1. A Quorum-Based Energy-Saving MAC Protocol Design for Wireless Sensor Networks Chih-Min Chao, Yi-Wei Lee IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, 2010

2. Outline Introduction Preliminaries Protocol description Simulation results Conclusions 2

3. Introduction Wireless sensors are battery powered. It is crucial for them to efficiently use their battery resources. Most of the existing power-saving protocols achieve power savings by periodically putting sensor nodes to sleep. Lower power efficiency Higher latency. 3

4. Introduction Many protocols have been proposed to extend the network lifetime of sensor networks Deployment protocols Power efficient medium access control protocols Routing protocols Energy-hole problem Sensor nodes that are closer to the sink deplete their power faster. 4

5. Problem Statement 5 Host A Host B 0 1 2 34 56 7 8 Time

6. Quorum Concept 6 012 345 678 n n RaRa RbRb CaCa CbCb Host A Host B 0 1 2 34 56 7 8 Time

7. QMAC Quorum-based MAC protocol 7

8. QMAC 8 Time frame Time B C D E A RTS CTS DATA ACK SIFS Sleep To reduce power consumption and determine the sleep frequency for each sensor node based on its own traffic load.

9. Preliminaries Time is divided into a series of time frames. All sensor nodes are time synchronized. Each node has a unique ID. Sensor nodes report their data to their common sink node. All sensor nodes have the same transmission range. All sensor nodes are static after deployment. 9

10. Preliminaries Sensor nodes are randomly and uniformly distributed in the network area. 10 Sink C1C1 C2C2 C3C3 C4C4 Hop Count=1 Hop Count=2 Hop Count=3 Hop Count=4

11. Quorum-Based Wake-Up Schedule A sensor node using an n × n grid will wake up 2n − 1 out of n 2 time frames. Grid size 11 The ratio of areas for different coronas C 1 :C 2 :C 3 :C 4 =1:3:5:7 A node in C 3 is responsible for relaying traffic for 7/5 nodes in C 4

12. Quorum-Based Wake-Up Schedule 12 The traffic load in C 3 is 1 + (7/5) × 1 = 2.4 The ratio of areas for different coronas C 1 :C 2 :C 3 :C 4 =1:3:5:7 The traffic load in C 1 is 1 + 3 × 5 = 16 The traffic load in C 2 is 1 + (5/3) × 2.4 = 5

13. Latency Reduction In allowing sensor nodes to sleep longer than one time frame to reduce energy consumption. The price for this saved energy, though, is higher latency. Next-hop group 13

14. Next-hop group Sink C1C1 C2C2 C3C3 C4C4 X One hop neighbor boundary Next hop group member 14

15. Simulation results NS2 DMAC The shortest transmission latency PMAC An adaptive energy-saving protocol 15 ParameterValueParameterValue Number of nodes400Power consumption Transmit, receive, idle, sleep 0.66,0.395,0.35, 0 W Circular of radius250mNode initial energy50J Transmission range75mSimulation time700s Channel capacity10 kb/s First corona2*2 Time frame100ms

16. Simulation results 16

17. Simulation results Fig. 9. Effect of different MAC protocols on the fraction of live sensor nodes at different coronas at simulation times of (a) 100 s, (b) 200 s, and (c) 300 s. 17

18. Simulation results 18

19. Simulation results 19

20. Simulation results 20

21. Simulation results 21

22. Simulation results 22

23. Simulation results 23 The number of nodes for networks with 3, 4, and 5 coronas is 225, 400, and 625.

24. Conclusions The sensor nodes have different loads due to their different distances to the sink The concept of quorum to enable sensor nodes to adjust their sleep durations based on their traffic loads. QMAC QMAC_LR Simulation results verify that our QMAC_LR reduces energy consumption and keeps the latency low. 24