1 Mitigate the Bottleneck of Underwater Acoustic Sensor Networks via Priority Scheduling Junjie Xiong, Michael R. Lyu, Kam-Wing Ng

Background Wireless sensor networks (WSNs) Underwater acoustic sensor networks (UWASNs)  Deployed in oceans Difference from terrestrial wireless sensor networks (TWSNs)  Wireless medium Sound (Electromagnetic waves)  Longer latency  Higher cost  Sparser deployment 2 Region Base station Sensor nodes

Ocean bottom monitoring by UWASNs 3

4 Outline Motivation Protocol Design Evaluation Conclusions

5 Motivation CTS 8ms RTS 8ms Propagation time 740ms DATA 80ms ACK 8ms CTS 8ms RTS 8ms Propagation time 3.7us DATA 80ms ACK 8ms Sender Receiver T A DATA transmission in UWASNs with CSMA/CA Sender Receiver T A DATA transmission in TWSNs with CSMA/CA

Motivation 6 DATA1: P->Q T1T1 I1I1 R1R1 DATA2: Q->S I2I2 R2R2 T2T2 T3T3 R3R3 DATA3: S->Q I3I3 DATA4: P->Q T4T4 I4I4 R4R4 T stands for transmitting R stands for receiving I stands for interference Node P Node Q Node S T T T Data transmission between 3 nodes in UWASNs DATA4: P->S T4T4 I4I4 R4R4 Collision! R2R2 R3R3 I1I1 R1R1

7 Motivation T stands for transmitting R stands for receiving I stands for interference Node P Node Q Base station Cycle Data transmission between 3 nodes TPTP IPIP RPRP TPTP IPIP RPRP TPTP IPIP RPRP TPTP IPIP RPRP TPTP IPIP RPRP TPTP IPIP RPRP TPTP IPIP RPRP TPTP IPIP RPRP IQIQ RQRQ TQTQ IQIQ RQRQ TQTQ IQIQ RQRQ TQTQ IQIQ RQRQ TQTQ IQIQ RQRQ TQTQ IQIQ RQRQ TQTQ IQIQ RQRQ TQTQ Utilize the propagation time Maximize the throughput by minimizing working period in a cycle

8 Outline Motivation Protocol Design Evaluation Conclusions

9 A Routing and Application based Scheduling Protocol (RAS) DATA1: P->Q T1T1 I1I1 R1R1 T stands for transmitting R stands for receiving I stands for interference Node P Node Q Node S T T T Data transmission between 3 nodes in UWASNs I1I1 R1R1 One time Three times We discover a unique scheduling problem that exists only in UWASNs: different scheduling element.

10 A Routing and Application based Scheduling Protocol (RAS) We design the Routing and Application based Scheduling protocol (RAS) which is composed of :  The TDMA based MAC mechanism  The static routing calculation  Centralized schedule calculation by utilizing application data direction  Calculate the traffic of each node.  Schedule the traffic transmission and reception.

11 A Routing and Application based Scheduling Protocol (RAS) Scheduling principles of RAS  At a node, guarantee a DR will not overlap any DT.  At a node, guarantee a DR will not overlap any IR.  At a node, a DT and one or more IR can coexist.  No DR from i-th hop node to (i+1)-th hop node.  At a node, use DR as the scheduling basis rather than DT or IR. DR: data reception IR: interference reception DT: data transmission DRDT Node m T DATA Scheduled DT

12 To be integrated to the previous slide DRDT Node m T DATA DRIR Node m T DATA Scheduled DT Scheduled IR

13 A Routing and Application based Scheduling Protocol (RAS) Congestion avoidance algorithm  Besides throughput, queue length, fairness are important  Step1: Schedule the BS's DR from 1 hop nodes.  Step2: Schedule the DR tier by tier: from inner tier to outer tier.  Step3: For each node m that is going to receive data packets from its children, arrange its DR from its children alternatively.

14 Outline Motivation Protocol Design Evaluation Conclusions

15 Performance Evaluation Network Throughput

16 Performance Evaluation Average End-to-end Delay

17 Performance Evaluation Average Maximum Queue Length per Node

18 Performance Evaluation Time Slots Required for the RAS Network Working Period

19 Outline Motivation Protocol Design Evaluation Conclusions

20 Conclusion We discover a unique scheduling problem that exists only in UWASNs. A priority scheduling protocol RAS is designed to provide communications for UWASNs.  RAS allows parallel transmissions, and thus improve the throughput and delay performance based on the scheduling principles.  RAS mitigates queue overflow and is scalable in calculating proper schedules.

21 Q & A Thank you!

UW-FlASHR UW-FLASHR (Achieving high channel utilization in a time- based acoustic mac protocol, ACM Mobicom Workshop on UnderWater Networks, 2008)  is a distributed TDMA based MAC protocol.  utilizes propagation delay to increase throughput.  employs no energy-saving mechanism.  suffers from collisions. 22

23 A Cross-layer Communications Protocol Design Advantages of RAS  Reduces mutual communications  Reduces energy consumption  Avoids collision, increases throughput, and reduces delay and queue overflow probability for each node

24 A Cross-layer Communications Protocol Design Scheduling algorithm formulation  Maximize the throughput by minimizing the working period of a cycle  The number of the decision variables equals the number of the packets to be received in a cycle.  Unique scheduling element: the combination of a DR, a DT and a sequence of IR to the other nodes.  The schedule principles. The time node m receives the Q mjw -th packet from its children node C mj

25 A Cross-layer Communications Protocol Design Congestion avoidance algorithm

26 A Cross-layer Communications Protocol Design Congestion avoidance algorithm

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