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An Improved Mesh Coordinated Channel Access Mechanism for IEEE 802.11s Wireless Mesh Networks

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An Improved Mesh Coordinated Channel Access Mechanism for IEEE 802.11s Wireless Mesh Networks Md. Shariful Islam, Muhammad Mahbub Alam and Choong Seon Hong – PowerPoint PPT presentation

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Title: An Improved Mesh Coordinated Channel Access Mechanism for IEEE 802.11s Wireless Mesh Networks


1
An Improved Mesh Coordinated Channel
Access Mechanism for IEEE 802.11s Wireless Mesh
Networks
  • Md. Shariful Islam, Muhammad Mahbub Alam and
    Choong Seon Hong
  • Networking Lab, Department of Computer
    Engineering
  • Kyung Hee University, Korea.
  • The third AsiaFI Winter School, 24-27 February,
    2010

2
Presentation Outline
  • Introduction
  • MCCA- an overview
  • Problem description
  • Proposed improved mesh coordinated channel
    access mechanism
  • Performance Analysis
  • Conclusions

3
Introduction
  • Wireless Mesh Networks (WMNS)
  • provide internet access to end-users
    with low cost.
  • Act as a wireless backbone
  • Most 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 802.11s comes up with an optional
    access mechanism
  • Mesh Coordinated Channel Access
    (MCCA)- allows to reserve future slots for
    collision free transmission of QoS data.

4
Contributions
  • Identify 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
    iMCCA
  • mechanism performs better than the existing
    schemes.

5
MCCA an overview
Reservation Phase
  • Each node identifies the free slots in its
    two-hop neighborhood by examining the MCCAOP
    advertisement (MADV) messages of adjacent nodes.
  • MADV includes
  • TX-RX-all slots for which the MP is either a
    transmitter of receiver
  • Interfering 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.

6
MCCA an overview (contd)
Access Phase
  • MCCA-owner
  • Needs to contend for the channel during its
    MCCAOP using
  • IEEE 802.11e EDCA contention parameters
  • Transmission must finish within the reserved
    MCCAOP
  • MCCA-aware
  • Refrain from transmission during known MCCAOP by
    setting
  • their NAV values
  • Non-MCCA
  • Do not honor MCCA reservation and allowed to
    contend for the channel during a MCCAOP

7
Problem description
  • Performance 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
    neighborhood
  • MCCAOP may be foreshortened if a non-MCCA node
    wins the backoff

8
Improved mesh coordinated channel access
mechanism
  • Proposed Access Mechanism
  • Introduce a new Inter Frame Space (IFS) for MCCA
    referred to as MCCA inter frame space (MIFS)
    as
  • MIFS SIFS aSlotTime
  • Non-MCCA nodes using EDCA waits for an
    Arbitration Inter Frame Space (AIFS) time before
    initiating backoff process.
  • AIFS SIFS AIFSN AC x aSlotTime
  • If the MCCA-owner finds that the medium is idle
    after MIFS time, it initiates the
    transmission without invoking any backoff
    process.

9
iMCCA- an example
  • MCCA-owner node x, non-MCCA node y and
    MCCA-aware node z
  • Node 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 transmission
  • Thus, MCCA-owners access during MCCAOP is
    guaranteed
  • Block ACK is used to further increase channel
    efficiency

10
Performance Evaluation
Simulation Parameters Simulation Parameters
Tool Network Simulator-2
Topology 3x3 grid
Area 150m x 150m
Packet Size 80 Byte
Interface 802.11a
MAF limit .43
Performance metrics Performance metrics
1. Cumulative throughput 2. MCCA utilization
11
Performance Evaluation (contd)
  • iMCCA allows to complete transmission during
    MCCAOP
  • Non-MCCA STAs do not starve
  • MCCA utilization becomes high with EMDA as
    non-MCCA STAs can not gain access during MCCAOP.

12
Conclusions
  • We propose an improved channel access mechanism
    to
  • enhance the effectiveness of MCCA mechanism
    introduced
  • in IEEE 802.11s.
  • Explicitly identify the problems with current
    access mechanism
  • provide 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.

13
  • Thank You..
  • QA
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