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SMART ANTENNAS FOR THIRD GENERATION TDMA (EDGE)

Jack H. Winters

AT&T Labs - Research

Red Bank, NJ 07701-7033

jhw@research.att.com

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

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

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