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Efficient and Reliable Broadcast in ZigBee Networks. Purdue University, Mitsubishi Electric Lab. To appear in SECON 2005. Outline. ZigBee network Broadcast problem Efficient and reliable forward node selection Performance evaluation. ZigBee. - PowerPoint PPT Presentation
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Efficient and Reliable Broadcast in ZigBee Networks
Purdue University, Mitsubishi Electric Lab.
To appear in SECON 2005
Outline
• ZigBee network
• Broadcast problem
• Efficient and reliable forward node selection
• Performance evaluation
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
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)
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
Example
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
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
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
ZiFA
Parent nodes may be missed: recheck
Do the same check for every node to assign state
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)
Illustrative example
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
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
Example
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
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‧
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
Number of rebroadcast node
• Varying network density (increase)• Varying radio range (more neighbor nodes)
Radio range = 25m Radio range = 55m
Coverage time
• Flooding is faster
Performance of ZiFA-R
• Introduce packet loss and retransmission
ZiFA-R has more forward node
Performance of ZiFA-R
Coverage ratio
Highest: flooding & ZiFA-R
Global is low cause it chooses min forward nodes
Performance of ZiRA
ZiRA is lower in coverage time
Conclusion
• Introduce ZigBee network into academic research
• A solution especially for zigbee network