1. Space Time Processing for Fixed Broadband Wireless A. Paulraj Gigabit Wireless & Stanford University ISART 6 -8 September, 2000 Boulder, CO

2. Essential Attributes of Broad Band Wireless (BWA) Network High Speed > 4-5 Mbps High QoS / Availability DSL / Cable like Low Costs $$$ High capacity High coverage CPE and Infrastructure unit costs Friendly Easy CPE Install Environmental/Regulatory Scalability (Multi-cell) Evolution to portability

3. BWA Network Architecture Multi-cell architecture Low BTS antennas (50 - 150 ft) Under-the-eave subscriber antennas Significant Non-LOS propagation (Rayleigh fading) Strong multi-path Low Doppler channels Mobile cellular-like network with all its challenges but with  50 Speed and  50 QoS

4. NAU= Network Access Unit BTS = Base Transceiver Station BSC = Base Station Controller BWA Network NAU IP NGU BSC BTSBTS BTSBTS BTSBTS Voice gateway Network Operations Center SMS Access Mux PSTN IP Gateway NAU NGU= Network Gateway Unit SMS= Subscription Management System

5. Data Rate & QoS Challenges F  50 High Data Rate F  50 QoS (0.999 Availability on Throughput, Delay, Jitter) Capacity (Bits/Hz/Cell) Coverage (Cell Radius)  0.4  0.2  0.4

6. Typical Propagation Scenario BTS Directional Antenna BTS Ht 30’-150’ Ht 8’-20’ 0.1 - 5 miles CPE Directional Antenna Distance to mobile scatterers

7. Path Loss (Mean Level) Signal Power (dB) Super Cell BTS ht: 1500ft Macro Cell BTS ht 150 ft Range in km Frequency: 2.5 GHz Ant Beamwidth: 90 deg Super Cell: Free Space model Macro/Micro Cell: Erceg’s model

8. K-Factor vs. Distance (Suburban BWA) ht = 15m, 90 deg. Rx antenna hr = 3m hr = 10m GW and AT&T measured data similar K = 0 is necessary assumption for reliable deployment --- hr = 10m --- hr = 3m

9. RMS Delay Spread vs Distance (Suburban BWA) RMS Delay Spread in Microseconds (dB) Distance in km GW experimental data similar

10. Doppler Spectrum - BWA - 3dB f max  0.05  f d  0.5 Hz

11. Signal Measurements Low Doppler, 0.05 Hz High Doppler, 0.5 Hz

12. C vs I Measurements

13. MIMO Measurements BTSCPE H22 H12 H21 H11

14. Spatial Multiplexing (SM) Offers Higher Speeds Each Eigen mode of the matrix channel can support a radio link. 11.4  1.5 speed up possible in 2 x 3 systems. Tx Rx H

15. Increasing Capacity/Coverage Coverage : Lower the C/N needed to close link - improves link budget Capacity: Lower C/I needed to close link - improves reuse factor –Use diversity, array gain, coding, etc to minimize required C/N or C/I to support a target PER –Use RLP and fragmentation to allow higher target PER –Use spatial multiplexing to run parallel channels

16. 00.10.20.30.40.50.60.70.8 100 120 140 160 180 200 220 Mode 6, Doppler 1Hz, MaxUtil 635 users, small files link utilization [%] mean throughput [Kbps ] Mean Per 1% Mean Per 5% Mean Per 10% 00.10.20.30.40.50.60.70.8 0 500 1000 1500 2000 2500 3000 Mode 6, Doppler 1Hz, MaxUtil 635 users, big files link utilization [%] mean throughput [Kbps] Mean Per 1% Mean Per 5% Mean Per 10% - TCP windowing algorithm yields the difference in the throughput of ‘small’ and ‘big’ files - Throughput = File size/ Mean transfer delay Throughput vs Utiliz. (vs PER)

17. Increasing Coverage Diversity is critical (Tx antenna, Rx antenna, frequency, pol) Directional CPE antennas Forward Error Correction (FEC) & ARQ Increase BTS & CPE height

18. Coverage vs Required C/N 051015202530 1 2 3 4 5 6 7 8 Range in Miles 1 x 1, NO RLP2 x 2, RLP Required C/ N

19. CDF of Tx-Rx Diversity - Measured Data -40-30-20-1001020 10 -4 10 -3 10 -2 10 10 0 Signal Power About Mean in dB Probability That Signal Power < Abscissa Before Combining After Combining 1 x 2 2 x 2 Probability of signal falling 10 dB below mean is 300 times lower with 2 x 2 compared 1 x 1

20. Increasing Spectrum Efficiency Reduce CCI to improve reuse - Increase signal diversity - Interference averaging - Antenna sectorization, beam forming, interference cancellation Reduce ACI to improve reuse - Careful frequency planning - Stringent emission masks, Rx filtering - Interference suppression Use link adaptation to exploit available C/N or C/I levels Use Radio Link Protocol to allow link to use high BER

21. C/ I After Combining - Measured Data C /I = 10 dB -40-30-20-1001020 10 -4 10 -3 10 -2 10 10 0 C/I About Mean in dB Probability That C/I < Abscissa Before Combining 1 x 2 2 x 2 After Combining Probability of C/I falling 15 dB below mean is 300 times lower with 2 x 2 compared to 1 x 1

22. Conclusion Achieving high capacity/coverage in a multi-cell BWA (  50 speed &  50 QoS compared to mobile cellular) network is a challenging problem. Many technologies help improve performance. MIMO antennas are a key leverage. Gigabit Wireless is a pioneer of MIMO for BWA networks