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David S. L. Wei Joint Work with Alex Chia-Chun Hsu and C.-C. Jay Kuo

Coexistence Mechanism Using Dynamic Fragmentation for Interference Mitigation between Wi-Fi and Bluetooth. David S. L. Wei Joint Work with Alex Chia-Chun Hsu and C.-C. Jay Kuo. Outline. Overview of Wi-Fi and Bluetooth Previous Work Dynamic Fragmentation Algorithm Results

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David S. L. Wei Joint Work with Alex Chia-Chun Hsu and C.-C. Jay Kuo

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  1. Coexistence Mechanism Using Dynamic Fragmentation for Interference Mitigation between Wi-Fi and Bluetooth David S. L. Wei Joint Work with Alex Chia-Chun Hsu and C.-C. Jay Kuo

  2. Outline • Overview of Wi-Fi and Bluetooth • Previous Work • Dynamic Fragmentation Algorithm • Results • Conclusion and Future Work

  3. Content • Overview of Wi-Fi and Bluetooth • 802.11/Wi-Fi • 802.15.1/Bluetooth • Coexistence in the UL band • Previous Work • Dynamic Fragmentation Algorithm • Results • Conclusion and Future Work

  4. Standard Modulation Frequency Data Rate Max. Distance 802.11a OFDM 5GHz 6 ~ 54 Mbps 60 ft. 802.11b DSSS (CCK) 2.4GHz 2~11 Mbps 300 ft. 802.11g CCK/OFDM 2.4GHz 20 ~ 54 Mbps 300 ft. 802.11n OFDM 2.4GHz >100 Mbps 300 ft. Overview of Wi-Fi and Bluetooth802.11 Wi-Fi • A dominating WLAN standard • Medium to high date rate, medium range < 100m • Use the ISM band • Large selection of commodities Industrial, Scientific, medical

  5. Overview of Wi-Fi and Bluetooth802.11 Medium Access Control • CSMA/CA • Carrier Sense Multiple Access / Collision Avoidance • Virtual Carrier Sensing • Request-to-send/Clear-to-send RTS/CTS • Network Allocation Vector NAV

  6. Overview of Wi-Fi and BluetoothExample: DCF mode Time • Distributed Coordination Function 1 BW RTS DATA DIFS Distributed Inter Frame Space Backoff Window SIFS ACK 2 CTS Short Inter Frame Space set NAV 3 BW BW* RTS DIFS DIFS

  7. Overview of Wi-Fi and Bluetooth802.15 Bluetooth • Popular WPAN standard • Low data rate, low cost, short range <10m • use frequency hopping to avoid collision • 1600 hops/s ~ 625 μs in every frequency channel • SCO and ACL link • Synchronous Connection-Oriented link • Real-time application: voice stream • HV-3 link: a packet is generated every 6 time slots • Asynchronous ConnectionLess link • Non-time-critical application: data traffic • DH-1/3/5 link: one packet occupied 1/3/5 time slot

  8. Overview of Wi-Fi and BluetoothCoexistence in the UL band 2.4835 2.4805 BT Frequency 625 μs 1 MHZ Channel 6 22 MHZ 2.4370 79 MHZ Wi-Fi 2.4015 2.4 GHz Time

  9. Overview of Wi-Fi and BluetoothCoexistence in the UL band • Packet loss caused by interference • Overlap both in time and in frequency • Over the SNR threshold

  10. Content • Overview of Wi-Fi and Bluetooth • Previous works • Adaptive Frequency Hopping • D-OLA and V-OLA • Fragmentation • Dynamic Fragmentation Algorithm • Results • Conclusion and Future work

  11. Previous Work802.15.2 Coexistence Working Group • Many suggestions on improving coexistence • Collaborative solutions • Devices could exchange information • Collocated and under a central controller • Non-collaborative solutions • No information exchange • Most common scenario

  12. Previous WorkAdaptive Frequency Hopping • Enhancement on BT, many variations • Non-collaborative solution • Distinguish good channels from bad ones • Keep the hopping sequence on good channels more frequently

  13. Previous WorkAdaptive Frequency Hopping 2.4835 2.4805 BT Frequency 2.4370 Wi-Fi 2.4015 2.4 GHz

  14. Previous WorkD-OLA and V-OLA • Proposed by Chiasserini and Rao, Infocom 2004 • Data OverLap Avoidance • Use different BT packet length to avoid bad channels • Voice OverLap Avoidance • Wi-Fi estimate the interference pattern of real-time packet • Shorten Transmission or Postpone Transmission • Increase delay • Not a pure non-collaborative solution

  15. DATA1 DATA2 Previous WorkFragmentation No fragmentation hdr ACK BW DATA DIFS 2 fragments ACK1 ACK2 BW DIFS

  16. Previous WorkFragmentation • Adaptive Fragmentation from 802.15.2 2001 • Adjust fragmentation according to Packet Error Rate PER • Many rounds before reach optimal length • Optimal Fragmentation by Howitt 2005 • Complexity is too high to determine the optimal fragment length at run time • No resolution on collision and interference • Need simple run time solution

  17. Content • Overview of Wi-Fi and Bluetooth • Previous works • Dynamic Fragmentation Algorithm • Interference model • State diagram of DFA • Determine threshold • Optimization • Results • Conclusion and Future Work

  18. Dynamic Fragmentation AlgorithmInterference model ACK DATA hdr 625 μs 366 μs Pf : Probability of BT hops on Wi-Fi frequency N : # of BT time slot overlapped by Wi-Fi packet τBT : Traffic load of BT σ : utilization of BT time slot N is crucial

  19. Dynamic Fragmentation AlgorithmState Diagram of DFA • 2 states • State 1, no fragmentation • State 2, DATA → n fragments • PER greater than P2, one state up if possible, further fragmentation • PER lower than P1 → one state down if possible • How to choose P1, P2? PER≤P2 PER>P2 2 1 PER≥P1 PER<P1

  20. DATA1 DATA1 DATA2 DATA1 Dynamic Fragmentation AlgorithmDetermine Threshold hdr ACK BW DATA DIFS ACK1 ACK2 BW DIFS Retransmission ACK1 BW ACK1 BW DIFS DIFS Double the backoff window

  21. Dynamic Fragmentation AlgorithmDetermine Threshold Time to transfer a packet with n fragments and suffer R retransmissions Compare the transmission time before and after state transition If true, then state transition is beneficial

  22. Dynamic Fragmentation AlgorithmDetermine Threshold Before state transition P is the current PER Assume geometric distribution Case 1: less or equal to BW upper-bound Case 2: greater than BW upper-bound

  23. Dynamic Fragmentation AlgorithmDetermine Threshold How to find PER after state transition? Same as previous slide Now we have all the parameters to calculate a theoretically correct threshold

  24. Wi-Fi Timing Cause Solution DATA1 DATA1 DATA2 DATA2 DATA2 DATA2 Dynamic Fragmentation AlgorithmOptimization Collision Interference From the beginning of a transmission Most likely not Traffic Jam Coexistence (BT) CSMA/CA Coexistence Mechanism Transmission failure on following fragments is due to Interference ACK1 ACK2 BW ACK2 BW DIFS DIFS With optimization ACK1 ACK2 ACK2 BW DIFS DIFS

  25. Dynamic Fragmentation AlgorithmOptimization Only first fragment needs backoff window when retransmission If true, then state transition is beneficial DFAm : with node mobility DFAs : static network (throughput performance can be optimized)

  26. Content • Overview of Wi-Fi and Bluetooth • Previous work • Dynamic Fragmentation Algorithm • Results • Conclusion and Future work

  27. ResultSimulation PER equation validation

  28. ResultSimulation Threshold equation validation Throughput improvement

  29. ResultSimulation: ACL link Throughput of the Wi-Fi and BT in the presence of BT ACL link

  30. ResultSimulation: 2 SCO links Throughput of the Wi-Fi and BT in the presence of 2 SCO links between BT master/slave

  31. ResultSimulation: delay Average Wi-Fi delay vs. BT traffic load

  32. Content • Overview of Wi-Fi and Bluetooth • Previous works • Dynamic Fragmentation Algorithm • Results • Conclusion and Future work

  33. Conclusion and Future workConclusion • Simple non-collaborative mechanism • Increase collision/interference resolution • Improve throughput and delay • Built a reliable, powerful model If PER > 0.6, DFAs 56%, DFAm 30%

  34. Conclusion and Future WorkCognitive Radio • Recent measurements by FCC shows 70% of the allocated spectrum is not utilized (US) • Improve spectrum efficiency Unlicensed bands • Need new solution for upcoming wireless service • Existing policy fragmented the spectrum • Bandwidth is scarce and expensive • Good frequencies are taken

  35. Conclusion and Future workCognitive Radio • Paradigm shift – Cognitive Radio by Mitola 1999 • “radio or system that senses its operational electromagnetic environment and can dynamically and autonomously adjust its radio operating parameters to modify system operation, such as maximize throughput, mitigate interference, facilitate interoperability,…” • IEEE 802.22, FCC, DARPA XG, OverDRiVE, SWRF, WWRF, …

  36. Conclusion and Future workCognitive Radio • Cognitive radio requirements • coexist with legacy wireless systems • use their spectrum resources • do not interfere with them • Cognitive radio properties • RF technology that "listens" to huge swaths of spectrum • Knowledge of primary users’ spectrum usage • Rules of sharing the available resources • Embedded intelligence to determine optimal transmission based on primary users’ behavior

  37. Conclusion and Future workCognitive Radio: spectrum hole Frequency F1 Exclude Spectrum F2 Gray space White space F3 Spectrum hole F4 F5 Time

  38. Thanks ^_^

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