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Space Time Processing for Fixed Broadband Wireless

Space Time Processing for Fixed Broadband Wireless. A. Paulraj Gigabit Wireless & Stanford University ISART 6 -8 September, 2000 Boulder, CO. Essential Attributes of Broad Band Wireless (BWA) Network. High Speed > 4-5 Mbps High QoS / Availability DSL / Cable like Low Costs $$$

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Space Time Processing for Fixed Broadband Wireless

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

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

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

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

  8. 40 30 20 K-Factor in dB 10 0 -10 -20 -1 0 1 10 10 10 Distance in km K-Factor vs. Distance (Suburban BWA) ht = 15m, 90 deg. Rx antenna ---hr = 10m --- hr = 3m hr = 10m GW and AT&T measured data similar hr = 3m K = 0 is necessary assumption for reliable deployment

  9. 10 5 0 -5 -10 -15 -20 -25 -1 0 1 10 10 10 RMS Delay Spread vs Distance (Suburban BWA) GW experimental data similar RMS Delay Spread in Microseconds (dB) Distance in km

  10. Doppler Spectrum - BWA - 3dB 0.05  fd 0.5 Hz fmax 

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

  12. C vs I Measurements

  13. MIMO Measurements H11 H12 BTS CPE H21 H22

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

  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. Throughput vs Utiliz. (vs PER) Mode 6, Doppler 1Hz, MaxUtil 635 users, small files Mode 6, Doppler 1Hz, MaxUtil 635 users, big files 220 3000 Mean Per 1% Mean Per 1% Mean Per 5% Mean Per 5% Mean Per 10% Mean Per 10% 200 2500 180 2000 mean throughput [Kbps] mean throughput [Kbps] 160 1500 140 1000 120 500 100 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 link utilization [%] link utilization [%] - Throughput = File size/ Mean transfer delay - TCP windowing algorithm yields the difference in the throughput of ‘small’ and ‘big’ files

  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 8 7 6 5 Range in Miles 4 3 2 1 0 5 10 15 20 25 30 2 x 2, RLP Required C/ N 1 x 1, NO RLP

  19. CDF of Tx-Rx Diversity - Measured Data 0 10 After Combining Before Combining -1 10 1 x 2 Probability That Signal Power < Abscissa -2 10 2 x 2 -3 10 -4 10 -40 -30 -20 -10 0 10 20 Signal Power About Mean in dB 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 0 10 -1 10 Before Combining After Combining C /I = 10 dB -2 Probability That C/I < Abscissa 10 1 x 2 2 x 2 -3 10 -4 10 -40 -30 -20 -10 0 10 20 C/I About Mean in dB 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

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