1. Multi-Channel MAC for Ad Hoc Networks: Handling Multi-Channel Hidden Terminals Using A Single Transceiver Nov 2011 Neng Xue Tianxu Wang

2. Our Thoughts Eval & Sum P rotocol Details I ntroduction 2 3 4 1 O utlines

3. I ntroduction

4. Intro Multiple Channels available in IEEE 802.11 3 channels in 802.11b 12 channels in 802.11a 1 defer 1 2 Single channelMultiple Channels A B C D A B C D

5. Intro Multi-Channel Hidden Terminals A B C RTS A sends RTS Channel 1 Channel 2 D

6. Intro Multi-Channel Hidden Terminals A B C CTS B sends CTS Channel 1 Channel 2 C does not hear CTS because C is listening on channel 2 D

7. Intro Multi-Channel Hidden Terminals A B C DATA C switches to channel 1 and transmits RTS Channel 1 Channel 2 Collision occurs at B RTS D D

8. Intro Related Work Previous work on multi-channel MAC

9. Intro Muliti-channel CSMA Protocol Assumes 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

10. Intro DCA Protocol Assumes 2 transceivers per host One transceiver always listens on control channel Negotiate channels using RTS/CTS/RES RTS/CTS/RES packets sent on control channel Sender includes preferred channels in RTS Receiver decides a channel and includes in CTS Sender transmits RES (Reservation) Sender sends DATA on the selected data channel

11. Key Ideas Protocol Details Multi-Channel MAC (MMAC) Protocol

12. 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

13. 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

14. Each node maintains PCL Records 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 nodes Count number of nodes that selected this channel to break ties Preferred Channel List (PCL) Key Ideas

15. Channel Negotiation In ATIM window, sender transmits ATIM to the receiver Sender includes its PCL in the ATIM packet Receiver selects a channel based on sender’s PCL and its own PCL Order of preference: HIGH > MID > LOW Tie breaker: Receiver’s PCL has higher priority For “LOW” channels: channels with smaller count have higher priority Receiver sends ATIM-ACK to sender including the selected channel Sender sends ATIM-RES to notify its neighbors of the selected channel

16. Key Ideas Channel Negotiation A B C D Time ATIM Window Beacon Interval Common ChannelSelected Channel Beacon

17. Key Ideas Channel Negotiation A B C D ATIM ATIM- ACK(1) ATIM- RES(1) Time ATIM Window Beacon Interval Common ChannelSelected Channel Beacon

18. 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 ChannelSelected Channel Beacon

19. 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 ChannelSelected Channel Beacon RTS CTS RTS CTS DATA ACK DATA Channel 1 Channel 2

20. Eval Performance Evaluation Simulation Model Simulation Results

21. Eval Simulation Model ns-2 simulator Transmission rate: 2Mbps Transmission range: 250m Traffic type: Constant Bit Rate (CBR) Beacon interval: 100ms Packet size: 512 bytes ATIM window size: 20ms Default number of channels: 3 channels Compared protocols 802.11: IEEE 802.11 single channel protocol DCA: Wu’s protocol MMAC: Proposed protocol

22. Eval Wireless LAN - Throughput 30 nodes64 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) 1 10 100 1000 2500 2000 1500 1000 500 Aggregate Throughput (Kbps) 2500 2000 1500 1000 500

23. Eval Multi-hop Network – Throughput 3 channels4 channels MMAC DCA 802.11 DCA MMAC Packet arrival rate per flow (packets/sec) 1 10 100 1000 Packet arrival rate per flow (packets/sec) 1 10 100 1000 Aggregate Throughput (Kbps) 1500 1000 500 0 2000 1500 1000 500 0

24. 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 Aggregate Throughput (Kbps) 4000 3000 2000 1000 0 4000 3000 2000 1000 0 Packet arrival rate per flow (packets/sec)

25. Advantages: One transceiver All the channels Sum Summary Disadvantages: Overhead Synchronization

26. Thoughts Future Works A better scheme for clock synchronization Switch channels inside the beacon interval

27. 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

28. Thank you