The Evolution of TDMA to

3G & 4G Wireless Systems

Nelson Sollenberger

AT&T Labs-Research

Wireless Systems Research Division

AT&T Wireless Services

• TDMA

– European GSM over 250 million

– North American TDMA ~ 50 million

– Japanese PDC ~ 50 million

• CDMA

– North American CDMA ~ 60 million (including S. Korea)

AT&T serves over 14 million subscribers with digital

TDMA technology and some remaining analog technology,

and provides packet data service with CDPD technology

Other TDMA operators

- Rogers AT&T

- Cingular (SBC & BellSouth)

- throughout Mexico, Central & South America

Cellular Telephony Handsets

Nokia

5160

Ericsson

PD 328

Motorola

StarTAC®

ST7790 Phone

Nokia

8860

Various TDMA phones available today

TDMA parameters

• 30 KHz channels (like analog & CDPD)

• 20 msec speech frames

• 24.3 kbaud symbol rate

• 3 time-slots/users

• 7.4 kbps ACELP speech coding

• 1/2-rate channel coding on important bits

interleaved over 2 bursts in 40 msec

• Differential pi/4-QPSK modulation

TDMA Capacity Roadmap

Reuse N = 7 N = 5 N = 4

Dual band base • Operation at 800 or 1900 MHz. Calls

can be set up on either frequency band and handed between them to manage traffic

• Additional spectrum at 1900 MHz adds directly to capacity of cell

Smart Antennas • Base station antennas systems that use

digital signal processing to cancel interference

2000 2001 2002

Base Station Power Control • Base stations only transmit power required to reach

mobile with adequate signal quality resulting in lower interference

Dynamic Channel Assignment • Network automatically assigns radio frequencies to cell

sites for more efficient utilization of frequencies

Discontinuous Transmission • Mobiles transmit only during when user is speaking.

Lowers interference in the system and increases talk time

IS-136 Smart Antenna Test Bed

•Reuse of 3/9 to 4/12, instead of 7/21, approximately 2x capacity

•Two dual polarization uplink antennas, downlink multibeam

antenna with 4 - 30° beams

•Shared linear power amplifier unit with Butler matrices

•Real-time downlink power control with beam tracking

Wireless Data Terminals

Nokia 9110

3COM

Palm VII

Nokia

3G vision Sierra PCMCIA

CDPD Modem

The new

Ericsson R380

phone, which

features

wireless data

functions

WIRELESS COMPUTING

WIRELESS

GROWTH

INTERNET

GROWTH

RF & DIGITAL

TECHNOLOGY

MOBILE

SOFTWARE

- web access

- e-mail

- file transfer

- location services

- streaming audio

& video

data

rate

1 M

384 k

64 k

9.6 k IS-136

IS-136+

EDGE

Wideband

OFDM

Macrocellular Wireless Data Evolution

& AT&T’s Roadmap

CDPD

GSM

IS-95

GPRS

IS-95+

WCDMA

1995 2000 2005

PDC

5 M

HDR

EDGE Technology Enhanced Data-rates for Global Evolution

• Evolutionary path to 3G services for GSM and TDMA

operators

• Builds on General Packet Radio Service (GPRS) air

interface and networks

• Phase 1 (Release’99 & 2002 deployment) supports best

effort packet data at speeds up to about 384 kbps

• Phase 2 (Release’2000 & 2003 deployment) will add

Voice over IP capability

GPRS Airlink

• General Packet Radio Service (GPRS)

• Same GMSK modulation as GSM

• 4 channel coding modes

• Packet-mode supporting up to about 144 kbps

• Flexible time slot allocation (1-8)

• Radio resources shared dynamically between speech

and data services

• Independent uplink and downlink resource allocation

EDGE Airlink

• Extends GPRS packet data with adaptive

modulation/coding

• 2x spectral efficiency of GPRS for best effort data

• 8-PSK/GMSK at 271 ksps in 200 KHz RF channels

supports 8.8 to 59.2 kbps per time slot

• Supports peak rates over 384 kbps

• Requires linear amplifiers with < 3 dB peak to average

power ratio using linearized GMSK pulses

• Initial deployment with less than 2x 1 MHz using 1/3

reuse with EDGE Compact as a complementary data

service

GPRS Networks

• consists of packet wireless access network and IP-based

backbone

• shares mobility databases with circuit voice services

and adds new packet switching nodes (SGSN & GGSN)

• will support GPRS, EDGE & WCDMA airlinks

• provides an access to packet data networks

– Internet

– X.25

• provides services to different mobile classes ranging

from 1-slot to 8-slot capable

• radio resources shared dynamically between speech

and data services

Compact vs Classic • Classic

– 4/12 reuse

– continuous downlinks on first 12 carriers

– 2.4 MHz x2 minimum spectrum

• Compact

– 1/3 reuse in space

– frame synchronized base stations

– reuse of 4 in time for control channels

– partial loading for traffic channels

– discontinuous downlinks

– 600 KHz x2 minimum spectrum

EDGE Channel Coding and Frame Structure

464 bits

1 data block

Convolutional

Coding

Rate = 1/3

Length = 7

Puncture Interleave

Burst N

Burst N+1

Burst N+2

Burst N+3 Burst

Format

8PSK

Modulate

1392 bits 1392 bits

348 bits/

burst

348 bits 468.75 bits

156.25 symbols/slot

0 1 2 3 4 5 6 7

8 Time Slots

1 Time Slot = 576.92 µs

Tail

symbols

3

Data

symbols

58

Tail

symbols

3

Data

symbols

58

Training

symbols

26

Guard

symbols

8.25

Modulation: 8PSK, 3 bits/symbol

Symbol rate: 270.833 ksps

Payload/burst: 348 bits

Gross bit rate/time slot: 69.6 kbps - overhead = 59.2 kbps user data

20 msec frame with 4 time-slots for each of 8 bearers

EDGE Modulation, Channel Coding & Bit Rates

Scheme Modulation Maximum

rate [kb/s]

Code Rate Family

MCS-9 59.2 1.0 A

MCS-8 54.4 0.92 A

MCS-7 44.8 0.76 B

MCS-6 29.6 0.49 A

MCS-5

8PSK

22.4 0.37 B

MCS-4 17.6 1.0 C

MCS-3 14.8 0.80 A

MCS-2 11.2 0.66 B

MCS-1

GMSK

8.8 0.53 C

EDGE Link Throughput

9

EDGE Compact System Performance

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70

Probability throughput < = X per timeslot

X (kb/s)

26 users/sector at 3.5 kbps average load per user

0

10

20

30

40

50

60

70

80

90

100

0 1000 2000 3000 4000 5000

Probability packet delay < = X

X (msec)

% %

0

50

100

150

200

250

300

9 18 27 36 45

single-slot

Multi-slot

Average User Throughput (kb/s)

EDGE Classic Multi-slot Gain

Ave. # of users per sector

EDGE Evolution

• Best effort IP packet data on EDGE

• Voice over IP on EDGE circuit bearers

• Network based intelligent resource assignment

• Smart antennas & adaptive antennas

• Downlink speeds at several Mbps based on wideband

OFDM and/or multiple virtual channels

0

5

10

15

20

25

30

35

40

45

50

55

Baseline Enhanced

Norm

ali

zed

voic

e ca

paci

ty

(Erl

an

g/S

ite/

MH

z)

GSM IS-136 EGPRS/GMSK/F EGPRS/8PSK/H

30 29

50

35

11

7

20

10

7.2 MHz Spectrum

* 1/3 reuse

* no shadow fading change due to mobility

*Signal-based power control is assumed for baseline EGRPS

*SINR-based power control & LI-DCA assumed for enhanced

VoIP over EDGE Bearer Performance

• Focused on GMSK full-rate & 8PSK half-rate EDGE channels with

dedicated MAC & random frequency hopping for 7.4 kbps voice coding

*This assumes 30 mph vehicle speed for micro fading

* SINR-based power control with adaptive target

Aggressive frequency re-use

High spectrum efficiency

Increased co-channel interference

Downlink Switched Beam Antenna

SIGNAL

OUTPUT

INTERFERENCE

SIGNAL

SIGNAL

OUTPUT

BEAMFORMER

WEIGHTS

Uplink Adaptive Antenna

SIGNAL

INTERFERENCE

BE

AM

FO

RM

ER

BEAM

SELECT

Smart antennas provide substantial interference

suppression for enhanced performance

Smart Antennas for EDGE • Key enhancement technique to improve system capacity and user experience

• Leverage Smart Antennas currently in development/deployment for IS-136 & GSM

EDGE Smart Antenna Processing

Dual Diversity Receiver Using DDFSE for Joint ISI

and CCI Suppression

Deinter-

leaver

Viterbi

Decoder

Soft Output

Output

Data

Receiver

Feed-forward

Filter

Symbol Timing

and Recovery

DDFSE

Equalizer

Equalizer

Training

Rx Rx Filter

Rx Rx Filter Feed-forward

Filter

• Simulation results show a 15 to 30

dBimprovement in S/I with 2 receive

antennas

• Real-time EDGE Test Bed supports

laboratory and field tests to demonstrate

improved performance

Jack Winters

Hanks Zeng

Ashutosh Dixit

EDGE 2-Branch Smart Antenna Performance Laboratory Tests

EDGE MCS-5 with Interference Suppression in a

Typical Urban Environment

Blo

ck

Err

or

Rate

Signal-to-Interference Ratio (dB)

20 dB SNR

Laboratory results show a 15 to 30 dB improvement

in S/I with 2 receive antennas

Improvement with Terminal Diversity and

Interference Suppression: User Experience

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70

No Diversity

Simple

DiversityInterference

Suppression

Prob. (throughput <=X) (%)

X (kb/s)

Typical user throughput increased from 30 to 45 kbps per time-slot

Prototype Dual Antenna

Handset

External Whip

Internal Patch

Multi-cell EDGE Compact Simulation

- 1/3 reuse

- 18 users per sector

- 3.5 kbps average load per user

• spectrum - 500 MHz to 3 GHz

• 3G EDGE/WCDMA network for uplink, downlink,

control and signalling

• 4G WOFDM high speed downlink

“a wireless cable modem”

• Complement to EDGE/UMTS

• High peak data rates (up to 10 Mb/s)

in a 5 MHz channel

4G Wireless: One View

Path Loss and Fading Challenge

Delay

Spread

Rayleigh

Fading

Path

Loss

rapid fading of 20 to 30 dB

(power varies by 100 to 1000 times

in level at rates of about 100 times per second)

path loss up to

~ 150 dB

(that is a 1 followed

by 15 zeroes)

Reflected signals

arrive spread out

over 5 to 20

microsecond

Cellular Interference Challenge

0.001

0.01

0.1

1

-5 0 5 10 15 20 25

1|3 reuse

2|6 reuse

3|9 reuse

4|12 reuse

7/21 reuse

Signal to Interference ratio in dB

Cum

ula

tive

Pro

bab

ilit

y

Each base station is equipped

with three 120 degree directional

antennas to reduce interference

& improve capacity

AT&T Labs-Research Work on 4G

• Smart antennas

• Multiple-Input-Multiple-Output Systems

• Space-Time Coding

• Dynamic Packet Assignment

• Wideband OFDM

MIMO Radio Channel Measurements

• Multiple antennas at both the base station and terminal can significantly increase data rates with sufficient multipath

• Ability to separate signals from closely spaced antennas has been demonstrated indoors and in AT&T-Lucent IS-136 field trial

• Lucent has demonstrated 26 bps/Hz in 30 kHz channel with 8 Tx and 12 Rx antennas indoors

• AT&T has performed measurements on 4 Tx by 4 Rx antenna configurations in full mobile & outdoor to indoor environments

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 by

10 feet and fixed multibeam antenna with 4 - 30° beams

• 4 coherent 1900 MHz receivers with real-time baseband

processing using 4 TI TMS320C40 DSPs

MIMO Measured Channel Capacity Potential Capacity Relative to a Single Antenna System

• Capacity increase close to 4 times that of a single antenna is possible with 4 transmit and 4 receive antennas

• Capacity for pedestrians is similar to mobile users

Performance Measure

• Complex channel measurement: H = [ H ij] for the ith

transmit and jth receive antenna

• Capacity (instantaneous and averaged over 1 second)

for 4 TX by 4 RX:

C = log2(det[I + (/4)H†H]) = log2(1 + (/4)i)

where is the total signal-to-noise ratio per antenna and

i is the ith eigenvalue of H†H

• To eliminate the effect of shadow fading, the capacity is

normalized to the average capacity with a single

antenna:

Cn = log2(1 + (/4)i) / (1/16) log2(1 + Hij)

Multiple Input Multiple Output Wireless

• RX diversity - HF, terrestrial microwave, cellular….

• TX frequency offset diversity & simulcasting for paging - 70’s

• Adaptive array processing in military systems

• TX diversity - 80’s

– frequency offset (channel decoding combining)

– delay (equalizer combining)

• Optimum combining for cellular (multipath channels) - 80’s

• Space-division multiple access - 80’s & 90’s

– angle-of-arrival based

– multi-path based (supports co-location & multi-channels per user)

• MIMO - 80’s & 90’s

– Multiple spatial channels using adaptive antenna arrays

– BLAST - successive interference cancellation combined with coding

– Space-Time coding

Space-Time Coding

How do you enhance TX delay diversity ( a repetition code)?

Multiple Antennas increase System

Capacity

• MIMO (BLAST & space-time coding) techniques

increase bit rate and/or quality on a link by creating

multiple channels and/or enhancing diversity

• Switched/steered beam antennas for base stations and

interference suppression/adaptive antennas for

terminals reduce interference, increasing system

capacity

OFDM for 4G Wireless

~ 6 kHz

~ 800

tones

~ 5 MHz

• OFDM is being increasingly used in

high -speed information transmission

systems:

- European HDTV

- Digital Audio Broadcast (DAB)

- Digital Subscriber Loop (DSL)

- IEEE 802.11 Wireless LAN

5 MHz channels

~ 6 KHz tones

~ 13/26 MHz sample rate

2048 FFT size (160 usec OFDM blocks)

256/512 sample OFDM block guard time

QPSK & 16-QAM modulation adaptive modulation/coding

1 to 2 msec time-slots in 20 to 40 msec frames

Mobile OFDM parameters: ex.

OFDM Characteristics • High peak-to-average power levels

• Preservation of orthogonality in severe multi-path

• Efficient FFT based receiver structures

• Enables efficient TX and RX diversity

• Adaptive antenna arrays without joint equalization

• Support for adaptive modulation by subcarrier

• Frequency diversity

• Robust against narrow-band interference

• Efficient for simulcasting

• Variable/dynamic bandwidth

• Used for highest speed applications

• Supports dynamic packet access

OFDM Robust Channel Estimation

FFT

FFT

synch word remove

data

received

signals

IFFT FFT

.

.

.

.

.

.

.

.

.

.

.

.

. . . . . .

data

Estimator 1

Estimator 2

2-branch

maximal-ratio

combining

WOFDM 2-Branch Diversity Performance

0.001

0.01

0.1

1

-1 0 1 2 3 4 5 6 7

CC, k=9

CC, k=3

RS

SNR (dB)

Wo

rd E

rror

Rat

e

Spectrum Efficiency

Efficiency: IS-136 0.04; IS-95 0.07; GSM 0.04

Source: G. J. Pottie, IEEE Personal Communications, pp. 50-67, October 1995

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

5 7.5 10 12.5 15

Synch CDMA

Dynamic Channel

Allocation with

Power Control

Dynamic Channel

Allocation

SNR (dB)

Efficiency

Dynamic Packet Assignment

1. Mobile locks to

the STRONGEST

base

2. Mobile sends measurements

of path losses for nearby bases

to serving base

3. Serving base

forwards

measurements

to nearby bases

4. Bases assign

channels to all

packets/mobiles

5. Bases forward

channel assignment

info to nearby

bases

~ 50 % improvement in performance

Wideband OFDM Staggered Frame

Frame 20 ms

1 2 4 1 2 4 .....

Superframe 80 ms

Superframe

80 ms

Control Slots Control Slots .....

3 3

4 ms

5 Blocks 5 Blocks 5 Blocks

group A group B group C group D

16 resources in 1 msec time-slots

1B 2 B

Sync & data

20 OFDM Blocks

data

5 Blocks

2 B

data

WOFDM Performance with Dynamic

Packet Assignment & 5 MHz of Spectrum

0

20

40

60

80

100

120

0 500 1000 1500 2000 2500 3000 3500

MR, No beam-forming

IS, No beam-forming

MR, Four beams per sector

IS, Four beams per sector

Ave

. U

ser

Pa

cket

Del

ay

(mse

c)

Throughput per site (kb/s)

OFDM Experimental Program

• Baseband signal processing based on commercial off-the-shelf

DSP hardware with some custom designed components

• Sony-provided 1900 MHz transceivers

• Real-time performance measured through RF channel fading simulator

• Phase 1 parameters:

- >384 kb/s end user data rate

- 800 kHz downlink bandwidth

- GSM-derived clocks (2.166 MHz sample rate with 512 FFT)

- 3.467 kbaud

- 189 OFDM tones with 4.232 kHz tone spacing

- differential detection

- Reed-Solomon channel coding

RF A/D FFT

Demodulator Erasure

detection Decoder

Data

Intf

RF A/D FFT

OFDM receiver

“Typical Urban” channel

800 kHz

Summary: Key Features of 4G W-OFDM

• IP packet data centric

• Support for streaming, simulcasting & generic data

• Peak downlink rates of 5 to 10 Mbps

• Full macro-cellular/metropolitan coverage

• Asymmetric with 3G uplinks (EDGE)

• Variable bandwidth - 1 to 5 MHz

• Adaptive modulation/coding

• Smart/adaptive antennas supported

• MIMO/BLAST/space-time coding modes

• Frame synchronized base stations using GPS

• Network assisted dynamic packet assignment