Reliable Reporting of Delay-Sensitive Events in Wireless Sensor-Actuator Networks

1. Reliable Reporting of Delay-Sensitive Events in Wireless Sensor-Actuator Networks Edith C.-H. Ngai†, Yangfan Zhou†, Michael R. Lyu†, and Jiangchuan Liu‡ †Department of Computer Science & Engineering, Chinese University of Hong Kong ‡School of Computing Science, Simon Fraser University The Third IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS'06), Vancouver, Canada, 9-12 Oct 2006.

2. Outline • Introduction • Related Work • Network Model and Objective • The Reliable Event Reporting Framework • Grid-Based Data Aggregation • Priority-Based Event Reporting • Actuator Allocation • Simulation Results • Conclusion The Third IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS'06)

3. WSAN • Collection of sensors and actuators • Sensors • small and low-cost devices with limited energy, sensing, computation, and transmission capability • passive devices for collecting data only and not interactive to the environments • Actuators • resource-rich devices equipped with more energy, stronger computation power, longer transmission range, and usually mobile • make decisions and perform appropriate actions in response to the sensor measurements The Third IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS'06)

4. WSAN • Sensors and actuators collaborate • sensors perform sensing and report the sensed data to the actuators • actuators then carry out appropriate actions in response • Applications • environmental monitoring • sensing and maintenance in large industrial plants • military surveillance, medical sensing, attack detection, and target tracking, etc. The Third IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS'06)

5. Our Focus • Design of a genericframework for reliable event reporting in WSANs • Suggest a delay- andimportance-aware reliability index for the WSANs • Non-uniform importance of the events can be exploredin the optimization The Third IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS'06)

6. Our Framework • Seamlessly integrates three key modules tomaximize the reliability index: • A multi-level dataaggregation scheme, which is fault-tolerant with error-pronesensors • A priority-based transmission protocol,which accounts for both the importance and delayrequirements of the events • An actuator allocationalgorithm, which smartly distributes the actuators tomatch the demands from the sensors. The Third IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS'06)

7. Related Work • Real-time communication protocol in WSN • SPEED [Hu et al. 2003] • Combines feedback control and non-deterministic QoS-aware geographic forwarding • Velocity Monotonic Scheduling [Lu et al. 2002] • Packet scheduling policy that accounts for both time and distance constraints • MMSPEED [Felemban et al. 2005] • Multi-path and multi-speed routing protocol for probabilistic QoS guarantee in WSN The Third IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS'06)

8. Related Work • Reliable transmission with error-prone sensors • Node-level fault tolerance (NLFT) [Aidemark et al. 2005] • Masks transient faults locally by using time-redundant task scheduling in nodes • Bi-criteria scheduling heuristic [Assayad et al. 2004] • Uses heuristic in data-flow graph to maximize reliability and minimize runtime • Routing in DTN [Jain et al. 2005] • Applies erasure code and data replication The Third IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS'06)

9. Related Work • Heterogeneous sensor networks • Anycast communication paradigm [Hu et al. 2004] • Constructs an anycast tree rooted at each event source and updates the tree dynamically • Power-aware many-to-many routing [Cayirci et al. 2005] • Actuator broadcasts registration messages, while sensors build their own routing tables • Distributed coordination framework[Melodia et al. 2005] • Sensors forward readings to the appropriate actuators by the data aggregation trees The Third IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS'06)

10. Network Model • Compose of sensors and actuators • Nodes aware of their locations • Divide the network into a number of grids cell for data aggregation • A subset of nodes, referred as reporting nodes, send data to the actuators • Anycast routing The Third IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS'06)

11. Objective • Reliability index • Measures the probability that event data are aggregated and received accurately within pre-defined latency bounds The Third IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS'06)

12. Workflow of Framework • Data aggregation • Delay- and importance-aware prioritized routing • Actuator allocation The Third IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS'06)

13. Grid-Based Data Aggregation The Third IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS'06)

14. Priority-Based Event Reporting • Priority queues • prioritized scheduling to speed up important event data transmission • queue utilization as an index for route selection to meet the latency bounds • first-in-first-out (FIFO) discipline The Third IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS'06)

15. Queueing Delay • The queueing delay of the highest priority queue: • The queueing delay of kth priority queue: The Third IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS'06)

16. Next Hop Selection • Consider node i receives new type of event data datae • It broadcasts a control message to its immediate neighbors • Every neighbors j replies with the message: The Third IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS'06)

17. Next Hop Selection • The end-to-end delay to actuator should be less than the latency bound Be • Node i first estimates the advancement hi,j towards the actuator a from i to j, and then the maximum delay from i to j, delayi,j. The Third IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS'06)

18. Next Hop Selection • Only neighbors with dq_max>0 will be considered as next hop • Node i starts inspecting the neighbors with λhigh=0 and λlow=0 • λlow =0 means it will not affect the transmission time for the existing packets in that node • λhigh =0 means it can be served with the highest priority • Node i calculates the maximum data rateλi,jthat it can forward while satisfying the latency bound: The Third IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS'06)

19. Data Transmission • Data packets are forwarded to the neighbor with the highest hi,jand λi,j • The intermediate nodes will update the latency bound Be before forwarding to next hop Be’= Be – (tdepart – tarrive) – dtran – dprop • Sensor will update its and the routes regularly • If the latency bound is not met, another route will be selected • In the worst case, if no alternative route, sensor may inform the previous nodeto select another route The Third IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS'06)

20. Actuator Allocation • The actuators may record the event frequency and re-arrange their standby positionsperiodically • Actuator allocation algorithm • The event frequency freqgof every grid g will be summed up • The field A will be equally divided in to two, denoted by A1 and A2, according to the frequency distribution • Each area is allocated with half of the actuators • The process repeats recursively for A1 and A2, until each subfield contains only one actuator The Third IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS'06)

21. Actuator Allocation The Third IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS'06)

22. Simulations • Simulator: NS-2 • Metrics • On-time Reachability • Average Delay • Overall Reliability • 4 events • 2 with high importance • 2 with low importance • Located in left bottom corner The Third IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS'06)

23. On-Time Reachability The Third IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS'06)

24. Average Delay The Third IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS'06)

25. Overall Reliability The Third IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS'06)

26. Actuator Allocation • Divide whole field into tree, with event occurrence probability 0.6, 0.333, and 0.067 • Data rate = 60pkt/s The Third IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS'06)

27. Conclusion • We provide a distributed and comprehensive solution for reliable event reporting and actuator coordination in WSAN • We formulate the event reporting problem and define reliability index • We provide a distributed data aggregation mechanism • We propose a reliable priority-based event reporting algorithm • We propose an actuator allocation algorithm • Simulation results are provided to demonstrate the effectiveness of our solutions The Third IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS'06)

28. Q & A The Third IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS'06)