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An Improved CDMA-Based MAC Protocol for Underwater Acoustic
Wireless Sensor Networks
Guangyu Fan, Huifang Chen, Lei Xie, Kuang Wang
IEEE WICOM 2011
The world's oceans cover over 70 % of its surface Underwater Wireless Sensor Networks (UWSNs)
Introduction
Underwater sensor network technology can be applied in many fields Environment monitoring Geographic data collection Offshore exploration Assisted navigation Disaster prevention Tactical surveillance
Introduction
Transmission rate WSN: 3 x 108 m/s UWSN: 1500 m/s
Propagation delay
Introduction
A
B
Propagation delay
B A
CDMA-based protocols Transmitter-oriented code assignment (TOCA) Receiver-oriented code assignment (ROCA) Path-oriented code assignment (POCA)
Introduction
Slotted FAMA
Related works
RTS
RTS
RTS
CTS
CTS
DATA
DATA
RTS
CTS DEFERS TRANSMISSIONS
A
B
C
MaximumPropagation Delay+CTS
Waste time !
In the paper, POCA-CDMA-MAC is proposed for UWASNs. It utilizes a round-robin method and CDMA technology to reduce
collisions of packets.
Goal
Assumption Sink can receive packets from multiple neighbors at the same time Routes will be built All sensor nodes are equipped with a half-duplex, omni-directional
transceiver
Network environment
Simulation
Parameter Value
Transmission range 7.5 km
Data packet 500 bytes
Static Nodes 8
Control packet 12.5 bytes
In the proposed MAC protocol prevent collision of packets and the length of the spreading sequence codes is shortened by using round-robin method CDMA technology
Each node encodes its packets with a spreading sequence, so the sink can receive packets from multiple neighbors at the same time.
Conclusion