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Enhancements to Wireless Local Area Networks

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  1. Enhancements to Wireless Local Area Networks Jack H. Winters Division Manager Wireless Systems Research Department AT&T Labs - Research Middletown, NJ jhw@research.att.com July 27, 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. $/Cell $/Sub $ 500,000 $ 1000 $ 100 $ 500 $ 100 $ 10 802.11a 5.5GHz Unlicensed 802.11b 2.4GHz Unlicensed 3G Wireless ~ 2GHz Current Systems Peak Data Rate High performance/price 100 Mbps 10 Mbps 1 Mbps BlueTooth 2.4GHz 100 kbps High ubiquity and mobility Range 10 feet 100 feet 1 mile 10 miles Mobile Speed 60 mph 2 mph 10 mph 30 mph

  5. Barker Barker CCK CCK 1 ms 11 chips 727 ns 8 chips Key 802.11b 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 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) Transmission modes:(dynamic rate shifting) Chip rate: 11 MHz Frequency band: Industrial, Scientific and Medical (ISM, unlicensed) 2.4 - 2.4835 GHz Bandwidth: 22 MHz at -30 dBc Channel spacing: 5 MHz Number of channels: Total of 14 (but only the first 11 are used in the US) Carrier accuracy: ±25 ppm

  6. 3.2 ms FFT G 4 ms 52=48+4 tones 64 point FFT Key 802.11a 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 R=2/3 48 4 ms Symbol duration: R=3/4 9 18 36 54 Guard interval: 800 ns Subcarrier spacing: 312.5 kHz Bandwidth: 16.56 MHz (22 MHz at -20 dBc) 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 accuracy @5.8GHz: 114 kHz * optional

  7. 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) • MobileStar outsources deployment to IBM Global Services • Jan 2001: Starbucks+MSN plans to install WLANs in all 3,000 stores • WayPort and Dell team to give customers wireless public Internet Access • http://www.wayport.com/ • Spontaneous appearance of neighborhood/residential access sites via consumer broadband wire-line connections

  8. 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 Community 802.11b LANs Bay Area 802.11b Access Point Map

  9. 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

  10. 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 Cellular Wireless Internet Wireless LAN’s Home Enterprise Public

  11. 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)

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

  13. Physical Layer Enhancements • Physical Layer research • Smart antennas for range/capacity enhancement (keeping within standards, using TDD) • Smart antennas using MIMO for 216 Mbps 802.11a • Equalizers for delay spread robustness • Adaptive coding/modulation, dynamic packet assignment, power control (using cellular techniques in WLANs) • Modification of 802.11a (a+) for the outdoor environment

  14. Physical Layer Enhancements • Physical Layer research • Experiments: • 20 MHz MIMO channel measurements • Smart antennas in 802.11b/a • 216 Mbps MIMO 802.11a • 4G streaming downlink

  15. SIGNAL INTERFERENCE BEAMFORMER WEIGHTS INTERFERENCE Smart Antennas 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)

  16. 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)

  17. 11.3 ft Prototype Dual Antenna Handset Rooftop Base Station Antennas MIMO Channel Testing MobileTransmitters Test Bed Receivers with RooftopAntennas W1 Tx Rx • Perform timing recovery and symbol synchronization • Record 4x4 complex channel matrix • Evaluate capacity and channel correlation W2 Rx Tx Rx Tx W3 Terminal Antennas on a Laptop Rx Tx W4 Synchronous test sequences LO LO Mobile Transmitters

  18. MIMO Antennas Base Station Antennas • 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 Laptop Prototype • 4 patch antennas at 1900 MHz separated by 3 inches (/2 wavelengths) • Laptop prototype made of brass with adjustable PCB lid

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

  20. 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 802.11b and 802.11a

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

  22. 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 4 ms - too short for efficient wide area operation Symbol duration: 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 error @5.8GHz: 114 kHz - too much for narrower channel spacing, even at 1.9 GHz

  23. OFDM tradeoffs DVB-T 2k mode 802.11a 4G Data rate 6, 9, 12, 18, 24, 36, 48, 54 Mb/s 2.56-8.96 Mb/s 4.98-31.67 Mb/s Tone modulation BPSK, QPSK, 16QAM, 64QAM QPSK, “16QAM,” “64QAM” QPSK,16QAM Coding rate [1/2, 2/3, 3/4, 5/6, 7/8] + RS(204,88) 1/2, 2/3, 3/4 1/2, 2/3, 3/4, 7/8 Nt 52 640 1705 4 ms 200 ms 231-280 ms tB 40 ms 7-56 ms tB-tF 800 ns 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

  24. Physical Layer Enhancements • Smart antennas for range/capacity enhancement (keeping within standards, using TDD) • Smart antennas using MIMO for 216 Mbps 802.11a • Equalizers for delay spread robustness • Adaptive coding/modulation, dynamic packet assignment, power control (using cellular techniques in WLANs) • Modification of 802.11a (a+) for the outdoor environment