Presentation on theme: "An Improved Mesh Coordinated Channel Access Mechanism for IEEE 802"— Presentation transcript:
1An Improved Mesh Coordinated Channel Access Mechanism for IEEE 802 An Improved Mesh Coordinated Channel Access Mechanism for IEEE s Wireless Mesh NetworksMd. Shariful Islam, Muhammad Mahbub Alam and Choong Seon HongNetworking Lab, Department of Computer EngineeringKyung Hee University, Korea.The third AsiaFI Winter School, February, 2010
2Presentation Outline Introduction MCCA- an overview Problem descriptionProposed improved mesh coordinated channel access mechanismPerformance AnalysisConclusions
3Introduction Wireless Mesh Networks (WMNS) provide internet access to end-users with low cost.Act as a wireless backboneMost of the traffic is to/from Internet and thus, gateway centric.Nodes can act both as an access point and relay node.High volume of traffic makes traditional EDCA less effective and it can not provide QoS guarantee.Upcoming IEEE s comes up with an optional access mechanismMesh Coordinated Channel Access (MCCA)- allows to reserve future slots for collision free transmission of QoS data.
4ContributionsIdentify the problems with current MCCA mechanism in the presence of contention from non-MCCA nodes.Introduce an improved channel access mechanism for MCCA.Through simulation we show that our proposed iMCCAmechanism performs better than the existing schemes.
5MCCA – an overviewReservation PhaseEach node identifies the free slots in its two-hop neighborhood by examining the MCCAOP advertisement (MADV) messages of adjacent nodes.MADV includesTX-RX-all slots for which the MP is either a transmitter of receiverInterfering Times report (IR)- all slots where the MP is neither tra-nsmitter nor receiver, but slots are busy because of transmission / reception of its neighbor.Sender initiates MCCAOP request with duration, offset and periodicity.Receiver replies with Setup Reply if slots do not overlap and its neighbor MPs’ MCCA Access Fraction (MAF) limit do not exceed.
6MCCA – an overview (cont’d) Access PhaseMCCA-ownerNeeds to contend for the channel during its MCCAOP usingIEEE e EDCA contention parametersTransmission must finish within the reserved MCCAOPMCCA-awareRefrain from transmission during known MCCAOP by settingtheir NAV valuesNon-MCCADo not honor MCCA reservation and allowed to contend for the channel during a MCCAOP
7Problem descriptionPerformance of MCCA is affected due the presence on non-MCCA node.Probability of collision increases as number of contending non-MCCA node increases in the neighborhoodMCCAOP may be foreshortened if a non-MCCA node wins the backoff
8Improved mesh coordinated channel access mechanism Proposed Access MechanismIntroduce a new Inter Frame Space (IFS) for MCCA referred to as MCCA inter frame space (MIFS) asMIFS = SIFS + aSlotTimeNon-MCCA nodes using EDCA waits for an Arbitration Inter Frame Space (AIFS) time before initiating backoff process.AIFS = SIFS + AIFSN [AC] x aSlotTimeIf the MCCA-owner finds that the medium is idle after MIFS time, it initiates the transmission without invoking any backoff process.
9iMCCA- an exampleMCCA-owner: node x, non-MCCA: node y and MCCA-aware: node zNode x starts transmitting after sensing the channel idle for MIFS period.Non-MCCA node y senses the channel as busy after its AIFS period.MCCA-aware node z already set its NAV and refrain from transmissionThus, MCCA-owner’s access during MCCAOP is guaranteedBlock ACK is used to further increase channel efficiency
11Performance Evaluation (cont’d) iMCCA allows to complete transmission during MCCAOPNon-MCCA STAs do not starveMCCA utilization becomes high with EMDA as non-MCCA STAs can not gain access during MCCAOP.
12Conclusions We propose an improved channel access mechanism to enhance the effectiveness of MCCA mechanism introducedin IEEE s.Explicitly identify the problems with current access mechanismprovide simple and straight forward solutions.Finally, simulation results demonstrate the effectiveness of the proposed scheme.Still a delayed start due to an ongoing transmission from non-MCCA node can affect the performance of MCCA.