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Nov 2011 Neng Xue Tianxu Wang

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.

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Nov 2011 Neng Xue Tianxu Wang

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

  2. Outlines Introduction 1 Protocol Details 2 Eval&Sum 3 Our Thoughts 4 Outlines

  3. Introduction

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

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

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

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

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

  9. 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 Intro

  10. 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 Intro

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

  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. MMAC 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 Key Ideas

  14. Preferred Channel List (PCL) 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 Key Ideas

  15. Channel Negotiation Common Channel Selected Channel A Beacon B C D Time ATIM Window Beacon Interval Key Ideas

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

  17. Channel Negotiation Common Channel Selected Channel ATIM- RES(1) ATIM A Beacon B ATIM- ACK(1) ATIM- ACK(2) C D ATIM Time ATIM- RES(2) ATIM Window Beacon Interval Key Ideas

  18. Channel Negotiation Common Channel Selected Channel ATIM- RES(1) RTS DATA Channel 1 ATIM A Beacon Channel 1 B CTS ACK ATIM- ACK(1) ATIM- ACK(2) CTS ACK Channel 2 C Channel 2 D ATIM DATA RTS Time ATIM- RES(2) ATIM Window Beacon Interval Key Ideas

  19. Performance Evaluation Simulation Model Simulation Results Eval

  20. 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 Eval

  21. Wireless LAN - Throughput 2500 2000 1500 1000 500 2500 2000 1500 1000 500 MMAC MMAC DCA DCA Aggregate Throughput (Kbps) 802.11 802.11 1 10 100 1000 1 10 100 1000 Packet arrival rate per flow (packets/sec) Packet arrival rate per flow (packets/sec) 30 nodes 64 nodes MMAC shows higher throughput than DCA and 802.11 Eval

  22. Multi-hop Network – Throughput 2000 1500 1000 500 0 1500 1000 500 0 MMAC MMAC DCA DCA Aggregate Throughput (Kbps) 802.11 802.11 1 10 100 1000 1 10 100 1000 Packet arrival rate per flow (packets/sec) Packet arrival rate per flow (packets/sec) 3 channels 4 channels Eval

  23. Throughput of DCA and MMAC(Wireless LAN) 4000 3000 2000 1000 0 4000 3000 2000 1000 0 6 channels 6 channels 2 channels Aggregate Throughput (Kbps) 2 channels 802.11 802.11 Packet arrival rate per flow (packets/sec) Packet arrival rate per flow (packets/sec) MMAC DCA MMAC shows higher throughput compared to DCA Eval

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

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

  26. 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 Our thoughts Thoughts

  27. Thankyou

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