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SMART ANTENNAS FOR TDMA

Jack H. Winters

AT&T Labs - Research

Red Bank, NJ 07701-7033

jhw@research.att.com

September 7, 2000

Aggressive frequency re-use(7/21,4/12,1/3)

High spectrum efficiency Increased co-channel interference

Downlink Switched Beam Antenna

SIGNALOUTPUT

INTERFERENCE

SIGNAL

SIGNALOUTPUT

BEAMFORMERWEIGHTS

Uplink Adaptive Antenna

SIGNAL

INTERFERENCE

BEAMFORMER

BEAMSELECT

Smart antennas provide substantial interference suppression for enhanced performance

Smart Antennas for TDMA•Key enhancement technique to improve system capacity and user experience• Leverage Smart Antennas currently in development/deployment for IS-136 TDMA

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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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SMART ANTENNAS IN SECOND GENERATION SYSTEMS

• IS-136 TDMA:– On uplink, with two receive antennas, in 1999 changed

from maximal ratio combining to optimum 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 (2002)• Limited deployment at base stations

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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 Antenna 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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Spatial Diversity: S/I = 0dB, AAA with 4 antennas vs. REF with 2 antennas

INTERFERENCE SUPPRESSION- OFFSET INTERFERER

0

-0.5

-1

-1.5

-2

-2.5

-3

-3.5

-410 20 300

BE

R

AAA(avg.)

REF (avg.)

AAA (data)·REF (data)

SNR (dB)

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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

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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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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

• 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)