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Enhancing IEEE 802.11 DCF with Location-Based Transmission Control

This study introduces Location Enhanced DCF (LED) to improve 802.11 DCF performance, addressing blocking probabilities and capture effects. LED includes physical and MAC layer designs for better transmission control and proposes analytics over simulations.

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Enhancing IEEE 802.11 DCF with Location-Based Transmission Control

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  1. Location Enhancementto IEEE 802.11 DCF Tamer Nadeem, Lusheng Ji, Ashok Agrawala, Jonathan Agre Department of Computer Science, University of Maryland

  2. IEEE 802.11 DCF • Basic: contention-based • DATA-ACK • Optional: reservation-based • RTS-CTS-DATA-ACK

  3. C A D B Really Need to Block some Transmission? ?

  4. Outline • Problem with 802.11 DCF • Location Enhanced DCF (LED) • Performance Evaluation • Conclusion and Future Works

  5. two transmission overlap in time and in frequency Capture Effect • The signals of the stronger transmission will capture the receiver modem, and signals of the weaker transmission will be rejected as noise capture condition

  6. C A D B Example of Capture Effect • Question: What is the unnecessaryblockingprobability in 802.11?

  7. Analysis of Blocking Probability • Model Definitions • Stations are uniformly distributed over an area with a density of δ • Each station has a transmission range R and a carrier sense range I • Each packet requires transmission time τ • One data packet is generated at a randomly selected time within every time interval T

  8. Analysis of Blocking Probability Friis free-space propagation model two-ray ground reflectionmodel Pt – transmission power Gt/Gr – transmitter/receiver antenna gain D – distance between sender and receiver λ – wavelength ht/hr –transmitter/receiver elevation L – system loss factor Capture condition:

  9. d(r,s)<= d(r,v)>= r must be located within the shaded area A(x)

  10. The probability that v’s transmission doesn’t corrupt the communication between s and r is:

  11. The probability that none of the stations within the carrier sensing range of a station will transmit is obtained by: • The probability that v’s transmission will not interfere with other transmissions (if any) in the interference range is: • The probability that v can transmit with the presence of a nearby transmission without corrupting this transmission is given by

  12. Analytical vs Simulation Result

  13. Analytical vs Simulation Result Actual unnecessary blocking probability Pb

  14. Summary • Calculation of Pb is still too conservative • The unnecessary blocking probability of 802.11 DCF is large

  15. Outline • Problem with 802.11 DCF • Location Enhanced DCF (LED) • Performance Evaluation • Conclusion and Future Works

  16. Basic Idea of LED • Include more information (e.g. location) of each transmission in the transmission • An overhearing station of a data delivery can compute and decide whether they should be silent

  17. Physical Layer Design • Capture a message in a message A new frame arrived?

  18. MAC Layer Design • New frame structure Transmitter Receiver

  19. MAC Layer Design • How to fill the field ENH? • The source fills the LOCT, PWRT, and GAINT fields with its own parameters • And the LOCR, PWRR, and GAINR with the destination’s parameters, if known • Any unknown parameters are set to NULL • Parameter Cache

  20. PHY-MAC Interaction

  21. Blocking Decision • If and , should not block • Set the CCA-Suppression Vector (CSV) • CCA=Clear Channel Assessment • On the other hand, should block • Set its NAV value

  22. CCA-Suppression Vector (CSV) • Why is CSV needed? • During the reception of a frame, a new stronger frame arrived: • Block? NAV is set to Max(the end of this new delivery, current NAV expiration time) • Don’t block? CSV is set Max(to end of the new frame, current CSV expiration time)

  23. Limitation of this LED • Does not consider path-loss in real world • Only considers the effects from its own potential transmission • Does not consider its own transmission can be correctly received

  24. Summary • Overall blocking decision: • When a station only detects carrier but can not decode the frame: • Aggressive: LED_CS • Conservative: LED_RX

  25. Outline • Problem with 802.11 DCF • Location Enhanced DCF (LED) • Performance Evaluation • Conclusion and Future Works

  26. The Experiment • ns-2 simulator, with modification • The competitors: • Original IEEE 802.11 DCF • LED_CS, LED_RX • MACAW • Performance measurements • Effective throughput, Packet collisions, Fairness

  27. VS Node Density

  28. VS Node Density

  29. VS Node Density

  30. VS Node Density

  31. VS Network load

  32. VS Network load

  33. VS Network load

  34. VS Network load

  35. VS Capture Factor

  36. VS Error Range

  37. VS Transmission Range

  38. VS Transmission Range

  39. Outline • Problem with 802.11 DCF • Location Enhanced DCF (LED) • Performance Evaluation • Conclusion and Future Works

  40. Conclusion and Future Works • Pros • LED may improve throughput as much as 22% over DCF with better fairness at the same time • Cons • Higher collisions • Future Works • Where are these collisions resulted from?

  41. Questions? Presented by Yuhao Zheng Thank you!

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