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Dynamic Rate Adaptation in IEEE 802.11 WLANs

Bob Kinicki PEDS March 26, 2007. Dynamic Rate Adaptation in IEEE 802.11 WLANs. Outline. Review CSMA/CA DCF basics Motivate Rate Adaptation Issues over increasingly complex configurations. List of Rate Adaptation Algorithms ARF RBAR MultiRate Retry CARA RRAA Final Thoughts.

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Dynamic Rate Adaptation in IEEE 802.11 WLANs

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  1. Bob Kinicki PEDS March 26, 2007 Dynamic Rate Adaptation in IEEE 802.11 WLANs

  2. Outline • Review CSMA/CA DCF basics • Motivate Rate Adaptation Issues over increasingly complex configurations. • List of Rate Adaptation Algorithms • ARF • RBAR • MultiRate Retry • CARA • RRAA • Final Thoughts PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  3. Basic CSMA/CA for DCF [N. Kim] PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  4. CSMA/CA (RTS/CTS) and Fragmentation [Zhu] PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  5. One-to-One Configuration {Ad Hoc} Access Point client PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  6. One-to-One Configuration {Ad Hoc} Access Point client PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  7. One-to-One Configuration {Ad Hoc} Access Point client Distance Effects : attenuation fading interference PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  8. Rate Adaptation attacks Distance [J. Kim] PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  9. Physical Layer Overhead [N. Kim] PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  10. Physical Layer Overhead [N. Kim] PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  11. BER vs SNR [Pavon] PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  12. Throughput vs SNR [Pavon] PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  13. Single AP multiple clients (homogeneous) client node contention effects: collisions hidden terminal client client Access Point client PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  14. Node Contention [N. Kim] PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  15. Single AP multiple clients (heterogeneous) client client node effects: collisions link capture hidden terminal performance anomaly AP queue overflow different NIC cards Access Point client client PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  16. Unfairness [Choi] PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  17. Multiple APsmultiple clients (heterogeneous) client client client client Access Point Access Point client client client client PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  18. Hidden Terminals [Wong] PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  19. Rate Adaptation Algorithms AARF ARF AMRR CARA CROAR DOFRA Fast-LA HRC LA LD-ARF MiSer MultiRateRetry MPDU OAR ONOE PER RBAR RFT RRAA SampleRate SwissRA PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  20. Rate Adaptation Algorithms 1997 ARF 1998 1999 2000 2001 RBAR 2002 MPDU OAR PER 2003 LA MiSer SwissRA 2004 AARF AMRR HRC MultiRateRetry 2005 Fast-LA LD-ARF RFT SampleRate 2006 CARA CROAR DOFRA RRAA 2007 ONOE?? PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  21. Rate Adaptation Algorithms Use recent history and probes: ARF AARF SampleRate Long interval smoothing to increase:ONOESampleRate Use multiple rates: MultiRateRetry AMRR RRAA Use RTS/CTS: RBAR OAR CROAR CARA LA :uses RSSI to approximate SNR, each node maintains 12 dynamic RSS thresholds. LD-ARF: puts checksum on header and uses NACK to signal link loss error Table lookup with thresholds:HRC MPDU(len,rSNR,count) Fragmentation: DOFRARFT PER MiSer SwissRA Fast-LA PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  22. “Round up the Usual Suspects” • ARF • RBAR • MultirateRetry PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  23. ARF Algorithm • If two consecutive ACK frames are not received correctly, the second retry and subsequent transmissions are done at a lower rate and a timer is started. • When the number of successfully received ACKs reaches 10 or the timer goes off, a probe frame is sent at the next higher rate. However, if an ACK is NOT received for this frame, the rate is lowered back and the timer is restarted. PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  24. RBAR Algorithm • {not 802.11 compatible} • Receivers control sender’s transmission rate. • RTS and CTS are modified to contain info on size and rate. • Uses analysis of RTS reception (RSSI?) to estimate SNR and send choice back to sender in CTS. • Receiver picks rate based on apriori SNR thresholds. PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  25. MultiRateRetry • AR5212 chipset with Atheros driver • Allows 9 FIFO queues with transmission descriptors containing ordered set of 4 pairs or rate and counts (r0/c0, r1/c1, r2/c2, r3/c3). • Algorithm tries each rate and drops down after count errors. PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  26. “New Kids on the Block” • CARA - Collision Aware Rate Adaptation • RRAA – Robust Rate Adaptation Algorithm PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  27. Collision Aware Rate Adaptation • Two methods for identifying collisions: • RTS probing • CCA detection RTS Probing • Assumes all RTS transmission failures are due to collisions. • Transmission failure after RTS/CTS must be due to channel errors. • RTS probing that enables an RTS/CTS exchange ONLY when a data frame transmission fails. PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  28. RTS Probing CARA default: • Data frame transmitted without RTS/CTS. • If the transmission fails, RTS/CTS exchange is activated for the next retransmission. If this retransmission fails, then the rate is lowered. • If retransmission is successful, stay at same rate and send next frame without RTS/CTS. PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  29. CCA Detection [J. Kim] PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  30. CARA-1 (with RTS Probing) [J. Kim] PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  31. CARA-2 (with CCA) [J. Kim] PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  32. Robust Rate Adaptation Algorithm • Goals: • Robust against random loss • Responsive to drastic changes • Three components: • Loss estimation • Rate change • Adaptive RTS filter PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  33. Loss Estimation • Instead of single probe frame, • Uses a loss estimation window and computes the estimated loss ratio over the window. • Uses upper and lower loss threshold for each rate and estimated loss ratio to decide when to switch rates. PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  34. Loss Ratio Thresholds [Wong] PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  35. Adaptive RTS Filter • Selective use of RTS/CTS. • Mentions CARA idea and problem of hidden terminals. • RTSwindow (RTSwnd) :: all frames sent RTS on. • Window is increased by one when last frame lost without RTS (potentially due to a collision) • When the last frame was lost with RTS or succeeded without RTS, RTSwnd is halved (assume no collision involved). PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  36. RRAA Performance [Wong] PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  37. Other Issues • Frame length effects • Using fragmentation • Saturation of the WLAN => AP queuing • Fairness PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  38. Random Thoughts • The major issue is designing rate adapatation for more complex scenarios and being able to determine the reasons for a frame loss. • The concern is the speed of the adaptation. • Several cross-layer papers attempt to coordinate rate adaptation with either streaming rate or TCP behavior. PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

  39. Questions? Thank You! PEDS March 26, 2007 - Wireless Rate Adaptation Algorithms

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