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 (low- rate, low-power) as MAC and PHY layer Network and higher layer is ratified in Dec. 2004

IEEE PHY layer: 16 channels in 2.4 ~ 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 = 25mRadio 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