Efficient and Reliable Broadcast in ZigBee Networks

1. Efficient and Reliable Broadcast in ZigBee Networks Purdue University, Mitsubishi Electric Lab. To appear in SECON 2005

2. Outline • ZigBee network • Broadcast problem • Efficient and reliable forward node selection • Performance evaluation

3. ZigBee • ZigBee Alliance: an industrial consortium has 100+ companies working on low-power wireless networked products • ZigBee spec chooses IEEE 802.15.4 (low-rate, low-power) as MAC and PHY layer • Network and higher layer is ratified in Dec. 2004

4. IEEE 802.15.4 • PHY layer: 16 channels in 2.4 ~ 2.4835 GHz (250kb/s); 10 channels in 915 MHz (40kb/s) and 868 MHz (20kb/s) • Provides link quality indication (LQI): quality of the received packet • MAC layer: CSMA/CA (optional: slotted CSMA/CA)

5. ZigBee network layer • The network layer builds a logical topology • A coordinator starts the network and assigns network addresses • The address is in a tree hierarchy • Given the address, all its tree neighbors can be derived

6. Example

7. Broadcast problem • Efficient: reduce the number of rebroadcast nodes • Reliable: packets are received even packet loss • Fast: to cover the network timely • Simple: low complexity in computation and storage

8. ZiFA • ZigBee forward node selection algorithm • Selects a subset of the source’s one-hop neighbors as forwarding node • Remove redundant broadcast • Assumption: every node knows its 1-hop neighbors’ addresses and # children • Every node knows its own tree hierarchy

9. ZiFA Draw the tree hierarchy Start from the bottom level Check whether the children are already the one-hop neighbor M: a set of nodes already covered

10. ZiFA Parent nodes may be missed: recheck Do the same check for every node to assign state

11. Further improve • The broadcast message comes from node u. If we know F(u), we can remove F(u) in our tree topology v receives from u8; F(u8)={v,u2)

12. Illustrative example

13. ZiFA-R • Reliability extension of ZiFA • The source node will wait until all its neighbors rebroadcast data. If not received, retransmission. • For ZiFA, non-forward node will not rebroadcast

14. ZiFA-R • Observation: broadcast data has higher probability to be received if sent by tree neighbors • At least one tree neighbor of a non-forward node should be a forward node

15. Example

16. Rebroadcast - ZiRA • Now it’s efficient and reliable, but may not be fast • Collisions occur if nodes blindly broadcast simultaneously • Solution: add a random waiting time • While waiting, it can reduce its candidate set based on the newly arrived data

17. Determine random wait • LQI: smaller LQI, longer distance • Might cover more nodes • Smaller waiting time • Degree: |N(v)| - |TN(u)| • Larger degree, more new nodes covered • Smaller waiting time • T = k ‧LQI / Degree

18. Simulation • ZigBee1: only tree neighbors as forward nodes • ZigBee2: all 1-hop neighbors rebroadcast • To avoid redundancy, ZiRA is implemented in ZigBee1,2 • Global: lower bound of forward node (approximation) • Other existing algorithms requires 2-hop neighbor information • Not suitable for ZigBee

19. Number of rebroadcast node • Varying network density (increase) • Varying radio range (more neighbor nodes) Radio range = 25m Radio range = 55m

20. Coverage time • Flooding is faster

21. Performance of ZiFA-R • Introduce packet loss and retransmission ZiFA-R has more forward node

22. Performance of ZiFA-R Highest: flooding & ZiFA-R Global is low cause it chooses min forward nodes Coverage ratio

23. Performance of ZiRA ZiRA is lower in coverage time

24. Conclusion • Introduce ZigBee network into academic research • A solution especially for zigbee network