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

Problem Long propagation delay

Introduction

RTS

RTS

RTS

CTS

CTS

DATA

DATA

RTS

CTS

A

B

C

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 !

RIPT

Related works

Disadvantage

Related works

Collision

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

POCA-CDMA-MAC

AP1

BP1

AP2

BP2

CP2 BP3BP4

AP5

BP5

CP5

AP6

BP6

CP6

CP7

Surface station

Sink

POCA-CDMA-MAC

AP1

BP1

AP2

BP2

CP2 BP3BP4

AP5

BP5

CP5

AP6

BP6

CP6

CP7

Sink

(s1,s2,s3,s4,s5,s6,s7)

POCA-CDMA-MAC

AP1

BP1

AP2

BP2

CP2 BP3BP4

AP5

BP5

CP5

AP6

BP6

CP6

CP7

Sink

(s2,s3,s4,s5,s6,s7)s1

POCA-CDMA-MAC

AP1

BP1

AP2

BP2

CP2 BP3BP4

AP5

BP5

CP5

AP6

BP6

CP6

CP7

Sink

(s2,s3,s4,s5,s6,s7)

s1

POCA-CDMA-MAC

AP1

BP1

AP2

BP2

CP2 BP3BP4

AP5

BP5

CP5

AP6

BP6

CP6

CP7

Sink

(s5,s6,s7)

s1

s2s3

s4

POCA-CDMA-MAC

AP1

BP1

AP2

BP2

CP2 BP3BP4

AP5

BP5

CP5

AP6

BP6

CP6

CP7

Sink

(s5,s6,s7)

s1

s2s3 s4

POCA-CDMA-MAC

AP1

BP1

AP2

BP2

CP2 BP3BP4

AP5

BP5

CP5

AP6

BP6

CP6

CP7

Sinks1

s2s3 s4

s5

s6

s7

POCA-CDMA-MACAP2

BP2

CP2

Sink

CP2

BP2

AP2

Sink

POCA-CDMA-MACAP2

BP2

CP2

Sink

CP2

BP2

AP2

Sink

POCA-CDMA-MACAP2

BP2

CP2

Sink

CP2

BP2

AP2

Sink

POCA-CDMA-MACAP2

BP2

CP2

Sink

CP2

BP2

AP2

Sink

Problem

POCA-CDMA-MACAP2

BP2

CP2

Sink

CP2

BP2

AP2

Sink

Solution

POCA-CDMA-MACAP2

BP2

CP2

Sink

CP2

BP2

AP2

Sink

Passing token

Simulation

Parameter Value

Transmission range 7.5 km

Data packet 500 bytes

Static Nodes 8

Control packet 12.5 bytes

Simulation

Simulation

Simulation

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