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2012 1/6 NSDI’08 Harnessing Exposed Terminals in Wireless Networks PowerPoint PPT Presentation


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2012 1/6 NSDI’08 Harnessing Exposed Terminals in Wireless Networks Mythili Vutukuru , Kyle Jamieson, and Hari Balakrishnan MIT Computer Science and Artificial Intelligence Laboratory. Introduction. A well-known way to maximize throughput: maximize the number of concurrent transmission

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2012 1/6 NSDI’08 Harnessing Exposed Terminals in Wireless Networks

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2012 1 6 nsdi 08 harnessing exposed terminals in wireless networks

2012 1/6

NSDI’08

Harnessing Exposed Terminals in Wireless Networks

MythiliVutukuru, Kyle Jamieson, and HariBalakrishnan

MIT Computer Science and Artificial Intelligence Laboratory


Introduction

Introduction

  • A well-known way to maximize throughput:

    maximize the number of concurrent transmission

  • A problem in Carrier Sense Multiple Access (CSMA):

    Exposed Terminal

  • To improve throughput in a wireless network by harnessing exposed terminals, this paper proposesCMAP – ina distributed and lightweight way.


Introduction1

Introduction


Exposed terminal

Exposed Terminal

AP1

AP2


Overview of cmap

Overview of CMAP

Key Insight:

  • Existing solutions:

    rules to predict which concurrent transmissions increase throughput (CSMA).

  • Instead:

    watch and discover which concurrent transmissions increase throughput (CMAP).


Cmap design

CMAP Design

Channel access:

  • The CMAP uses a distributed data structure called the conflict map

  • Use empirical observations of packet losses to populate the conflict map


Cmap design1

CMAP Design


Cmap design2

CMAP Design


Cmap design3

CMAP Design


Cmap design4

CMAP Design

Windowed retransmission protocol

  • Link Layer ACK : stop-and wait retransmission protocol

  • CMAP: The ACKs sent by receivers are cumulative and contain a bitmap indicating which packets in the window have been received.


Cmap design5

CMAP Design

Backoff policy:

Hidden interference : receivers report the loss rate over a window of packets in every cumulative ACK, and senders back off when this loss rate exceeds a threshold.

  • loss rate < threshold :

    contention window(CW) = 0

  • Loss rate > threshold :

    contention window(CW) = (CWstart,CWmax)


Cmap design6

CMAP Design

  • Handling Multiple Bitrates

  • annotate the interferer lists and defer tables with the bit-rates

  • The extensions to handle multiple power levels are similar.

  • Beyond Unicast Transmissions

  • Broadcast - treated as a collection of unicast transmissions

  • opportunistic routing - annotate the packet reception rates


Implementation

Implementation


Evaluation

Evaluation

  • CMAP、CSMAenable、 CSMA disable


Exposed terminals

Exposed terminals


Senders in range

Senders in-range


Senders out of range

Senders out of range


Access point topology

Access Point Topology

  • divide the testbedinto six “regions”

  • designate one node in each region as an AP

  • each AP is out of the communication range of every other AP

  • Clients : the set of nodes in that region that have a potential transmission link to that AP


Access point topology1

Access Point Topology


Conclusions

Conclusions

  • presented the design, prototype implementation, and experimental evaluation of CMAP

  • CMAP uses empirical observations of packet loss to build a distributed data structure – conflict maps

  • CMAP successfully avoiding conflicting concurrent transmissions and increase the aggregate throughput

  • CMAP improves aggregate throughput by up to 47% and median per-sender throughput by 1.8× over 802.11


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