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Beamforming Antennas for
Wireless Communications
Yikun Huang, Ph.D.
ECE/CCB
November 24 2003
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Outline
Phased Array Antennas
Vector Antennas
Beamforming antennas for WLAN
Conclusion
Introduction
Beamforming and its applicationsBeamforming antennas vs. omnidirectional antennas
Direction of arrival (DOA) estimationBeamformingBasic configurations: fixed array and adaptive array
smart antenna systems:switched array and adaptive array
DOA and polarizationsuper CART3-loop and 2-loop vector antenna arrayDirection of arrival (DOA) estimationVector antenna vs. phased array antenna
Infrastructure modeAn indoor WLAN designAd hoc modeAd hoc WLAN for rural area
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Applications Description
RADAR Phased array RADAR; air traffic control; synthetic apertureRADAR
SONAR Source location and classification
Communications Smart antenna systems; Directional transmission andreception; sector broadcast in satellite communications
Imaging Ultrasonic; optical; tomographic
Geophysical Exploration Earth crust mapping; oil exploration
Astrophysical Exploration High resolution imaging of universe
Biomedical Neuronal spike discrimination; fetal heart monitoring;tissue hyperthermia; hearing aids
Source: B.D.Van Veen and K.M. Buckley, University of Michigan, Beamforming: A
Versatile approach to spatial filtering,1988
Applications of beamforming technology
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Phased array RADAR
http://www.nssl.noaa.gov/rrdd/par/parimages/images/PAR_Dome4.jpg -
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Phased array spike sorting
0.139
0.544
E y1 n t( )
1 . 2 1 040 t
0.056
0.205
E y2 n t( )
1 . 2 1 04
0 t
0.042
0.187
Ey3n t( )
1 .2 1 04
0 t
Sorted
Spike of
individual
neurons.
1
2
3
4
1 6
5
6
7
8
9
1 4
1 5
1 3
1 2
1 1
1 0
0.139
0.534
R n 3 t( )
1.2 104
0 t
0.183
0.539
R n 5 t( )
1.2 104
0 t
0.147
0.534
R n 7 t( )
1.2 104
0 t
0.147
0.534
R n 9 t( )
1.2 104
0 t
0.183
0.539
R n 11 t( )
1.2 104
0 t
0.139
0.534
R n 13 t( )
1 .2 1 04
0 t
0.14
0.534
R n 1 t( )
1 . 2 1 04
0 t
0.148
0.534
Rn 1 5 t( )
1 . 2 1 04
0 t
Neuronal
spikesrecorded by
electrodearray
Phasedarrayspikeso
rtingsystem
Center for Computational Biology, MSU
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Patterns, beamwidth & Gain
Isotropic dipole
topview(horizontal)
sideview(vertical)
half-wave dipole beamformer
21/
Half-power
beam width
Half-powerbeam width
Half-powerbeam width
Main lobe
side lobes
nulls
21/78
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Beamformers vs. omnidirectional antennas
1) Beamformers have much higher Gain than omnidirectional antennas:Increase coverage and reduce number of antennas!
Gain:2
1
NG
GN
0
30
60
90
120
150
180
210
240
270
300
330
6
4
2
0
6
9.961 107
Field 6 0 ( )
Field 2 0 ( )
Field 1 0 ( )
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Beamformers vs. omnidirectional antennas
2) Beamformers can reject interference while omnidirectionalantennas cant: Improve SNRand system capacity!
3) Beamformers directionally send down link information to theusers while omnidirectional antennas cant: save energy!
user
interference
user
interferencenull
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Beamformers vs. omnidirectional antennas
user user
null
multipath
4) Beamformers provide N-fold diversity Gain of omnidirectional antennas:increase system capacity(SDMA)
5) Beamformers suppress delay spread:improve signal quality
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DOA estimation
kd
dkkk sinsin
2
phase delay
1 2 3 4 5 6 7 NN-2 N-1N-3
d
kk d sin
k
Plane wave
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Beamforming
phase shifters
1 2 3 4 5 6 7 NN-2 N-1N-3
k
1,,k 2,,k 3,,k 4,,k 5,,k 6,,k 7,,k N-3,,k N-2,,k N-1,,k N,,k
)sin)((
, kdN kkN 1
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phased array (fixed/adaptive) configurations-time domain
Basic phased array configurations
Narrowband
sN(k)
s2(k)
s1(k)
.
.
.
w*N
w*2
w*1
)(ky
broadband
sN(k)
s2(k)
s1(k)
.
.
.
)(ky
w*N,0 w*N,1 w*N,k-1.
.
.
Z-1 Z-1
w*2,0 w*2,1 w*2,k-1.
.
.
Z-1 Z-1
w*1,0 w*1,1 w*1,k-1.
.
.
Z-1 Z-1
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phased array (fixed/adaptive) configuration-frequency domain
Basic phased array configurations
sN(k)
s2(k)
s1(k)
.
.
.
-+
I
F
F
T
MSE
F
F
T
w*N
w*2
w*1
)(ky
)(tdF
FT
F
F
T
F
F
T
broadband
.
.
.
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Smart antenna systems
Military
networks
Cellularcommunication
networks
Wirelesslocal areanetworks
switched arrayadaptive array
switched arrayadaptive array
switched arrayadaptive array
Wi-Fi Data rate:11Mbps3G Data rate:100kbps
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Switched array (predetermined)
top view(horizontal)
Smart antenna systems
interference
user
1
2
3
45
6
7
8
9
10
1112 13
14
15
16
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user 1
Interference 1top view(horizontal)
user 2
Smart antenna systems
Interference 2
Adaptive array
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Smart antenna system
www.vivato.net
12
100
In door range(Mixed Office)
11 Mbps: up to 300m5.5 Mbps: up to 400m
2 Mbps: up to 500m1 Mbps: up to 600m
Out door range(outdoor to indoor)
11 Mbps: up to 1.00km
5.5 Mbps: up to 1.25km2 Mbps: up to 2.00km1 Mbps: up to 2.50km
Out door range(outdoor to outdoor)
11 Mbps: up to 4.20km5.5 Mbps: up to 5.10km
2 Mbps: up to 6.00km1 Mbps: up to 7.20km
Active user per switch 100
Example: Vivato 2.4 GHz indoor & outdoor Wi-Fi Switches
(EIRP=44dBm;Gain=25 dBi;3-beam)
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Polarization
circular
E
linear
=0
E
E
ellipse
=45
X
Y
Z
iE
ji eE sin
Eicos
E
E
=90
E
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SuperCARTCompact array radiolocation technology
Flam&Russell,Inc.,1990U.S. Patent No., 5,300,885;1994Frequency range: 2 30 MHz
Super CART
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3-loop
V6
V4
V3
V1 V2
V5
Y
XL
eZIV )0(0
L
eZIV )(
iHz 0
I
iEy 0
Ikb0.5
b
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2-loop
HE
S
Steering vector
a
cos
esin
sincoscossin
sin
coscossin
hh
e
e
j
z
x
z
y
0
0
00
00
0
4
H
ii E00
1222 zyx eee
1222 zyx hhh
Blind point
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Vector antennas vs. spatial array antennas
Vector antennas measure: ,,,,andpower simultaneously,no phase shift device, or synchronization is needed.
Phased array antennas with omnidirectional element measure:
,,andpower
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Source: Nehorai,A.,University of Illinois at Chicago
Vector antennas vs. spatial array antennas
VA
SA
VA SA
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Vector antennas vs. spatial array antennas
Phased array antennas: spatial ambiguities exist
2211ff sinsin
1 2 3 4 5 6 7
k
k
1 2 3 4 5 6 7
1
2
P ,,,,h,h,h,e,e,e zyxzyx Vector antenna: no ambiguities for DOA estimation
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Vector antennas Vs. phased array antennas
Disadvantages of vector antennas
Cheap?
Can use hardware and software of existingcommunicationsystems for performance?
f=2.4GHz, =0.125m; vector antenna size: 0.0125m ~ 0.063m
Phased array:d/2=0.063m;L=(N-1)d: 0.188m-0.69m(N=412)
f=800MHz, =0.375m; antenna size: 0.04m ~ 0.19m
Phased array:d/2=0.19m;L=(N-1)d: 0.56m-2.06m(N=412)
Low profile?
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source:M.R. Andrews et al., Nature, Vol. 409(6818), 18 Jan. 2001, pp 316-318.
Working in scattering environment
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(a) 2-dipole(monopole)
Low profile antennas with polarization diversity
(c) dipole-loop
(b) 2-loop
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TDD/TDMA
Packet switching
AAP1 AP2
user
Handoff between Apswas not standardized
at the same time as802.11b
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Packet switching: 3 beam system
top view(horizontal)
i
ii
P
PPd 11
P. Sanchis, et al. 02
iP
1iP
1iP
1221
12
1221
dddd
dd
i
i
i
DOA
),/(/),/(
),/(/
max
max
max
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An indoor WLAN design
A 4-story office building (including basement), high 30 m, wide 60m and long 100m. We planto install a Vivato switched array on the 3rd floor.
L=100m
h=30m
w=60m
Switched array
3
2
1
Basement
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An indoor WLAN design
Data rate 1Mbps, 2Mbps, 5.5Mbps, 11Mbps
APs EIEP 44dBm
APs antenna Gain GA 25 dBi
PC antenna Gain GP 0 dBi
Shadowing 8dB
APs antenna receiving sensitivity Smin -95dBm ,-92dBm, ,-89dBm, -86dBm
APs Noise floor -178dBm/Hz
Body/orientation loss 2dB
Soft partition attenuate factor (p= number) p1.39 dB
Concrete-wall attenuate factor(q= number) q2.38 dB
Average floor attenuation(floor number) 14.0dB(1),19.0dB(2),23.0dB(3),26.0dB(4)
Frequency 2.4GHz
Reference pathloss PL0 (LOS/NLS, r=1m) 45.9dB/ 50.3dB
Pathloss exponent (LOS/NLS, r=1m) 2.1/3.0
Pathloss standard deviation (LOS/NLS) 2.3dB/4.1dB
Average floor attenuation(floor number) 14.0dB(1),19.0dB(2),23.0dB(3),26.0dB(4)
Data of APs antenna is from www.vivato.net
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An indoor WLAN design
Mean pathloss with smin: PGSEIRPL min
osdflsmwallowable LLLLLLPL
Path loss model: )log()(
0
010
r
rPLrPL
alPLrPL )(
The coverage ranges are:r=36m,29m,23m and 18m for date rate at 1Mbps, 2Mbps,5.5Mbps and 11Mbps respectively
Allowable pathloss:
Case 1: user is on the 3rd floor: 3 concrete walls, 3 soft partitions
The coverage ranges are: r=176m,140m,111m and 88m for date rate at 1Mbps,
2Mbps, 5.5Mbps and 11Mbps respectively .
Case 2: user is in the basement : 3 floors; 2 concrete walls, 3 soft partitions
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Beamforming antennas in ad hoc networks
P.Gupta and P.R. Kumar,00
throughputo
btained
by
eachn
ode
nnlog
W~
Beam-formingantennas
?
newroutingprotocol
newchannelaccessscheme
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Beamforming antennas in ad hoc networks
interference
target
Phased patchantenna
D.Lu and D.Rutledge,Caltech,02
Z0=50
Z0=50,L/2 Z0=25,L/2
Series resonant patch array
Phased patch array
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Beamforming antennas in ad hoc networks
Medium Access Control Protocol(CSMA/CA)CSMA/CA:carrier sense multiple access/collision avoidance( for omnidirectional antennas)
(Scheduled/On-demand)Packet routing
Neighbor discovery
No standard MAC protocols for directional antenna
Ad hoc networks may achieve better performance in some casesusing beamforming antennas.
No obvious improvement for throughput using beamforming antennas
Neighbor discovery become more complex using beamforming antennas.
Beamforming antennas can significantly increasing node andnetwork lifetime in ad hoc networks.
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1) traditional exposed node
problem for omnidirectionalantennas
Channel access
Source:Y Ko et al., 00
A B C D E
RTS
CTSDATA
ACK
RTS
CTS
DATA
DATA
DATA
ACK
A B C D E
RTS
CTS CTS
DATA
DATA
ACK
RTS
CTS CTS
DATA
DATA
ACK
1) No coverage change. May save power.2) B may not know the location of C.
The nodes
areprohibit totransmit orreceivesignals
The nodeis free totransmit orreceivesignals
The node isblocked tocommunicate with C
2) Omnidirectional and
directional antennas solvethe exposed node problem
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Channel access
A B C D E
RTS
CTS
CTS
DATA
RTS
collision
deafcollision
A B C D E
RTS
CTS
DATA
DATA
RTS
3) beamforming antennas create new problems
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Neighbor discovery
AB
C
D
E
A
t
NtHello
AP Neighbors
A B,C
B A,C
C A,B,E
D E
E C,D
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Ad hoc WLAN for rural area
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Conclusion
Beamforming antenna systems improve wireless
network performance-increase system capacity
-improve signal quality
-suppress interference and noise
-save power
Beamforming antennas improve infrastructurenetworks performance. They may improve ad hocnetworks performance. New MAC protocol
standards are needed.Vector antennas may replace spatial arrays to
further improve beamforming performance