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Multi-Channel MAC for Ad Hoc Networks: Handling Multi-Channel Hidden Terminals Using A Single Transceiver. Nov 2011 Neng Xue Tianxu Wang. O utlines. I ntroduction. 1. P rotocol Details. 2. E val & Sum. 3. O ur Th oughts. 4. Outlines. I ntroduction. 1. 1. 2. defer. - PowerPoint PPT Presentation
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Multi-Channel MAC for Ad Hoc Networks: Handling Multi-Channel
Hidden Terminals Using A Single Transceiver
Nov 2011Neng Xue
Tianxu Wang
Our Thoughts
Eval & Sum
Protocol Details
Introduction
2
3
4
1
Outlines
Outlines
Introduction
Intro
Multiple Channels available in IEEE 802.11
• 3 channels in 802.11b• 12 channels in 802.11a
1
defer
1
2
Single channel Multiple Channels
A
B
CD
A
B
CD
Intro
Multi-Channel Hidden Terminals
A B CRTS
A sends RTS
Channel 1
Channel 2
D
Intro
Multi-Channel Hidden Terminals
A B CCTS
B sends CTS
Channel 1
Channel 2
C does not hear CTS because C is listening on channel 2
D
Intro
Multi-Channel Hidden Terminals
A B CDATA
C switches to channel 1 and transmits RTS
Channel 1
Channel 2
Collision occurs at B
RTS DD
Intro
Related Work
Previous work on multi-channel MAC
Intro
Muliti-channel CSMA ProtocolAssumes N transceivers per host
Capable of listening to all channels simultaneously
Sender searches for an idle channel and transmits on the channel [Nasipuri99WCNC]
Extensions: channel selection based on channel condition on the receiver side [Nasipuri00VTC]
Disadvantage: High hardware cost
Intro
DCA ProtocolAssumes 2 transceivers per host
One transceiver always listens on control channel
Negotiate channels using RTS/CTS/RES
RTS/CTS/RES packets sent on control channelSender includes preferred channels in RTS Receiver decides a channel and includes in CTSSender transmits RES (Reservation)
Sender sends DATA on the selected data channel
Key Ideas
Protocol Details
Multi-Channel MAC (MMAC) Protocol
Proposed Protocol (MMAC) Assumptions
• Each node is equipped with a single transceiver
• The transceiver is capable of switching channels
• Multi-hop synchronization is achieved by other means
Key Ideas
Idea similar to IEEE 802.11 PSM
Divide time into beacon intervals
At the beginning of each beacon interval, all nodes must listen to a predefined common channel for a fixed duration of time (ATIM window)
Nodes negotiate channels using ATIM messages
Nodes switch to selected channels after ATIM window for the rest of the beacon interval
MMAC
Key Ideas
Each node maintains PCLRecords usage of channels inside the transmission range
High preference (HIGH)Already selected for the current beacon interval
Medium preference (MID)No other vicinity node has selected this channel
Low preference (LOW)This channel has been chosen by vicinity nodesCount number of nodes that selected this channel to break ties
Preferred Channel List (PCL)
Key Ideas
Key Ideas
Channel Negotiation
A
B
C
DTime
ATIM Window
Beacon Interval
Common Channel Selected Channel
Beacon
Key Ideas
Channel Negotiation
A
B
C
D
ATIM
ATIM-ACK(1)
ATIM-RES(1)
Time
ATIM Window
Beacon Interval
Common Channel Selected Channel
Beacon
Key Ideas
Channel Negotiation
A
B
C
D
ATIM
ATIM-ACK(1)
ATIM-RES(1)
ATIM-ACK(2)
ATIM ATIM-RES(2)
Time
ATIM Window
Beacon Interval
Common Channel Selected Channel
Beacon
Key Ideas
Channel Negotiation
A
B
C
D
ATIM
ATIM-ACK(1)
ATIM-RES(1)
ATIM-ACK(2)
ATIM ATIM-RES(2)
Time
ATIM Window
Beacon Interval
Common Channel Selected Channel
Beacon
RTS
CTS
RTS
CTS
DATA
ACK
ACK
DATA
Channel 1
Channel 1
Channel 2
Channel 2
Eval
Performance Evaluation
Simulation ModelSimulation Results
Eval
Simulation Modelns-2 simulator
Transmission rate: 2MbpsTransmission range: 250m
Traffic type: Constant Bit Rate (CBR)Beacon interval: 100ms
Packet size: 512 bytesATIM window size: 20ms
Default number of channels: 3 channels
Compared protocols802.11: IEEE 802.11 single channel protocol
DCA: Wu’s protocolMMAC: Proposed protocol
Eval
Wireless LAN - Throughput
30 nodes 64 nodes
MMAC
DCA
802.11
MMAC shows higher throughput than DCA and 802.11
802.11
DCA
MMAC
Packet arrival rate per flow (packets/sec) Packet arrival rate per flow (packets/sec)1 10 100 1000 1 10 100 1000
2500
2000
1500
1000
500
Agg
rega
te T
hrou
ghpu
t (K
bps)
2500
2000
1500
1000
500
Eval
Multi-hop Network – Throughput
3 channels 4 channels
MMAC
DCA
802.11802.11
DCA
MMAC
Packet arrival rate per flow (packets/sec)1 10 100 1000
Packet arrival rate per flow (packets/sec)1 10 100 1000
Agg
rega
te T
hrou
ghpu
t (K
bps)
1500
1000
500
0
2000
1500
1000
500
0
Eval
Throughput of DCA and MMAC(Wireless LAN)
DCA MMAC
2 channels
802.11
MMAC shows higher throughput compared to DCA
6 channels
802.11
2 channels
6 channels
Agg
rega
te T
hrou
ghpu
t (K
bps) 4000
3000
2000
1000
0
4000
3000
2000
1000
0
Packet arrival rate per flow (packets/sec) Packet arrival rate per flow (packets/sec)
Advantages:
• One transceiver
• All the channels
Sum
Summary
Disadvantages:
• Overhead
• Synchronization
Thoughts
Future Works
• A better scheme for clock synchronization
• Switch channels inside the beacon interval
Thoughts
Our thoughts• Should we limit the certain channel assignment when
congestion
• How to decide the ATIM windows length comparing to the data transmission length
• When the RES message was not back, the update to the PCL is a mistake
Thank you