The Evolution of TDMA to 3G

1
The Evolution of TDMA to 3G 4G Wireless Systems

• Nelson Sollenberger
• ATT Labs-Research
• Wireless Systems Research Division

2
ATT Wireless Services
ATT 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 ATT -
Cingular (SBC BellSouth) - throughout
Mexico, Central South America
3
Cellular Telephony Handsets
Ericsson PD 328
Motorola StarTAC ST7790 Phone
Nokia 5160
Nokia 8860
Various TDMA phones available today
4
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

5
TDMA Capacity Roadmap
2000
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

6
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

7
Wireless Data Terminals
Nokia 3G vision
Sierra PCMCIA CDPD Modem
The new Ericsson R380 phone, which features
wireless data functions
Nokia 9110
3COM Palm VII
8
WIRELESS COMPUTING
WIRELESS GROWTH
INTERNET GROWTH
- web access - e-mail - file transfer - location
services - streaming audio video
RF DIGITAL TECHNOLOGY
MOBILE SOFTWARE
9
Macrocellular Wireless Data Evolution ATTs
Roadmap
Wideband OFDM
5 M
1 M
HDR
data rate
384 k
EDGE
WCDMA
GPRS
64 k
IS-136
IS-95
PDC
9.6 k
IS-136
GSM
CDPD
IS-95
1995
2000
2005
10
EDGE TechnologyEnhanced 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 (Release99 2002 deployment) supports
  best effort packet data at speeds up to about 384
  kbps
• Phase 2 (Release2000 2003 deployment) will add
  Voice over IP capability

11
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

12
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 lt 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

13
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

14
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

15
EDGE Channel Coding and Frame Structure
Burst N
Convolutional CodingRate 1/3Length 7
464 bits 1 data block
Puncture
Interleave
Burst N1
348 bits/burst
1392 bits
1392 bits
Burst N2
Burst Format
8PSK Modulate
Burst N3
156.25 symbols/slot
348 bits
468.75 bits
20 msec frame with 4 time-slots for each of 8
bearers
8 Time Slots
0
1
2
3
4
5
6
7
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
16
EDGE Modulation, Channel Coding Bit Rates
17
EDGE Link Throughput
9
18
EDGE Compact System Performance
Probability throughput lt X per timeslot
Probability packet delay lt X


X (kb/s)
X (msec)
26 users/sector at 3.5 kbps average load per user
19
EDGE Classic Multi-slot Gain
Average User Throughput (kb/s)
Ave. of users per sector
20
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

21
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

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
This assumes 30 mph vehicle speed for micro
fading SINR-based power control with adaptive
target
22
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

Downlink Switched Beam Antenna
SIGNAL OUTPUT
Aggressive frequency re-use ? High spectrum
efficiency ? Increased co-channel interference
Smart antennas provide substantial interference
suppression for enhanced performance
23
EDGE Smart Antenna Processing

• 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
24
EDGE 2-Branch Smart Antenna Performance
Laboratory Tests
EDGE MCS-5 with Interference Suppression in
a Typical Urban Environment
20 dB SNR
Block Error Rate
Signal-to-Interference Ratio (dB)
Laboratory results show a 15 to 30 dB improvement
in S/I with 2 receive antennas
25
Improvement with Terminal Diversity and
Interference Suppression User Experience
Prob. (throughput ltX) ()
Prototype Dual Antenna Handset
External Whip
Internal Patch
X (kb/s)
Multi-cell EDGE Compact Simulation - 1/3 reuse -
18 users per sector - 3.5 kbps average load per
user
Typical user throughput increased from 30 to 45
kbps per time-slot
26
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)
  in a 5 MHz channel

• spectrum - 500 MHz to 3 GHz
• 3G EDGE/WCDMA network for uplink, downlink,
• control and signalling

27
Path Loss and Fading Challenge
Reflected signals arrive spread out over 5 to
20 microsecond
Delay Spread
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)
28
Cellular Interference Challenge
Each base station is equipped with three 120
degree directional antennas to reduce
interference improve capacity
Cumulative Probability
Signal to Interference ratio in dB
29
ATT Labs-Research Work on 4G

• Smart antennas
• Multiple-Input-Multiple-Output Systems
• Space-Time Coding
• Dynamic Packet Assignment
• Wideband OFDM

30
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
  ATT-Lucent IS-136 field trial
• Lucent has demonstrated 26 bps/Hz in 30 kHz
  channel with 8 Tx and 12 Rx antennas indoors
• ATT has performed measurements on 4 Tx by 4 Rx
  antenna configurations in full mobile outdoor
  to indoor environments

31
MIMO Channel Measurement System
Transmitter
Receive System

• 4 antennas mounted on a laptop
• 4 coherent 1 Watt 1900 MHz transmitters with
  synchronous waveform generator

• 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

32
MIMO Measured Channel CapacityPotential 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

33
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(detI (?/4)HH) ? log2(1 (?/4)?i)
• where ? is the total signal-to-noise ratio per
  antenna and
• ?i is the ith eigenvalue of HH
• 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)

34
Multiple Input Multiple Output Wireless

• RX diversity - HF, terrestrial microwave,
  cellular.
• TX frequency offset diversity simulcasting for
  paging - 70s
• Adaptive array processing in military systems
• TX diversity - 80s
• frequency offset (channel decoding combining)
• delay (equalizer combining)
• Optimum combining for cellular (multipath
  channels) - 80s
• Space-division multiple access - 80s 90s
• angle-of-arrival based
• multi-path based (supports co-location
  multi-channels per user)
• MIMO - 80s 90s
• Multiple spatial channels using adaptive antenna
  arrays
• BLAST - successive interference cancellation
  combined with coding
• Space-Time coding

35
Space-Time Coding
How do you enhance TX delay diversity ( a
repetition code)?
36
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

37
OFDM for 4G Wireless

• 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
38
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

39
OFDM Robust Channel Estimation
FFT
received signals
data
FFT
synch word
remove data
Estimator 1
. . .
. . .
IFFT
FFT
2-branch maximal-ratio combining
. . .
. . .
Estimator 2
. . . . . .
40
WOFDM 2-Branch Diversity Performance
41
Spectrum Efficiency
Efficiency
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

42
Dynamic Packet Assignment
50 improvement in performance
43
Wideband OFDM Staggered Frame
Superframe
Superframe
80 ms
80 ms
.....
1
4
2
4
3
1
2
3
Frame
20 ms
.....
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
1B
2 B
2 B
data
data
Sync data
44
WOFDM Performance with Dynamic Packet Assignment
5 MHz of Spectrum
45
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
• - gt384 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

46
Typical Urban channel
800 kHz
RF
A/D
FFT
Demodulator
Erasure detection
Decoder
Data Intf
RF
A/D
FFT
OFDM receiver
47
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