The Evolution of TDMA to 3G & 4G Wireless Systems

Nelson Sollenberger AT&T Labs-Research Wireless Systems Research Division

AT&T Wireless Services

• • AT&T serves over 14 million subscribers with digital TDMA technology and some remaining analog technology, and provides packet data service with CDPD technology TDMA – European GSM over 250 million – North American TDMA ~ 50 million – Japanese PDC ~ 50 million CDMA – North American CDMA ~ 60 million (including S. Korea) Other TDMA operators - Rogers AT&T - Cingular (SBC & BellSouth) - throughout Mexico, Central & South America

Cellular Telephony Handsets

Nokia 5160 Nokia 8860 Ericsson PD 328 Various TDMA phones available today Motorola StarTAC® ST7790 Phone

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

2000

TDMA Capacity Roadmap

2001 2002 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



Dynamic Channel Assignment

•

Network automatically assigns radio frequencies to cell sites for more efficient utilization of frequencies



Base Station Power Control

•

Base stations only transmit power required to reach mobile with adequate signal quality resulting in lower interference



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

Sierra PCMCIA CDPD Modem Nokia 9110 The new Ericsson R380 phone, which features 3COM functions Palm VII Nokia 3G vision

WIRELESS GROWTH

WIRELESS COMPUTING

INTERNET GROWTH - web access - e-mail - file transfer - location services - streaming audio & video RF & DIGITAL TECHNOLOGY MOBILE SOFTWARE

Macrocellular Wireless Data Evolution & AT&T’s Roadmap

5 M Wideband OFDM 1 M

data rate

384 k 64 k 9.6 k HDR EDGE WCDMA GPRS IS-136+ IS-95+ PDC GSM CDPD IS-136 IS-95 1995 2000 2005

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 Burst N 464 bits 1 data block Convolutional Coding Rate = 1/3 Length = 7 1392 bits Puncture 1392 bits Interleave Burst N+1 348 bits/ burst Burst N+2 156.25 symbols/slot 8PSK Modulate 468.75 bits Burst Format 348 bits 20 msec frame with 4 time-slots for each of 8 bearers Burst N+3 8 Time Slots 0 1 2 3 4 5 6 7 1 Time Slot = 576.92 µs Tail symbols 3 Data symbols 58 Training symbols 26 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 Data symbols 58 Tail symbols 3 Guard symbols 8.25

EDGE Modulation, Channel Coding & Bit Rates

Scheme

MCS-9 MCS-8 MCS-7 MCS-6 MCS-5 MCS-4 MCS-3 MCS-2 MCS-1

Modulation

8PSK GMSK

Maximum rate [kb/s]

59.2

54.4

44.8

29.6

22.4

17.6

14.8

11.2

8.8

Code Rate

1.0

0.92

0.76

0.49

0.37

1.0

0.80

0.66

0.53

Family

B C A A A B A B C

EDGE Link Throughput

9

EDGE Compact System Performance

Probability throughput < = X per timeslot Probability packet delay < = X

%

100 90 80 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70

X (kb/s)

%

100 90 80 70 60 50 40 30 20 10 0 0 1000 2000 3000 4000 5000

X (msec)

26 users/sector at 3.5 kbps average load per user

EDGE Classic Multi-slot Gain

Average User Throughput (kb/s)

300 250 200 150 100 50 0 9 single-slot Multi-slot 18 27 36

Ave. # of users per sector

45

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

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

20 15 10 5 0 55 50 45 40 35 30 25 7.2 MHz Spectrum 7 11 30 29 10 20 35 50 Baseline Enhanced GSM IS-136

* 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

EGPRS/GMSK/F EGPRS/8PSK/H

*This assumes 30 mph vehicle speed for micro fading * SINR-based power control with adaptive target

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

SIGNAL

Uplink Adaptive Antenna

SIGNAL OUTPUT INTERFERENCE BEAMFORMER WEIGHTS

Downlink Switched Beam Antenna

SIGNAL BEAM SELECT SIGNAL OUTPUT

Aggressive frequency re-use



High spectrum efficiency



Increased co-channel interference

INTERFERENCE

Smart antennas provide substantial interference suppression for enhanced performance

EDGE Smart Antenna Processing

Dual Diversity Receiver Using DDFSE for Joint ISI and CCI Suppression Output Data Viterbi Decoder Receiver Rx Rx Filter

Symbol Timing and Recovery

Feed-forward Filter Deinter leaver Soft Output

DDFSE Equalizer

Rx Rx Filter Feed-forward Filter

Equalizer Training

Jack Winters Hanks Zeng Ashutosh Dixit • •

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

EDGE 2-Branch Smart Antenna Performance Laboratory Tests EDGE MCS-5 with Interference Suppression in a Typical Urban Environment 20 dB SNR Signal-to-Interference Ratio (dB) 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

Prob. (throughput <=X) (%)

Prototype Dual Antenna Handset External Whip Internal Patch

100 90 80 70 60 50 40 30 20 10 0 0

Multi-cell EDGE Compact Simulation - 1/3 reuse - 18 users per sector - 3.5 kbps average load per user

10 20 30

X (kb/s)

40 50 No Diversity Simple Diversity Interference Suppression 60 70

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

4G Wireless: One View

• 4G WOFDM high speed downlink “a wireless cable modem” • Complement to EDGE/UMTS • High peak data rates (up to 10 Mb/s) • spectrum - 500 MHz to 3 GHz • 3G EDGE/WCDMA network for uplink, downlink, in a 5 MHz channel control and signalling

Path Loss and Fading Challenge

Delay Spread Reflected signals arrive spread out over 5 to 20 microsecond Path Loss path loss up to ~ 150 dB (that is a 1 followed by 15 zeroes) Rayleigh Fading rapid fading of 20 to 30 dB (power varies by 100 to 1000 times in level at rates of about 100 times per second)

Cellular Interference Challenge

1 0.1

0.01

Each base station is equipped with three 120 degree directional antennas to reduce interference & improve capacity

1|3 reuse 2|6 reuse 3|9 reuse 4|12 reuse 7/21 reuse 0.001

-5 0 5 10 15 20

Signal to Interference ratio in dB

25

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

] transmit and

j th

receive antenna for the

i th •

Capacity (instantaneous and averaged over 1 second) for 4 TX by 4 RX:

•

where

 C = log 2 (det[

I

 i + (

is the

i  th /4)

H † H

]) =  log

eigenvalue of

2 (1 + (

H † H

 /4)  i )

is the total signal-to-noise ratio per antenna and To eliminate the effect of shadow fading, the capacity is normalized to the average capacity with a single antenna:

C n =  log 2 (1 + (  /4)  i ) / (1/16)  log 2 (1 + 

H

ij )

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

~ 800 tones ~ 6 kHz ~ 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 Mobile OFDM parameters: ex.

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

• • • • • • • • • • • •

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

received signals FFT FFT remove data 2-branch maximal-ratio combining synch word Estimator 1 IFFT .

.

.

.

.

.

.

.

.

.

.

.

FFT . . . . . .

Estimator 2 data

WOFDM 2-Branch Diversity Performance

1 0.1

0.01

0.001

-1 0 1 2 3 4

SNR (dB)

5 6 7 CC, k= 9 CC, k= 3 RS

Spectrum Efficiency

Efficiency 1 0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0 Synch CDMA Dynamic Channel Allocation with Power Control Dynamic Channel Allocation 5 7.5

10 12.5

15 SNR (dB)

Source: G. J. Pottie,

IEEE Personal Communications

, pp. 50-67, October 1995 Efficiency: IS-136 0.04; IS-95 0.07; GSM 0.04

Dynamic Packet Assignment

2. Mobile sends measurements of path losses for nearby bases to serving base 4. Bases assign channels to all packets/mobiles 1. Mobile locks to the

STRONGEST

base 3. Serving base forwards measurements to nearby bases

~ 50 % improvement in performance

5. Bases forward channel assignment info to nearby bases

Wideband OFDM Staggered Frame

2 Superframe 80 ms 3 1 Frame 20 ms 4 1 2 Superframe 80 ms 3 4 .....

Control Slots .....

Control Slots 16 resources in 1 msec time-slots 4 ms 20 OFDM Blocks 5 Blocks 5 Blocks 5 Blocks 5 Blocks group A group B group C group D 2 B data 1B Sync & data 2 B data

WOFDM Performance with Dynamic Packet Assignment & 5 MHz of Spectrum

120 100

MR, No beam-forming IS, No beam-forming MR, Four beams per sector IS, Four beams per sector

80 60 40 20 0 0 500 1000 1500 2000 2500 3000 3500

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

“Typical Urban” channel

800 kHz

RF A/D FFT RF A/D FFT Demodulator Erasure detection OFDM receiver Decoder Data Intf

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