A Reliable and Efficient MAC Protocol for Underwater Acoustic Sensor Networks

Junjie Xiong, Michael R. Lyu, and Kam-Wing Ng

International Journal of Distributed Sensor Networks 2011 Speaker : Chuan-Heng, Chi

Introduction Goals Network environment RAS Protocol RRAS Protocol Simulation Conclusion

Outline

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 Data acquisition Underwater exploration Unattended environmental monitoring systems Prevention of natural disasters Military purpose

Introduction

Transmission rate WSN: 3 x 108 m/s UWSN: 1500 m/s

Propagation delay

Introduction

A

B

Propagation delay

B A

We design an e cient priority scheduling protocol called RAS ffiat the MAC layer of BS

We propose RRAS to improve the network reliability

Goals

The typical application we discuss is the ocean bottom surveillance application All nodes generate the same amount of data and send them to the

BS

Network environment

Initialization phase (1) Synchronization (2) Construct tree topology and static routing (3) BS knows all of the transmission requirements

RAS Protocol

BS

Scheduling Principle The transceiver cannot receive when it is transmitting

DR: data receive DT: data transmit IR: interference receive

(A)~(F)

RAS Protocol

(A) A DR duration must not overlap any DT duration

RAS Protocol

B

T

T

B

A

A

Data

Data

DataData

(B) A DR duration must not overlap any IR duration

RAS Protocol

B

T1

A

A

B Data

Data

T2

T1

Data

Data

T2

(C) A DR duration must not overlap any other DR duration

RAS Protocol

B

T1

A

A

B

Data

Data

T1

DataData

(D) A DT duration and IR duration(s) can overlap

RAS Protocol

B

T1

A

A

B Data

Data

T2

T1

Data

Data

T2

(E) No DR from ith hop node to (i+ 1)th hop node (F) A node considers DR duration as the scheduling basis rather

than DT or IR duration

RAS Protocol

Step 1: Schedule the BS’s DR from 1-hop nodes

RAS Protocol

BS

Step 2:

RAS Protocol

BS

‧‧‧

Step 3:

RAS Protocol

BSA

B

BS

BA

PA1,PA2,PA3 PB1,PB2,PB3

Sequence:{PA1, PB1, PA2, PB2, PA3, PB3}

Problem Since packet loss is very common in UWASNs, RAS is not

reliable.

RAS Protocol

This paper focus on the packet loss caused by the volatile wireless environment RRAS utilizes the NACK-retransmission mechanism to improve

the overall system reliability

RRAS Protocol

RRAS Protocol

One node loss packet

RRAS Protocol

n

BA

PA1,PA2,PA3 PB1,PB2,PB3

Sequence:{PA1, PB1, PA2, PB2, PA3, PB3}

One node loss packet

RRAS Protocol

n

BA

PA1,PA2,PA3 PB1,PB2,PB3

Sequence:{PA1, PB1, PA2, PA3, PB3}

One node loss packet

RRAS Protocol

n

BA

PA1,PA2,PA3 PB1,PB2,PB3

Sequence:{PA1, PB1, PA2, PA3, PB3}

NACK

One node loss packet

RRAS Protocol

n

BA

PA1,PA2,PA3 PB1,PB2,PB3

Sequence:{PA1, PB1, PA2, PA3, PB3}

PB2 retransmission

Multiple nodes loss packets

RRAS Protocol

n

DA B C

Multiple nodes loss packets

RRAS Protocol

n

DA B C

NACK

Multiple nodes loss packets

RRAS Protocol

n

DA B C

retransmission packet

Multiple nodes loss packets

RRAS Protocol

n

DA B C

NACK

Multiple nodes loss packets

RRAS Protocol

n

DA B C

retransmission packet

Problem Since the control frame exchanges deteriorate the UWASN

e ciency greatlyffi

RRAS Protocol

This paper employ simple ALOHA that is, a node could transmit a packet when it is not receiving or transmitting More efficient

RRAS Protocol

We define the states of a node after the data transmission period as (α, β)

RRAS Protocol

(N,N)no retransmission (N,Y)waiting for NACK (Y,N)sending NACK to child (Y,Y)waiting for NACK from parent sending NACK to child

RRAS Protocol

When does the retransmission packet send back to parent?

Analysis of retransmission time If it does not adopt ALOHA

RRAS Protocol

parent

child

NACKRetransmission data

Analysis of retransmission time If it adopt ALOHA

ALOHA allows parallel transmission among NACKs from different node

RRAS Protocol

parent

child

NACKRetransmission data

Analysis of retransmission time If it adopt ALOHA

RRAS Protocol

Simulation

UW-FLASHR UW-FLASHR uses control frame handshaking to reserve parallel

transmissions

Simulation

Simulation

Simulation

Simulation

Simulation

In this paper, we propose RAS protocol in UWASNs To improve the e ciencyffi

The reliable RAS is implemented to achieve a tradeo between ffthe reliability and e ciencyffi

Conclision