Dynamic Rate Adaptation in IEEE 802.11 WLANs

Dynamic Rate Dynamic Rate Adaptation in IEEE Adaptation in IEEE

802.11 WLANs802.11 WLANsBob KinickiBob Kinicki

PEDS March 26, 2007PEDS March 26, 2007

PEDS March 26, 2007 - PEDS March 26, 2007 - Wireless Rate Adaptation Wireless Rate Adaptation AlgorithmsAlgorithms

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OutlineOutlineOutlineOutline

Review CSMA/CA DCF basicsReview CSMA/CA DCF basics Motivate Rate Adaptation Issues over Motivate Rate Adaptation Issues over increasingly complex configurations.increasingly complex configurations.

List of Rate Adaptation AlgorithmsList of Rate Adaptation Algorithms ARFARF RBARRBAR MultiRate RetryMultiRate Retry CARACARA RRAARRAA Final ThoughtsFinal Thoughts


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Basic CSMA/CA for DCFBasic CSMA/CA for DCFBasic CSMA/CA for DCFBasic CSMA/CA for DCF

[N. Kim]


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CSMA/CA (RTS/CTS) and CSMA/CA (RTS/CTS) and FragmentationFragmentation

CSMA/CA (RTS/CTS) and CSMA/CA (RTS/CTS) and FragmentationFragmentation

[Zhu]


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One-to-One Configuration {Ad Hoc}


AccessPoint client


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AccessPoint client


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AccessPoint client

Distance Effects :attenuation

fadinginterference


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Rate Adaptation attacks Rate Adaptation attacks DistanceDistance

Rate Adaptation attacks Rate Adaptation attacks DistanceDistance

[J. Kim]


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Physical Layer OverheadPhysical Layer OverheadPhysical Layer OverheadPhysical Layer Overhead

[N. Kim]


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Physical Layer OverheadPhysical Layer OverheadPhysical Layer OverheadPhysical Layer Overhead

[N. Kim]


1111

BER vs SNRBER vs SNRBER vs SNRBER vs SNR

[Pavon]


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Throughput vs SNRThroughput vs SNRThroughput vs SNRThroughput vs SNR

[Pavon]


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Single AP multiple clients (homogeneous)

Single AP multiple clients (homogeneous)

AccessPoint client

client

client

client

node contention effects:

collisionshidden terminal


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Node ContentionNode ContentionNode ContentionNode Contention

[N. Kim]


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Single AP multiple clients Single AP multiple clients (heterogeneous)(heterogeneous)

Single AP multiple clients Single AP multiple clients (heterogeneous)(heterogeneous)

AccessPoint client

clientclient

client

node effects:

collisionslink capturehidden terminalperformance anomalyAP queue overflowdifferent NIC cards


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UnfairnessUnfairnessUnfairnessUnfairness

[Choi]


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Multiple APsmultiple clients (heterogeneous)

Multiple APsmultiple clients (heterogeneous)

AccessPoint client

clientclient

client

AccessPoint

client

clientclient

client


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Hidden TerminalsHidden TerminalsHidden TerminalsHidden Terminals

[Wong]


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Rate Adaptation AlgorithmsRate Adaptation AlgorithmsRate Adaptation AlgorithmsRate Adaptation Algorithms

AARF AARF ARFARF AMRRAMRR

CARACARA CROARCROAR DOFRADOFRA

Fast-LAFast-LA HRCHRC LA LA

LD-ARFLD-ARF MiSerMiSer MultiRateRetryMultiRateRetry

MPDUMPDU OAROAR ONOEONOE

PERPER RBARRBAR RFTRFT

RRAARRAA SampleRate SampleRate SwissRASwissRA


2020


1997 1997 ARFARF19981998199919992000200020012001 RBARRBAR20022002 MPDUMPDU OAR OAR PER PER20032003 LALA MiSer MiSer SwissRA SwissRA20042004 AARFAARF AMRR AMRR HRC HRC

MultiRateRetryMultiRateRetry20052005 Fast-LA LD-ARF RFTFast-LA LD-ARF RFT SampleRate SampleRate20062006 CARACARA CROAR CROAR DOFRA RRAA DOFRA RRAA20072007

ONOE??ONOE??


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Use recent history and probes:Use recent history and probes: ARF AARF ARF AARF SampleRateSampleRate

Long interval smoothing to increase:Long interval smoothing to increase: ONOEONOE SampleRateSampleRate

Use multiple rates:Use multiple rates: MultiRateRetry AMRR RRAA MultiRateRetry AMRR RRAAUse RTS/CTS:Use RTS/CTS: RBAR OAR CROAR CARA RBAR OAR CROAR CARALA :LA :uses RSSI to approximate SNR, each node uses RSSI to approximate SNR, each node

maintains 12 dynamic RSS thresholds.maintains 12 dynamic RSS thresholds.LD-ARF: LD-ARF: puts checksum on header and uses NACK puts checksum on header and uses NACK

to signal link loss errorto signal link loss errorTable lookup with thresholds:Table lookup with thresholds:HRC HRC

MPDU(len,rSNR,count)MPDU(len,rSNR,count)Fragmentation:Fragmentation: DOFRA DOFRA RFTRFT

PER PER MiSerMiSer SwissRA SwissRA Fast-LA Fast-LA


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““Round up the Usual Round up the Usual Suspects”Suspects”

““Round up the Usual Round up the Usual Suspects”Suspects”

ARFARF RBARRBAR MultirateRetryMultirateRetry


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ARF AlgorithmARF AlgorithmARF AlgorithmARF Algorithm

If If twotwo consecutive ACK frames are not consecutive ACK frames are not received correctly, the second retry and received correctly, the second retry and subsequent transmissions are done at a subsequent transmissions are done at a lower rate and a timer is started.lower rate and a timer is started.

When the number of successfully When the number of successfully received ACKs reaches received ACKs reaches 1010 or the timer or the timer goes off, a goes off, a probe frame probe frame is sent at the is sent at the next higher rate. However, if an ACK is next higher rate. However, if an ACK is NOT received for this frame, the rate is NOT received for this frame, the rate is lowered back and the timer is restarted. lowered back and the timer is restarted.


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RBAR AlgorithmRBAR AlgorithmRBAR AlgorithmRBAR Algorithm

{not 802.11 compatible}{not 802.11 compatible} Receivers control sender’s Receivers control sender’s transmission rate.transmission rate.

RTS and CTS are modified to contain RTS and CTS are modified to contain info on size and rate.info on size and rate.

Uses analysis of RTS reception (RSSI?) Uses analysis of RTS reception (RSSI?) to estimate SNR and send choice back to estimate SNR and send choice back to sender in CTS.to sender in CTS.

Receiver picks rate based on apriori Receiver picks rate based on apriori SNR thresholds.SNR thresholds.


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MultiRateRetryMultiRateRetryMultiRateRetryMultiRateRetry

AR5212 chipset with Atheros AR5212 chipset with Atheros driverdriver

Allows 9 FIFO queues with Allows 9 FIFO queues with transmission descriptors transmission descriptors containing ordered set of 4 pairs containing ordered set of 4 pairs or rate and counts (r0/c0, r1/c1, or rate and counts (r0/c0, r1/c1, r2/c2, r3/c3).r2/c2, r3/c3).

Algorithm tries each rate and Algorithm tries each rate and drops down after count errors. drops down after count errors.


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““New Kids on the Block”New Kids on the Block”““New Kids on the Block”New Kids on the Block”

CARA - Collision Aware Rate CARA - Collision Aware Rate Adaptation Adaptation

RRAA – Robust Rate Adaptation RRAA – Robust Rate Adaptation AlgorithmAlgorithm


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Collision Aware Rate Collision Aware Rate AdaptationAdaptation

Collision Aware Rate Collision Aware Rate AdaptationAdaptation

Two methods for identifying collisions:Two methods for identifying collisions:– RTS probing– CCA detection

RTS ProbingRTS Probing Assumes all RTS transmission failures Assumes all RTS transmission failures are due to collisions.are due to collisions.

Transmission failure after RTS/CTS Transmission failure after RTS/CTS must be due to channel errors.must be due to channel errors.

RTS probing that enables an RTS/CTS RTS probing that enables an RTS/CTS exchange ONLY when a data frame exchange ONLY when a data frame transmission fails.transmission fails.


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RTS ProbingRTS ProbingRTS ProbingRTS Probing

CARA default:CARA default: Data frame transmitted without Data frame transmitted without RTS/CTS.RTS/CTS.

If the transmission fails, RTS/CTS If the transmission fails, RTS/CTS exchange is activated for the next exchange is activated for the next retransmission. If this retransmission. If this retransmission fails, then the rate retransmission fails, then the rate is lowered.is lowered.

If retransmission is successful, stay If retransmission is successful, stay at same rate and send next frame at same rate and send next frame without RTS/CTS. without RTS/CTS.


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CCA DetectionCCA DetectionCCA DetectionCCA Detection

[J. Kim]


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CARA-1 (with RTS Probing)CARA-1 (with RTS Probing)CARA-1 (with RTS Probing)CARA-1 (with RTS Probing)

[J. Kim]


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CARA-2 (with CCA)CARA-2 (with CCA)CARA-2 (with CCA)CARA-2 (with CCA)

[J. Kim]


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Robust Rate Adaptation Robust Rate Adaptation AlgorithmAlgorithm

Robust Rate Adaptation Robust Rate Adaptation AlgorithmAlgorithm

Goals: Goals: – Robust against random loss– Responsive to drastic changes

Three components:Three components:– Loss estimation– Rate change– Adaptive RTS filter


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Loss EstimationLoss EstimationLoss EstimationLoss Estimation

Instead of single probe frame,Instead of single probe frame, Uses a loss estimation window Uses a loss estimation window and computes the estimated loss and computes the estimated loss ratio over the window.ratio over the window.

Uses upper and lower loss Uses upper and lower loss threshold for each rate and threshold for each rate and estimated loss ratio to decide estimated loss ratio to decide when to switch rates.when to switch rates.


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Loss Ratio ThresholdsLoss Ratio ThresholdsLoss Ratio ThresholdsLoss Ratio Thresholds

[Wong]


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Adaptive RTS FilterAdaptive RTS FilterAdaptive RTS FilterAdaptive RTS Filter

Selective use of RTS/CTS.Selective use of RTS/CTS. Mentions CARA idea and problem of Mentions CARA idea and problem of hidden terminals.hidden terminals.

RTSwindow (RTSwnd) :: RTSwindow (RTSwnd) :: all frames all frames sent RTS on.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).


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RRAA PerformanceRRAA PerformanceRRAA PerformanceRRAA Performance

[Wong]


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Other IssuesOther IssuesOther IssuesOther Issues

Frame length effectsFrame length effects Using fragmentationUsing fragmentation Saturation of the WLAN => AP Saturation of the WLAN => AP queuingqueuing

FairnessFairness


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Random ThoughtsRandom ThoughtsRandom ThoughtsRandom Thoughts

The major issue is designing rate The major issue is designing rate adapatation for more complex adapatation for more complex scenarios and being able to determine scenarios and being able to determine the reasons for a frame loss.the reasons for a frame loss.

The concern is the speed of the The concern is the speed of the adaptation.adaptation.

Several cross-layer papers attempt to Several cross-layer papers attempt to coordinate rate adaptation with either coordinate rate adaptation with either streaming rate or TCP behavior.streaming rate or TCP behavior.


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Questions?Questions?Questions?Questions?

Thank You!Thank You!

Dynamic Rate Adaptation in IEEE 802.11 WLANs

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