - 20 dB
• Range dependence
– Some guiding in hallways reduces loss compared with free space
– Excess loss due to propagation through walls gives exponential decrease
with distance
– Propagation between floors may take diffraction paths when floor loss is
high
• Blockage by people moving close to one end of link results in 20
dB fades
July 2003
29
© 2003 by H. L. Bertoni
Spatial Fading of Pulsed Signals
•
•
•
•
July 2003
Envelope Detector
Impulse versus pulse response
Power delay profiles
Fading statistics
30
© 2003 by H. L. Bertoni
Detector Output for Pulsed Source
Envelope of received voltage
Ve(t)
Transmitted Pulse
p(t) e jt
Exam ple:
f  2 GHz, T  1 f  0.5 n
t
t
Bandwidt h = BW = 5 MHz
Period Average Received Power
Pulse width~ 1 BW = 200 ns
Pt  V t  1 R
2
Received Pulse
Ve( t ) e j t
P(t)
t
July 2003
Power delay profile
t
31
© 2003 by H. L. Bertoni
Time Delay Profiles for Pulsed Sources
Transmission in a
large office building
Transmission in a city
of mixed size buildings
Experimental License Progress Report to FCC from Telesis Technology Laboratory, August, 1991.
July 2003
32
© 2003 by H. L. Bertoni
Impulse Response Due to Multipath
Source
(t)
V(t)
t
Received Volt age V t   an t   n 
n
an  amplitude ofn ray
th
 n  Ln /C  t ravel t im e of the
n th ray
For non- overlapping im pulses,
Pt  V t    an2t   n 
2
n
 sum of ray powers
July 2003
33
© 2003 by H. L. Bertoni
Multipath Response for Finite Width Pulse
V(t)
Source
p(t) e j t
Overlapping Pulse Envelopes
t
Clusters of rays arrivals that overlap in time
Received Volt age V t   an pt   n e jk Ln e jt
n
For partially overlapping pulses,
Pt  V t    an am pt   n  pt   m e jk Ln  Lm
2
n
m
P hase differences lead t o fading of ray clust ers
July 2003
34
© 2003 by H. L. Bertoni
Spatial Fading of Ray Clusters
Seen from Power Delay Profiles at 16 Points Along a Line and Separated by l /4
Tx
LOS
N-LOS
location
location
x
l/4
x
x1
l/4
July 2003
x1
35
© 2003 by H. L. Bertoni
Indoor Power Delay Profiles at 2.4 GHz
Line-of-Sight link
Obscured link
H.L. Bertoni, S. Kim and W. Honcharenko, "Review of In-Building Propagation Phenomena at UHF Frequencies,", Proc. of the IEEE
ASILOMAR-29, pp. 761-765, 1996.
July 2003
36
© 2003 by H. L. Bertoni
Determining the Fading Statistics of Individual
Receive Pulses
1. Divide received signal into N time bins of duration Tc.
2. Average voltage envelope at each location xm over time bins
1 nTc
Vm,n 
Ve x m,t dt

T  n1Tc
3. Normalize voltage in each time bin to the average over all locations xm
rm,n 
Vm,n
1 15
V
16 m  0 m,n
4. Construct CDF for the 16N values of the random variable rm,n
July 2003
37
© 2003 by H. L. Bertoni
CDF of Indoor Pulse Fading Statistics
(a) Engineering Building
(b) Retail Store
S. Kim, H. L. Bertoni and A Stem, "Pulse Propagation Characteristics at 2.4 GHz Inside Buildings,” IEEE
Trans. on Veh. Tech., Vol. 45, pp. 579-592,1996.
July 2003
38
© 2003 by H. L. Bertoni
Spatial Averaging of Power Delay Profile
P t  
1
P t, rdA

A areea
In term s of individually arrival rays
Pt, r    an am pt   n  pt   m e jk Ln  Lm 
A
r
n
n1 m 1
where an is the complex ray amplitude.
If  n is a unit vector in the direction of
m
t hen th ray at t he center of the area t hen, Ln
Ln  Ln0   r   n
Ln 0
 n  Ln c   n0   n
where
Tx
 n   r   n c
July 2003
39
 n  r
Lm 0
© 2003 by H. L. Bertoni
Spatial Average Power Profile (cont.)
Tc  widt h of pulse  1 BW  1 10MHz  100ns.
Relative delay  n  1m c  3.3ns  Tc .
Because  n  TC
pt   n 0   n pt   m 0   m   pt   n 0  pt   m 0 
and
Pt, r    an am pt   n 0 pt   m 0 e jkL n0  Lm0  exp jk r   n   m 
n1 m 1
T he spat ial average becom es
P t     a a pt   n 0 pt   m 0 e
 jk L n0  Lm0 

n m
n1 m 1
If  n   m 1 k  r for all n  m, t hen
1
A
1
A
  exp jk r  
n
  m  dA
area
  exp jk r  
n
  m dA   n,m
area
and Pt   an p t   n .
2
2
n
July 2003
40
© 2003 by H. L. Bertoni
Method for Finding Small Area Time Delay Profile
Fixed Unit
1.2 meter
(4 Foot)
Square
Individual power delay profiles (offset 50 dB)
D. M. J. Devasirvatham, "Multipath Time Delay Spread in the Digital
Portable Radio Environment," IEEE Communications Magazine, vol. 25,
pp. 13-21, 1987.
Average of power delay profiles
July 2003
41
© 2003 by H. L. Bertoni
Delay Spread and Coherence
Bandwidth
• Measures of delay spread
• Comparison of time and frequency response
• Coherence Bandwidth
July 2003
42
© 2003 by H. L. Bertoni
Excess Delay and RMS Delay Spread
Mean Excess D elay

T0 
 tP t dt
0

 Pt dt
0
RMS Delay Spread

 R2 MS 
2
t

T
P t dt


0

0

 Pt dt
0
T.S. Rappaport, Wireless Communications, Prentice Hall PTR, Upper Saddle River,
NJ, p.163, 1996.
July 2003
43
© 2003 by H. L. Bertoni
Delay Spread vs Distance and Room Size
50
House4
40
House3
House2
Mean RMS Delay Spread (nsec)
30
20
10
0
2
4
6
8
10
Separation on LOS Paths (m)
70
60
50
40
30
House
20
Office1
10
Office2
0
100
200
300
400
Room Area (m2)
July 2003
44
H.K. Chung and H.L. Bertoni, "Indoor Propagation
Characteristics at 5.2 GHz in Home and Office
Environments," Journal of Communication and
Networks; Vol. 4; No. 3; pp. 176-188, 2002.
© 2003 by H. L. Bertoni
Coherence Bandwidth of the Channel
• Pulse response carries information about the frequency
dependence of the channel
– Fourier transform of the complex voltage envelope for pulsed
source gives the channel transfer function over the bandwidth
of the transmitted pulse
1
H( f ) 
2

 V (t)exp(j2ft)dt

Requires phase information of V (t).
– Fourier transform of the received power envelope for pulse sources
gives the coherence function for frequencies separated by f
1 
2
R(f ) 
V (t) exp(j2ft)dt

2 
Does not require phase information
July 2003
45
© 2003 by H. L. Bertoni
Fourier Transform Pair of Channel Response
Multiple rays on non-LOS path
Dominant ray on LOS path
A.A.M. Saleh, et al, “Distributed Antennas for Indoor Radio
Communications,”IEEE, CH2424-0/87/0000-0076, 1987
July 2003
46
© 2003 by H. L. Bertoni
Coherence Function from Measured |H(f)|
C(f,f)
For real volt ages,
Correlation funct ion
E Vi ( f )Vi ( f  f )  E Vi ( f )
2
C( f ,f ) 
July 2003


E Vi ( f )  E Vi ( f )
2
2
47
© 2003 by H. L. Bertoni
Coherence Bandwidth of Channels
(f = 5.2 GHz)
July 2003
48
© 2003 by H. L. Bertoni
Coherence Function from Impulse Response
Channel responseh(t) in t he time dom ain andH ( f ) in t he frequency domain
Coherence function: R(f )  E H  ( f  f )H ( f )
Using the Fourier represent at ion for
H ( f ) in t erms ofh(t)
  *

j 2   f  f  t1  f t2 
Rf   E   h (t1 )h(t 2 )e
dt1dt2 
 


  Eh (t )h(t )e

*
1
j 2   f  f  t1  f t2 
dt1 dt2
2


For random uncorrelat ed scat terers
E h (t1 )h(t2 ) E h(t1 )
*

and Rf  
 E  h(t ) e
2
j 2  ft1
1

Making t he spat ial ergodic assumpt ion
E h(t1 )
t hen R f  
 P t
(t  t )
1
2
dt1


2
2

h(t1 )
2
 P t
e j 2 ft dt1

July 2003
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© 2003 by H. L. Bertoni
Example of Coherence Function
Suppose t hat t he power delay profile is
exponential in time
1
P(t) 
expt  R MS U t 
2 R MS
T hen the coherence funct ion is given by

 2
R(f ) 
1
0

expt  R MS e
j 2 ft
P(t) dB
t
dt
R MS

1 
1
2 
1 j2f R MS 

1
1
Magnitude of t he coherence funct ionR(f ) 
2 1 2f 2
R MS
will have value equal to 1/2 it s maximum when
2 f  R MS  3 or
f 
July 2003
3
2 R MS
50
© 2003 by H. L. Bertoni
Measured Delay Profile and Its Transform
(Retail Store, f = 2.4 GHz)
P(t)
R(f)
S. Kim, H. L. Bertoni and A Stem, "Pulse Propagation Characteristics at 2.4 GHz Inside Buildings,” IEEE
Trans. on Veh. Tech., Vol. 45, pp. 579-592,1996.
July 2003
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© 2003 by H. L. Bertoni
Coherence Bandwidth of Channels
(Engineering Building and Retail Store, f = 2.4 GHz)
LOS Path
Lightly Obstructed Path
Heavily Obstructed Path
Engineering Building
Site
f = f 1- f 2 (MHz)
42.62
east1
45.82
east2
18.5
s1
44
s2
30.3
ne2
10.75
east3
8.46
nw1
8.85
s3
6.5
s4
7.11
sw1
Retail Store
site
f = f 1- f 2 (MHz)
>100
ke1
36
kn1
kse1
ksw1
kw2
kne1
kw1
5.94
7.45
5.53
5.03
6.71
f1 and f2 are the values at which R(f) is 1/2 its maximum value
S. Kim, H. L. Bertoni and A Stem, "Pulse Propagation Characteristics at 2.4 GHz Inside Buildings,” IEEE
Trans. on Veh. Tech., Vol. 45, pp. 579-592,1996.
July 2003
52
© 2003 by H. L. Bertoni
Summary of Delay Spread and Coherence
Bandwidth
• Indoor LOS paths at 1.5 and 2.4 GHz
– Impulse response and derived coherence function show dominant early
arrival that has slow spatial fading
– Weak frequency dependence of the channel transfer function H( j ) and
wide coherence bandwidth {for R(f)/R(0) = 1/2}
• Indoor LOS paths at 5.2 GHz
– No dominant arrival, Rayleigh spatial fading, rapid variations of H( j )
similar to n-LOS paths
• N-LOS paths have many rays of nearly equal amplitudes
– Many echoes stretched over time
– Rapid spatial fading of individual peaks
– Rapid frequency fading of H( j )
– Narrow coherence bandwidth
July 2003
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© 2003 by H. L. Bertoni