TreeMAC: Localized TDMA MAC Protocol for Real-time High-data-rate Sensor Networks

1. TreeMAC: Localized TDMA MAC Protocol for Real-time High-data-rate Sensor Networks Wen-Zhan Song, Renjie Huang, Behrooz Shirazi Sensorweb Research Laboratory, Washington State University Richard LaHusen Cascades Volcano Observatory, U.S. Geological Survey IEEE PerCom 2009

2. Outline • Introduction • Related Works • Goal • TreeMAC Protocol Principles and Design • Sensor Tested Evaluation • Conclusion

3. Introduction • Wireless sensor network MAC protocol • Non Real-time WSN • Event oriented WSN • Low duty-cycle • Low data-rate • Energy conservation • Real-time WSN • Monitoring industrial processes、geophysical environments WSN • High duty-cycle • High data-rate • High throughput • Low congestion

4. 1 1 1 1 1 1 Allocation slot Introduction • Real-time WSN MAC • If using equal channel access traditional MAC protocols • Not fair resource allocation • ALOHA • CSMA • … Sink congestion c 6 a d b f e

5. Introduction • Real-time WSN MAC protocol design • Fair resource allocation • Nodes in a network should get channel access opportunity proportional to their demands. • Limited resource • The limited radio bandwidth available to sensor nodes • Packet loss problem • Congestion • Interference • Multipath effects

6. Related Works • Three categories • Synchronized approaches • TDMA, Pre-scheduled wake-up pattern • S-MAC (INFOCOM 2002), T-MAC (SenSys 2003) • Asynchronous approaches • CSMA, Independent wake-up pattern • B-MAC (SenSys 2004) • Hybrid approach • CSMA + TDMA • Z-MAC (2005)

7. Related Works [8] M. Ma and Y. Yang. “Funneling-mac: A localized, sink-oriented mac for boosting fidelity in sensor networks,” ACM SenSys, 2006. • Funneling-MAC[8] • Hybrid TDMA and CSMA protocol • It uses TDMA scheduling in the intensity region to mitigate the funneling effect. • CSMA in the rest of the network to provide flexibility. funneling effect Packet loss, packet collision, congestion and high delay time

8. Related Works [8] M. Ma and Y. Yang. “Funneling-mac: A localized, sink-oriented mac for boosting fidelity in sensor networks,” ACM SenSys, 2006. • Funneling-MAC[8] • Disadvantages • The sink node has relatively longer transmission range and can reach all nodes in intensity region. • Only operates in the intensity region close to the sink and not across the complete sensor field.

9. Goal • On real-time wireless sensor network. • To design localized TDMA MAC protocol to achieve high throughput and low congestion.

10. TreeMAC Protocol Principles and Design • Assumption • Every node has same transmission power. • Every node has constant bit rate traffic. • It divides time into cycles. • It divides each cycle into N frames and each frame into 3 slots {0,1,2} • 1 cycle = N · frames = N · 3slots. If N = 16

11. Sink TreeMAC Protocol Principles and Design • Many-to-one routing generation • CSMA • Using Shortest Path Tree • Each node finds the lowest cost path to the root. • Consider radio signals strength. o p a l b n f c m h g d k e i j

12. Sink 1+3 1 1 1 TreeMAC Protocol Principles and Design • Obtaining Tree Structure Information • CSMA • Discover neighbors and collect information • Hop-count • Slot demand (itself + subtree nodes) o p a l b n f c m h g d k e i j

13. TreeMAC Protocol Principles and Design • Slot assignment in a frame • Avoid vertical two-hop interference • Frame assignment in a cycle • Avoid horizontal two-hop interference • TreeMAC packet scheduling

14. Sink Sink Sink TreeMAC Protocol Principles and Design • Slot assignment in a frame • Avoid vertical two-hop interference 1-hop Sa=0 1-hop a 1-hop a Sa=0 Sa=0 a interference interference 2-hop b 2-hop Sb= 0 b 2-hop Sb=1 b 3-hop Sc= 0 c 3-hop c 3-hop Sc= 2 Slot=2 Slot=0 Slot=1 c 4-hop Sd= 0 d Su {0, 1, 2}: the assigned transmittable time slot of each frame to node u. lu: the depth of node u in the routing tree, e.g., hop count to the sink.

15. Sink Sa=(1 – 1 )mod 3=0 Sb=(2 – 1 )mod 3=1 allocation Sc=(3 – 1 )mod 3=2 allocation TreeMAC Protocol Principles and Design • Slot assignment in a frame • Avoid vertical two-hop interference • Each node u calculates its transmittable time slot • If a node u gets X slots assigned from it’s parent, then it can assign at most X − x slots to its children, where x is its own slot demand. 1-hop a 2-hop b localized TDMA MAC 3-hop c Su {0, 1, 2}: the assigned transmittable time slot of each frame to node u. lu: the depth of node u in the routing tree, e.g., hop count to the sink.

16. Sink Sink 1-hop 1-hop a a 2-hop 2-hop 2-hop 2-hop c c b b TreeMAC Protocol Principles and Design • Frame assignment in a cycle • Avoid horizontal two-hop interference • Each node u assigns its children frames. Fu: the assigned frames set of each cycle to node u. For sink node, Fsink is the set of all N frames. Cu: the children set of node u. Cu: the k-th child of node u.

17. Sink TreeMAC Protocol Principles and Design • Frame assignment in a cycle • Avoid horizontal two-hop interference • Each node u assigns its children frames. 1-hop a 2-hop 2-hop c b Fu: the assigned frames set of each cycle to node u. For sink node, Fsink is the set of all N frames.

18. TreeMAC Protocol Principles and Design • Frame assignment in a cycle • Avoid horizontal two-hop interference • Each node u assigns its children frames. a c b d βu: the slot demands of node u. Note that there are many ways to reflect bandwith demand with tradeoffs. γu: the number of pending packets generated by node u itself in the link layer packet queue. Certainly, γu≦βu. Cu: the children set of node u. Cu: the k-th child of node u.

19. TreeMAC Protocol Principles and Design • Frame assignment in a cycle • Avoid vertical two-hop interference • Each node u assigns its children frames. faireness βu: the slot demands of node u. Note that there are many ways to reflect bandwith demand with tradeoffs. γu: the number of pending packets generated by node u itself in the link layer packet queue. Certainly, γu≦βu. Cu: the children set of node u. Cu: the k-th child of node u.

20. data conrtol msg sender receiver receiver data TreeMAC Protocol Principles and Design • TreeMAC packet scheduling • Let F be the current frame per cycle • S be current slot per frame, each node u takes the following actions: If u=b, S=2 If u=b, S=0 If u=b, S=1 Sa=0 Sa=0 Sa=0 a a a Sb=1 b Sb=1 b Sb=1 b Sc=2 c c Sc=2 c Sc=2

21. Sleep/snoop sleep/snoop sleep data TreeMAC Protocol Principles and Design • TreeMAC packet scheduling • Let F be the current frame per cycle • S be current slot per frame, each node u takes the following actions: If u=c, F=3, S=2 If u=c, F=4, S=1 If u=c, F=4, S=0 Fa={1,2,3,4,5} Sa= 0 Fa={1,2,3,4} , Sa= 0 Fa={1,2,3,4} , Sa= 0 a a a control msg Fb={2,3} ,Sb=1 d c b Fc=4, Sc=1 Fd=5 ,Sd=1 b c d b c d Fc=3 ,Sc=1 Fd=4 ,Sd=1 Fb=2 ,Sb=1 Fc=3 ,Sc=1 Fd=4 ,Sd=1 Fb=2 ,Sb=1 Fb=3 ,Se=2 e

22. Sensor Tested Evaluation • Simulation on TinyOS sensor network test bed. • Imote2 sensor mote • An advanced wireless sensor node platform. • CPU: PXA271 XScale • 802.15.4 compliant radio chip: CC2420 • effective data rate: 250 kbps • Work in a low frequency(13 MHz) mode • Data payload size: 74 bytes • Sensor nodes: 24 • Simulation area size: 4×6 grid • Comparison Protocols • Funneling-MAC • CSMA

23. Sensor Tested Evaluation • Evaluation Parameter

24. Sensor Tested Evaluation • Evaluation Results • Network throughput fixed data rate 8 pps. 24 nodes packet per second

25. Sensor Tested Evaluation • Evaluation Results 24 nodes and fixed data rate 8 pps.

26. Sensor Tested Evaluation ri : the average rate of packets delivered from the ith sensor N : the number of sensors in the network. • Network Fairness fairness index:

27. Sensor Tested Evaluation • Signaling Overhead

28. Conclusion • TreeMAC is an innovative localized TDMA MAC protocol and designed to achieve high throughput and low congestion with low overhead. • TreeMAC in theory and demonstrated that it achieves much better throughput and energy efficiency than CSMA and Funneling-MAC in a real sensor network test bed.