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SMART ANTENNAS FOR THIRD GENERATION TDMA (EDGE)
Jack H. Winters
AT&T Labs - Research
Red Bank, NJ 07701-7033
October 3, 2000
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OUTLINE
• Smart Antenna Overview
• 2G System Applications
• 3G System Applications:– EDGE– MIMO-EDGE– OFDM-MIMO-EDGE
• Conclusions
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WIRELESS SYSTEM IMPAIRMENTSWireless communication systems are limited in performance and capacity by:
Delay Spread CoChannel
Interference
Rayleigh Fading
Limited Spectrum
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SMART ANTENNAS
Today: Cellular systems with sectorization (120°) handoffs between sectors
For higher performance Narrower sectors Too many handoffs
Smart Antenna definition: Multibeam antenna or adaptive array without handoffs between beams
f1
f2
f3
f4
f5
f6
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Smart Antennas
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
SIGNAL OUTPUT
SIGNAL
INTERFERENCE
INTERFERENCEBEAMFORMER
WEIGHTS
SIGNAL OUTPUT
BEAM SELECT
SIGNAL
BE
AM
FOR
ME
R
Adaptive Antenna ArraySwitched Multibeam Antenna
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BASE STATION DIVERSITY OPTIONS (4 ANTENNAS)
24 (12 ft)3 (1.5 ft)
3 or 24
Spatial Diversity Angle DiversityPolarization
Diversity
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Smart Antennas
Rooftop Base Station Antennas
11.3 ft
Prototype Dual Antenna Handset
Prototype Smart
Antenna for Laptops
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INTERFERENCE NULLINGLine-Of-Sight Systems
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
User 1
User 2
User 1
Signal•••
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INTERFERENCE NULLINGMultipath Systems
User 1
User 2
User 1
Signal•••
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).
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MIMO CAPACITY INCREASE
• With M antennas at both the base station and mobiles, M independent channels can be provided in the same bandwidth if the multipath environment is rich enough.
• 1.2 Mbps in a 30 kHz bandwidth using 8 transmit and 12 receive antennas demonstrated by Lucent (indoors).
• Separation of signals from two closely-spaced antennas 5 miles from the base station demonstrated by AT&T/Lucent.
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• Delay spread: Delay spread over [(M-1) / 2]T or M-1 delayed signals (over any delay) can be eliminated
• Typically use temporal processing with spatial processing for equalization:
EQUALIZATION
LE
LE
MLSE/DFE
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SMART ANTENNAS IN SECOND GENERATION SYSTEMS
• IS-136 TDMA:– On uplink, with two receive antennas, in 1999
changed from maximal ratio combining to MMSE combining
• Software change only - provided 3-4 dB gain in interference-limited environments
• Combined with power control on downlink (software change only) - increased capacity through frequency reuse reduction
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SMART ANTENNAS IN SECOND GENERATION SYSTEMS
• Techniques proposed a decade before implementation, but:– MMSE combining: SMI degrades performance
when interference is not present• Solution: Diagonal loading with beta=f(I/N)
– Power control: 1 second reporting delay of mobile BER and RSSI – unstable at pedestrian speeds
• Solution: Use uplink RSSI (diversity) with mobile BER
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SMART ANTENNAS IN SECOND GENERATION SYSTEMS
• IS-136 TDMA:– On uplink, with two receive antennas, in 1999 changed
from maximal ratio combining to MMSE combining• Software change only - provided 3-4 dB gain in interference-
limited environments
• Combined with power control on downlink (software change only) - increased capacity through frequency reuse reduction
– Use of 4 antennas (adaptive array uplink/multibeam, with power control, downlink) extends range and/or doubles capacity (N=7 to 4 or 3)
• Clears spectrum for EDGE deployment (2001)
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IS-136 Smart Antenna System
ADAPTIVE ANTENNA RECEIVER
4 Branches
TRANSMITTER
RADIO UNIT
RSSI, BER
DUPLEXERS
BEAM SCANNING RECEIVER
1 per N radios•
SP
LIT
TE
R
Power ControlShared LPAs
Atten
Atten
Atten
Atten
• 4 Branch adaptive antenna uplink for range extension and interference suppression
• Fixed switched beam downlink with power control for increased coverage and capacity
• Uplink and downlink are independent
• Shared linear power amplifiers reduce amplifier requirements to handle maximum traffic load
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SMART ANTENNAS IN THIRD GENERATION SYSTEMS: EDGE
• High data rate ( 384 kbps) service based on GSM, for both Europe and North America
• 8PSK at 270.833 ksps
• 26 symbol training sequence
• 1/3, 3/9 or 4/12 reuse
576.92 s
58 5826 8.2533
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ADAPTIVE ARRAYS IN EDGE
Spatial-Temporal processing using DDFSE for interference suppression
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ADAPTIVE ARRAYS IN EDGE
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DDFSEEqualizer
ChannelDecoder
Rx
Rx
OutputData
EDGE Smart Antenna ProcessingDual Diversity Receiver Using Delayed Decision Feedback Sequence Estimator
for Joint Intersymbol Interference and Co-channel Interference Suppression
• Simulation results show a 15 to 30 dB improvement in S/I with 2 receive antennas
• Real-time EDGE Test Bed supports laboratory and field link level tests to demonstrate improved performance
Wireless Systems Research
Blo
ck E
rro
r R
ate
Signal -to-Interference Ratio (dB)
EDGE with Interference Suppression in a Typical Urban Environment
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Multiple-Input Multiple-Output (MIMO) Techniques for 3G Wireless Systems
• Multiple antennas at both the base station and terminal can significantly increase data rates if the multipath environment is rich enough
sufficient multipath low correlation high spectral efficiency
• With 4 transmit and receive antennas 4 independent data channels can be provided in the same bandwidth
• Data rates as high as 1.5 Mbps (4x384 kbps) may be possible for EDGE or as high as 40 Mbps for Wideband OFDM (also can be used in WCDMA/HDR)
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MIMO-EDGE
• Goal: 4 transmit / 4 receive antennas in EDGE can theoretically increase capacity 4-fold with the same total transmit power (3.77X384 kbps = 1.45 Mbps is actual theoretical increase)
• Issues:– Joint spatial-temporal equalization
– Weight adaptation
– Mobile channel characteristics to support MIMO-EDGE
• Our approach:– Development of multi-antenna EDGE testbed
– Development of 2X2 and 4X4 DDFSE architecture with MMSE combining using successive interference cancellation
– Mobile channel measurements
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MIMO Channel Testing
TxW1
TxW2
TxW3
TxW4
LO
Synchronoustest
sequences
Rx
Rx
Rx
Rx
• Record complex correlation of each transmit waveform on each receive antenna, C4x4
• Compute CHC correlation matrix to determine potential capacity and predict performance
• Compute fading correlation across receive array
LO
Mobile Transmitter Test Bed Receiver with RooftopAntennas
Transmit Antenna Configurations
Space diversity
Space / polarization diversity
Space / pattern diversity
Space / polarization / pattern diversity
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MIMO Channel Measurement System
Transmitter
• 4 antennas mounted on a laptop
• 4 coherent 1 Watt 1900 MHz transmitters with synchronous waveform generator
Receive System
• Dual-polarized slant 45° PCS antennas separated by10 feet and fixed multibeam antenna with 4 - 30° beams
• 4 coherent 1900 MHz receivers with real-time baseband processing using 4 TI TMS320C40 DSPs
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EDGE with Wideband OFDM - MIMO Downlink
• High data rates (>1 Mbps) required on downlink only
• OFDM eliminates need for temporal processing => simplified MIMO processing for much higher data rates
• With 1.25 MHz bandwidth, QPSK, OFDM-MIMO with 4 antennas at base station and terminal => 10 Mbps downlink
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SMART ANTENNA EVOLUTION FOR TDMA
• IS-136:
• Optimum combining uplink / power control downlink at all base stations with existing 2Rx/1Tx antennas
• 4Rx/4Tx antenna upgrade (adaptive uplink/multibeam downlink) for N=7 to 4 to clear spectrum for EDGE
• EDGE:
• S-T processing with IS-136 smart antennas (Data followed by VoIP)
• MIMO-EDGE (1.5 – 2.4 Mbps)
• Wideband OFDM-MIMO downlink (10 - 40 Mbps)
• 4Rx/4Tx base station with software radio for software evolution at base station with terminal replacements
• Research issues: Deployment strategies / integration with DCA, PC, adaptive modulation and coding / improved weight adaptation with CCI