1. 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

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 Previous Work
Coexistence in the UL band
Previous Work
Dynamic Fragmentation Algorithm
Simulation Results
Conclusion and Future Work

4. Overview of Wi-Fi and Bluetooth 802.11/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
802.11a
802.11b
802.11g
802.11n
Standard
OFDM
DSSS (CCK)
CCK/OFDM
Modulation
5GHz
2.4GHz
Frequency
6 ~ 54 Mbps
2 ~11 Mbps
20 ~ 54 Mbps
>100 Mbps
Data Rate
60 ft.
300 ft.
Max. Distance

5. Overview of Wi-Fi and Bluetooth 802.11 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 Bluetooth Example: DCF mode
Time
Distributed Coordination Function 1
DIFS BW
RTS
DATA
Distributed Inter Frame Space
Backoff Window
SIFS 2
CTS
ACK
Short Inter Frame Space 3 BW
set NAV
DIFS
DIFS
BW*
RTS

7. Overview of Wi-Fi and Bluetooth 802.15.1/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: a packet occupies 1/3/5-time slots

8. Overview of Wi-Fi and Bluetooth Interference between Wi-Fi and BT
2.4835
2.4805
Frequency
625 μs
1 MHZ
Channel 6
2.4370
22 MHZ
79 MHZ
2.4015
2.4 GHz
Time

9. Overview of Wi-Fi and Bluetooth Coexistence 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 Work 802.15.2 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 Work Adaptive 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 Work Adaptive Frequency Hopping
2.4835
2.4805 BT
Frequency
2.4370
Wi-Fi
2.4015
2.4 GHz

14. Previous Work D-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. Previous Work Fragmentation
No fragmentation
hdr BW
DATA
ACK
DIFS
2 fragments
DATA1
ACK1
DATA2
ACK2
DIFS BW

16. Previous Work Fragmentation
Adaptive Fragmentation from
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 Algorithm Interference model
DATA
ACK
hdr
625 μs
366 μs
Pf : Probability of BT packets hops into Wi-Fi frequency band
N : # of BT time slots overlapped with Wi-Fi packet
τBT : Traffic load of BT
σ : utilization of BT time slot
N is crucial

19. Dynamic Fragmentation Algorithm State Transition of DFA
State 1, no fragmentation
If PER > P2, enter State 2
Otherwise, remain at State 1
State 2, DATA → n fragments
If PER < P1, return to State 1
Otherwise, remain at State 2
PER≤P2
PER>P2 1 2
PER≥P1
PER<P1
How to determine P1, P2?

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

21. Dynamic Fragmentation Algorithm Determine 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 Algorithm Determine 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 Algorithm Determine Threshold
How to find PER after state transition?
Could be obtained in a similar way
Now we have all the parameters to determine the theoretically right threshold

24. Dynamic Fragmentation Algorithm Optimization
Timing
Cause
Solution
Wi-Fi
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 BW
DATA1
ACK1
DATA2
ACK2 BW
DATA2
ACK2
DIFS
DIFS
In a static network, no collision would happen in the middle of a transmission. We thus can take away the unnecessary BW of retransmission.
DIFS BW
DATA1
ACK1
DATA2
ACK2
DATA2
ACK2
SIFS

25. Dynamic Fragmentation Algorithm Optimization
Only first fragment needs backoff window when retransmission
If true, then state transition is beneficial
DFAm : with node mobility
DFAs : static network

26. Content Overview of Wi-Fi and Bluetooth Previous Work
Dynamic Fragmentation Algorithm
Simulation Results
Equation Validation
Throughput
Delay
Conclusion and Future Work

27. Simulation Result Simulation
PER equation validation
Threshold equation validation (P2)
Throughput improvement

28. Simulation Result Simulation: Throughput
Throughput of the Wi-Fi and BT in the presence of BT ACL link
Throughput of the Wi-Fi and BT in the presence of 2 SCO links between BT master/slave

29. Simulation Result Simulation: Delay
Average Wi-Fi delay vs. BT traffic load

30. Content Overview of Wi-Fi and Bluetooth Previous works
Dynamic Fragmentation Algorithm
Results
Conclusion and Future Work

31. Conclusion and Future work Conclusion
Simple non-collaborative mechanism
Increase collision/interference resolution
Improve throughput and delay
Developed a reliable and useful model
If PER > 0.6, DFAs 56%, DFAm 30%

32. Thanks ^_^