Zhong Zhou +, Zheng Peng +, Jun-Hong Cui +, Zaihan Jiang * Handling Triple Hidden Terminal Problems for Multichannel MAC in Long-Delay Underwater Sensor Networks IEEE Transactions on Mobile Computing VOL.11 NO.1, Computer Science & Engineering Department, University of Connecticut * US Naval Research Laboratory, Acoustic Division,

Outline Introduction Triple Hidden Terminal Problems Protocol Description Analysis Performance Evaluation Conclusion

Introduction Underwater sensor networks have a wide range of aquatic application Pollution monitoring Mine-countermeasure Offshore exploration Submarine detection Electromagnetic signal does not work well due to its quick attenuation in water Using acoustical waveform to instead

Introduction Difference between underwater environment and terrestrial counterpart Propagation speed of acoustic signal The available bandwidth is extremely limited Multipath spread is severe Doppler spread/shift

Introduction Multichannel MAC protocol can improve the network throughput Multichannel MAC protocol in underwater MAC protocol for single channel networks cannot be directly used in multichannel High expense of underwater transceivers Triple hidden terminal problem

Introduction Cooperative Underwater Multichannel MAC(CUMAC) Single transceiver Multichannel Multi-hop

Triple Hidden Terminal Problem Triple hidden terminal problem Multi-hop hidden terminal problem Multichannel hidden terminal problem Long-delay hidden terminal problem

Triple Hidden Terminal Problem Multichannel hidden terminal problem Node c Node b Node d Node a Data on Channel 2 RTS CTS Data on Channel 1 RTS CTS Data on Channel 1 CTS Collision

Triple Hidden Terminal Problem Long-delay hidden terminal problem Node c Node b Node d Node a abdc RTS CTS(1) Data on Channel 1 Collision

Protocol Description System Model Multiple same bandwidth channels Only one acoustic transceiver Transmission range R Two node do not interfere with each other if their distance large than R Evert sensor is assumed to know it own location information

Protocol Description Overview Node b Node a Node b Node a Control Channel Data Channel Channel Negotiation Data Transmission RTS Beacon(1)CTS(2) Node c Beacon(1) Beacon(2) CTS(2) Data(2) The available channel set cooperative collision detection

Protocol Description Cooperative Collision Detection Neighboring nodes cooperate with each other to select a suitable channel A node will listen to the control channel if it does not have data to send The node can obtain the channel usage information of its neighbors by overhearing the control channel The node will notify the reviver if selected channel collides with current transmission

Protocol Description Cooperative Collision Detection S d c a e h Data Channel 1 RTS Beacon(1,d) Notify(1)

Protocol Description Two Critical Problem in Cooperative Collision Detection Heterogeneous Collision Region Location information contains in the control packets Data Channel 1 RTS S d a e b Beacon(1,d)

Protocol Description Two Critical Problem in Cooperative Collision Detection Heterogeneous Collision Region Location information contains in the control packets Redundant Collision Notification Out-of-band tone device - tone device S d c a e h Data Channel 1 RTS Beacon(1,d) Notify(1) collision

Protocol Description A simple tone solution Tone Pulse Sequence S1S1 S2S2 d1d1 d2d2 Data Channel 1 RTS Beacon(2,d 2 ) Beacon(1,d 1 ) Notify(1) ?

Protocol Description Tone Pulse Sequence A sequence of n periodic tone pulse sends with period τ i A node that has detected collision will send out a tone sequence at Node j Node i Beacon Tone Contains τ i Tone τiτi τiτi

Protocol Description If receiver receives tone at detection point, the collision happens Detection Point Node j Node i Beacon Tone τiτi τiτi τiτi Detection Point

Protocol Description Node e Node c Node f Node b RTS a b c d e f tone Beacon τbτb τbτb τcτc τcτc tone

Protocol Description a b c d Node c Node b Node d Node a RTS Beacon(1,b) 2T+n τ b τbτb τbτb Beacon(2,b) 2T+n τ b CTS τbτb τbτb

Analysis node density ρ The average numbers of neighbors Traffic is possion distribution with parameter λ The duration of tone pulse t tp Tone pulse for node i τ i in range

Analysis False Alarm probability There will be no collision on selected channel, CUMAC mistakenly make the decision A node j selects the same periodicity and a tone plus destined for node j arrives at decision point (for i) The probability that a node j selects same sequence with i The probability that a tone pulse destined for node j arrives at node i decision point

Analysis The probability that there are k other ongoing channel negotiation which might interfere with I The false alarm probability

Analysis False Approval Probability There exists potential collisions on the selected channel, CUMAC fail to detect it Only happens when no neighbors oppose to a false decision Node did not on the control CTS had been collide The probability that a node stay on the control channel The average collision probability On control channel The probability successfully receives CTS/beacon

Performance Evaluation NS-2 Simulator 8 channels Bandwidth of each channel is 1kbps Speed of acoustic signal 1500m/s Transmission Range 500m Tone pulse 2ms Periodicity of tone pulse 12ms~60ms Average data length 300 bytes

Performance Evaluation

Conclusion A single-transceiver multi-channel protocol in underwater Handling multi-hop hidden terminal problem Handling multi-channel hidden terminal problem Handling long delay hidden terminal problem