A Generalized Coverage-Preserving Scheduling in WSNs. a Case Study in Structural Health Monitoring

Transcription

1 A Generalized Coverage-Preserving Scheduling in WSNs a Case Study in Structural Health Monitoring March 29,2017 Sensor Web Architecture and Protocols Fereshteh Mahdavi

2 Outline Backgraound Scope of this work Specific feature of Strauctural Health Monitoring Systems(SHM) Overall strategy of SHM Heuristic Method Geneteic Algorithm Simulation and Experimental Evaluations References

3 Background 1. Structural Health Monitoring structural monitoring is a regular observation of a structure over a period of time in order to understand its behavior. It can be used to watch over bridges, tunnels, and other buildings. 2. Why do we want structural health monitoring? Because we want to confirm a structure is safe in its everyday use. It can be used to spot problems before they result in damage to a structure. 3. Generalized Coverage-Preserving Scheduling in WSNs. It is based on sensor set instead of individual sensors and contributes to fulfill the monitoring task in a given area.

4 The scope of this work 1. Monitoring vibration in a structure. 2. Energy-Efficient Coverage-Preserving Scheduling(EECPS): Partition nodes into cover sets and determines which nodes should be activated at a certain time to extend the system s lifetime. 3.Taking Structural Health Monitoring(SHM) as an example to illustrate how to support EECPS in some specific applications of WSNs.

5 WSN of the Golden Gate Bridge to detect cracks

6 Specific Feature of SHM To detect an event, we requires collaboration from multiple sensors. Therefore, solutions based on the assumption that each node has a fixed coverage area, and once the event/target occurs in this area, it can be detected by this sensor, are not suitable for SHM. This assumption may not be valied in all apllications.

7 Features to Locate Damage Every structure oscillates with amplitude at some frequencies. These frequencies are called NATURAL FREQUENCIES. When a structure is vibrating under one natural frequency, the corresponding vibration pattern is called the MODE SHAPE of this natural frequency. f = { f 1,f 2, f 3,, f n } φ = {φ 1,φ 2, φ 3,, φ n } Set of natural frequency Set of mode shape

8 How Structural Damage is Detected? Detecting structural damage relies on the vibrational features of the structure, which are always extracted from data collected at multiple sensor nodes. Natural Frequencies, are identified in the sink to detect damage.

9 Problem Maximum SHM Cover Set Problem (MSSP): means to divide sensors into multiple SHM cover sets with the total number of rounds. MSSP is NP-hard. So, two methods to solve the MSSP are proposed.

10 Heuristic this method is divided into two stages: 1-First, a set of candidate single-hop SHM sets are enumerated. Svi = {S1vi, S2vi,...} 2- The problem reduced to the knapsack problem. C V =S V1 U S V2 U S Vm = {S1, S2,, SM}

11 Genetic Algorithm Method Repeat First: create an initial population such as sensor covers for each node by Randomly select a 0 from the segment and set it to 1 Second: evaluate fitness of each individual: considering energy consumption and coverage Third: select and drop Until there is no improvement in the maximum fitness value for ten consecutive generations

12 Inputs of Genetic Algorithm

13 Simulation A total of 60 wireless sensor nodes are used in this location. These 60 locations are selected using domain knowledge from civil engineering.

14 Results from Heuristic Method

15 Results from Heuristic Method

16 Compare Results from the Heuristic and GA

17 Contributions 1. Redefine the coverage based on a sensor set instead of individual sensors. 2. Two methods are proposed in SHM, to partition nodes into qualified cover sets to maximize system lifetime

18 Reference: X. Liu and et al., A Generalized Coverage-Preserving Scheduling in WSNs: a Case Study in Structural Health Monitoring in IEEE INFOCOM 2014-IEEE Conference on Computer Communications

19 Thank You.