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
Outline
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Introduction
Goals
Network environment
RAS Protocol
RRAS Protocol
Simulation
Conclusion
Introduction
 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
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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
A
B
Propagation delay
B
A
Goals
 We design an efficient priority scheduling protocol called RAS
at the MAC layer of BS
 We propose RRAS to improve the network reliability
Network environment
 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
RAS Protocol
 Initialization phase
 (1) Synchronization
 (2) Construct tree topology and static routing
 (3) BS knows all of the transmission requirements
BS
RAS Protocol
 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
B
T
A
A
T
Data
Data
Data
B
Data
RAS Protocol
 (B) A DR duration must not overlap any IR duration
B
A
T1
Data
T1
B
Data
A
T2
Data
Data
T2
RAS Protocol
 (C) A DR duration must not overlap any other DR duration
T1
A
B
B
Data
T1
Data
Data
A
Data
RAS Protocol
 (D) A DT duration and IR duration(s) can overlap
B
A
T1
Data
T1
B
Data
A
T2
Data
Data
T2
RAS Protocol
 (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
BS
RAS Protocol
 Step 2:
BS
RAS Protocol
 Step 3:
Sequence:{PA1, PB1, PA2, PB2, PA3, PB3}
BS
A
BS
B
A
PA1,PA2,PA3
B
PB1,PB2,PB3
RAS Protocol
 Problem
 Since packet loss is very common in UWASNs, RAS is not reliable.
RRAS 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
Sequence:{PA1, PB1, PA2, PB2, PA3, PB3}
n
A
PA1,PA2,PA3
B
PB1,PB2,PB3
RRAS Protocol
 One node loss packet
Sequence:{PA1, PB1, PA2, PA3, PB3}
n
A
PA1,PA2,PA3
B
PB1,PB2,PB3
RRAS Protocol
 One node loss packet
Sequence:{PA1, PB1, PA2, PA3, PB3}
n
NACK
A
PA1,PA2,PA3
B
PB1,PB2,PB3
RRAS Protocol
 One node loss packet
Sequence:{PA1, PB1, PA2, PA3, PB3}
n
PB2 retransmission
A
PA1,PA2,PA3
B
PB1,PB2,PB3
RRAS Protocol
 Multiple nodes loss packets
n
A
B
C
D
RRAS Protocol
 Multiple nodes loss packets
n
NACK
A
B
C
D
RRAS Protocol
 Multiple nodes loss packets
n
retransmission packet
A
B
C
D
RRAS Protocol
 Multiple nodes loss packets
n
NACK
A
B
C
D
RRAS Protocol
 Multiple nodes loss packets
n
retransmission packet
A
B
C
D
RRAS Protocol
 Problem
 Since the control frame exchanges deteriorate the UWASN
efficiency greatly
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
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(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
When does the retransmission packet send back to parent?
RRAS Protocol
 Analysis of retransmission time
 If it does not adopt ALOHA
parent
Retransmission
data
child
NACK
RRAS Protocol
 Analysis of retransmission time
 If it adopt ALOHA
 ALOHA allows parallel transmission among NACKs from different
node
parent
Retransmission
data
child
NACK
RRAS Protocol
 Analysis of retransmission time
 If it adopt ALOHA
Simulation
Simulation
 UW-FLASHR
 UW-FLASHR uses control frame handshaking to reserve parallel
transmissions
Simulation
Simulation
Simulation
Simulation
Conclision
 In this paper, we propose RAS protocol in UWASNs
 To improve the efficiency
 The reliable RAS is implemented to achieve a tradeoff between
the reliability and efficiency