Transcript WOCC Talk - Jack Winters' Home Page.

Smart Antennas for Mobile Wireless
Systems
Jack H. Winters
May 6, 2003
[email protected]
[email protected]
OUTLINE
• Smart Antennas
• Adaptive Arrays
• MIMO
• System Applications
• Radio Resource Management
• Conclusions
2
Smart Antennas
Switched Multibeam Antenna
Adaptive Antenna Array
SIGNAL
BEAMFORMER
SIGNAL
BEAM
SELECT
SIGNAL
OUTPUT
SIGNAL
OUTPUT
INTERFERENCE
INTERFERENCE
BEAMFORMER
WEIGHTS
Smart Antennas can significantly improve the performance of wireless systems
• Higher antenna gain / diversity gain  Range extension and multipath mitigation
• Interference suppression  Quality and capacity improvement
• Suppression of delayed signals  Equalization of ISI for higher data rates
• Multiple signals in the same bandwidth  Higher data rates
Switched Multibeam versus Adaptive Array Antenna: Simple beam tracking, but limited
interference suppression and diversity gain
3
COMBINING TECHNIQUES
Selection:
Output
• Select antenna with the highest received signal power
• P0M = P0M
4
COMBINING TECHNIQUES (CONT.)
Maximal ratio combining:
W1

Output
WM
• Weight and combine signals to maximize signal-to-noise ratio (Weights
are complex conjugate of the channel transfer characteristic)
• Optimum technique with noise only
• BERM  BERM (M-fold diversity gain)
5
OPTIMUM COMBINING (ADAPTIVE
ANTENNAS)
• Weight and combine signals to maximize signal-tointerference-plus-noise ratio (SINR)
- Usually minimize mean squared error (MMSE)
• Utilizes correlation of interference at the antennas to
reduce interference power
• Same as maximal ratio combining when interference is
not present
6
INTERFERENCE NULLING
Line-Of-Sight Systems
User 1
•
•
•

User 1
Signal
User 2
Utilizes spatial dimension of radio environment to:
• Maximize signal-to-interference-plus-noise ratio
• Increase gain towards desired signal
• Null interference: M-1 interferers with M antennas
7
INTERFERENCE NULLING
Multipath Systems
User 1
•
•
•

User 1
Signal
User 2
Antenna pattern is meaningless, but performance is based on the number of
signals, not number of paths (without delay spread).
=> A receiver using adaptive array combining with M antennas and N-1 interferers can
have the same performance as a receiver with M-N+1 antennas and no interference, i.e.,
can null N-1 interferers with M-N+1 diversity improvement (N-fold capacity increase).
8
PHASED ARRAYS
• Fixed (or steerable) beams
• Consider cylindrical array with M elements (/2 spacing)
- Diameter  (M / 4) feet at 2 GHz
•With small scattering angle ( = 4):
r
Mobile
- Margin = 10log10M (dB)

- Number of base stations = M-1/2
- Range = M1/4
• Disadvantages:
Base Station
- No diversity gain (unless use separate antenna)
- With large scattering angle , gain is limited for beamwidths  
9
CDMA with Adaptive Array
10
Range Increase with CDMA Signals
Single beam for all
RAKE fingers results in
range limitation with
angular spread for
multibeam antenna
(phased array)
11
Range Increase with CDMA Signals - Different Beams per Finger
7
Adaptive Array
6
3M-fold
Diversity
Phased Array
Theory
60°
Normalized
Range
5
45°
20°
10°
0=3°
4
3-fold
3° Diversity
10°
20°
45°
60°
3
5 Spacing
FIXED SECTORS, 0=60°
2
10
1
2
log10 (M)
3
12
ANTENNA AND DIVERSITY GAIN
Antenna Gain: Increased average output signal-to-noise ratio
- Gain of M with M antennas
- Narrower beam with /2-spaced antenna elements
Diversity Gain: Decreased required receive signal-to-noise ratio for a given BER averaged
over fading
- Depends on BER - Gain for M=2 vs. 1:
•5.2 dB at 10-2 BER
•14.7 dB at 10-4 BER
- Decreasing gain increase with increasing M - 10-2 BER:
•5.2 dB for M=2
•7.6 dB for M=4
•9.5 dB for M=
- Depends on fading correlation
• Antenna diversity gain may be smaller with RAKE receiver in CDMA
13
DIVERSITY TYPES
Spatial: Separation – only ¼ wavelength needed at
terminal
Polarization: Dual polarization (doubles number of
antennas in one location
Pattern: Allows even closer than ¼ wavelength
 4 or more antennas on a PCMCIA card
 16 on a handset
 Even more on a laptop
14
ADAPTIVE ARRAYS FOR TDMA BASE STATIONS
AT&T Wireless Services and Research - Field Trial with Lucent
7/96-10/96
24 (12 ft)
3 (1.5 ft)
Field trial results for 4 receive antennas on the uplink:
3 (1.5 ft)
• Range extension: 40% reduction in the number of base stations can be obtained 4 to 5 dB
greater margin  30% greater range
• Interference suppression: potential to more than double capacity
Operation with S/I close to 0 dB at high speeds  greater capacity and quality
15
INTERFERENCE NULLING
Multipath Systems
User 1
•
•
•

User 1
Signal
User 2
Antenna pattern is meaningless, but performance is based on the number of
signals, not number of paths (without delay spread).
=> A receiver using adaptive array combining with M antennas and N-1 interferers can
have the same performance as a receiver with M-N+1 antennas and no interference, i.e.,
can null N-1 interferers with M-N+1 diversity improvement (N-fold capacity increase).
16
Multiple-Input Multiple-Output (MIMO) Radio
•
•
With M transmit and M receive antennas, can provide M independent channels, to
increase data rate M-fold with no increase in total transmit power (with sufficient
multipath) – only an increase in DSP
–
Indoors – up to 150-fold increase in theory
–
Outdoors – 8-12-fold increase typical
AT&T measurements show 4x data rate & capacity increase in all mobile &
indoor/outdoor environments (4 Tx and 4 Rx antennas)
–
216 Mbps 802.11a (4X 54 Mbps)
–
1.5 Mbps EDGE
–
19 Mbps WCDMA
17
MIMO Channel Testing
Test Bed Receivers with Rooftop
Antennas
Mobile Transmitters
W1
Tx
W2
Tx
W3
• Perform timing
recovery and
symbol
synchronization
Rx
• Record 4x4
complex channel
matrix
Rx
Tx
• Evaluate capacity
and channel
correlation
Rx
Tx
W4
Synchronous
test
sequences
Rx
LO
Terminal Antennas
on a Laptop
LO
11.3 ft
Prototype Dual
Antenna Handset
Rooftop Base Station Antennas
Mobile Transmitters
18
MIMO Antennas
Base Station Antennas
Laptop Prototype
• 4 patch antennas at 1900 MHz separated
by 3 inches (/2 wavelengths)
• Laptop prototype made of brass with
adjustable PCB lid
• Antennas mounted on 60 foot tower on 5 story office
building
• Dual-polarized slant 45 1900 MHz sector antennas and
fixed multibeam antenna with 4 - 30 beams
19
MIMO Field Test Results
• Measured capacity
distribution is close to the
ideal for 4 transmit and 4
receive antennas
20
Current Systems
Peak Data Rate
High performance/price
UWB
100 Mbps
3.1-10.6 GHz
802.11a
5.5GHz Unlicensed
10 Mbps
802.11b
$/Cell
$/Sub
$ 500,000
$ 500
$ 1000
$ 100
$ 100
$ 10
2.4GHz Unlicensed
1 Mbps
BlueTooth
100 kbps
2.4GHz
High ubiquity and mobility
3G Wireless
~ 2GHz
10 feet
2 mph
100 feet
10 mph
1 mile
30 mph
10 miles Range
60 mph Mobile Speed
21
Wireless System Enhancements
Peak Data Rate
UWB
100 Mbps
3.1-10.6 GHz
High performance/price
802.11a
5.5GHz Unlicensed
10 Mbps
802.11b
2.4GHz Unlicensed
1 Mbps
$/Cell
$/Sub
$ 500,000
$ 500
$ 1000
$ 100
$ 100
$ 10
Enhanced
BlueTooth
100 kbps
2.4GHz
High ubiquity and mobility
3G Wireless
~ 2GHz
10 feet
2 mph
100 feet
10 mph
1 mile
30 mph
10 miles
60 mph
Range
Mobile Speed
22
Smart Antennas for Cellular
• Key enhancement technique to increase system capacity, extend coverage, and
improve user experience in cellular (IS-136)
SIGNAL
Uplink Adaptive Antenna
SIGNAL
OUTPUT
INTERFERENCE
BEAMFORMER
WEIGHTS
SIGNAL
In 1999, combining at base stations changed
from MRC to MMSE for capacity increase
INTERFERENCE
BEAMFORMER
Downlink Switched Beam Antenna
BEAM
SELECT
SIGNAL
OUTPUT
Cellular Data
•
•
•
•
CDPD (US) < 10 kbps
GPRS = 30-40 kbps
EDGE/1xRTT = 80 kbps
WCDMA = 100 kbps (starting in Japan, but not
for several years in US)
24
WLANs: 802.11b
Barker
Barker
1 ms
11 chips
CCK
CCK
727 ns
8 chips
Key 802.11b Physical Layer Parameters:
Data rate:
Modulation/Spreading:
Transmission modes:
(dynamic rate shifting)
Chip rate:
Frequency band:
Bandwidth:
Channel spacing:
Number of channels:
• 1, 2, 5.5, 11 Mbps
• Direct Sequence Spread Spectrum (DSSS)
• DBPSK, DQPSK with 11-chip Barker code (1, 2 Mbps)
(this mode stems from the original 802.11 standard)
• 8-chip complementary code keying (CCK) (5.5, 11 Mbps)
• optional: packet binary convolutional coding (PBCC), 64 state, rate 1/2 CC
(BPSK 5.5 Mbps, QPSK 11 Mbps)
11 MHz
Industrial, Scientific and Medical (ISM, unlicensed) 2.4 - 2.4835 GHz
22 MHz - TDD
5 MHz
Total of 14 (but only the first 11 are used in the US), with only
3 nonoverlapping channels
25
WLANs: 802.11a (g in 2.4 GHz band)
3.2 ms
FFT
G
4 ms
52=48+4 tones
64 point FFT
Key 802.11a Physical Layer Parameters:
Data rate:
Modulation:
Coding rate:
Subcarriers:
Pilot subcarriers:
FFT size:
Symbol duration:
Guard interval:
Subcarrier spacing:
Bandwidth:
Channel spacing:
Frequency band:
Number of channels:
6, 9, 12, 18, 24, 36, 48, 54 Mbps
BPSK, QPSK, 16QAM, 64QAM
1/2, 2/3, 3/4
User data rates (Mbps):
52
BPSK QPSK QAM16 QAM64
4
R=1/2
6
12
24
64
R=2/3
48
4 ms
R=3/4
9
18
36
54
800 ns
312.5 kHz
16.56 MHz - TDD
20 MHz
Unlicensed national infrastructure (U-NII), 5.5 GHz
Total of 12 in three blocks between 5 and 6 GHz
:
26
Smart Antennas for WLANs
Smart
Antenna
AP
Smart
Antenna
AP
Interference
Smart Antennas can significantly improve the performance of WLANs
• TDD operation (only need smart antenna at access point or terminal for performance improvement
in both directions)
• Interference suppression  Improve system capacity and throughput
–
Supports aggressive frequency re-use for higher spectrum efficiency, robustness in the ISM band (microwave
ovens, outdoor lights)
• Higher antenna gain  Extend range (outdoor coverage)
• Multipath diversity gain  Improve reliability
• MIMO (multiple antennas at AP and laptop)  Increase data rates
27
Internet Roaming
•
Seamless handoffs between WLAN and WAN
– high-performance when possible
– ubiquity with reduced throughput
Cellular Wireless
•
•
•
•
Management/brokering of consolidated WLAN
and WAN access
Adaptive or performance-aware applications
Nokia GPRS/802.11b PCMCIA card
NTT DoCoMo WLAN/WCDMA trial
Internet
Wireless LAN’s
Enterprise
Home
Public
28
Smart Antennas
•
•
•
•
•
Adaptive MIMO
– Adapt among:
• antenna gain for range extension
• interference suppression for capacity (with frequency
reuse)
• MIMO for data rate increase
With 4 antennas at access point and terminal, in 802.11a have the
potential to provide up to 216 Mbps in 20 MHz bandwidth within
the standard
In EDGE/GPRS, 4 antennas provide 4-fold data rate increase (to 1.5
Mbps in EDGE)
In WCDMA, BLAST techniques proposed by Lucent, with 19 Mbps
demonstrated
In UWB, smart antennas at receiver provide range increase at data
rates of 100’s Mbps
29
Enhancements
•
Smart Antennas (keeping within standards):
– Range increase
– Interference suppression
– Capacity increase
– Data rate increase using multiple transmit/receive antennas
(MIMO)
•
Radio resource management techniques (using cellular
techniques in WLANs):
– Dynamic packet assignment
– Power control
– Adaptive coding/modulation/smart antennas
30
Radio Resource Management
•
Use cellular radio resource management techniques in
WLANs: Adaptive coding/modulation, dynamic packet
assignment, power control
•
Use software on controller PC for multiple access points to
analyze data and control system
• Power control to permit cell ‘breathing’ (for traffic spikes)
• Dynamic AP channel assignment
– Combination of radio resource management and smart antennas
yields greater gains than sum of gains
31
Cell Breathing in WLAN Systems
AP
AP
AP
AP
AP
AP
AP
AP
AP
AP
AP
AP
AP
AP
• Measure traffic load for each access point
• Shrink overloaded cell by reducing RF power
• Expand others to cover abandoned areas
32
Adaptive Channel Assignment
Initial Assignment
After one iteration
1
2
High traffic
load
2
3
Cochannel
interference
3
1
2
3
2
1
3
3
3
1
2
2
2
3
• Assign channels to maximize capacity as traffic load changes
33
Smart Antennas
SIGNAL
SIGNAL
OUTPUT
INTERFERENCE
INTERFERENCE
BEAMFORMER
WEIGHTS
Smart Antennas significantly improve performance:
• Higher antenna gain with multipath mitigation (gain of M with M-fold diversity) 
Range extension
• Interference suppression (suppress M-1 interferers)  Quality and capacity
improvement
• With smart antennas at Tx/Rx  MIMO capacity increase(M-fold)
34
Conclusions
• We
are evolving toward our goal of universal high-speed wireless
access, but technical challenges remain
• These challenges can be overcome by the use of:
– Smart antennas to reduce interference, extend range, increase data
rate, and improve quality, without standards changes
– Radio resource management techniques, in combination with smart
antennas, and multiband/multimode devices
35