Smart Antennas for Mobile Wireless Systems Jack H

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 2

Smart Antennas Switched Multibeam Antenna Adaptive Antenna Array SIGNAL BEAMFORMER SIGNAL BEAM SELECT SIGNAL OUTPUT INTERFERENCE BEAMFORMER WEIGHTS 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 3

COMBINING TECHNIQUES Selection: Output • Select antenna with the highest received signal power • P 0 M = P 0 M 4

COMBINING TECHNIQUES (CONT. ) Maximal ratio combining: W 1 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 (M-fold diversity gain) 5

OPTIMUM COMBINING (ADAPTIVE ANTENNAS) • Weight and combine signals to maximize signal-tointerference-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 6

INTERFERENCE NULLING Line-Of-Sight Systems User 1 • • • User 1 Signal User 2 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 7

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). 8

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): r Mobile - Margin = 10 log 10 M (d. B) - Number of base stations = M-1/2 - Range = M 1/4 • Disadvantages: Base Station - No diversity gain (unless use separate antenna) - With large scattering angle , gain is limited for beamwidths 9

CDMA with Adaptive Array 10

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

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

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 d. B at 10 -2 BER • 14. 7 d. B at 10 -4 BER - Decreasing gain increase with increasing M - 10 -2 BER: • 5. 2 d. B for M=2 • 7. 6 d. B for M=4 • 9. 5 d. B for M= - Depends on fading correlation • Antenna diversity gain may be smaller with RAKE receiver in CDMA 13

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 14

ADAPTIVE ARRAYS FOR TDMA BASE STATIONS AT&T Wireless Services and Research - Field Trial with Lucent 7/96 -10/96 24 (12 ft) 3 (1. 5 ft) Field trial results for 4 receive antennas on the uplink: 3 (1. 5 ft) • Range extension: 40% reduction in the number of base stations can be obtained 4 to 5 d. B greater margin 30% greater range • Interference suppression: potential to more than double capacity Operation with S/I close to 0 d. B at high speeds greater capacity and quality 15

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). 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 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 4 x data rate & capacity increase in all mobile & indoor/outdoor environments (4 Tx and 4 Rx antennas) – – – 216 Mbps 802. 11 a (4 X 54 Mbps) 1. 5 Mbps EDGE 19 Mbps WCDMA 17

MIMO Channel Testing Mobile Transmitters W 1 Tx W 2 • Perform timing recovery and symbol synchronization Rx • Record 4 x 4 complex channel matrix Rx Tx • Evaluate capacity and channel correlation Rx Tx W 4 Synchronous test sequences Rx Tx W 3 Test Bed Receivers with Rooftop Antennas LO Terminal Antennas on a Laptop LO 11. 3 ft Prototype Dual Antenna Handset Rooftop Base Station Antennas Mobile Transmitters 18

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 19

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

Current Systems Peak Data Rate 100 Mbps High performance/price UWB 3. 1 -10. 6 GHz 802. 11 a 5. 5 GHz Unlicensed 10 Mbps 802. 11 b $/Cell $/Sub $ 500, 000 $ 500 $ 100 $ 10 2. 4 GHz Unlicensed 1 Mbps Blue. Tooth 100 kbps 2. 4 GHz High ubiquity and mobility 3 G Wireless ~ 2 GHz 10 feet 2 mph 100 feet 10 mph 1 mile 30 mph 10 miles Range 60 mph Mobile Speed 21

Wireless System Enhancements Peak Data Rate UWB 100 Mbps 3. 1 -10. 6 GHz High performance/price 802. 11 a 5. 5 GHz Unlicensed 10 Mbps 802. 11 b 2. 4 GHz Unlicensed 1 Mbps $/Cell $/Sub $ 500, 000 $ 500 $ 100 $ 10 Enhanced Blue. Tooth 100 kbps 2. 4 GHz High ubiquity and mobility 3 G Wireless ~ 2 GHz 10 feet 2 mph 100 feet 10 mph 1 mile 30 mph 10 miles 60 mph Range Mobile Speed 22

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

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

WLANs: 802. 11 b Barker 1 ms 11 chips CCK 727 ns 8 chips Key 802. 11 b Physical Layer Parameters: Data rate: Modulation/Spreading: Transmission modes: (dynamic rate shifting) Chip rate: Frequency band: Bandwidth: Channel spacing: Number of channels: • 1, 2, 5. 5, 11 Mbps • 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 - TDD 5 MHz Total of 14 (but only the first 11 are used in the US), with only 3 nonoverlapping channels 25

WLANs: 802. 11 a (g in 2. 4 GHz band) 3. 2 ms FFT G 4 ms 52=48+4 tones 64 point FFT Key 802. 11 a 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: 6, 9, 12, 18, 24, 36, 48, 54 Mbps BPSK, QPSK, 16 QAM, 64 QAM 1/2, 2/3, 3/4 User data rates (Mbps): 52 BPSK QAM 16 QAM 64 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 k. Hz 16. 56 MHz - TDD 20 MHz Unlicensed national infrastructure (U-NII), 5. 5 GHz Total of 12 in three blocks between 5 and 6 GHz : 26

Smart Antennas for WLANs Smart Antenna AP 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 27

Internet Roaming • Seamless handoffs between WLAN and WAN – high-performance when possible – ubiquity with reduced throughput Cellular Wireless • Management/brokering of consolidated WLAN and WAN access • • • Adaptive or performance-aware applications Nokia GPRS/802. 11 b PCMCIA card NTT Do. Co. Mo WLAN/WCDMA trial Internet Wireless LAN’s Enterprise Home Public 28

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

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 30

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 31

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

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

Smart Antennas SIGNAL OUTPUT INTERFERENCE BEAMFORMER WEIGHTS 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) 34

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, increase data rate, and improve quality, without standards changes – Radio resource management techniques, in combination with smart antennas, and multiband/multimode devices 35