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 AT&T Labs - Research 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 AT&T Labs - Research OUTLINE • Current Systems • Current Trends • Strategy Proposal • Technical Issues AT&T Labs - Research Current Systems Peak Data Rate High performance/price 100 Mbps 802.11a 5.5GHz Unlicensed 10 Mbps 802.11b $/Cell $/Sub $ 500,000 $ 500 $ 1000 $ 100 $ 100 $ 10 2.4GHz Unlicensed 1 Mbps BlueTooth 100 kbps 2.4GHz High ubiquity and mobility 3G Wireless ~ 2GHz 10 feet 2 mph 100 feet 10 mph 1 mile 30 mph 10 miles Range 60 mph Mobile Speed AT&T Labs - Research Barker Barker 1 ms 11 chips CCK CCK 727 ns 8 chips Key 802.11b Physical Layer Parameters: Data rate: Modulation/Spreading: Transmission modes: (dynamic rate shifting) Chip rate: Frequency band: Bandwidth: Channel spacing: Number of channels: Carrier accuracy: 1, 2, 5.5, 11 Mbps (adaptation to our needs for 1 Mbps only) 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) 11 MHz Industrial, Scientific and Medical (ISM, unlicensed) 2.4 - 2.4835 GHz 22 MHz at -30 dBc 5 MHz Total of 14 (but only the first 11 are used in the US) ±25 ppm AT&T Labs - Research 3.2 ms FFT 52=48+4 tones 64 point FFT G 4 ms Key 802.11a Physical Layer Parameters: Data rate: Modulation: Coding rate: Subcarriers: Pilot subcarriers: FFT size: Symbol duration: Guard interval: Subcarrier spacing: Bandwidth: Channel spacing: Frequency band: Number of channels: Carrier accuracy: Carrier accuracy @5.8GHz: 6, 9*, 12, 18*, 24, 36*, 48*, 54* Mbps BPSK, QPSK, 16QAM, 64QAM* 1/2, 2/3, 3/4* User data rates (Mbps): 52 BPSK QPSK QAM16 QAM64 4 R=1/2 6 12 24 64 R=2/3 48 4 ms R=3/4 9 18 36 54 800 ns 312.5 kHz 16.56 MHz (22 MHz at -20 dBc) 20 MHz Unlicensed national infrastructure (U-NII) Total of 12 in three blocks between 5 and 6 GHz 20 ppm 114 kHz * optional AT&T Labs - Research 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 AT&T Labs - Research 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) • Bay Area 802.11b Access Point Map Australia AT&T Labs - Research 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 AT&T Labs - Research Internet Roaming • Seamless handoffs between WLAN and WAN – high-performance when possible Cellular Wireless – ubiquity with reduced throughput • • management/brokering of consolidated WLAN and WAN access adaptive or performance-aware applications – I-mobile, CC/PP, location based Internet Wireless LAN’s Enterprise Home Public AT&T Labs - Research 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) AT&T Labs - Research Physical Layer Enhancements Peak Data Rate High performance/price 100 Mbps 802.11a 5.5GHz Unlicensed 10 Mbps 802.11b 2.4GHz Unlicensed 1 Mbps $/Cell $/Sub $ 500,000 $ 500 $ 1000 $ 100 $ 100 $ 10 Enhanced BlueTooth 100 kbps 2.4GHz High ubiquity and mobility 3G Wireless ~ 2GHz 10 feet 2 mph 100 feet 10 mph 1 mile 30 mph Range 10 miles 60 mph Mobile Speed AT&T Labs - Research 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 AT&T Labs - Research 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 AT&T Labs - Research Smart Antennas SIGNAL SIGNAL OUTPUT INTERFERENCE INTERFERENCE BEAMFORMER WEIGHTS 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) AT&T Labs - Research 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) AT&T Labs - Research MIMO Channel Testing Test Bed Receivers with Rooftop Antennas Mobile Transmitters W1 Tx W2 Tx W3 • Perform timing recovery and symbol synchronization Rx • Record 4x4 complex channel matrix Rx Tx • Evaluate capacity and channel correlation Rx Tx W4 Synchronous test sequences Rx LO Terminal Antennas on a Laptop LO 11.3 ft Prototype Dual Antenna Handset Rooftop Base Station Antennas Mobile Transmitters AT&T Labs - Research MIMO Antennas Base Station Antennas Laptop Prototype • 4 patch antennas at 1900 MHz separated by 3 inches (/2 wavelengths) • Laptop prototype made of brass with adjustable PCB lid • 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 AT&T Labs - Research MIMO Field Test Results • Measured capacity distribution is close to the ideal for 4 transmit and 4 receive antennas AT&T Labs - Research 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 AT&T Labs - Research Standards Evolution Peak Data Rate High performance/price 100 Mbps 802.11a 5.5GHz Unlicensed 10 Mbps 802.11b $/Cell $/Sub $ 500,000 $ 500 $ 1000 $ 100 $ 100 $ 10 2.4GHz Unlicensed 1 Mbps BlueTooth 100 kbps 2.4GHz High ubiquity and mobility 3G Wireless ~ 2GHz 10 feet 2 mph 100 feet 10 mph 1 mile 30 mph Range 10 miles 60 mph Mobile Speed AT&T Labs - Research 3.2 ms FFT G 4 ms 52=48+4 tones 64 point FFT Issues: Data rate: Modulation: Coding rate: Subcarriers: Pilots subcarriers: FFT size: Symbol duration: Guard interval: Subcarrier spacing: Bandwidth: Channel spacing: Carrier accuracy: Carrier error @5.8GHz: 6, 9, 12, 18, 24, 36, 48, 54 Mbps BPSK, QPSK, 16QAM, 64QAM 1/2, 2/3, 3/4 52 - insufficient for high data rates in wide area 4 - insufficient if number of subcarriers increased 64 - too small for number of carriers in crowded spectrum 4 ms - too short for efficient wide area operation 800 ns - too short for wide area operation 312.5 kHz - too large for narrow channels 16.56 MHz - too large for spectrum available 20 MHz 20 ppm - leads to too much carrier error 114 kHz - too much for narrower channel spacing, even at 1.9 GHz AT&T Labs - Research OFDM tradeoffs 802.11a 4G DVB-T 2k mode 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 Coding rate BPSK, QPSK, 16QAM, 64QAM QPSK,16QAM QPSK, “16QAM,” “64QAM” 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 231-280 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 AT&T Labs - Research 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 AT&T Labs - Research