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