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Smart Antennas for Mobile Wireless Systems

Smart Antennas for Mobile Wireless Systems. Jack H. Winters. May 6, 2003 jack@jackwinters.com jwinters@motia.com. OUTLINE. Smart Antennas Adaptive Arrays MIMO System Applications Radio Resource Management Conclusions. Smart Antennas. SIGNAL. SIGNAL. BEAM SELECT. SIGNAL OUTPUT.

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Smart Antennas for Mobile Wireless Systems

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  1. Smart Antennas for Mobile Wireless Systems Jack H. Winters May 6, 2003 jack@jackwinters.com jwinters@motia.com

  2. OUTLINE • Smart Antennas • Adaptive Arrays • MIMO • System Applications • Radio Resource Management • Conclusions

  3. Smart Antennas SIGNAL SIGNAL BEAM SELECT SIGNAL OUTPUT BEAMFORMER INTERFERENCE BEAMFORMER WEIGHTS INTERFERENCE Switched Multibeam Antenna Adaptive Antenna Array SIGNAL OUTPUT • Smart Antennas can significantly improve the performance of wireless systems • Higher antenna gain / diversity gain  Range extension and multipath mitigation • Interference suppression  Quality and capacity improvement • Suppression of delayed signals  Equalization of ISI for higher data rates • Multiple signals in the same bandwidth  Higher data rates • Switched Multibeam versus Adaptive Array Antenna: Simple beam tracking, but limited interference suppression and diversity gain

  4. Output COMBINING TECHNIQUES Selection: • Select antenna with the highest received signal power • P0M = P0M

  5. COMBINING TECHNIQUES (CONT.) Maximal ratio combining: W1 Output  WM • Weight and combine signals to maximize signal-to-noise ratio (Weights are complex conjugate of the channel transfer characteristic) • Optimum technique with noise only • BERM BERM (M-fold diversity gain)

  6. OPTIMUM COMBINING (ADAPTIVE ANTENNAS) • Weight and combine signals to maximize signal-to-interference-plus-noise ratio (SINR) • - Usually minimize mean squared error (MMSE) • Utilizes correlation of interference at the antennas to reduce interference power • Same as maximal ratio combining when interference is not present

  7. User 1 User 1 Signal  • • • User 2 INTERFERENCE NULLING Line-Of-Sight Systems • Utilizes spatial dimension of radio environment to: • Maximize signal-to-interference-plus-noise ratio • Increase gain towards desired signal • Null interference: M-1 interferers with M antennas

  8. INTERFERENCE NULLING Multipath Systems User 1 User 1 Signal  • • • User 2 Antenna pattern is meaningless, but performance is based on the number of signals, not number of paths (without delay spread). => A receiver using adaptive array combining with M antennas and N-1 interferers can have the same performance as a receiver with M-N+1 antennas and no interference, i.e., can null N-1 interferers with M-N+1 diversity improvement (N-fold capacity increase).

  9. PHASED ARRAYS • Fixed (or steerable) beams • Consider cylindrical array with M elements (/2 spacing) • - Diameter  (M / 4) feet at 2 GHz • With small scattering angle ( = 4): • - Margin = 10log10M (dB) • - Number of base stations = M-1/2 • - Range = M1/4 • Disadvantages: • - No diversity gain (unless use separate antenna) • - With large scattering angle , gain is limited for beamwidths   r Mobile  Base Station

  10. CDMA with Adaptive Array

  11. Range Increase with CDMA Signals Single beam for all RAKE fingers results in range limitation with angular spread for multibeam antenna (phased array)

  12. 7 Adaptive Array Phased Array Theory 6 3M-fold Diversity 5 60° 45° 20° 3-fold Diversity 10° Normalized Range 3° 4 0=3° 10° 20° 45° 60° 3 5 Spacing FIXED SECTORS, 0=60° 2 1 0 1 2 3 log10 (M) Range Increase with CDMA Signals - Different Beams per Finger

  13. ANTENNA AND DIVERSITY GAIN • Antenna Gain: Increased average output signal-to-noise ratio • - Gain of M with M antennas • - Narrower beam with /2-spaced antenna elements • Diversity Gain: Decreased required receive signal-to-noise ratio for a given BER averaged over fading • - Depends on BER - Gain for M=2 vs. 1: • 5.2 dB at 10-2 BER • 14.7 dB at 10-4 BER • - Decreasing gain increase with increasing M - 10-2 BER: • 5.2 dB for M=2 • 7.6 dB for M=4 • 9.5 dB for M= • - Depends on fading correlation • Antenna diversity gain may be smaller with RAKE receiver in CDMA

  14. 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

  15. 24 (12 ft) 3 (1.5 ft) 3 (1.5 ft) ADAPTIVE ARRAYS FOR TDMA BASE STATIONS AT&T Wireless Services and Research - Field Trial with Lucent 7/96-10/96 • Field trial results for 4 receive antennas on the uplink: • Range extension: 40% reduction in the number of base stations can be obtained 4 to 5 dB greater margin  30% greater range • Interference suppression: potential to more than double capacity • Operation with S/I close to 0 dB at high speeds  greater capacity and quality

  16. INTERFERENCE NULLING Multipath Systems User 1 User 1 Signal  • • • User 2 Antenna pattern is meaningless, but performance is based on the number of signals, not number of paths (without delay spread). => A receiver using adaptive array combining with M antennas and N-1 interferers can have the same performance as a receiver with M-N+1 antennas and no interference, i.e., can null N-1 interferers with M-N+1 diversity improvement (N-fold capacity increase).

  17. 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 data rate & 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 • 19 Mbps WCDMA

  18. 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

  19. 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

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

  21. $/Cell $/Sub UWB 3.1-10.6 GHz $ 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

  22. $/Cell $/Sub UWB 3.1-10.6 GHz $ 500,000 $ 1000 $ 100 $ 500 $ 100 $ 10 802.11a 5.5GHz Unlicensed 802.11b 2.4GHz Unlicensed 3G Wireless ~ 2GHz Wireless System 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

  23. BEAM SELECT SIGNAL SIGNAL OUTPUT BEAMFORMER INTERFERENCE Smart Antennas for Cellular • Key enhancement technique to increase system capacity, extend coverage, and improve user experience in cellular (IS-136) Uplink Adaptive Antenna SIGNAL SIGNAL OUTPUT INTERFERENCE BEAMFORMER WEIGHTS Downlink Switched Beam Antenna In 1999, combining at base stations changed from MRC to MMSE for capacity increase

  24. Cellular Data • CDPD (US) < 10 kbps • GPRS = 30-40 kbps • EDGE/1xRTT = 80 kbps • WCDMA = 100 kbps (starting in Japan, but not for several years in US)

  25. WLANs: 802.11b 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 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 - TDD Channel spacing: 5 MHz Number of channels: Total of 14 (but only the first 11 are used in the US), with only 3 nonoverlapping channels

  26. WLANs: 802.11a (g in 2.4 GHz band) 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 - TDD Channel spacing: 20 MHz Frequency band: Unlicensed national infrastructure (U-NII), 5.5 GHz Number of channels: Total of 12 in three blocks between 5 and 6 GHz :

  27. Smart Antenna Smart Antenna AP AP Smart Antennas for WLANs Interference Smart Antennas can significantly improve the performance of 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

  28. 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 • Nokia GPRS/802.11b PCMCIA card • NTT DoCoMo WLAN/WCDMA trial Cellular Wireless Internet Wireless LAN’s Home Enterprise Public

  29. 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, with 19 Mbps demonstrated • In UWB, smart antennas at receiver provide range increase at data rates of 100’s Mbps

  30. 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

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

  32. Cell Breathing in WLAN Systems AP AP AP AP AP AP AP AP AP AP AP AP AP AP • Measure traffic load for each access point • Shrink overloaded cell by reducing RF power • Expand others to cover abandoned areas

  33. Cochannel interference High traffic load Adaptive Channel Assignment Initial Assignment After one iteration 2 1 3 3 2 3 3 1 2 3 1 2 2 2 3 2 3 1 • Assign channels to maximize capacity as traffic load changes

  34. SIGNAL INTERFERENCE BEAMFORMER WEIGHTS INTERFERENCE Smart Antennas SIGNAL OUTPUT • 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)

  35. Conclusions • We are 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, increasedata rate, and improve quality, without standards changes • Radio resource management techniques, in combination with smart antennas, and multiband/multimode devices

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