Coexistence of a Novel MAC Protocol for Wireless Ad hoc Networks and the IEEE 802.11

transcript

Jesús Alonso-Zárate, Elli Kartsakli, Luis Alonso, and Christos Verikoukis

May 2010, Cape Town, South Africa, ICC 2010

2/28ICC 2010 Cape Town, South Africa jesus.alonso@cttc.es

Outline

1) Introduction

2) 802.11 overview

3) DQMAN overview

4) Coexistence Methodology

5) Simulation Results

6) Conclusions

Outline

1) Introduction

2) 802.11 overview

3) DQMAN overview

6) Conclusions

Introduction

• Context: Wireless Local Area Networks (ad hoc)

• Focus: Medium Access Control protocols (MAC protocols)

• 1999: IEEE 802.11 and the Distributed Coordination Function (DCF)

• Since then letter soup (a,b,g,e,n, …), but few changes to MAC

• MAC very inefficient for high number of users or heavy data traffic

• Result: vast amount of new MAC protocols have been proposed

Introduction

• Problem and motivation:

1) Higher performance, at the cost of

2) Non-backwards compatibility

• Contribution:

1) Methodology for the coexistence of DQMAN and the DCF

2) Methodology can be applied to other MAC protocols.

Outline

1) Introduction

2) 802.11 overview

3) DQMAN overview

6) Conclusions

The IEEE 802.11: Overview

• DCF mandatory access method• Based on CSMA (listen-before-talk)• Collision Resolution Algorithm Binary Exponential Backoff (BEB)• Defines two modes of operation:

1) Basic access transmission of data + ACK

2) Collision Avoidance access adds a handshake RTS/CTS• Reduces the duration of collisions (long data packets)• Protection against hidden terminals

The IEEE 802.11: The BEB algorithm

• Slotted backoff

• Random backoff counter in the interval [0,CWi]

• CWmin minimum size of the contention window

• CWMAX maximum size of the contention window

• Backoff counter decreased by one unit after each slot if channel sensed idle, otherwise, the counter is frozen

min2 , .ii MAXCW min CW CW

The IEEE 802.11: Basic Access

Source

Destination

Others CW

DIFS SIFS DIFS

• Clear Channel Assessment (CCA) Distributed Inter Frame Space (DIFS)• Short Inter Frame Space (SIFS) propagation, processing, turnaround delays• Virtual Carrier Sensing Network Allocation Vector (NAV)• Positive ACK (ACK timeout in case of error)

The IEEE 802.11: Collision Avoidance

Source

Destination

Others CW

NAV RTS

NAV CTS

NAV DATA

• Inclusion of handshake:• RTS: Request to Send• CTS: Clear to Send

Outline

1) Introduction

2) 802.11 overview

3) DQMAN overview

6) Conclusions

DQMAN: Overview I

1) DQMAN extension of DQCA

2) DQCA requires a central coordination point

3) Approach in DQMAN:

1) Master-Slave,

2) Self-organizing,

3) Spontaneous,

4) Passive (no explicit clustering overhead),

5) Dynamic CLUSTERING.

4) Master, slave and idle stations.

5) Masters pretend to be temporary infrastructure for their local neighborhood

6) Clusters are temporary

Master Service Set (MSS)

DQMAN: Overview II

Station 3: SLAVE

Station 2: SLAVE

Station 1: SLAVE

Station 0: MASTER FBPFBP

Data from 1 to 3

Contention WindowSlaves with data to transmit select

a minislot at random where to send an Access Request Sequence (ARS)

Busy tones

Feedback information about the state of each of the access minislots. With this information, stations can execute the MAC protocol rules

in a distributed manner

SIFS Short Inter Frame Space

Outline

1) Introduction

2) 802.11 overview

3) DQMAN overview

6) Conclusions

Coexistence

• Assume that DQMAN stations are dual

• Default access: DCF of the IEEE 802.11 Standard

• Dual stations → special RTS → dual-RTS:

• If the destination is a DCF station, it responds with a CTS

• If the destination station is a dual station it can initiate a DQMAN phase by becoming master

• For the DQMAN phase, legacy stations should remain silent by properly updating the NAV with the FBP → dual-CTS

Coexistence

Format of regular RTS and CTS packets

Frame Control Duration Rx. Address Tx. Address CRC

Frame Control Duration Rx. Address CRC

Protocol Version

Type of frame (control)

Subtype:RTS or CTS

B0 B1 B15… B8 B9 …

B8: To APB9: From AP

16 Control Flags (1-bit)

Coexistence

Dual-RTS and Dual-CTS (FBP)

Protocol Version

Subtype:RTS or CTS

B0 B1 B15… B8 B9 …

Coexistence

Protocol Version

Subtype:RTS or CTS

B0 B1 B15… B8 B9 …

Coexistence

Protocol Version

Subtype:RTS or CTS

B0 B1 B15… B8 B9 …

Coexistence

d-Station 3: M

d-Station 2

Station 1

d-Station 0 RTSd

d-Station 3: M

d-Station 2

Station 1

d-Station 0

CTSd CTSd

Backoff

Coexistence

A minimum DCF operation time is now performed to enable access to legacy stations

Outline

1) Introduction

2) 802.11 overview

3) DQMAN overview

6) Conclusions

Simulation Results

5 DQMAN dual stations + 5 legacy stations

Simulation Results

Outline

1) Introduction

2) 802.11 overview

3) DQMAN overview

6) Conclusions

Conclusions

• Lots of MAC protocols with high performance for WLAN

• IEEE 802.11 is there Backwards compatibility is a must

• Coexistence methodology presented in this paper

• DQMAN with IEEE 802.11

• In simulation, it works!

• Can be extended to any other MAC protocol

• Next step: try a real testbed to see if it works.

Jesús Alonso-Zárate jesus.alonso@cttc.eswww.cttc.es

Questions?

Thanks for your kind attention!

Coexistence of a Novel MAC Protocol for Wireless Ad hoc Networks and the IEEE 802.11

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