1 Smart Antennas for Mobile Wireless Systems Jack H. Winters May 6, 2003

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

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

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

5 COMBINING TECHNIQUES (CONT.) Weight and combine signals to maximize signal-to-noise ratio (Weights are complex conjugate of the channel transfer characteristic) Optimum technique with noise only BER M  BER M (M-fold diversity gain) Maximal ratio combining: W1W1 WMWM  Output

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 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 User 1 User 2  User 1 Signal

8 INTERFERENCE NULLING Multipath Systems User 1 User 2  User 1 Signal 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 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 = 10log 10 M (dB) - Number of base stations = M -1/2 - Range = M 1/4 Disadvantages: - No diversity gain (unless use separate antenna) - With large scattering angle , gain is limited for beamwidths   PHASED ARRAYS Base Station Mobile r 

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

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 BER 14.7 dB at BER - Decreasing gain increase with increasing M 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 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 24 (12 ft) 3 (1.5 ft)

16 INTERFERENCE NULLING Multipath Systems User 1 User 2  User 1 Signal 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 a (4X 54 Mbps) –1.5 Mbps EDGE –19 Mbps WCDMA

18 Rx MIMO Channel Testing W1W1 W2W2 W3W3 W4W4 LO Synchronous test 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 Rooftop Antennas Terminal Antennas on a Laptop Tx Rooftop Base Station Antennas 11.3 ft Prototype Dual Antenna Handset Mobile Transmitters

19 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  beams 4 patch antennas at 1900 MHz separated by 3 inches ( /2 wavelengths) Laptop prototype made of brass with adjustable PCB lid

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

21 Current Systems 10 feet100 feet1 mile10 miles 100 kbps 1 Mbps 10 Mbps 100 Mbps 3G Wireless ~ 2GHz BlueTooth 2.4GHz a 5.5GHz Unlicensed b 2.4GHz Unlicensed Peak Data Rate Range 2 mph10 mph30 mph 60 mph $ 500,000 $ 1000 $ 100 $ 500 $ 100 $ 10 $/Cell $/Sub High performance/price High ubiquity and mobility Mobile Speed UWB GHz

22 Wireless System Enhancements 10 feet100 feet1 mile10 miles 100 kbps 1 Mbps 10 Mbps 100 Mbps 3G Wireless ~ 2GHz BlueTooth 2.4GHz a 5.5GHz Unlicensed b 2.4GHz Unlicensed Peak Data Rate Range 2 mph10 mph30 mph 60 mph $ 500,000 $ 1000 $ 100 $ 500 $ 100 $ 10 $/Cell $/Sub High performance/price High ubiquity and mobility Mobile Speed Enhanced UWB GHz

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

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

25 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 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 b Physical Layer Parameters: Chip rate:11 MHz Frequency band:Industrial, Scientific and Medical (ISM, unlicensed) GHz Bandwidth:22 MHz - TDD Channel 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  s 11 chips Barker 727 ns 8 chips CCK WLANs: b

26 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 Mbps Modulation:BPSK, QPSK, 16QAM, 64QAM Coding rate:1/2, 2/3, 3/4 Subcarriers:52 Pilot subcarriers:4 G 3.2  s 4  s FFT 52=48+4 tones 64 point FFT Key a Physical Layer Parameters: Symbol duration: 4  s Guard interval:800 ns Subcarrier spacing:312.5 kHz Bandwidth:16.56 MHz - TDD Channel spacing:20 MHz FFT size:64 : BPSKQPSKQAM16QAM R=1/2 48 R=2/ R=3/4 User data rates (Mbps): Frequency band: Number of channels: WLANs: a (g in 2.4 GHz band)

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

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 Enterprise Home Public Internet Wireless LAN’s

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 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

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

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

34 Smart 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 BEAMFORMER WEIGHTS SIGNAL OUTPUT

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