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

Our Thoughts Eval & Sum P rotocol Details I ntroduction O utlines

I ntroduction

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

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

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

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

Intro Related Work Previous work on multi-channel MAC

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

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

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

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

Idea similar to IEEE 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

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

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

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

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

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

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

Eval Performance Evaluation Simulation Model Simulation Results

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 : IEEE single channel protocol DCA: Wu’s protocol MMAC: Proposed protocol

Eval Wireless LAN - Throughput 30 nodes64 nodes MMAC DCA MMAC shows higher throughput than DCA and DCA MMAC Packet arrival rate per flow (packets/sec) Aggregate Throughput (Kbps)

Eval Multi-hop Network – Throughput 3 channels4 channels MMAC DCA DCA MMAC Packet arrival rate per flow (packets/sec) Packet arrival rate per flow (packets/sec) Aggregate Throughput (Kbps)

Eval Throughput of DCA and MMAC (Wireless LAN) DCA MMAC 2 channels MMAC shows higher throughput compared to DCA 6 channels channels 6 channels Aggregate Throughput (Kbps) Packet arrival rate per flow (packets/sec)

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

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

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

Thank you