High-Performance MAC for High-Performance MAC for High-Capacity Wireless LANsHigh-Capacity Wireless LANs

Yuan Yuan, Daqing Gu, William Arbaugh, and Jinyun ZhangYuan Yuan, Daqing Gu, William Arbaugh, and Jinyun Zhang

Computer Science Department, University of MarylandComputer Science Department, University of Maryland

13th International Conference on Computer 13th International Conference on Computer Communications and Networks (ICCCN), 2004Communications and Networks (ICCCN), 2004

OutlineOutline

IntroductionIntroductionLimited of current IEEE CSMA/CA MACLimited of current IEEE CSMA/CA MACAAdaptive daptive DDistributed istributed CChannel hannel AAccess ccess

(ADCA) MAC protocol(ADCA) MAC protocolSimulationsSimulationsConclusionsConclusions

IntroductionIntroduction

Recent advances provide very high-capability Recent advances provide very high-capability wireless links at the PHY layerwireless links at the PHY layer802.11n802.11n802.15.3a802.15.3a

IntroductionIntroduction

MAC layer throughput achieved by DCF MAC layer throughput achieved by DCF when PHY layer is 216 Mb/swhen PHY layer is 216 Mb/s

Two Challenges for High-Two Challenges for High-performance MAC Design (1)performance MAC Design (1)

How to minimize the protocol overheadHow to minimize the protocol overheadControl messagesControl messages, , contention backoffcontention backoff, and , and

inter-frame spacing parametersinter-frame spacing parameters incur high incur high overheadoverhead

When PHY rate increases, the data-carrying When PHY rate increases, the data-carrying time shrinks as the time shrinks as the overhead time remains overhead time remains fixedfixed

Two Challenges for High-Two Challenges for High-performance MAC Design (2)performance MAC Design (2)

How to improve the overall channel How to improve the overall channel throughput by leveraging the throughput by leveraging the good channel good channel qualityquality of hosts of hostsWireless channel condition of a host is Wireless channel condition of a host is

location dependent and time varyinglocation dependent and time varying

SummarySummary

Current MAC solutions are not designed Current MAC solutions are not designed for the high-capacity PHY layerfor the high-capacity PHY layer802.11802.11: incurs considerable overhead: incurs considerable overhead802.11e802.11e: focuses on MAC QoS but does little : focuses on MAC QoS but does little

to improve channel efficiencyto improve channel efficiency802.15.3802.15.3: works well for constant-bit-rate : works well for constant-bit-rate

multimedia apps., but is not efficient for multimedia apps., but is not efficient for bursted data apps. bursted data apps.

GoalGoal

This paper proposes This paper proposes AAdaptive daptive DDistributed istributed CChannel hannel AAccess (ADCA) MAC for high-ccess (ADCA) MAC for high-capability PHY in capability PHY in infrastructure mode infrastructure mode bybyAdaptive batch transmissionAdaptive batch transmissionOpportunistic selection of high rate hostsOpportunistic selection of high rate hosts

Overview of ADCAOverview of ADCA

1.1. Each station initiates its parameter Each station initiates its parameter according to received according to received Beacon frameBeacon frame

2.2. When a station When a station winswins channel contention, channel contention, it will independently determine whether it it will independently determine whether it is eligible for accessing channelis eligible for accessing channel

ADCA Parameters (1)ADCA Parameters (1)

Each station initiates values for Each station initiates values for SSff, , RRff, , BBff

and and AAff according to received Beacon according to received Beacon

frameframeSSff: reference packet size: reference packet size

RRff: reference rate: reference rate

BBff: reference batch size: reference batch size

AAff: number of back-to-back transmitted frame: number of back-to-back transmitted frame

ADCA Parameters (2)ADCA Parameters (2)

Each station maintains two credit countEach station maintains two credit countCreditCredithh: an accumulated credit for channel : an accumulated credit for channel

accessing timeaccessing timeCreditCreditll: an accumulated credit for stations : an accumulated credit for stations

when stations win the contention, but not when stations win the contention, but not access channelaccess channel

ADCAADCA

A station winschannel contention

Rate of the station R is greater than Rf

Yes

No

Number of packets B allowing for transmitting

is greater than Bf

Creditl is greater thanthe present threshold

No

Backoff and increase credit

YesTransmit Bpackets

Yes Transmit Bpackets

NoBackoff and increase credit

RR >= >= RRffNumber of packets

allowing for transmitting in this

transmission

RR < < RRff

PHY/MAC ParametersPHY/MAC Parameters

Ns-2 simulator is usedNs-2 simulator is used

Service differentiation mechanism is similar to 802.11e

Throughput vs. Transmission RateThroughput vs. Transmission Rate

((SSff//RRff)*)*BBff = 3ms = 3ms

RRff = 216Mb/s = 216Mb/s

SSff = 1280B = 1280B

AAff = 3 = 3

Throughput vs. Throughput vs. RRff

10 hosts with UDP 10 hosts with UDP flowsflows

5 hosts transmit at 5 hosts transmit at 216Mb/s and source 216Mb/s and source rate is 20Mb/srate is 20Mb/s

5 hosts transmit at 5 hosts transmit at 54Mb/s and source 54Mb/s and source rate is 5Mb/srate is 5Mb/s

Packet size = 1280BPacket size = 1280B ((SSff//RRff)*)*BBff = 3ms = 3ms

AAff = 1 = 1

Throughput Gain vs. Background Throughput Gain vs. Background TrafficTraffic

Packet size = 1280BPacket size = 1280B ((SSff//RRff)*)*BBff = 3ms = 3ms

AAff = 1 = 1

Mean Delay vs. Background FlowsMean Delay vs. Background Flows

ThroughputThroughput

Mean DelayMean Delay

ThroughputThroughput

Mean DelayMean Delay

ConclusionsConclusions

ADCA minimizes the MAC overhead via ADCA minimizes the MAC overhead via adaptive batch transmission and block adaptive batch transmission and block ACKACK

ADCA ensures the same access time ADCA ensures the same access time among high-rate hostsamong high-rate hosts

Thank you!!Thank you!!