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 10 8 m/s  UWSN: 1500 m/s  Propagation delay Introduction A B Propagation delay BA

 We design an e ffi cient priority scheduling protocol called RAS at 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

 (B) A DR duration must not overlap any IR duration RAS Protocol B T1T1 A A B Data T2T2 T1T1 T2T2

 (C) A DR duration must not overlap any other DR duration RAS Protocol B T1T1 A A B Data T1T1

 (D) A DT duration and IR duration(s) can overlap RAS Protocol B T1T1 A A B Data T2T2 T1T1 T2T2

 (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 BS A B BA P A1,P A2,P A3 P B1,P B2,P B3 Sequence:{P A1, P B1, P A2, P B2, P A3, P B3 }

 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

 One node loss packet RRAS Protocol n BA P A1,P A2,P A3 P B1,P B2,P B3 Sequence:{P A1, P B1, P A2, P B2, P A3, P B3 }

 One node loss packet RRAS Protocol n BA P A1,P A2,P A3 P B1,P B2,P B3 Sequence:{P A1, P B1, P A2, P A3, P B3 }

 One node loss packet RRAS Protocol n BA P A1,P A2,P A3 P B1,P B2,P B3 Sequence:{P A1, P B1, P A2, P A3, P B3 } NACK

 One node loss packet RRAS Protocol n BA P A1,P A2,P A3 P B1,P B2,P B3 Sequence:{P A1, P B1, P A2, P A3, P B3 } P B2 retransmission

 Multiple nodes loss packets RRAS Protocol n DABC

 Multiple nodes loss packets RRAS Protocol n DABC NACK

 Multiple nodes loss packets RRAS Protocol n DABC retransmission packet

 Multiple nodes loss packets RRAS Protocol n DABC NACK

 Multiple nodes loss packets RRAS Protocol n DABC retransmission packet

 Problem  Since the control frame exchanges deteriorate the UWASN e ffi ciency 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

 (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

 In this paper, we propose RAS protocol in UWASNs  To improve the e ffi ciency  The reliable RAS is implemented to achieve a tradeo ff between the reliability and e ffi ciency Conclision