Deployment Analysis in Underwater Acoustic Wireless Sensor Networks

Transcription

1 Deployment Analysis in Underwater Acoustic Wireless Sensor Networks D. Pompili, T. Melodia, I.F. Akyildiz Broadband and Wireless Networking Laboratory School of Electrical and Computer Engineering Georgia Institute of Technology Speaker: 1/29

2 Outline Propose 2D and 3D architectures for UW-ASNs State objectives of the paper Study graph properties of 2D oceanbottom UW-ASNs Propose and evaluate 3D deployment strategies Conclusions and future work 2/29

3 Two-dimensional Architecture 3/29

4 Three-dimensional Architecture 4/29

5 Objectives 2D Architecture: Determine the minimum number of sensors and uw-gateways to achieve communication and sensing coverage Provide guidelines on how to choose the optimal deployment surface area, given a target region 3D Architecture: Evaluate different deployment strategies Determine the minimum number of sensors needed to achieve the target sensing coverage 5/29

6 Related Work Few papers studied deployment issues for underwater sensor networks Sensing and communication coverage were addressed for terrestrial sensor networks However, previous deployment solutions and theoretical bounds assume: Spatio-temporal correlation Mobile sensors Redeployment of nodes These assumptions may not hold in UW-ASNs 6/29

7 Related Work In [1], sensor coverage is achieved by moving sensor nodes after an initial random deployment However, [1] requires either: Mobile sensor nodes or Redeployment of nodes [1] Y. Zou and K. Chakrabarty. Sensor Deployment and Target Localization Based on Virtual Forces. In Proc. of IEEE INFOCOM, volume 2, pages , San Francisco, CA, USA, Apr /29

8 Related Work It is shown in [2] that The sensing range required for sensing coverage is greater than the transmission range that guarantees network connectivity Since in typical applications the transmission range is greater than the sensing range The network is guaranteed to be connected when sensing coverage is guaranteed [2] V. Ravelomanana. Extremal Properties of Threedimensional Sensor Networks with Applications. IEEE Transactions on Mobile Computing, 3(3): , July/Sept /29

9 Graph Properties of Bottom UW-ASNs We analyze the graph properties of devices (sensors and uw-gateways) when they are deployed on the ocean surface, sink, and reach the bottom We study the trajectory of sinking devices deployed on the ocean surface when: Sensors are randomly deployed on the ocean surface (e.g., scattered from an airplane), or Sensors are accurately positioned on the surface (e.g., released from a vessel) 9/29

10 Triangular-grid Surface Deployment Sensors with same sensing range r Optimal deployment to cover a 2D area with minimum number of sensors: Center sensors at the vertex of a grid of equilateral triangles 10/29

11 Triangular-grid Coverage Coverage= η(d) d/r=sqrt(3) d/r=2 (η *,d/r * )=(0.95,1.95) Sensing coverage Ratio of sensor distance and sensing range=d/r= Ratio of sensor distance and sensing range (d/r) 11/29

12 Minimum No. of Sensors in Tri-grid Minimum no. of sensors A 1 =100x100m 2 A 2 =300x200m 2 r=10m r=15m r=20m r=25m r=30m r=35m Area: lxh= 100x100m r in[10,35]m Minimum no. of sensors r=10m r=15m r=20m r=25m r=30m r=35m Area: lxh= 300x200m d*/r= Ratio of sensor distance and sensing range (d * /r) d*/r= Ratio of sensor distance and sensing range (d * /r) N * * * * l d + 2 3h 6d 4 3r ( l, h, d, r) = * * d 3d 12/29

13 Assumptions on Ocean Currents Assumptions in this paper: No significant vertical movement of ocean water, i.e., the considered area is neither an upwelling nor a downwelling The velocity of the ocean current depends on depth H different ocean current layers with different width Current in each layer has a fixed module and angular deviation (with known statistics) This allows modeling the thermohaline circulation (the ocean s conveyor belt), i.e., deep ocean currents that flow with constant velocity and direction within certain depths 13/29

14 Trajectory of a Sinking Device 14/29

15 15/29 Dynamic System of a Sinking Object F W is the weight force F B is the buoyant force (Archimede s principle) F R is the fluid resistance force F C is the force of the current ( ) v v A C F v A K F g V F g V F where a V F F F F C C C R w R w B W C R B W r r r r r r r r r r r r r r = = = = = σ µ ρ ρ ρ ρ,,, :, = + = + = + ρ ρ ρ ρ µρ ρ σ ρ σ ρ σ ρ σ W z W y c xy xy x c xy xy g z V A K z v V A C y V A C y v V A C x V A C x Projecting onto x, y, z

16 Communication Properties of 2D ASNs The dynamic system characterizes the sinking behavior of sensors and gateways P P f S f G = = P P 0 S 0 G + P + P The objective is to describe: The horizontal displacement of sensors and gateways The main communication properties of clusters with a gateway as cluster head, e.g., study the maximum and average sensor-gateway distance ( v ( v The average and standard deviation of number of sensors in each cluster G 0 S S ) 0 G ) 16/29

17 Average Horizontal Displacements =500m Uw 3 =500m 2 =100m Uw 2 =100m 1 =50m Uw 1 =50m Average displacement [m] Sensor displacement depths= 50,100,500m Uw-gateway displacements depths= 50,100,500m Velocity of current [m/s] 17/29

18 Sensor-gateway Dist. vs. No. gateways Maximum and average sensor < > uw gateway distance [m] V 1 =100x100x50m 3 V 2 =300x200x100m 3 V 3 =1000x1000x500m 3 Average sensorgateway distance D 3 =1000x1000x500m 3 D 3 =1000x1000x500m 3 D 2 =300x200x100m 3 D 2 =300x200x100m 3 D 1 =100x100x50m 3 D 1 =100x100x50m 3 Maximum sensorgateway distance No. of deployed uw gateways 18/29

19 Deployment Surface Area: Margins (a): Current direction unknown (b): Statistical knowledge of current direction The side surface margins in the unknown current direction case (a) are larger than those computed if some information about the current direction can be leveraged (b) 19/29

20 3D Deployment Strategies We propose three deployment strategies for three-dimensional UW-ASNs to obtain a target coverage of the 3D region 3D-random strategy Bottom-random strategy Bottom-grid strategy Winch-based sensor devices are anchored to the bottom of the ocean in such a way that they cannot drift with currents Sensors are assumed to know their final positions by exploiting localization techniques 20/29

21 3D-random Deployment Strategy 3D-random Does not require any form of coordination from the surface station Sensors are randomly deployed on the bottom, where they are anchored Sensors randomly choose a depth and float to the selected depth 21/29

22 Bottom-random Deployment Strategy Bottom-random Sensors are randomly deployed on the bottom, where they are anchored Surface station is informed about their position on the bottom Surface station calculates the depth for each sensor to achieve the target coverage ratio Sensors are assigned a target depth and float to the desired position 22/29

23 Bottom-grid Deployment Strategy Bottom-grid Needs to be assisted by one or multiple AUVs, which deploy the sensors Grid deployment on the bottom of the ocean Each sensor is also assigned a desired depth by the AUV and accordingly floats to achieve the target coverage ratio 23/29

24 3D-random Coverage 1 Coverage of the 3D space (random deployment) Fraction of 3D space covered No. sensors=9 No. sensors=16 No. sensors=25 No. sensors=36 No. sensors=49 No. sensors=64 No. sensors=81 No. sensors= Normalized sensing range 24/29

25 Bottom-random Coverage 1 Coverage of the 3D space (2D random deployment) Fraction of 3D space covered No. sensors=9 No. sensors=16 No. sensors=25 No. sensors=36 No. sensors=49 No. sensors=64 No. sensors=81 No. sensors= Normalized sensing range 25/29

26 Bottom-grid Coverage 1 Coverage of the 3D space (2D grid deployment) Fraction of 3D space covered No. sensors=9 No. sensors=16 No. sensors=25 No. sensors=36 No. sensors=49 No. sensors=64 No. sensors=81 No. sensors= Normalized sensing range 26/29

27 Sensing Range Bound Minimum sensing range (coverage ratio=0.9) Minimum sensing range (coverage ratio=1) Sensing range bound 0.4 Sensing range Number of sensors Minimum normalized sensing range that guarantees coverage ratios of 1 and 0.9 with the bottom-random strategy and the theoretical bound on the minimum normalized sensing range derived in [2] 27/29

28 Conclusions Deployment strategies for 2D and 3D architectures for UW-ASNs Deployment analysis in order to: Determine the minimum number of sensors to achieve the application-dependent target sensing and communication coverage Provide guidelines on how to choose the deployment surface area, given a target region Determine the minimum number of uwgateways, given some desired communication properties of clusters 28/29

29 Future Work Two-dimensional UW-ASNs: We will extend the current worst-case study to set surface margins in order to take into account statistical information about currents Three-dimensional UW-ASNs: We will develop a mathematical framework to study the 3D sensing coverage We will devise a distributed algorithm to set and adjust the depth of sensors 29/29