Analyzing Multi-channel MAC Protocols
for Underwater Sensor Networks
Presenter: Zhong Zhou
Outline
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Introduction
Related work
System model and analysis
Performance evaluation
Conclusions
Introduction
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Underwater sensor networks (UWSN)
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Long propagation delay
High error rate
MAC protocols for UWSN
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Single-channel MAC
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R-MAC et. al
Multi-channel MAC
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Previous work shows higher throughput
Related work
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Multi-channel MAC for terrestrial networks
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Multi-channel with Aloha
Multi-channel with RTS/CTS
Split phase
Multi-channel MAC for UWSN
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Multi-channel with Aloha
Multi-channel with RTS/CTS
To our best knowledge, No work analyzes multi-channel
MAC for UWSN !
Contributions
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Analyze two generalized multi-channel
protocols
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Random channel allocation
RTS/CTS based channel allocation
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Tight upper bound and lower bound
Comparison of Multi-channel protocols
Assumptions(1)
Assumptions(2)
Multi-channel with Aloha
Multi-channel with RTS/CTS
Analysis for Multi-channel with Aloha
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The probability of successfully transmitting a
packet is
Analysis for Multi-channel with Aloha
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Because the input traffic is assumed to be a
poisson process for every node
Analysis for Multi-channel with Aloha
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And then, we can get
Analysis for Multi-channel with Aloha
Analysis for Multi-channel with Aloha
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Optimal bandwidth allocation between
control and data channel can be written as:
And we can get:
Analysis for Multi-channel with
RTS/CTS
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Analyzing the control channel
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Previous work shows that the completion time of
successfully RTS/CTS exchanged can be
accurately modeled by a poisson process
Its collision probability can be written as :
The net traffic to the data channels is :
Problems with data channels
Analyzing the data channels
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Markov chain can no longer model the
system as it does in the terrestrial networks
Three stochastic processes interacts
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Packet arriving process
Channel allocation process
Packet leaving process
Instead of investigating the system itself, we
try to find its upper bound and lower bound!
Basic virtual system (1)
We discrete the system and confine the collision to every 2t area
Basic virtual system (2)
The lengths of the collision region for every packet in both
systems are same. since the input is the same poisson process,
the performance of these two system are the same
Lower bound system
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the available channel set of every packet will keep the same as
that in the beginning of a slot. The channels that are released
can be reused during this slot in the original virtual system.
However, this will not happen in the confined system. They are
only available to the packets in the next slot.
Compared to the original virtual system, the number of
available channels for every packet in every slot is smaller
because the released channels in this slot will not be available
to the packets in the same slot any more.
this confined system will have higher collision probability than
the original virtual system. It can be served as the lower bound
of the original virtual system.
Upper bound system
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the release of channels occurs at the beginning of a
slot and thus these channels are available to all
packets in this slot.
Compared with the original virtual system, the
number of the available channels for every packet in
one slot will be larger because all released channels
will be available for all packets in the slot.
this revised system must have lower collision
probability and can be served as the upper bound of
the original virtual system
Solving upper bound and lower bound
systems
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The upper bound and lower bound systems
can be accurately modeled by Markov chain
and we can calculate its performance
Performance evaluation
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Simulation setting
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Fully connected network with 50 nodes
Propagation delay : 0.3s
Data packet: 200 bytes
Control packet: 10bytes
Data channels: 16.
Overall bandwidth: 17kbps
Simulation results
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Optimal bandwidth for multi-channel with Aloha
Upper bound and lower bound
Comparisons
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Effects of number of channels
Effects of input traffic
Effects of the length of data packets
Effects of propagation delay
Conclusions
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We analyze two general multi-channel
protocols for UWSN
We compare these two protocols with
different network parameters
Simulation results show that our theoretical
result are quite accurate
Future work
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Explore more complicated multi-channel
MAC protocols
Investigate multi-channel protocols in multihop UWSN environments.