Beamforming Antennas for Wireless Communications

1
Beamforming Antennas for Wireless
Communications
Yikun Huang, Ph.D. ECE/CCB Yikun_at_cns.montana.edu N
ovember 24 2003
2
Outline
Introduction
Beamforming and its applications Beamforming
antennas vs. omnidirectional antennas
Phased Array Antennas
Direction of arrival (DOA) estimation Beamforming
Basic configurations fixed array and adaptive
array smart antenna systemsswitched array and
adaptive array
Vector Antennas
DOA and polarization super CART 3-loop and 2-loop
vector antenna array Direction of arrival (DOA)
estimation Vector antenna vs. phased array antenna
Beamforming antennas for WLAN

• Infrastructure mode
• An indoor WLAN design
• Ad hoc mode
• Ad hoc WLAN for rural area

Conclusion
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Applications of beamforming technology
Source B.D.Van Veen and K.M. Buckley, University
of Michigan, Beamforming A Versatile approach
to spatial filtering,1988
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Phased array RADAR
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Phased array spike sorting
Center for Computational Biology, MSU
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Patterns, beamwidth Gain
side lobes
Main lobe
top view(horizontal)
nulls
Half-power beam width
Half-power beam width
Half-power beam width
side view(vertical)
Isotropic dipole
half-wave dipole
beamformer
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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
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Beamformers vs. omnidirectional antennas
2) Beamformers can reject interference while
omnidirectional antennas cant Improve SNR and
system capacity!
null
3) Beamformers directionally send down link
information to the users while omnidirectional
antennas cant save energy!
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Beamformers vs. omnidirectional antennas
4) Beamformers provide N-fold diversity Gain of
omnidirectional antennas increase system
capacity(SDMA)
5) Beamformers suppress delay spreadimprove
signal quality
multipath
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DOA estimation
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Beamforming
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Basic phased array configurations
Narrowband
broadband
phased array (fixed/adaptive) configurations-time
domain
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Basic phased array configurations
phased array (fixed/adaptive) configuration-freque
ncy domain
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Smart antenna systems
Cellular communication networks
Wireless local area networks
Military networks
switched array adaptive array
switched array adaptive array
switched array adaptive array
3G Data rate100kbps
Wi-Fi Data rate11Mbps
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Smart antenna systems
top view(horizontal)
4
5
6
3
7
2
1
8
user
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16
10
15
11
14
12
13
Switched array (predetermined)
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Smart antenna systems
top view(horizontal)
Interference 1
user 1
user 2
Interference 2
Adaptive array
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Smart antenna system
 

• Example Vivato 2.4 GHz indoor outdoor Wi-Fi
  Switches
• (EIRP44dBmGain25 dBi3-beam)

www.vivato.net
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Polarization
circular
E?
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Super CART
SuperCART Compact array radiolocation
technology FlamRussell,Inc.,1990 U.S. Patent
No., 5,300,8851994 Frequency range 2 30 MHz
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3-loop
b
kb?0.5
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2-loop
Blind point
Steering vector
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Vector antennas vs. spatial array antennas
Vector antennas measure ?,?,?,?, and power
simultaneously, no phase shift device, or
synchronization is needed.
Phased array antennas with omnidirectional
element measure ?,?, and power
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Vector antennas vs. spatial array antennas
VA
VA
SA
SA
Source Nehorai,A.,University of Illinois at
Chicago
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Vector antennas vs. spatial array antennas
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Vector antennas Vs. phased array antennas
Disadvantages of vector antennas

Low profile?
f2.4GHz, ? 0.125m vector antenna size 0.0125m
0.063m Phased arrayd? ?/20.063mL(N-1)d
0.188m-0.69m(N412)
f800MHz, ? 0.375m antenna size 0.04m
0.19m Phased arrayd? ?/20.19mL(N-1)d
0.56m-2.06m(N412)
Cheap? Can use hardware and software of existing
communication systems for performance?
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Working in scattering environment
sourceM.R. Andrews et al., Nature, Vol.
409(6818), 18 Jan. 2001, pp 316-318.
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Low profile antennas with polarization diversity

1. 2-dipole(monopole)

(b) 2-loop
(c) dipole-loop
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Packet switching
A
Handoff between Aps was not standardized at the
same time as 802.11b
TDD/TDMA
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Packet switching 3 beam system
top view(horizontal)
P. Sanchis, et al. 02
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An indoor WLAN design
A 4-story office building (including basement),
high 30 m, wide 60m and long 100m. We plan to
install a Vivato switched array on the 3rd floor.
Switched array
3
2
h30m
1
Basement
w60m
L100m
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An indoor WLAN design
Data of APs antenna is from www.vivato.net
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An indoor WLAN design
Mean pathloss with smin
Allowable pathloss
Path loss model
Case 1 user is on the 3rd floor 3 concrete
walls, 3 soft partitions
The coverage ranges are r176m,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
The coverage ranges arer36m,29m,23m and 18m for
date rate at 1Mbps, 2Mbps, 5.5Mbps and 11Mbps
respectively
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Beamforming antennas in ad hoc networks
P.Gupta and P.R. Kumar,00
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Beamforming antennas in ad hoc networks
D.Lu and D.Rutledge,Caltech,02
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Beamforming antennas in ad hoc networks

• Medium Access Control Protocol(CSMA/CA)

CSMA/CAcarrier sense multiple access/collision
avoidance ( for omnidirectional antennas)

• No standard MAC protocols for directional
  antenna

• No obvious improvement for throughput using
  beamforming antennas

Neighbor discovery

• Neighbor discovery become more complex using
  beamforming antennas.

Packet routing
(Scheduled/On-demand)

• Ad hoc networks may achieve better performance
  in some cases using beamforming antennas.

• Beamforming antennas can significantly
  increasing node and network lifetime in ad hoc
  networks.

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Channel access
1) traditional exposed node problem for
omnidirectional antennas
2) Omnidirectional and directional antennas solve
the exposed node problem
A
B
C
D
E
A
B
C
D
E
RTS
RTS
RTS
CTS
CTS
CTS
CTS
RTS
DATA
DATA
DATA
CTS
CTS
DATA
The nodes are prohibit to transmit or receive
signals
DATA
DATA
DATA
DATA
The node is free to transmit or receive signals
ACK
ACK
ACK
ACK
The node is blocked to communicate with C
1) No coverage change. May save power. 2) B may
not know the location of C.
SourceY Ko et al., 00
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Channel access
3) beamforming antennas create new problems
A
B
C
D
E
A
B
C
D
E
RTS
RTS
CTS
CTS
RTS
DATA
CTS
RTS
DATA
collision
DATA
deaf
collision
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Neighbor discovery
Nt
Hello
t
A
 
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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 infrastructure
  networks performance. They may improve ad hoc
  networks performance. New MAC protocol standards
  are needed.
• Vector antennas may replace spatial arrays to
  further improve beamforming performance