Utilization Based Duty Cycle Tuning MAC Protocol for Wireless Sensor Networks Shih-Hsien Yang, Hung-Wei Tseng, Eric Hsiao-Kuang Wu, and Gen-Huey Chen Computer Science and Information Engineering, National Taiwan University, Taipei, Taiwan, R.O.C. Computer Science and Information Engineering, National Central University, Chung-Li, Taiwan, R.O.C. Global Telecommunications Conference, GLOBECOM '05. IEEE

2 Outline Introduction Related Work U-MAC Design Simulation Conclusion

3 Introduction Wireless sensor network are formed by a great quantity of sensor nodes. Battery-powered and not recharge easily Prolong the lifetime of the nodes is an important issue. Lowering energy consumption may result in higher latency

4 Related work- DSMAC A B listen sleep listen sleep listen sleep listen sleep listen (My queue is empty || avg delay 10%) Halve 20% 80% 10% 90%

5 Related work- DSMAC A B listen sleep listen sleep listen sleep listen (0 < current energy consumption level < T E && avg delay > D max && my duty cycle < 40%) Double 10% 90% 20% 80%

6 U-MAC Design Several problems arise from the adoption of S-MAC Uniform duty cycle Different tasks assign a fixed duty cycle Latency:Sleep delay Idle listening after transmission A node will keep idle listening until next frame after data transmission if ends inside the sleep period DSMAC tunes duty cycle by doubling or halving According to delay and the emptiness of packet queue. Source node: 0,1 Sink : 3,4 Intermediate node:

7 U-MAC Design A. Various Duty Cycle B. Utilization Based Tuning of Duty Cycle C. Selective Sleeping After Transmission

8 U-MAC Design- Various Duty Cycle Each node can be assigned different periodically listen and sleep schedules As in S-MAC Nodes exchange schedules and synchronize clock with their neighbors with a fixed period Nodes receiving SYNC packets will not adopt the same schedule from their neighbors

9 U-MAC Design- Utilization Based Tuning of Duty Cycle Every nodes in a sensor network have their own different traffic loads According to what tasks they take and locations Sending node: compute the suffered sleep delay (d) during the current transmission, and attach d in the following data packets Receiving node: extracts d from data packet and adds d to the total sleep delay D, and refresh the packet count

10 U-MAC Design- Utilization Based Tuning of Duty Cycle Sleep delay Total delay

11 Threshold of high traffic load Upper limit of duty cycle Threshold of low traffic load Lower bound of duty cycle Average sleep delay

12 U-MAC Design- Utilization Based Tuning of Duty Cycle A’ A listen sleep listen sleep listen sleep listen U >U high and duty cycle < DCmax Increase n% 10% 90% 15% 85% listen

13 U-MAC Design- Utilization Based Tuning of Duty Cycle A’ A listen sleep listen sleep listen sleep listen sleep listen U DC min and D <D max Decrease n% 20% 80% 15% 85%

14 U-MAC Design- Selective Sleeping After Transmission Idle listening after transmission Idle: waste energy

15 U-MAC Design- Selective Sleeping After Transmission Selective Sleeping When transmission is finished, a node checks if it is at scheduled sleep time It goes to sleep if it’s at scheduled sleep time

16 Simulation NS-2 Initial duty cycle: 20% Bandwidth:20kbps Data packet size:400Bytes (10Bytes for SYNC,RTS,CTS) Transmission power Receiving power Idle power Sleeping power mW 13.5 mW 15 W 15 μ W DC max DC min U high U low D max40%10% seconds ± ± n% (2%)

17 Simulation Topology 1 Energy consumptionLatency UMAC w/o SS: Without selective sleep

18 Simulation Topology 1 The duty cycle for all nodes node2 node4 Node 1 node3 node0

19 Topology 2 Simulation Energy consumptionLatency

20 Conclusion U-MAC balance between energy consumption and latency Assign proper duty cycles for nodes with different tasks and network locations U-MAC includes several schemes Various duty cycle Utilization based tuning of duty cycles Selective sleeping after transmission

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