Introduction
Underwater sensor networks (UWSN)– Long propagation delay– High error rate
MAC protocols for UWSN– Single-channel MAC
R-MAC et. al
– Multi-channel MAC Previous work shows higher throughput
Related work
Multi-channel MAC for terrestrial networks– Multi-channel with Aloha– Multi-channel with RTS/CTS – Split phase
Multi-channel MAC for UWSN– Multi-channel with Aloha– Multi-channel with RTS/CTS
To our best knowledge, No work analyzes multi-channel MAC for UWSN !
Contributions
Analyze two generalized multi-channel protocols– Random channel allocation– RTS/CTS based channel allocation
Tight upper bound and lower bound
Comparison of Multi-channel protocols
Analysis for Multi-channel with Aloha
Because the input traffic is assumed to be a poisson process for every node
Analysis for Multi-channel with Aloha
Optimal bandwidth allocation between control and data channel can be written as:
And we can get:
Analysis for Multi-channel with RTS/CTS
Analyzing the control channel– Previous work shows that the completion time of s
uccessfully 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 :
Analyzing the data channels
Markov chain can no longer model the system as it does in the terrestrial networks
Three stochastic processes interacts – 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 (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
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
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
The upper bound and lower bound systems can be accurately modeled by Markov chain and we can calculate its performance
Performance evaluation
Simulation setting– Fully connected network with 50 nodes– Propagation delay : 0.3s– Data packet: 200 bytes– Control packet: 10bytes– Data channels: 16.– Overall bandwidth: 17kbps
Conclusions
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