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