1. Energy-Efficient Wake-Up Scheduling for Data Collection and Aggregation Yanwei Wu, Member, IEEE, Xiang-Yang Li, Senior Member, IEEE, YunHao Liu, Senior Member, IEEE, and Wei Lou IEEE TPDS, vol. 21, no. 2, 2010, pp. 275-287.

2. Outline 2  Introduction  System model and assumption  Homogeneous wireless sensor networks  Heterogeneous wireless sensor networks  Formation of data gathering tree  Performance evaluation  Conclusion

3. Introduction  Wireless sensors are often powered by batteries and have limited computing and memory resources.  Schedule the nodes’ activities to reduce energy consumption.  Previous studies did not consider all possible energy consumption by wireless sensors,  Wasted listening, and the state transitions. 3

4. Introduction 4  Traditionally, the scheduling algorithms often schedule the individual activities for each sensor one by one.  Find the best time slots for sending and receiving data.  Communication and interference range.  Homogeneous wireless sensor networks  Heterogeneous wireless sensor networks

5. Introduction 5  A scheduling should reduce the state transitions to increase the lifetime of a sensor.  To minimize the sensor’s wake-up times in a scheduling period.  Any sensor node needs only to wake up at most twice in our protocol.  Once for continuously receiving all packets from its children nodes and once for sending its own data to its parent node.

6. System model and assumption 6  Network System Models  Problem Description

7. Network System Models 7  Tree-based  All data will be collected and sent to the sink.  Each wireless node will use a fixed power to communicate with its neighboring sensors.  The fixed power transmission by a node v i will define an interference range.  R I (v i ) such that the transmission of node v i will interfere the reception of any node v k when  The physical link is reliable if v i can communicate with v j. vkvk vivi vjvj

8. Problem Description 8  Energy-Efficient Scheduling  Data Collection Tree Construction

9. Problem Description- Energy-Efficient Scheduling 9  The amount of slots assigned to a node v i for transmitting should be enough.  A node v i with children nodes u 1, u 2,..., u j should be active for receiving at the time slots when these children nodes send data to v i. The observed link reliability Packets received from its children nodes {0,1}

10. Problem Description- Energy-Efficient Scheduling 10  Any node can only be in one of the states.  All transmissions should be interference-free. {0,1}

11. Problem Description- Energy-Efficient Scheduling 11  Notice that the energy cost by a node v i in all states is  The energy cost for state transitions is The objective of a schedule S is to minimize the summation of these two energy costs. Slot size Energy consumption of # {0,1}

12. Problem Description- Data Collection Tree Construction 12  Tree T is given for the data collection or aggregation.  The total energy cost of the optimum activities scheduling based on this tree is the lowest.  The objective is to find a data collection tree T that should satisfy the data requirements of all nodes.  NP-hard problem.

13. Goals 13  This paper use a TDMA for scheduling node activities to reduce the energy consumption.  Focused on the energy cost by the radio.  Transmitting, receiving, listening, and sleeping.

14. Outline  Introduction  System model and assumption  Homogeneous wireless sensor networks  Heterogeneous wireless sensor networks  Formation of data gathering tree  Performance evaluation  Conclusion 14

15. Homogeneous wireless sensor networks- Centralized Activity Scheduling 15 The total number of time slots that node v i should wake up to receive the data from its children is: Parent node Child node

16. Homogeneous wireless sensor networks- Centralized Activity Scheduling 16 Conflicting Cluster

17. Homogeneous wireless sensor networks- Centralized Activity Scheduling 17 4 1-hop 4-hop 3-hop 2-hop 1/2 The node z is within the distance at most 3R I from node p. The sensors from conflicting clusters C j,l can only be distributed inside the circle with the radius 3R I z q v p RI(p)RI(p) RT(p)RT(p) u

18. Homogeneous wireless sensor networks- Centralized Activity Scheduling 18  Schedule the clusters in the decreasing order of their weight W i.  Then each child v j will be assigned a consecutive w j time slots from this chunk. Time slot W j,i :The clusters which conflict with cluster C i and are scheduled before cluster C i. g j,i : Gaps,non-conflicting clusters, which could be assigned to cluster C i. WiWi {w 1,w 2,w 3 … }

19. Homogeneous wireless sensor networks- Centralized Activity Scheduling 19 SWSW SYNSYN SWSW SYNSYN SWSW SYNSYN SWSW SYNSYN Time slot g j,1 g j,2 g j,3 g j,4 w j,1 w j,2 w j,3 w j,4 C4C4 C5C5 C2C2

20. Homogeneous wireless sensor networks- Centralized Activity Scheduling (More discussions) 20  Besides reducing the energy consumption and increasing network throughput  Another important issue in WSNs is to reduce the delay.  Instead of scheduling using the available earliest time slots, this paper use the latest available time slots. SWSW SYNSYN SWSW SYNSYN SWSW SYNSYN SWSW SYNSYN Time slot g j,1 g j,2 g j,3 g j,4 w j,1 w j,2 w j,3 w j,4 didi uiui d i,w i =3 u i,w i =4 didi uiui

21. Homogeneous wireless sensor networks- Distributed Activity Scheduling (TTL) 21 SWSW SYNSYN SWSW SYNSYN SWSW SYNSYN SWSW SYNSYN Time slot g j,1 g j,2 g j,3 g j,4 w j,1 w j,2 w j,3 w j,4 C4C4 C7C7 IamScheduled

22. Outline  Introduction  System model and assumption  Homogeneous wireless sensor networks  Heterogeneous wireless sensor networks  Formation of data gathering tree  Performance evaluation  Conclusion 22

23. Heterogeneous wireless sensor networks - Centralized Activity Scheduling 23 SWSW SYNSYN SWSW SYNSYN SWSW SYNSYN SWSW SYNSYN Time slot g j,1 g j,2 g j,3 g j,4 w j,1 w j,2 w j,3 w j,4 C2C2 C3C3 First divide the sensors into buckets according to their interference radii. Interference Range : B 1 <B 2 <B 3 C4C4

24. Heterogeneous wireless sensor networks - Distributed Activity Scheduling (TTL) 24 SWSW SYNSYN SWSW SYNSYN SWSW SYNSYN SWSW SYNSYN Time slot g j,1 g j,2 g j,3 g j,4 w j,1 w j,2 w j,3 w j,4 C6C6 C7C7 First divide the sensors into buckets according to their interference radii. C1C1

25. Formation of data gathering tree -Connected dominating set 25  Energy efficiency is a critical issue in WSNs since the sensor nodes are with limited energy.

26. Performance evaluation 26  Randomly placing 32 sensors in a square 5*5 square meters.  Transmission radius as 1m.  Interference radius as 2m.

27. Performance evaluation 27  Impact of Data Rate

28. Performance evaluation 28  Impact of Number of Nodes

29. Performance evaluation 29  Impact of Heterogeneous Nodes

30. Conclusion 30  In this paper proposed an efficient centralized and distributed scheduling algorithms.  Remove the unnecessary listening cost  Reduce the energy cost for state switching and clock synchronization.  Every node needs only to wake up at most twice in one scheduling period  One for receiving data from its children and one for sending data to its parent.