1. Self Organization and Energy Efficient TDMA MAC Protocol by Wake Up for Wireless Sensor Networks Zhihui Chen and Ashfaq Khokhar ECE Department, University of Illinois at Chicago IEEE International Conference on Sensor and Ad Hoc Communications and Networks (SECON 2004)

2. Outline Introduction Overview TDMA-W Protocol Simulation Results Conclusion

3. Introduction --- Sensor Networks General properties Low traffic rate Low power Battery recharging is usually unavailable Stationary sensor nodes MAC protocol Constraint Low traffic rate Power resource Objective Optimize the node lifetime

4. Introduction --- Proposed MAC Protocol Key idea The host can sense their arrivals and open the door at the right time TDMA-based A TDMA frame for each node s-slot (Transmit/Send slot), w-slot (Wakeup slot) Procedure Self-organization Channel Access Advantage Collision-free

5. Overview s-slot for each node is unique in its two-hop range several nodes can share a w-slot nodes 1, 4 and 5: w-slot (slot 7) nodes 2, 3 and 6: w-slot (slot 8) idea assumption network topology channel activity

6. Channel and Traffic Model Single channel Fixed transmission range Communication range is a circle Packet loss is only due to transmission contention Events are Poisson distributed Network is synchronized

7. TDMA-W Protocol --- Self-Organization Procedure s-slot selection START END s-slot announcement w-slot selection w-slot announcement collision ? terminated ? random selection Packet broadcast (node ID, s-slot number, one-hop neighbors’ IDs, and their s-slot assignments) Check whether one of the 2-hop neighbors has the same s-slot no new nodes join s-slot assignments are not changed no collisions are detected Packet broadcast (s-slot selections of all 2-hop neighbors) s-slot announcement Unused slot or any s-slot being used by the nodes beyond its 2-hop neighbors Packet with w-slot broadcast No Yes

8. TDMA-W Protocol --- Channel Access counters initialization self-organization send w-slot packet during w-slot of destination send data during s-slot any outgoing data ? out_counter < 0 ? decrease out_counter send data during s-slot No Yes No Yes receive data any incoming data ? Yes decrease in_counter No go to sleep in_counter < 0 ? keep listening No Yes turn on during the s-slot of the sender any wakeup packet ? Yes do nothing No in_counter out_counter

9. Simulation Results --- Parameters Simulation toolMATLAB communication toolbox No. of nodes100 Area size 500ft  500ft Data rate1M bps (IEEE 802.11 DSSS basic rate) Slot length4 ms TDMA-w frame duration1 sec (i.e., 1 TDMA frame has 250 slots) Data packet length256 bytes Control packet length about 20 bytes (RTS, CTS, ACK in S-AMC; Wakeup packet in TDMA-W) Buffer length5 initial counter value3

10. Simulation Results More collision happened  time for self-organization increases with the increase in the number of nodes

11. Simulation Results --- Power Consumption Simulation time: 600 secs TDMA-W: 0.16% ~ 0.7%, 10% S-MAC: 4.7% ~ 10.1%  power consumption of TDMA-W is only 1.5% ~ 15% as much as S-MAC  network lifetime of TDMA-W is 6.67 times longer than 10% S-MAC One-hop random traffic One-to-all broadcast operation traffic All-to one reduction operation traffic

12. Simulation Results --- Transmission Delay One-hop random traffic All-to one reduction operation traffic High traffic load (event arrival rate > 0.5)  delay in S-MAC increase due to congestion Delay for TDMA-W is much higher than S-MAC  traffic can travel multiple hops in a second in S-MAC  traffic can only travel one hop in a second in TDMA-W

13. Conclusion Efficient protocols for Self-organization and channel access control TDMA-based Save much power than 10% S-MAC Collision-free Reliable transmission is guaranteed Feasible delay