Jesús Alonso-Zárate, Elli Kartsakli, Luis Alonso, and Christos Verikoukis
May 2010, Cape Town, South Africa, ICC 2010
Coexistence of a Novel MAC Protocol for Wireless Ad hoc Networks and the IEEE 802.11
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Outline
1) Introduction
2) 802.11 overview
3) DQMAN overview
4) Coexistence Methodology
5) Simulation Results
6) Conclusions
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Outline
1) Introduction
2) 802.11 overview
3) DQMAN overview
4) Coexistence Methodology
5) Simulation Results
6) Conclusions
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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
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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.
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Outline
1) Introduction
2) 802.11 overview
3) DQMAN overview
4) Coexistence Methodology
5) Simulation Results
6) Conclusions
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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
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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
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The IEEE 802.11: Basic Access
DATA
ACK
Source
Destination
Others CW
NAV
DIFS SIFS DIFS
Time+
CW
• 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)
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The IEEE 802.11: Collision Avoidance
DATA
ACK
Source
Destination
Others CW
DIFS
RTS
SIFS
CTS
SIFS
NAV RTS
NAV CTS
NAV DATA
DIFS
Time+
SIFS
• Inclusion of handshake:• RTS: Request to Send• CTS: Clear to Send
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Outline
1) Introduction
2) 802.11 overview
3) DQMAN overview
4) Coexistence Methodology
5) Simulation Results
6) Conclusions
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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
M
S2
S1
S3S4
S6
S5
ID
ID
ID
Master Service Set (MSS)
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DQMAN: Overview II
Time+
Station 3: SLAVE
Station 2: SLAVE
Station 1: SLAVE
Station 0: MASTER FBPFBP
Data from 1 to 3
ACK
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
1 2 3
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Outline
1) Introduction
2) 802.11 overview
3) DQMAN overview
4) Coexistence Methodology
5) Simulation Results
6) Conclusions
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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
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Coexistence
Format of regular RTS and CTS packets
Frame Control Duration Rx. Address Tx. Address CRC
Frame Control Duration Rx. Address CRC
RTS
CTS
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)
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Coexistence
Dual-RTS and Dual-CTS (FBP)
Frame Control Duration Rx. Address Tx. Address CRC
Frame Control Duration Rx. Address CRC
RTS
CTS
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)
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Coexistence
Dual-RTS and Dual-CTS (FBP)
Frame Control Duration Rx. Address Tx. Address CRC
Frame Control Duration Rx. Address CRC
RTS
CTS
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)
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Coexistence
Dual-RTS and Dual-CTS (FBP)
Frame Control Duration Rx. Address Tx. Address CRC
Frame Control Duration Rx. Address CRC
RTS
CTS
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)
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Coexistence
Time+
d-Station 3: M
d-Station 2
Station 1
d-Station 0 RTSd
CTSd
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Time+
d-Station 3: M
d-Station 2
Station 1
d-Station 0
DATA
RTSd
CTSd CTSd
DATA
CTSd
Backoff
Backoff
Backoff
NAV
Coexistence
A minimum DCF operation time is now performed to enable access to legacy stations
NAV
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Outline
1) Introduction
2) 802.11 overview
3) DQMAN overview
4) Coexistence Methodology
5) Simulation Results
6) Conclusions
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Simulation Results
MTO
5 DQMAN dual stations + 5 legacy stations
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Simulation Results
5 DQMAN dual stations + 5 legacy stations
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Simulation Results
5 DQMAN dual stations + 5 legacy stations
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Outline
1) Introduction
2) 802.11 overview
3) DQMAN overview
4) Coexistence Methodology
5) Simulation Results
6) Conclusions
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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.