1. 2005/8/2NTU NSLAB1 Self Organization and Energy Efficient TDMA MAC Protocol by Wake Up for Wireless Sensor Networks Zhihui Chen and Ashfag Khokhar ECE/CS University of Illinois at Chicago IEEE SECON 2004 Presented by Jeffrey

2. 2005/8/2NTU NSLAB2 Outline Introduction Channel and Traffic Assumption TDMA-W: Details –Self-Organization –TDMA-W Channel Access Protocol –Performance Analysis of TDMA-W Simulation Results Conclusion

3. 2005/8/2NTU NSLAB3 Outline Introduction Channel and Traffic Assumption TDMA-W: Details –Self-Organization –TDMA-W Channel Access Protocol –Performance Analysis of TDMA-W Simulation Results Conclusion

4. 2005/8/2NTU NSLAB4 Wireless Sensor Networks (WSNs) Are Unique Traffic rate is very low –Typical communication frequency is at minutes or hours level Sensor networks are battery powered and recharging is usually unavailable –Energy is an extremely expensive resource

5. 2005/8/2NTU NSLAB5 Wireless Sensor Networks (WSNs) Are Unique Sensor nodes are generally stationary after their deployment Sensor nodes coordinate with each other to implement a certain function –Traffic is not randomly generated as those in mobile ad hoc networks

6. 2005/8/2NTU NSLAB6 Previous Energy-Efficient MAC Protocols for WSNs “An Energy-Efficient MAC Protocol for Wireless Sensor Networks” –W. Ye, J. Heidemann and D. Estrin –IEEE INFOCOM ’02 –S-MAC (10% S-MAC)

7. 2005/8/2NTU NSLAB7 Previous Energy-Efficient MAC Protocols for WSNs “An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks” –T. Dam and K. Langendoen –ACM SENSYS ’03“ –T-MAC

8. 2005/8/2NTU NSLAB8 Concentrate traffic to fixed periods? Increases contention probability Incurs unnecessary retransmissions S-MAC proposes to perform RTS/CTS handshake procedure Duty rate or portion of listening period of S-MAC should be carefully chosen T-MAC adapts duty cycle to the traffic rate

9. 2005/8/2NTU NSLAB9 Previous Energy-Efficient MAC Protocols for WSNs “Energy-Efficient, Collision-Free Medium Access Control for Wireless Sensor Networks” –V. Rajendran, K. Obraczka and J.J. Garcia-Luna-Aceves –ACM SENSYS ’03 –TRAMA

10. 2005/8/2NTU NSLAB10 Scheduling Data transmissions are scheduled in advance to avoid contention TDMA-W –TDMA-Wakeup –Each node is assigned two slots –Transmission/Send slot (s-slot) –Wakeup slot (w-slot)

11. 2005/8/2NTU NSLAB11 56781234567812 1 ZZZZZZ ZZZZZZ Listen Wake up Nd3 Send ZZZZZZ ZZZZZZ ZZZZZZ ZZZZZZ ZZZZZZ Listen ZZZZZZ ZZZZZZ ZZZZZZ 2 ZZZZZZ ZZZZZZ ZZZZZZ Wake up Nd3 ZZZZZZ Send ZZZZZZ ZZZZZZ ZZZZZZ ZZZZZZ ZZZZZZ Listen ZZZZZZ ZZZZZZ 3 ZZZZZZ ZZZZZZ Wake up Nd4 Listen Send ZZZZZZ ZZZZZZ ZZZZZZ ZZZZZZ Listen ZZZZZZ ZZZZZZ 4 ZZZZZZ ZZZZZZ Wake up Nd6 ZZZZZZ ZZZZZZ ListenSend ZZZZZZ ZZZZZZ Listen ZZZZZZ ZZZZZZ ZZZZZZ 5 ZZZZZZ ZZZZZZ Wake up Nd6 ZZZZZZ ZZZZZZ ZZZZZZ ZZZZZZ Send ZZZZZZ Listen ZZZZZZ ZZZZZZ ZZZZZZ 6 ZZZZZZ ZZZZZZ ZZZZZZ ZZZZZZ ZZZZZZ ZZZZZZ ZZZZZZ ZZZZZZ ZZZZZZ ZZZZZZ

12. 2005/8/2NTU NSLAB12 Outline Introduction Channel and Traffic Assumption TDMA-W: Details –Self-Organization –TDMA-W Channel Access Protocol –Performance Analysis of TDMA-W Simulation Results Conclusion

13. 2005/8/2NTU NSLAB13 Channel and Traffic Assumption Ideal physical layer –The only reason for packet loss is transmission contention –No packet loss due to noise Three types of traffic pattern –One-to-all broadcast –All-to-one reduction –One-hop random traffic

14. 2005/8/2NTU NSLAB14 Channel and Traffic Assumption A TDMA-W frame lasts for T frame seconds T frame is known to all nodes and is preset before deployment A TDMA-W frame is divided into slots Each node is assigned one slot for transmission and one slot for wakeup Networks are synchronized

15. 2005/8/2NTU NSLAB15 Outline Introduction Channel and Traffic Assumption TDMA-W: Details –Self-Organization –TDMA-W Channel Access Protocol –Performance Analysis of TDMA-W Simulation Results Conclusion

16. 2005/8/2NTU NSLAB16 Self-Organization Assign time slots to the sensors within each TDMA-W frame Assume sensor networks has data rate of 1 Mbps Transmission of a 512 byte packet occupies the channel for about 3.9 ms Assume a TDMA-W frame of 1 second divided into 256 slots –Each slot is of 3.9 ms –Capable of communicating 512 bytes

17. 2005/8/2NTU NSLAB17 Self-Organization Scheme 1.Each node randomly selects a slot with uniform probability among all slots to be its s-slot 2.During its selected s-slot, each node broadcasts –Its node ID –Its s-slot number –Its one-hop neighbors’ IDs and their s-slot assignments –Slot number of any s-slot during which this node has identified a collision

18. 2005/8/2NTU NSLAB18 Self-Organization Scheme 3.When a node is not transmitting, it turns on its receiver circuit and listens to the traffic from neighbors The node should record all the information being broadcast by all its neighbors Their s-slot assignments and their node IDs The slot number of any slot being broadcast as a collision-prone slot

19. 2005/8/2NTU NSLAB19 Self-Organization Scheme 4.If a node determines that –it is involved in a collision –or finds out that one of its two-hop neighbors has the same s-slot –It then randomly selects an unused slot and go to step 2

20. 2005/8/2NTU NSLAB20 Self-Organization Scheme 5.If –no new nodes are joining in –or s-slot assignments are not changing –or no collisions are detected for a certain period –It implies all neighbor nodes are found and all the s-slots are final

21. 2005/8/2NTU NSLAB21 Self-Organization Scheme 6.Each node broadcasts the s-slot selections of their two-hop neighbors. Each node identifies an unused slot or any s-slot being used by the nodes beyond its two-hop neighbors and declares it as its w- slot Note that w-slots need not be unique 7.Each node broadcasts its w-slot and the self-organization is complete

22. 2005/8/2NTU NSLAB22 Can Detect Any Two-hop Collisions

23. 2005/8/2NTU NSLAB23 Undetectable One Hop Collision To solve this problem –Let a node go to the listening mode in its assigned s-slot with a probability

24. 2005/8/2NTU NSLAB24 Deadlock To listen during s-slot with a probability To set a collision counter

25. 2005/8/2NTU NSLAB25 Outline Introduction Channel and Traffic Assumption TDMA-W: Details –Self-Organization –TDMA-W Channel Access Protocol –Performance Analysis of TDMA-W Simulation Results Conclusion

26. 2005/8/2NTU NSLAB26 TDMA-W Channel Access Protocol 1.Each node maintains a pair of counters for every neighbors –Outgoing counters –Incoming counters –These counters are preset to an initial value 2.If no outgoing data is sent to a node in a TDMA-W frame –The node decrements the corresponding outgoing counter by one –Otherwise it resets the counter to the initial value

27. 2005/8/2NTU NSLAB27 TDMA-W Channel Access Protocol 3.If no incoming data is received from a neighboring node in a TDMA-W frame –The node decrements the corresponding incoming counter by one –If the counter is less than or equal to zero, the node stop listening to that slot starting from next TDMA-W frame

28. 2005/8/2NTU NSLAB28 TDMA-W Channel Access Protocol 4.If a outgoing data transmission request arrives –The node first checks the outgoing counter –If the counter is greater than zero, then the link is considered active and the packet can be sent out during the s-slot –If the counter is less than or equal to zero, a wakeup packet is sent out during the w-slot of the destination node prior to the data transmission

29. 2005/8/2NTU NSLAB29 TDMA-W Channel Access Protocol 5.If a node receives a wakeup packet in its w-slot –It turns itself on during the s-slot corresponding to the source node ID contained in the wakeup packet –If a collision is detected in the w-slot More than one node intends to send data The node then searches all its neighbors for incoming traffic

30. 2005/8/2NTU NSLAB30 Packet Content Wakeup packet contains only the source and the destination information Data packet may only contain the destination information –Omit source ID since the source ID is determined by the s-slot

31. 2005/8/2NTU NSLAB31 Broadcast If a data packet is to be broadcast to multiple nodes –The destination address contains a special identifier to mark it as a broadcast message –Before sending a broadcast data packet The node should wakeup all its neighbors that intend to receive this packet In the case when multiple users share the same w- slot –The destination field of the wakeup message should also be set to a broadcast address

32. 2005/8/2NTU NSLAB32 Outline Introduction Channel and Traffic Assumption TDMA-W: Details –Self-Organization –TDMA-W Channel Access Protocol –Performance Analysis of TDMA-W Simulation Results Conclusion

33. 2005/8/2NTU NSLAB33 Performance Analysis of TDMA-W Let us fix the position of the w-slot

34. 2005/8/2NTU NSLAB34 Average Delay

35. 2005/8/2NTU NSLAB35 Outline Introduction Channel and Traffic Assumption TDMA-W: Details –Self-Organization –TDMA-W Channel Access Protocol –Performance Analysis of TDMA-W Simulation Results Conclusion

36. 2005/8/2NTU NSLAB36 Deployment of Sensor Nodes Nodes are deployed randomly in a 500x500 sq. ft. area Communication range is 100 feet for all nodes Assume an IEEE 802.11 basic rate of 1 Mbps as the physical layer transmission rate Slot length is set to be 4 ms –Long enough for transmitting a 512-byte packet T frame is set to one second –A TDMA-W frame has 250 slots

37. 2005/8/2NTU NSLAB37 Simulation Results of Self- Organization Protocol

38. 2005/8/2NTU NSLAB38 Power Consumption Power consumption –Transmission : Receiving/Listening : Sleeping = 1.83 : 1 : 0.001 10% S-MAC –Use RTS/CTS frames to reserve channel for node-to- node traffic –Use ACK packet to acknowledge the successful transmission –If data or ACK packet is corrupted by collision, the data packet is retransmitted

39. 2005/8/2NTU NSLAB39 Power Consumption The network is synchronized –All the nodes become active at the same time All data packets are fixed to be 256 bytes in length Control packets (RTS, CTS, ACK in S- MAC and Wakeup packet in TDMA-W) are about 20 bytes in length Assume energy consumption for a control packet is 1/10 of a data packet

40. 2005/8/2NTU NSLAB40 Power Consumption Initial value for counters is set to 3 Transmission buffer length is set to 50 packets Both TDMA-W and S-MAC are run for 10 minutes

41. 2005/8/2NTU NSLAB41 Power Consumption of One-Hop Random Traffic

42. 2005/8/2NTU NSLAB42 Delay of Random One-Hop Traffic

43. 2005/8/2NTU NSLAB43 Delay of All to One Reduction Operation Traffic

44. 2005/8/2NTU NSLAB44 Outline Introduction Channel and Traffic Assumption TDMA-W: Details –Self-Organization –TDMA-W Channel Access Protocol –Performance Analysis of TDMA-W Simulation Results Conclusion

45. 2005/8/2NTU NSLAB45 Conclusion Efficient protocols TDMA-W for self- organization and channel access control in wireless sensor networks are proposed Proposed protocols were verified using extensive simulations Proposed protocols only consume 1.5% to 15% power of 10% S-MAC –6 to 67 times better than 10% S-MAC

46. 2005/8/2NTU NSLAB46 Conclusion Proposed scheme responds to the event with a delay comparable to S-MAC for one-hop traffic Proposed protocol is collision free for data traffic so reliable transmission is guaranteed for all types of traffic

47. 2005/8/2NTU NSLAB47 Comments Strength –Great improvement in the power consumption Weakness –Verify results by using simulation (MATLAB) with not so practical assumptions –Delay could be significant –Scalability would be poor Large overhead in memory

48. 2005/8/2NTU NSLAB48 Thank you very much for your attention!