1. 산업 및 시스템 공학과 통신시스템 및 인터넷보안연구실 20075273 김효원 Optimizing Tree Reconfiguration for Mobile Target Tracking in Sensor Networks Wensheng Zhang and Guohong Cao The Pennsylvania State University INFOCOM 2004

2. Telecommunication System & Internet Security Lab. Outline  Introduction  Overview of DCTC  Optimizing TR Schemes  Root Replacement  OCR(Optimized Complete Reconfiguration)  OIR(Optimized Interception-based Reconfig.)  Performance Evaluation  Conclusion 2

3. Telecommunication System & Internet Security Lab.  Introduction  Overview of DCTC  Optimizing TR Schemes  Performance Evaluation  Conclusion 3

4. Telecommunication System & Internet Security Lab. Introduction  Sensor network  Advances in micro-electro-mechanics and wireless communication  Adopted to many military and civil application  Sensor collaboration  limitations of sensor node  Obtain fine-grain, high-precision sensing data 4

5. Telecommunication System & Internet Security Lab. Introduction  Sensor collaboration issue in target tracking  Sensor node promptly detect target, generate reports and send in fast and energy efficient way  In this paper,  use DCTC framework and optimize tree reconfiguration to minimize energy consumption  propose 2 optimized schemes  OCR(Optimized Complete Reconfiguration)  OIR(Optimized Interception-based Reconfiguration) 5

6. Telecommunication System & Internet Security Lab.  Introduction  Overview of DCTC  Basic Structure  Details  Problem of Optimizing Tree Reconfiguration  Optimizing TR Schemes  Performance Evaluation  Conclusion 6

7. Telecommunication System & Internet Security Lab. Overview of DCTC  Dynamic Convoy Tree-based Collaboration  Basic structure of DCTC 7

8. Telecommunication System & Internet Security Lab. Overview of DCTC  Dynamic Convoy Tree-based Collaboration  Construct Initial Convoy Tree 8 Target Enters the detection region Nodes close to target construct initial convoy tree by selecting root using root election algorithm The other node in monitoring region are added to convoy tree

9. Telecommunication System & Internet Security Lab. Overview of DCTC  Dynamic Convoy Tree-based Collaboration  Collecting Sensing Data via Tree  Tree Expansion and Pruning 9 As target moves, some nodes far away from target are pruned Root should predict target moving direction and activate right group of sensor node

10. Telecommunication System & Internet Security Lab. Overview of DCTC  Dynamic Convoy Tree-based Collaboration  Tree Reconfiguration if necessary 10 As target moves, many nodes become far away from target and energy may be wasted To reduce overhead, root should be replaced by node closer to the center of monitoring region

11. Telecommunication System & Internet Security Lab. Overview of DCTC  Problem of Optimizing Tree Reconfiguration  Total energy in convoy tree sequence  Convoy tree sequence  As trees are reconfigured, a sequence of trees exists at different data collection time  Optimizing tree reconfiguration = finding min-cost convoy tree sequence 11 Data collection Tree reconfiguration

12. Telecommunication System & Internet Security Lab.  Introduction  Overview of DCTC  Optimizing TR Schemes  Root Replacement  OCR(Optimized Complete Reconfiguration)  OIR(Optimized Interception-based Reconfig.)  Performance Evaluation  Conclusion 12

13. Telecommunication System & Internet Security Lab. Optimizing TR Schemes  Reconfiguration of convoy tree  Convoy tree is reconfigured in two step 13

14. Telecommunication System & Internet Security Lab. Optimizing TR Schemes  Reconfiguration of convoy tree  Convoy tree is reconfigured in two step 14

15. Telecommunication System & Internet Security Lab. Optimizing TR Schemes  Root Replacement  Rule 15 1. Root predicts L t+1 (t+1 : next data collection time) 2. Distance check (dr : threshold) 3. Determine Root change (R→R’ )

16. Telecommunication System & Internet Security Lab. Optimizing TR Schemes  Root Replacement  Rule 16 4. Send message grid head 5. Grid head select new root (the node closest to L t+1 ) New Root Old Root 1.Tree have a short height and small energy consumption during data collection 2.Root that is far away from sensing node may consume lots of network bandwidth and power to send data

17. Telecommunication System & Internet Security Lab. Optimizing TR Schemes  Generic Method for Optimizing d r  Overall energy consumption = data collection + tree reconfiguration  Selecting appropriate value for d r is important  Large d r → high overhead for data collection  Small d r → high overhead for tree reconfiguration  Selecting Optimal d r → minimizes overall energy consumption 17

18. Telecommunication System & Internet Security Lab. Optimizing TR Schemes  Generic Method for Optimizing d r  Average energy consumption during k(v) 18 : root replacement occurring time : data collection overhead (energy consumption) (distance between root and target is x) : target moving velocity : tree reconfiguration overhead (energy consumption) (distance between root and target is x)

19. Telecommunication System & Internet Security Lab. Optimizing TR Schemes  Generic Method for Optimizing d r  To minimize →  Nodes do not have to compute k(v) on-line  The function can be calculated off-line and distributed to the related sensor node  In the following section..  For computing k(v)  Describe how to compute E d (x), E t (x) in OCR, OIR 19

20. Telecommunication System & Internet Security Lab.  Introduction  Overview of DCTC  Optimizing TR Schemes  Root Replacement  OCR(Optimized Complete Reconfiguration)  OIR(Optimized Interception-based Reconfig.)  Performance Evaluation  Conclusion 20

21. Telecommunication System & Internet Security Lab. Optimizing TR Schemes  Optimized Complete Reconfiguration (OCR)  OCR scheme  Reconfigures all nodes in the tree 21 After complete reconfiguration Before complete reconfiguration After root replacement Broadcast reconf(R, R’)

22. Telecommunication System & Internet Security Lab. Optimizing TR Schemes  Optimized Complete Reconfiguration (OCR)  OCR scheme  Algorithm executed by root R’ 22 drdr

23. Telecommunication System & Internet Security Lab. Optimizing TR Schemes  Optimized Complete Reconfiguration (OCR)  OCR scheme  Algorithm executed by node i in the tree 23 drdr : set of neighbors of node i : parent of node i : children of node i : message to init tree reconfig. : message to detach i from Pi : message to attach i to j Ni 중 R’ 과의 거리가 최소가 되는 노드

24. Telecommunication System & Internet Security Lab. Optimizing TR Schemes  Optimized Complete Reconfiguration (OCR)  Overhead Analysis (Data Collection)  Energy consumed to send report to R from node P(x, y)  Energy consumed by data collection 24 # of hop (using (A2)) node density # of hop in the area data report size (A2) # of hop between two nodes is proportional to geographic distance

25. Telecommunication System & Internet Security Lab. Optimizing TR Schemes  Optimized Complete Reconfiguration (OCR)  Overhead Analysis (Tree Reconfiguration)  Reconfiguration occurs exactly when  Each node sends detach message to old parent  Each node sends attach message to new parent  Energy consumed by tree reconfiguration 25 control message size

26. Telecommunication System & Internet Security Lab.  Introduction  Overview of DCTC  Optimizing TR Schemes  Root Replacement  OCR(Optimized Complete Reconfiguration)  OIR(Optimized Interception-based Reconfig.)  Performance Evaluation  Conclusion 26

27. Telecommunication System & Internet Security Lab. Optimizing TR Schemes  Optimized Interception-Based Reconfig. (OIR)  OIR scheme  Only reconfigures a small part of the tree 27 After interception based reconfig. Process of interception-based reconfig. After root replacement Broadcast reconf(R, R’) between (l 0, l 1 ) in morintoring region

28. Telecommunication System & Internet Security Lab. Optimizing TR Schemes  Optimized Interception-Based Reconfig. (OIR)  OIR scheme  Algorithm executed by root R’ 28 E d (x), E t (x) is calculated by Eq(11), Eq(12)

29. Telecommunication System & Internet Security Lab. Optimizing TR Schemes  Optimized Interception-Based Reconfig. (OIR)  OIR scheme  Algorithm executed by node i in the tree 29 drdr and between (l 0, l 1 ) in morintoring region

30. Telecommunication System & Internet Security Lab. Optimizing TR Schemes  Optimized Interception-Based Reconfig. (OIR)  Overhead Analysis (Data Collection)  For nodes between lines l 0 and l 1  Energy consumed to collect data (P 0 locates between l 0 and l 1 ) 30 # of hop (between P 0, R)

31. Telecommunication System & Internet Security Lab. Optimizing TR Schemes  Optimized Interception-Based Reconfig. (OIR)  Overhead Analysis (Data Collection)  For nodes on the left side of l 1  Path between P 1 and R may not be optimized  Energy consumed to collect data (P 0 locates left side of l 1 ) 31 n is small → c 1 is small (c 1 = 1.1 in this paper)

32. Telecommunication System & Internet Security Lab. Optimizing TR Schemes  Optimized Interception-Based Reconfig. (OIR)  Overhead Analysis (Data Collection)  For nodes on the right side of l 0  Similar to previous case  Path between P 2 and R may not be optimized  Energy consumed to collect data (P 2 locates right side of l 0 ) 32

33. Telecommunication System & Internet Security Lab. Optimizing TR Schemes  Optimized Interception-Based Reconfig. (OIR)  Overhead Analysis (Data Collection)  Energy consumed by data collection 33

34. Telecommunication System & Internet Security Lab. Optimizing TR Schemes  Optimized Interception-Based Reconfig. (OIR)  Overhead Analysis (Tree Reconfiguration)  Reconfiguration occurs exactly when  Each node within l 0, l 1 sends detach msg. to old parent  Each node within l 0, l 1 sends attach msg. to new parent  Energy consumed by tree reconfiguration 34

35. Telecommunication System & Internet Security Lab. Optimizing TR Schemes  Comparison between OCR & OIR  OCR and OIR take different approaches to optimize overall energy consumption  OCR : higher priority to data collection  OIR : higher priority to tree reconfiguration  OIR outperforms OCR when velocity is high, s d /s c or d s /d c is small  High velocity : OIR has smaller tree reconfig. overhead  s d /s c small : OIR has smaller data collection overhead  d s /d c small : OIR has smaller data collection overhead 35

36. Telecommunication System & Internet Security Lab.  Introduction  Overview of DCTC  Optimizing TR Schemes  Performance Evaluation  Energy Consumption Results  Data Collection Delay  Impact of Movement Prediction Accuracy  Conclusion 36

37. Telecommunication System & Internet Security Lab. Performance Evaluation  Simulation  Evaluate performance of proposed schemes  Compare to other non-optimized reconf. scheme  Non-optimized reconfiguration schemes 37

38. Telecommunication System & Internet Security Lab. Performance Evaluation  Energy Consumption Results  Comparing Energy Consumption  Varying v, s d /s c and d s /d c  As v increase → energy consumption increases  OCR > ACR > CCR, OIR > AIR > ACR  CCR > CIR  Tree reconf. frequency is low → Data collection dominates  AIR > ACR  Tree reconf. frequency is high → Tree reconf. dominates  OIR > OCR (s d /s c,d s /d c : small)  OCR > OIR (s d /s c,d s /d c : large) 38

39. Telecommunication System & Internet Security Lab. Performance Evaluation  Data Collection Delay  Frequent reconfiguration reduce height of tree  ACR > OCR > CCR, AIR > OIR > CIR  Compared to CR, IR changed small part of tree → larger height  ACR > AIR, OCR > OIR, CCR > CIR  Data collection delay of OIR and OCR are not optimal  But, difference to the optimal value is reasonable 39

40. Telecommunication System & Internet Security Lab. Performance Evaluation  Impact of Movement Prediction Accuracy  Simulation Model  Every 10sec, target may change its moving direction and/or velocity  With probability p k, the direction and velocity of target keep unchanged  Simulation Results  As pk drops, energy consumption increases  As pk drops, the chance of wrong prediction increases → Increasing reconfiguration overhead  Energy consumption does not increase too much if pk is not very low 40

41. Telecommunication System & Internet Security Lab.  Introduction  Overview of DCTC  Problem of Optimizing Tree Reconfiguration  Optimizing TR Schemes  Performance Evaluation  Conclusion 41

42. Telecommunication System & Internet Security Lab. Conclusions  Optimizing tree reconfiguration when target moves  Formulize as finding min-cost convoy tree seq.  Solved it by proposing  OCR (Optimized Complete Reconfiguration)  Minimize data collection energy  OIR (Optimized Interception-based Reconfiguration)  Minimize tree reconfiguration energy  OCR, OIR optimizes by selecting appropriate root replacement threshold to minimize energy  Simulation results, Optimized schemes are better  OIR outperforms OCR when s d or s c is small 42