Low Power, Low Delay: Opportunistic Routing meets Duty Cycling Olaf Landsiedel 1, Euhanna Ghadimi 2, Simon Duquennoy 3, Mikael Johansson 2 1 Chalmers University of Technology, Sweden 2 KTH Royal Institute of Technology, Sweden 3 Swedish Institute of Computer Science (SICS), Sweden IPSN 2012 Presenter: SY

This Paper Opportunistic Routing for wireless sensor network – Duty cycled nodes Benefits – Improve energy efficiency – Reduce end-to-end delay – Increase resilience to link dynamics

Unicast Routing in Duty‐Cycled WSNs Routing protocol: selects next hop MAC: wait for next hop to wakeup – Assume: no synchronization

Unicast Routing in Duty‐Cycled WSNs Routing protocol: selects next hop MAC: wait for next hop to wakeup – Assume: no synchronization

Opportunistic Forwarding The node that – Wakes up first – Successflly receives the packet – Provides routing progress Forward the packet

Outline System design Evaluation Conclusion

DODAG Topology: DODAG – Destination oriented directed acyclic graph Requirements of routing metric – Builds loop free DODAG – Minimize energy: radio-on time – Minimize delay

Expected Duty Cycled Wakeups (EDC) Single hop EDC: 1/(sum of neighbors link quality) – Left case: A has a single neighbor with a perfect link, its single hop EDC is 1/1 = 1; – Right case: A has two neighbors both having perfect links, its single hop EDC is 1/(1 + 1) = 0:5; – Middle case: A has two neighbors with link qualities 1 and Its single hop EDC is 1/(1 + 0:25) = 0:8. Single hop EDC Link quality

Overall EDC – Sum of single hop EDC and neighbors’ EDC Which neighbors to include? – Forwarder set Single hop EDC EDC of neighbor Weight

Forwarders Set Sort neighbor nodes by EDC Add one by one (from lowest) Find minimum EDC

Forwarding Cost Forwarding cost w – Constant value, transmission penalty – Increase w decrease forwarders set Fewer hops to destination Increase delay and energy consumption – Too low: increase the risk of routing loop To balance delay and energy with routing progress and stability

Link Estimation Link quality = (Rate of packet overheard)/(forwarding rate) Rate of packet overheard – Wakeup, listen to the radio, record packet overheard Forwarding rate – Header field contain the average forwarding rate Bootstrap – Probing during initialization

Unique Forwarder Make sure only one node forward the packet 1.Majority of cases  only one receiver

Unique Forwarder – Cont. Coordination algorithm – Demand a single ACK If (sender) receives multiple ACK – Resend the packet If (receiver) detect link-layer duplicate – Send second ACK with 50% probability – Data transmission overhearing If overhears same packet, cancels transmission – Network-layer duplication detection Detect duplication at network layer

Outline System design Evaluation Conclusion

Setup Testbed – Indriya(Singapore): 120 nodes – Twist(Berlin): 96 nodes Compare – CTP Metrics – Delay, Duty cycle, # of TX nodes, Reliability Implementation – TinyOS, default MAC – Wakeup every 2s (optimal for CTP) – Randomly generate a packet every 4 minutes

System Calibration Choose w=0.1

Indriya, 0 dBm Tx Power

Indriya, -10 dBm Tx Power

Twist, 0 dBm Tx Power

Impart of Churn Remove average 10 nodes every 15 minutes Reduce from 120 to 30 nodes

Convergence

Wakeup Interval

Outline System design Evaluation Conclusion

Discussion And Limitation Works best at high network density Optimal at lower wakeup rates – Compare to CTP At high wakeup rate – CTP and ORW are similar Not well suited for high throughput applications

Conclusion New routing metric – Taken energy into account Real implementation – Previous works mostly analytical and simulation Paper writing – A bit harder to get the big picture