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A Reliable and Efficient MAC Protocol for Underwater Acoustic Sensor Networks. Junjie Xiong , Michael R. Lyu , and Kam -Wing Ng. Speaker : Chuan-Heng , Chi. International Journal of Distributed Sensor Networks 2011. Outline. Introduction Goals Network environment RAS Protocol
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A Reliable and Efficient MAC Protocol for Underwater Acoustic Sensor Networks JunjieXiong, Michael R. Lyu, and Kam-Wing Ng Speaker : Chuan-Heng, Chi International Journal of Distributed Sensor Networks 2011
Outline 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 • Data acquisition • Underwater exploration • Unattended environmental monitoring systems • Prevention of natural disasters • Military purpose
Introduction B A A B Propagation delay • Transmission rate • WSN:3x 108 m/s • UWSN: 1500 m/s • Propagation delay
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 BS • Initialization phase • (1) Synchronization • (2) Construct tree topology and static routing • (3) BS knows all of the transmission requirements
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 T B A A Data T Data Data B Data (A) A DR duration must not overlap any DT duration
RAS Protocol B T1 T2 A Data T1 T2 B Data A Data (B) A DR duration must not overlap any IR duration Data
RAS Protocol T1 A B Data B T1 Data Data A Data (C) A DR duration must not overlap any other DR duration
RAS Protocol B T1 T2 A Data T1 T2 B Data A Data (D) A DT duration and IR duration(s) can overlap Data
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 BS Step 1: Schedule the BS’s DR from 1-hop nodes
RAS Protocol ‧‧‧ BS Step 2:
RAS Protocol Sequence:{PA1, PB1, PA2, PB2, PA3, PB3} BS BS B A B A PA1,PA2,PA3 PB1,PB2,PB3 Step 3:
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 Sequence:{PA1, PB1, PA2, PB2, PA3, PB3} n A B PA1,PA2,PA3 PB1,PB2,PB3 One node loss packet
RRAS Protocol Sequence:{PA1, PB1, PA2, PA3, PB3} n A B PA1,PA2,PA3 PB1,PB2,PB3 One node loss packet
RRAS Protocol Sequence:{PA1, PB1, PA2, PA3, PB3} n NACK A B PA1,PA2,PA3 PB1,PB2,PB3 One node loss packet
RRAS Protocol Sequence:{PA1, PB1, PA2, PA3, PB3} n PB2 retransmission A B PA1,PA2,PA3 PB1,PB2,PB3 One node loss packet
RRAS Protocol n A B C D Multiple nodes loss packets
RRAS Protocol n NACK A B C D Multiple nodes loss packets
RRAS Protocol n retransmission packet A B C D Multiple nodes loss packets
RRAS Protocol n NACK A B C D Multiple nodes loss packets
RRAS Protocol n retransmission packet A B C D Multiple nodes loss packets
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 When does the retransmission packet send back to parent? (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 parent Retransmission data NACK child • Analysis of retransmission time • If it does not adopt ALOHA
RRAS Protocol parent Retransmission data NACK child • Analysis of retransmission time • If it adopt ALOHA • ALOHA allows parallel transmission among NACKs from different node
RRAS Protocol • Analysis of retransmission time • If it adopt ALOHA
Simulation • UW-FLASHR • UW-FLASHR uses control frame handshaking to reserve parallel transmissions
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