khaled hatem almotairi and xuemin (sherman) shen department of electrical and computer engineering...
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Khaled Hatem Almotairi and Xuemin (Sherman) Shen
Department of Electrical and Computer EngineeringUniversity of Waterloo 200 University Avenue West Waterloo, Ontario,Canada
IEEE Globecom 2010
Introduction Goal System Model Exposed Terminal Problem MMAC-HR Performance Evaluation Conclusion
Introduction Goal System Model Exposed Terminal Problem MMAC-HR Performance Evaluation Conclusion
With the increasing number of new inventions or applications, wireless media become more congested
Many MAC protocols have been proposed to improve the network performance using multiple channels Dynamic Channel Assignment (DCA) protocol Channel-Hopping Multiple Access (CHMA) SSCH: Slotted Seeded Channel Hopping for Capacity Improvement in
IEEE 802.11 Ad-Hoc Wireless Networks
Dynamic Channel Assignment (DCA) protocol Two interfaces
▪ One is fixed on the control transmitted RTS/CTS/RES packets
▪ Other switches between data channel transmitted data/ACK packets
Criticism Exposed terminal problem
Channel-Hopping Multiple Access (CHMA) Common hopping Dwell time is for a handshake No carrier sense is needed
Criticism Too many switching between frequencies Clock synchronization Busy receiver problem
Data channel
Data channel
A→BA→B
C→DC→D
A C
SSCH: Slotted Seeded Channel Hopping for Capacity Improvement in IEEE 802.11 Ad-Hoc Wireless Networks
Parallel rendezvous One radio interface
Criticism Busy receiver problem
Improve the network performance following features: Does not require clock synchronization Uses channel hopping without exchanging information Distributed Based on CSMA/CA for all channels
MMAC-HR: Multi-channel Medium Access Control with Hopping Reservation M channels▪ 1 is control channel
▪ M-1 are data channels Each node has two interfaces▪ Fixed interface
▪ Switchable interface
Nodes transmit at the maximum power, Pmax
Introduction Goal System Model Exposed Terminal Problem MMAC-HR Performance Evaluation Conclusion
ch4ch3
A B D EC
RTS
CTS(3)
data_ch3
ACK_ch3
RTS
CTS(3)
CTS(3)
Decoded signalNot decoded signal
SilenceSilence
DIFS
CCCC ch3 CC CC CCch3
Introduction Goal System Model Exposed Terminal Problem MMAC-HR Performance Evaluation Conclusion
Contention Window Size CWs : for Switchable interface CWf : for Fixed interface
CTS packet include Chi : current channel i of the receiver
Wt : waiting time Rt : reservation time for switchable interface
nrsv : for tracking the number of reservation nodes If nrsv=0 means the node is idle
Every node has two interface, one is fixed in the control channel, other is hopping randomly between data channels
Control Channel
Data channel_1
Data channel_2s
f
C Fixed interfaceSwitchable interface
Time
s
Rt
Control Channel
Data channel_1
Data channel_2
RTS CTS
CTSChi : Data channel_1 Wt : 0 / Tmax (maximum packet in Chi )Rt
s
DC E
f ff
Time
Nodes change the RTS/CTS in the control channel
Control Channel
Data channel_1
Data channel_2
RTS CTS
s
ss
DC E
f ff
Time
After receive the CTS, node C first check whether it’s switching interface in the chi
Yes: contention chi
No: listen chi for WR time then contention C
DATAACK
WR
If Collision In control channel: CWs × 2 In data channel: CWf × 2
If Rt expires Node C reset CWs
Restart
TCTS : transmission time of a CTS packetSt : switching delayτ : maximum propagation delay
Introduction Goal System Model Exposed Terminal Problem MMAC-HR Performance Evaluation Conclusion
Compare with DCA and IEEE802.11use ns-2.30 Transmission range 250 meters 100 nodes placed randomly in 500×500 m2
45 flows 50 different scenarios Each scenarios last 100s
MMAC-HR: Optimize the network performance Resolves the multichannel exposed terminal problem Not require synchronization