1. Non-Location-Based Mobile Sensor Relocation in a Hybrid Static-Mobile Wireless Sensor Network Fang-Jing Wu, Hsiu-Chi Hsu, and Yu-Chee Tseng Department of Computer Science National Chiao-Tung University Hsin-Chu, Taiwan Chi-Fu Huang Department of Computer Science and Information Engineering National Chung Cheng University Chia-Yi, Taiwan SENSORCOMM, 2009

2. Outline Introduction Related Work Goal Network Model and Problem Definition Distributed Data-Pump Relocation Protocol Simulation Results Conclusion

3. Introduction Wireless sensor network Energy Unbalanced Problem sensor sink

4. Related Work [9] use mobile-data-collectors to move along pre-planned paths to collect data from static sensors Long delays [9] M. Ma and Y. Yang. Data gathering in wireless sensor networks with mobile collectors. IEEE IPDPS, 2008. data-pump (mobile-data-collector) rendezvous sensor

5. Related Work [19] proposes a SODaR protocol to deal with funneling problem (non-location-based) based on two-tier architecture [19] G. Yang, B. T. amd Daji Qiao, and W. Zhang. Sensoraided overlay deployment and relocation for vast-scale sensor networks. IEEE INFOCOM,2008. sink (with long-range and short-range wireless interface) data-pump (with long-range and short-range wireless interface) sensor (with short-range wireless interface) short-range interface long-range interface × ×

6. Related Work [19] proposes a SODaR protocol to deal with funneling problem (non-location-based) based on two-tier architecture [19] G. Yang, B. T. amd Daji Qiao, and W. Zhang. Sensoraided overlay deployment and relocation for vast-scale sensor networks. IEEE INFOCOM,2008.

7. Related Work [19] proposes a SODaR protocol to deal with funneling problem (non-location-based) Not balance the load of data-pump [19] G. Yang, B. T. amd Daji Qiao, and W. Zhang. Sensoraided overlay deployment and relocation for vast-scale sensor networks. IEEE INFOCOM,2008. G

8. Goal Based on the same two-tier architecture as in [19] To design a distributed range-free relocation protocol for data-pumps to achieve both connectivity and load balance

9. Distributed Data-Pump Relocation Protocol Network Model and Assumption Based on tow-tier network with static sink m 0 A set of static sensor S = {s 1,s 2,…,s n } A set of mobile data-pumps M = {m 1,m 2,…,m e } Every node has a short-range antenna Each of the sink and data-pumps has a long-range antenna e << n

10. Problem Definition Distributed Data-Pump Relocation Protocol unattached data-pumps attached data-pumps

11. Problem Definition Distributed Data-Pump Relocation Protocol Use virtual Voronoi graph

12. Problem Definition Distributed Data-Pump Relocation Protocol Use virtual Voronoi graph Conectivity: To enforce all data-pumps to remain attached to m 0 after relocation Load balance: Balance the number of sensors in the virtual Voronoi cells

13. Problem Definition Distributed Data-Pump Relocation Protocol Use virtual Voronoi graph Conectivity: To enforce all data-pumps to remain attached to m 0 after relocation Load balance: Balance the number of sensors in the virtual Voronoi cells master data-pump of s j the set of sensors served by m i minimize where

14. Distributed Data-Pump Relocation Protocol Balancing Mode for Attached Data-Pumps Connecting Mode for Unattached Data-Pumps Synchronization Between Phases

15. Distributed Data-Pump Relocation Protocol Balancing Mode for Attached Data-Pumps Phase 1 Virtual cell construction Phase 3 Connectivity maintenance between mobile Phase 4 Navigation by sensors Phase 2 Cell center estimation

16. Balancing Mode for Attached Data-Pumps Phase 1:Virtual cell construction m1m1 Step1: m i will broadcast a Cell(m i, h) message using its short-range antenna. Step2: When any s j receives a Cell(m i, h) message, it will check the following conditions: (i) χ(s j ) = NULL and (ii) h < h(s j ). Step3: If any of the above conditions is true, sj will set χ (s j ) = m i, set h(s j ) = h, and broadcast a Cell(m i ; h+1) message. m2m2 Cell(m 1, 1) Cell(null, ∞ ) Cell(m 2, 1) Cell(m 1, 1 ) Cell(m 1, 2 ) Cell(m 2, 2 ) Cell(m 1, 2 ) Cell(m 2, 1 )

17. Balancing Mode for Attached Data-Pumps Phase 1:Virtual cell construction s1s1 m1m1 Step1: m i will broadcast a Cell(m i, h) message using its short-range antenna. Step2: When any s j receives a Cell(m i, h) message, it will check the following conditions: (i) χ(s j ) = NULL and (ii) h < h(s j ). Step3: If any of the above conditions is true, sj will set χ (s j ) = mi, set h(s j ) = h, and broadcast a Cell(m i ; h+1) message. m2m2 Cell(m 1, 1) Cell(m 2, 1) Cell(m 1, 2) Cell(m 2, 2) χ(s 1 ) = m 1 χ(s j ): master data-pump of s j

18. Balancing Mode for Attached Data-Pumps Phase 2: Cell center estimation Each m i will try to identify the center sensor cn(m i ) of its cell C(m i ) m0m0 m1m1 m3m3 m2m2

19. Balancing Mode for Attached Data-Pumps Phase 2: Cell center estimation Each m i will try to identify the center sensor cn(m i ) of its cell C(m i ) m0m0 m1m1 m3m3 m2m2 1 Step1: Broadcast a CENTER(cn(m i )) message around sensors in C(m i ) to form a spanning tree rooted at itself. Step2: Each sensor s j will calculate the depth (d j ) and the number of sensors of the sub-tree rooted at itself (n j ). Step3: Then, each sensor s j can compute a load index as follows: ε j = α ‧ n j + ( 1 - α ) ‧ d j 0 ≦ α ≦ 1 68 42 70 55 114 cn(m 1 )=m 1 ex, α = 1,ε 1 = 114 is maximal cn(m 1 ) = s 1 d max : Maximaul depth of subtree rooted at m i ’s children (except subtree rooted at s c ) h(s c,m i ) : Short-range antenna hop count from s c to m i ex, = 1 ． (349-114)/(5-1) = 58.75

20. Phase 2: Cell center estimation Each m i will try to identify the center sensor cn(m i ) of its cell C(m i ) m0m0 m1m1 m3m3 m2m2 1 Step1: Broadcast a CENTER(cn(m i )) message around sensors in C(m i ) to form a spanning tree rooted at itself. Step2: Each sensor s j will calculate the depth (d j ) and the number of sensors of the sub-tree rooted at itself (n j ). Step3: Then, each sensor s j can compute a load index as follows: ε j = α ‧ n j + ( 1 - α ) ‧ d j 0 ≦ α ≦ 1 68 42 70 55 114 2 cn(m 1 ) = s 1 44 70 ex, α = 1,ε 2 = 70 is maximal m 1 ’s Q = {s 1 } cn(m 1 ) = s 1 = 1 ． (349-70)/(4-1) = 93

21. Balancing Mode for Attached Data-Pumps Phase 3: Connectivity maintenance between mobile Each data-pump m i must choose an attached data-pump to be its parent, denoted by P(m i ) for keeping attached. m6m6 m4m4 m1m1 m0m0 m5m5 m2m2 m3m3 H(m 6 )=1 H(m 5 )=1 H(m 1 )=1 H(m 2 )=1 H(m 3 )=2 H(m 4 )=2 Select_parent

22. Balancing Mode for Attached Data-Pumps Phase 3: Connectivity maintenance between mobile Each data-pump m i must choose an attached data-pump to be its parent, denoted by P(m i ) for keeping attached. m6m6 m4m4 m1m1 m0m0 m5m5 m2m2 m3m3 H(m 6 )=1 P(m 6 )=m 0 H(m 5 )=1 P(m 5 )=m 0 H(m 1 )=1 P(m 1 )=m 0 H(m 2 )=1 P(m 2 )=m 0 H(m 3 )=2 H(m 4 )=2 P(m 4 )=m 2 m 3 run for Δt p to counnt N C P(m3) Select_parent Become_child P(m 3 )=m 1 N C P( m 3) = 1 Add m 3 to L c (m 1 )

23. Phase 3: Connectivity maintenance between mobile Each data-pump m i must choose an attached data-pump to be its parent, denoted by P(m i ) for keeping attached. Balancing Mode for Attached Data-Pumps m6m6 m4m4 m1m1 m0m0 m5m5 m2m2 m3m3 H(m 6 )=1 P(m 6 )=m 0 H(m 5 )=1 P(m 5 )=m 0 H(m 1 )=1 P(m 1 )=m 0 H(m 2 )=1 P(m 2 )=m 0 H(m 3 )=2 H(m 4 )=2 P(m 4 )=m 2 m 3 ‘s timer Δt p is expired P(m 3 )=m 1 Confirm Parent(m 3,N c p(m3) )

24. Phase 3: Connectivity maintenance between mobile Each data-pump m i must choose an attached data-pump to be its parent, denoted by P(m i ) for keeping attached. Balancing Mode for Attached Data-Pumps m6m6 m4m4 m1m1 m0m0 m5m5 m2m2 m3m3 H(m 6 )=1 P(m 6 )=m 0 H(m 5 )=1 P(m 5 )=m 0 H(m 1 )=1 P(m 1 )=m 0 H(m 2 )=1 P(m 2 )=m 0 H(m 3 )=2 H(m 4 )=2 P(m 4 )=m 2 m 3 ‘s timer Δt p is expired P(m 3 )=m 1 m7m7 Select_parent β N P (mi) + (1 -β) φ(P(m i ),m i ) Cost(P(m i )) =

25. Balancing Mode for Attached Data-Pumps Phase 4: Navigation by sensors Each data-pump m i start to move along the sequence of sensors in the history of cn(m i ), denoted by Q m0m0 m1m1 m3m3 m2m2 1 5 4 2 3 68 42 70 55 114 Q={s 1 } Navigation_Request(s 1 )

26. Balancing Mode for Attached Data-Pumps Phase 4: Navigation by sensors Each data-pump m i start to move along the sequence of sensors in the history of cn(m i ), denoted by Q m1m1 1 5 4 2 3 68 42 70 55 114 Q={s 1 } Come_Here(s 1 ) … … … … Try D 1, …,D K directions1

27. m1m1 Balancing Mode for Attached Data-Pumps Phase 4: Navigation by sensors Each data-pump m i start to move along the sequence of sensors in the history of cn(m i ), denoted by Q m1m1 1 5 4 2 3 68 42 70 55 114 Q={s 1 } Come_Here(s 1 ) 1 5 4 2 3 68 42 70 55 114 Q={s 1 } m2m2 m0m0 Come_Here(s 1 ) Navigation_Complete(s 1 )

28. Connecting Mode for Unattached Data Pumps This mode is to enforce each unattached data-pump m i to move, based on the local information, toward the sink until it is attached. m3m3 m1m1 m0m0 m4m4 m2m2 m5m5 h(s j, sink) M 5 send Connection_Request Message to nearby sensor Nearby sensors response Connection_Reply(h(s j,sink)) message to m 5

29. Connecting Mode for Unattached Data Pumps This mode is to enforce each unattached data-pump m i to move, based on the local information, toward the sink until it is attached. m3m3 m1m1 m0m0 m4m4 m2m2 1 m 5 send Navigation_Request(s 1 ) message to s 1 m5m5 Come_Here(s 1 )

30. Synchronization Between Phases One possible approache to synchronize the phases between data-pumps Coordinated by the sink Phase1,2 Start Phase3 Start Phase4 Start Wait all data-pumps finish Sink Control by Sink

31. Simulation Results Environment and Parameters Number of sensors20000 sensors Number of data-pumps75 data-pumps short-range antennaZigBee, r c = 60 m long-range antennaWiFi, R c = 240 m α (find center phase)0.5 β (Connectivity phase)0.5 Runs of Simulation100 runs RfRf Sink

32. Simulation Results [6] R. K. Jain. The Art of Computer Systems Performance Analysis: Techniques for Experimental Design, Measurement, Simulation, and Modeling. John Wiley and Sons, New York, 1991. (10+10+10) 2 / 3*(100+100+100) =900/900=1 (25+4+1) 2 / 3*(625+16+1) =900/1926 ≒ 0.467

33. Simulation Results The number of data-pumps

34. Simulation Results

36. Conclusion To prolong network lifetime, the paper propose a distributed mobile data-pump relocation protocol to achieve the connectivity and load balance. Simulation results show that our protocol can provide prominent load balance among mobile data-pumps Future work The future work will consider to relocate data-pumps when sensors have different traffic load such that data-pumps’ load could be balanced.