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