1. Khaled Hatem Almotairi and Xuemin (Sherman) Shen Department of Electrical and Computer Engineering University of Waterloo 200 University Avenue West Waterloo, Ontario,Canada IEEE Globecom 2010

2.  Introduction  Goal  System Model  Exposed Terminal Problem  MMAC-HR  Performance Evaluation  Conclusion

3.  Introduction  Goal  System Model  Exposed Terminal Problem  MMAC-HR  Performance Evaluation  Conclusion

4.  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

5.  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

6.  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 A→BA→B A→BA→B C→DC→D C→DC→D AC

7.  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

8.  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

9.  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, P max

10.  Introduction  Goal  System Model  Exposed Terminal Problem  MMAC-HR  Performance Evaluation  Conclusion

11. ch4ch3 A B D EC RTS CTS(3) data_ch3 ACK_ch3 RTS CTS(3) Decoded signal Not decoded signal Silence DIFS CC ch3 CC ch3

12.  Introduction  Goal  System Model  Exposed Terminal Problem  MMAC-HR  Performance Evaluation  Conclusion

13.  Contention Window Size  CW s : for Switchable interface  CW f : for Fixed interface  CTS packet include  Ch i : 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

14.  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_2 s f C C Fixed interface Switchable interface Time s Rt

15. Control Channel Data channel_1 Data channel_2 RTS CTS Ch i : Data channel_1 Wt : 0 / T max (maximum packet in Ch i ) Rt s D D C C E E f ff Time  Nodes change the RTS/CTS in the control channel

16. Control Channel Data channel_1 Data channel_2 RTS CTS s ss D D C C E E f ff Time  After receive the CTS, node C first check whether it’s switching interface in the ch i Yes: contention ch i No: listen ch i for WR time then contention C C DATA ACK WR

17.  If Collision  In control channel: CW s × 2  In data channel: CW f × 2  If Rt expires  Node C reset CW s  Restart T CTS : transmission time of a CTS packet St : switching delay τ : maximum propagation delay

19.  Introduction  Goal  System Model  Exposed Terminal Problem  MMAC-HR  Performance Evaluation  Conclusion

20.  Compare with DCA and IEEE802.11use ns-2.30  Transmission range 250 meters  100 nodes placed randomly in 500×500 m 2  45 flows  50 different scenarios  Each scenarios last 100s

24.  MMAC-HR:  Optimize the network performance  Resolves the multichannel exposed terminal problem  Not require synchronization