Fourth Generation Cellular Systems and Smart Antennas

Jack H. Winters

April 9, 2002

jack@jackwinters.com

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

OUTLINE

• Current Systems

• Current Trends

• Strategy Proposal

• Technical Issues

Current Systems

10 feet 100 feet 1 mile 10 miles

100 kbps

1 Mbps

10 Mbps

100 Mbps

3G Wireless~ 2GHz

BlueTooth2.4GHz

802.11a5.5GHz Unlicensed

802.11b2.4GHz Unlicensed

Peak Data Rate

Range

2 mph 10 mph 30 mph 60 mph

$ 500,000

$ 1000

$ 100

$ 500

$ 100

$ 10

$/Cell $/SubHigh performance/price

High ubiquity and mobility

Mobile Speed

Cellular Data

• CDPD (US) < 10 kbps

• GPRS = 30-40 kbps

• EDGE = 80 kbps

• WCDMA = 100 kbps (starting in Japan, but not for several years in US)

Data rate: • 1, 2, 5.5, 11 MbpsModulation/Spreading: • Direct Sequence Spread Spectrum (DSSS)

• DBPSK, DQPSK with 11-chip Barker code (1, 2 Mbps) (this mode stems from the original 802.11 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)

Barker

Key 802.11b Physical Layer Parameters:

Chip rate: 11 MHzFrequency band: Industrial, Scientific and Medical (ISM, unlicensed) 2.4 - 2.4835 GHz

Bandwidth: 22 MHz - TDDChannel spacing: 5 MHz

Total of 14 (but only the first 11 are used in the US), with only 3 nonoverlapping channels

Number of channels:

Transmission modes:(dynamic rate shifting)

CCK

1 s11 chips

Barker

727 ns8 chips

CCK

Unlicensed national infrastructure (U-NII), 5.5 GHz

Total of 12 in three blocks between 5 and 6 GHz

Data rate: 6, 9, 12, 18, 24, 36, 48, 54 MbpsModulation: BPSK, QPSK, 16QAM, 64QAM

Coding rate: 1/2, 2/3, 3/4Subcarriers: 52

Pilot subcarriers: 4

G

3.2 s

4 s

FFT

52=48+4 tones64 point FFT

Key 802.11a Physical Layer Parameters:

Symbol duration: 4 sGuard interval: 800 ns

Subcarrier spacing: 312.5 kHzBandwidth: 16.56 MHz - TDD

Channel spacing: 20 MHz

FFT size: 64

:

BPSK QPSK QAM16 QAM64

6 12 24R=1/2

48R=2/3

9 18 36 54R=3/4

User data rates (Mbps):

Frequency band:

Number of channels:

Current Trends

• Business WLANs dominate, but home usage growing faster (8 million WLANs sold last year)

• Spontaneous appearance of neighborhood/residential access sites via consumer broadband wire-line connections

• Public WLAN offerings for enterprise and home users when they are away from the office or home

– Players:

• Wayport: Covers over 450 hotels & 9 airports US, Canada, UK

• Aggregators:

– Deep Blue Wireless (hotels and coffee houses)

– Joltage

– Sputnik

– hereUare

– Boingo Wireless/

Community 802.11b LANs

• 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 802.11b Access Point Map

Possible Strategies

• Broadband Residential Access

– Provide 802.11b’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 802.11b 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

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

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

• Audio (music)

• Video

• Mobility

• Higher data rates (54 Mbps - 802.11a and higher)

• Virtual personal/office (remote workforce) environment

Technical Issues

• Voice/Music streaming/Video streaming (802.11e)

• Universal coverage (Internet roaming)

• Range

• Higher data rates

• Capacity/Interference)

• Key constraint: Stay within existing standards/standard evolution (enhance performance within standards and drive standards evolution)

Internet Roaming

• 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

• Nokia GPRS/802.11b PCMCIA card

• NTT DoCoMo WLAN/WCDMA trial

Cellular Wireless

EnterpriseHome

Public

Internet

Wireless LAN’s

Technical Issues

• Voice/Music streaming/Video streaming (802.11e)

• Universal coverage (Internet roaming)

• Range

• Higher data rates

• Capacity/Interference)

• Key constraint: Stay within existing standards/standard evolution (enhance performance within standards and drive standards evolution)

Wireless System Enhancements

10 feet 100 feet 1 mile 10 miles

100 kbps

1 Mbps

10 Mbps

100 Mbps

3G Wireless~ 2GHz

BlueTooth2.4GHz

802.11a5.5GHz Unlicensed

802.11b2.4GHz Unlicensed

Peak Data Rate

Range

2 mph 10 mph 30 mph 60 mph

$ 500,000

$ 1000

$ 100

$ 500

$ 100

$ 10

$/Cell $/SubHigh performance/price

High ubiquity and mobility

Mobile Speed

Enhanced

Enhancements

• Smart Antennas (keeping within standards):

– Range increase

– Interference suppression

– Capacity increase

– Data rate increase using multiple transmit/receive antennas (MIMO)

• Radio resource management techniques (using cellular techniques in WLANs):

– Dynamic packet assignment

– Power control

– Adaptive coding/modulation/smart antennas

• Modification of 802.11a/4G (a+) for one cellular/WLAN standard

Smart AntennasSmart Antennas

Smart Antennas significantly improve performance:

• Higher antenna gain with multipath mitigation (gain of M with M-fold diversity) Range extension

• Interference suppression (suppress M-1 interferers) Quality and capacity improvement

• With smart antennas at Tx/Rx MIMO capacity increase(M-fold)

SIGNAL

INTERFERENCE

INTERFERENCEBEAMFORMER

WEIGHTS

SIGNAL OUTPUT

In 1999, combining at base stations changed from MRC to MMSE for capacity increase

Downlink Switched Beam Antenna

INTERFERENCE

SIGNAL

SIGNALOUTPUT

BEAMFORMERWEIGHTS

Uplink Adaptive Antenna

SIGNALOUTPUT

SIGNAL

INTERFERENCE

BE

AM

FO

RM

ER

BEAMSELECT

Smart Antennas for Cellular

• Key enhancement technique to increase system capacity, extend coverage, and improve user experience in cellular (IS-136)

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 total transmit power (with sufficient multipath) – only an increase in DSP

– Indoors – up to 150-fold increase in theory

– Outdoors – 8-12-fold increase typical

• AT&T measurements show 4x bit rates & capacity increase in all mobile & indoor/outdoor environments (4 Tx and 4 Rx antennas)

– 216 Mbps 802.11a (4X 54 Mbps)

– 1.5 Mbps EDGE

– WCDMA

Rx

Rx

Rx

MIMO Channel Testing

W1

W2

W3

W4

LO

Synchronoustest

sequences

Rx

• Perform timing recovery and symbol synchronization

• Record 4x4 complex channel matrix

• Evaluate capacity and channel correlation

LO

Mobile Transmitters Test Bed Receivers with RooftopAntennas

Terminal Antennas on a Laptop

Tx

Tx

Tx

Tx

Rooftop Base Station Antennas

11.3 ft

Prototype Dual Antenna Handset

Mobile Transmitters

DIVERSITY TYPES

Spatial: Separation – only ¼ wavelength needed at terminal

Polarization: Dual polarization (doubles number of antennas in one location

Pattern: Allows even closer than ¼ wavelength

4 or more antennas on a PCMCIA card

16 on a handset

Even more on a laptop

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 4 - 30 beams

• 4 patch antennas at 1900 MHz separated by 3 inches (/2 wavelengths)

• Laptop prototype made of brass with adjustable PCB lid

• Measured capacity distribution is close to the ideal for 4 transmit and 4 receive antennas

MIMO Field Test Results

Smart Antennas for WLANs

• TDD operation (only need smart antenna at access point or terminal for performance improvement in both directions)

• 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)• Multipath diversity gain Improve reliability• MIMO (multiple antennas at AP and laptop) Increase data rates

APSmart

Antenna

Interference

Smart Antennas can significantly improve the performance of WLANs

APSmart

Antenna

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 802.11a 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

Radio Resource Management

• Use cellular radio resource management techniques in WLANs: Adaptive coding/modulation, dynamic packet assignment, power control

– Not available on market

• Current system administrators and users unaware of capacity/coverage issues

• Performance statistics generated in current WLANs, but interpretation difficult

– Techniques:

• Use software on controller PC for multiple access points to analyze data and control system

• Power control to permit cell ‘breathing’ (for traffic spikes)

• Dynamic AP channel assignment– Combination of radio resource management and smart antennas yields

greater gains than sum of gains

Cell Breathing in WLAN Systems

•Measure traffic load for each access point•Shrink overloaded cell by reducing RF power•Expand others to cover abandoned areas

AP

AP

AP

AP

AP

AP

AP

AP

AP

AP

AP

AP

AP

AP

Adaptive Channel Assignment

3 1 2

2 3

2 3

1

1

3 1 2

2 2

3 3

3

2

Initial Assignment After one iteration

• Assign channels to maximize capacity as traffic load changes

Cochannelinterference

High trafficload

Standards Evolution

10 feet 100 feet 1 mile 10 miles

100 kbps

1 Mbps

10 Mbps

100 Mbps

3G Wireless~ 2GHz

BlueTooth2.4GHz

802.11a5.5GHz Unlicensed

802.11b2.4GHz Unlicensed

Peak Data Rate

Range

2 mph 10 mph 30 mph 60 mph

$ 500,000

$ 1000

$ 100

$ 500

$ 100

$ 10

$/Cell $/SubHigh performance/price

High ubiquity and mobility

Mobile Speed

802.11a+

Coding rate: 1/2, 2/3, 3/4Subcarriers: 52 - insufficient for high data rates in wide area

Pilots subcarriers: 4 - insufficient if number of subcarriers increased

Symbol duration: 4 s - too short for efficient wide area operationGuard interval: 800 ns - too short for wide area operation

Subcarrier spacing: 312.5 kHz - too large for narrow channelsBandwidth: 16.56 MHz - too large for spectrum available

Channel spacing: 20 MHz

G

3.2 s

4 s

FFT

Carrier accuracy: 20 ppm - leads to too much carrier errorCarrier error @5.8GHz: 114 kHz - too much for narrower channel spacing,

even at 1.9 GHz

Issues for 802.11a:

Data rate: 6, 9, 12, 18, 24, 36, 48, 54 MbpsModulation: BPSK, QPSK, 16QAM, 64QAM

52=48+4 tones64 point FFT

FFT size: 64 - too small for number of carriers in crowded spectrum

Coding rate: 1/2, 2/3, 3/4subcarriers:

G

230.4 s

FFT

Data rate: 1.66, 2.5, 3.33, 5, 6.66, 10, 13.33, 15 MbpsModulation: BPSK, QPSK, 16QAM, 64QAM

832 = 52*16

204.8 s

832=768+64 tones2048 point FFT

Changes for high-mobility operation:

FFT size: 2048 = 64*32Symbol duration: 230.4 s = 3.2*64 + .8*32

Guard interval: 25.6 s = .8*32Subcarrier spacing: 4.833 kHz = 312.5/64

Bandwidth: ~5 MHz 16.56/4Channel spacing: 5 MHz 20/4Carrier accuracy: .5 ppm for 5 GHz, 1 ppm for 2.4 GHz

Carrier error @5.8GHz: 2.9 kHz, 1.9 kHz @ 1.9 GHz

Pilot subcarriers: 64 = 4*16BPSK QPSK QAM16 QAM64

1.66 3.33 6.66R=1/2

13.33R=2/3

2.5 5 10 15R=3/4

User data rates (Mbps):

OFDM tradeoffs

802.11aDVB-T

2k mode4G

Datarate

6, 9, 12, 18, 24, 36, 48, 54 Mb/s

Tonemodulation

BPSK, QPSK,16QAM, 64QAM

Codingrate

1/2, 2/3, 3/4

Nt 52

tB 4 s

tB-tF 800 ns

ft 312.5 kHz

fB 16.56 MHz

fop ~5 GHz

4.98-31.67 Mb/s

QPSK, “16QAM,” “64QAM”

[1/2, 2/3, 3/4, 5/6,7/8] + RS(204,88)

1705

231-280 s

7-56 s

4.464 kHz

7.6 MHz

~500 MHz

2.56-8.96 Mb/s

QPSK,16QAM

1/2, 2/3, 3/4, 7/8

640

200 s

40 s

6.25 kHz

4 MHz

~2 GHz

Conclusions

• We evolving toward our goal of universal high-speed wireless access, but technical challenges remain

• These challenges can be overcome by the use of:

– Smart antennas to reduce interference, extend range, increase data rate, and improve quality, without standards changes

– Radio resource management techniques, in combination with smart antennas – further enhanced by a standards evolution to 4G