1. Fourth Generation Cellular Systems and Smart Antennas
Jack H. Winters
Division Manager
Wireless Systems Research Department
AT&T Labs - Research
Middletown, NJ
November 15, 2001

2. Goal Wireless communications, anywhere, in any form In any form:
high-speed data (Internet)
voice
audio (music)
video
Anywhere:
home
buildings (office)
pedestrian
vehicles
Secure wireless virtual office

3. OUTLINE
Current Systems
Current Trends
Strategy Proposal
Technical Issues

4. High performance/price High ubiquity and mobility
Current Systems
Peak Data Rate
$ 500,000
$ 1000
$ 100
$ 500
$ 10
$/Cell
$/Sub
High performance/price
100 Mbps
802.11a
5.5GHz Unlicensed
10 Mbps
802.11b
2.4GHz Unlicensed
3G Wireless
~ 2GHz
1 Mbps
BlueTooth
2.4GHz
100 kbps
High ubiquity and mobility
10 feet
100 feet
1 mile
10 miles
Range
2 mph
10 mph
30 mph
60 mph
Mobile Speed

5. Cellular Data
CDPD (US) < 10 kbps
GPRS (Asia/trials in US) = 30 kbps (limited work at AT&T Labs since AWS spinoff)
EDGE (AWS scaling back plans) = 80 kbps
WCDMA = 100 kbps (starting in Japan, but not for several years in US)

6. Key 802.11b Physical Layer Parameters:
Barker
Barker
CCK
CCK
1 ms
11 chips
727 ns
8 chips
Key b Physical Layer Parameters:
Data rate:
1, 2, 5.5, 11 Mbps (adaptation to our needs for 1 Mbps only)
Modulation/Spreading:
Direct Sequence Spread Spectrum (DSSS)
DBPSK, DQPSK with 11-chip Barker code (1, 2 Mbps) (this mode stems from the original standard)
8-chip complementary code keying (CCK) (5.5, 11 Mbps)
optional: packet binary convolutional coding (PBCC), 64 state, rate 1/2 CC (BPSK 5.5 Mbps, QPSK 11 Mbps)
Transmission modes: (dynamic rate shifting)
Chip rate:
11 MHz
Frequency band:
Industrial, Scientific and Medical (ISM, unlicensed) GHz
Bandwidth:
22 MHz - TDD
Channel spacing:
5 MHz
Number of channels:
Total of 14 (but only the first 11 are used in the US)
Carrier accuracy:
±25 ppm

7. User data rates (Mbps):
3.2 ms
FFT G
4 ms
52=48+4 tones
64 point FFT
Key a Physical Layer Parameters:
Data rate:
6, 9*, 12, 18*, 24, 36*, 48*, 54* Mbps
Modulation:
BPSK, QPSK, 16QAM, 64QAM*
Coding rate:
1/2, 2/3, 3/4*
User data rates (Mbps):
Subcarriers: 52
BPSK
QPSK
QAM16
QAM64
Pilot subcarriers: 4
R=1/2 6 12 24
FFT size: 64
Symbol duration:
4 ms
R=2/3 48
Guard interval:
800 ns
R=3/4 9 18 36 54
Subcarrier spacing:
312.5 kHz
Bandwidth:
16.56 MHz - TDD
Channel spacing:
20 MHz
Frequency band:
Unlicensed national infrastructure (U-NII)
Number of channels:
Total of 12 in three blocks between 5 and 6 GHz
Carrier accuracy:
20 ppm
Carrier
114 kHz
* optional

8. Current Trends
Enterprise and Home users are all potential public WLAN users when they are away from the office or home.
Players: MobileStar, WayPort, AerZone, …
Soon to cover over 400 hotels & 50 airports US, Canada, UK
$2.50/quarter-hour
$15 ~ $60/month (depending on minutes cap) (struggling to define pricing)
Jan 2001: Starbucks+MSN plans to install WLANs in all 3,000 stores
WayPort and Dell team to give customers wireless public Internet Access
Spontaneous appearance of neighborhood/residential access sites via consumer broadband wire-line connections

9. Community 802.11b LANs Bay Area 802.11b Access Point Map North America
Bay Area Wireless User Group
Equip2rip (Oahu, HI)
Guerrilla.net (Boston)
Pdx Personal Telco
pdxwireless.org (Portland, Oregon)
SBAY.ORG Wireless Network (San Francisco Bay Area)
Seattle Wireless (Seattle)
Seattle Wireless Internet Project
SFLAN (San Francisco)
Xlan (Seattle)
Europe
Consume (London, UK)
Elektrosmog (Stockholm and Gothenburg)
Wlan.org.uk (UK)
Wireless France (France)
Wireless MediaPoli (Helsinki)
Australia
Bay Area b Access Point Map

10. Possible Strategies Broadband Residential Access
Provide b’s to selected cable modem customers or pole locations for universal wireless high-speed data coverage (1 mile radius) with access to other homes in neighborhood
Since cable modem is at 1.5 Mbps and b is at 11 Mbps, provide fiber to these selected homes or poles (economical for selected homes)
Broadband Business Access
Fiber to building access points (e.g., floors)
Extend to residences for virtual offices

11. WLAN Overlay for Broadband Cable Infrastructure
HYBRID FIBER WIRELESS
Logical fit with cable infrastructure
Responds to ad-hoc and organized competition
Potential for higher data rate alternative to DOCSIS
Synergy with streaming digital media

12. Hybrid Fiber Wireless
Run fiber down streets (or to selected homes/businesses) to access points (1 mile apart) for universal coverage with one infrastructure)
Start with wireless data access (802.11b)
Extend range and migrate to:
Voice (802.11e)
Audio (music)
Video
Mobility
Higher data rates (54 Mbps a => 216 Mbps)
Virtual personal/office (remote workforce) environment

13. Internet Roaming Internet Wireless LAN’s Cellular Wireless Home
Seamless handoffs between WLAN and WAN
high-performance when possible
ubiquity with reduced throughput
management/brokering of consolidated WLAN and WAN access
adaptive or performance-aware applications
I-mobile, CC/PP, location based
Cellular Wireless
Internet
Wireless LAN’s
Home
Enterprise
Public

14. Technical Issues Voice Music streaming Video streaming
Secure virtual office
Universal coverage
Range (delay spread)
Mobility
High data rates
Capacity (interference)
Key constraint: Stay within existing standards/standard evolution (enhance performance within standards and drive standards evolution)

15. Physical Layer Enhancements
Peak Data Rate
$ 500,000
$ 1000
$ 100
$ 500
$ 10
$/Cell
$/Sub
High performance/price
100 Mbps
802.11a
5.5GHz Unlicensed
10 Mbps
802.11b
2.4GHz Unlicensed
3G Wireless
~ 2GHz
1 Mbps
Enhanced
BlueTooth
2.4GHz
100 kbps
High ubiquity and mobility
Range
10 feet
100 feet
1 mile
10 miles
2 mph
10 mph
30 mph
60 mph
Mobile Speed

16. Physical Layer Enhancements
Physical Layer research
Smart antennas for range/capacity enhancement (keeping within standards, using TDD)
Smart antennas using MIMO for 216 Mbps a
Equalizers for delay spread robustness
Adaptive coding/modulation, dynamic packet assignment, power control (using cellular techniques – radio resource management - in WLANs)
Modification of a (a+) for the outdoor environment

17. Physical Layer Enhancements
Physical Layer research
Experiments:
20 MHz MIMO channel measurements
Smart antennas in b/a
216 Mbps MIMO a
4G streaming downlink

18. Smart Antennas Smart Antennas significantly improve performance:
SIGNAL
INTERFERENCE
BEAMFORMER WEIGHTS
SIGNAL OUTPUT
Smart Antennas significantly improve performance:
Higher antenna gain  Range extension (50 to 100% greater coverage)
Interference suppression  Quality and capacity improvement (>2x)
MIMO capacity increase (with smart antennas at Tx/Rx)

19. Smart Antennas for Cellular
Key enhancement technique to increase system capacity, extend coverage, and improve user experience
Uplink Adaptive Antenna
INTERFERENCE
SIGNAL
OUTPUT
BEAMFORMER
WEIGHTS
Downlink Switched Beam Antenna
SIGNAL
OUTPUT
INTERFERENCE
BEAMFORMER
BEAM
SELECT
Aggressive frequency re-use  High spectrum efficiency  Increased co-channel interference
Smart antennas provide substantial interference suppression for enhanced performance

20. Multiple-Input Multiple-Output (MIMO) Radio
With M transmit and M receive antennas, can provide M independent channels, to increase data rate M-fold with no increase in transmit power (with sufficient multipath)
AT&T measurements show 4x bit rates & capacity increase in full mobile & indoor/outdoor environments (4 Tx and 4 Rx antennas)
216 Mbps a
1.5 Mbps EDGE
WCDMA

21. Test Bed Receivers with Rooftop Antennas Terminal Antennas on a Laptop
MIMO Channel Testing
Mobile Transmitters
Test Bed Receivers with Rooftop Antennas W1 Tx Rx
Perform timing recovery and symbol synchronization
Record 4x4 complex channel matrix
Evaluate capacity and channel correlation W2 Tx Rx W3 Tx Rx
Terminal Antennas on a Laptop W4 Tx Rx
Prototype Dual Antenna Handset
Synchronous
test
sequences LO LO
Rooftop Base Station Antennas
11.3 ft
Mobile Transmitters

22. MIMO Antennas Base Station Antennas Laptop Prototype
Antennas mounted on 60 foot tower on 5 story office building
Dual-polarized slant 45 1900 MHz sector antennas and fixed multibeam antenna with  beams
4 patch antennas at 1900 MHz separated by 3 inches (/2 wavelengths)
Laptop prototype made of brass with adjustable PCB lid

23. MIMO Field Test Results
Measured capacity distribution is close to the ideal for 4 transmit and 4 receive antennas

24. Smart Antennas for WLANsAP
Smart
Antenna AP
Smart
Antenna
Interference
Smart Antennas can significantly improve the performance of WLANs
TDD operation
Interference suppression  Improve system capacity and throughput
Supports aggressive frequency re-use for higher spectrum efficiency, robustness in the ISM band (microwave ovens, outdoor lights)
Higher antenna gain  Extend range (outdoor coverage) and lower cost (gain limits)
Multipath diversity gain  Improve reliability
MIMO (multiple antennas at AP and laptop)  Increase data rates

25. Smart Antennas Adaptive MIMO
Adapt among:
antenna gain for range extension
interference suppression for capacity (with frequency reuse)
MIMO for data rate increase
With 4 antennas at access point and terminal, in a have the potential to provide up to 216 Mbps in 20 MHz bandwidth within the standard
In EDGE/GPRS, 4 antennas provide 4-fold data rate increase (to 1.5 Mbps in EDGE)
In WCDMA, BLAST techniques proposed by Lucent

26. Delay Spread Robustness
When path length differences approach data rate, ISI degrades performance:
802.11b/a can only tolerate about 200 ns rms of delay spread
Outdoor environment can have several microseconds of delay spread
=> Enhance receiver with equalizer in b and a

27. Capacity
When users in adjacent cells request same data stream (video/audio), use simulcasting (same signal at same frequency from all access points)
In a, enhances coverage while frequency reuse of 1 increases capacity
Lack of cochannel interference enhances MIMO advantage
Adaptively adjust between simulcasting and unicasting

28. High performance/price High ubiquity and mobility
Standards Evolution
Peak Data Rate
$ 500,000
$ 1000
$ 100
$ 500
$ 10
$/Cell
$/Sub
High performance/price
100 Mbps
802.11a
5.5GHz Unlicensed
10 Mbps
802.11b
2.4GHz Unlicensed
802.11a +
3G Wireless
~ 2GHz
1 Mbps
BlueTooth
2.4GHz
100 kbps
High ubiquity and mobility
Range
10 feet
100 feet
1 mile
10 miles
2 mph
10 mph
30 mph
60 mph
Mobile Speed

29. Issues: FFT G Data rate: 6, 9, 12, 18, 24, 36, 48, 54 Mbps Modulation:
3.2 ms
FFT G
4 ms
52=48+4 tones
64 point FFT
Issues:
Data rate:
6, 9, 12, 18, 24, 36, 48, 54 Mbps
Modulation:
BPSK, QPSK, 16QAM, 64QAM
Coding rate:
1/2, 2/3, 3/4
Subcarriers:
52 - insufficient for high data rates in wide area
Pilots subcarriers:
4 - insufficient if number of subcarriers increased
FFT size:
64 - too small for number of carriers in crowded spectrum
Symbol duration:
4 ms - too short for efficient wide area operation
Guard interval:
800 ns - too short for wide area operation
Subcarrier spacing:
312.5 kHz - too large for narrow channels
Bandwidth:
16.56 MHz - too large for spectrum available
Channel spacing:
20 MHz
Carrier accuracy:
20 ppm - leads to too much carrier error
Carrier
114 kHz - too much for narrower channel spacing,
even at 1.9 GHz

30. User data rates (Mbps):
204.8 ms
FFT G
230.4 ms
832= tones
2048 point FFT
Changes for high-mobility operation:
Data rate:
1.66, 2.5, 3.33, 5, 6.66, 10, 13.33, 15 Mbps
Modulation:
BPSK, QPSK, 16QAM, 64QAM
Coding rate:
1/2, 2/3, 3/4
BPSK
QPSK
QAM16
QAM64
1.66
3.33
6.66
R=1/2
13.33
R=2/3
2.5 5 10 15
R=3/4
User data rates (Mbps):
subcarriers:
832 = 52*16
Pilot subcarriers:
64 = 4*16
FFT size:
2048 = 64*32
Symbol duration:
230.4 ms = 3.2* *32
Guard interval:
25.6 ms = .8*32
Subcarrier spacing:
4.833 kHz = 312.5/64
Bandwidth:
~5 MHz » 16.56/4
Channel spacing:
5 MHz » 20/4
Carrier accuracy:
.5 ppm for 5 GHz, 1 ppm for 2.4 GHz
Carrier
2.9 kHz, GHz

31. OFDM tradeoffs
DVB-T
2k mode
802.11a 4G
Data
rate
6, 9, 12, 18, 24,
36, 48, 54 Mb/s
Mb/s
Mb/s
Tone
modulation
BPSK, QPSK,
16QAM, 64QAM
QPSK, “16QAM,”
“64QAM”
QPSK,16QAM
Coding
rate
1/2, 2/3, 3/4
1/2, 2/3, 3/4, 7/8
[1/2, 2/3, 3/4, 5/6,
7/8] + RS(204,88) Nt 52
640
1705 tB
4 ms
200 ms ms
tB-tF
800 ns
40 ms
7-56 ms ft
312.5 kHz
6.25 kHz
4.464 kHz fB
16.56 MHz
4 MHz
7.6 MHz
fop
~5 GHz
~2 GHz
~500 MHz

32. Smart Antennas for Cellular and 802.11 Conclusions
Smart antennas can improve user experience and system capacity by reducing interference, extending range, increasing data rates, and improving quality
Smart antennas are implemented in the physical layer with little or no impact on standards
We will leverage our expertise and experience in the development and deployment of smart antennas for cellular to develop smart antennas for WLANs