1. Exploring the Energy-Latency Trade-off for Broadcasts in Energy-Saving Sensor Networks Matthew J. Miller, Cigdem Sengul, Indranil Gupta Department of Computer Science University of Illinois Urbana-Champaign IEEE ICDCS 2005.6

2. outlines Introduction Energy-efficient Communication in Wireless Sensor Networks Probability-Based Broadcast Forwarding (PBBF) Analytical Results Simulation Results Conclusion Future Work

3. Introduction Sensor nodes are inherently resource constrained. Offer better reliability and performance to a sensor network application Provide enough flexibility for a designer to choose the appropriate operation point on the resource-performance spectrum.

4. Introduction Broadcast is useful to applications for disseminating sensor data, instructions, and code updates. The goal is to design a broadcast protocol that allows a range of operating points from which an application designer can choose. PBBF (Probability-Based Broadcast Forwarding), which is a MAC-layer approach and can be integrated into any sleep scheduling protocol

5. Related Work Gossip-Based Ad Hoc Routing [5], site percolation model Achieving a given level of reliability requires the probability of forwarding to be beyond a threshold. The approach does not allow an energy-latency trade- off. PBBF protocol bond percolation model Two knobs, p and q, can be tuned to explore the energy-latency trade-off.

6. Energy-efficient Communication in Wireless Sensor Networks Efficient Broadcast Protocols Sleep Scheduling Mechanisms

7. Efficient Broadcast Protocls SPIN protocols [6,MobileCom 1999] Incorporate negotiation in order to avoid deficiencies of the class flooding approach. [15][16] Virtual infrastructure [5,Infocom 2002][13] To forward a message with some probability (i.e., gossip)

8. Sleep Scheduling Mechanisms reduce energy consumption in WSNs Active-sleep cycle IEEE 802.11 PSM, S-MAC, T-MAC Additional low-power wake- up radio problem Increasing latency redundant packets

9. Probability-Based Broadcast Forwarding (PBBF) PBBF exploits the redundancy in broadcast communication and forwards packets using a probability-based approach The goal is to ensure that, with high probability, a node receives at least one copy of each broadcast packet, while reducing the latency due to sleeping. p=0.5q=0.5 N1 N2 N3

10. The two Knobs p It is the probability that a node rebroadcasts a packet immediately without ensuring that any of its neighbors are active q It is the probability that for a given node and a given time instant when it is supposed to be asleep due to its active-sleep schedule, the node instead stays awake in the expectation that it might be a receiver of an immediate broadcast

11. Probability-Based Broadcast Forwarding (PBBF) PBBF exploits the redundancy in broadcast communication and forwards packets using a probability-based approach The goal is to ensure that, with high probability, a node receives at least one copy of each broadcast packet, while reducing the latency due to sleeping. p=0.5q=0.5 N1OO N2 ♦ X N3XO

12. Probability-Based Broadcast Forwarding (PBBF) PBBF exploits the redundancy in broadcast communication and forwards packets using a probability-based approach The goal is to ensure that, with high probability, a node receives at least one copy of each broadcast packet, while reducing the latency due to sleeping. p=0.5q=0.5 N1 ♦ O N2OO N3 ♦♦

13. Probability-Based Broadcast Forwarding (PBBF) PBBF exploits the redundancy in broadcast communication and forwards packets using a probability-based approach The goal is to ensure that, with high probability, a node receives at least one copy of each broadcast packet, while reducing the latency due to sleeping. p=0.5q=0.5 N1 ♦ O N2OO N3 ♦♦

14. Pseudo-code for PBBF Sleep-Decision-Handler() 1 /* Called at the end of active time */ 2 /* If stayOn is true, remain on; otherwise sleep*/ 3 stayOn  false 4 5 If DataToSend=ture or DataToRecv=true 6 then 7 stayOn  ture 8 else if Uniform-Rand(0,1) < q 9 then stayOn  true --------------------------------------------------------------------------------------- Receive-Broadcast(pkt) 1. /* Called when broadcast packet pkt is received */ 2. If Uniform-Rand(0,1) < p 3. then Send(pkt) 4. else Enqueue(nextPktQueue,pkt)

15. Analytical Results Reliability Energy Latency Energy-Latency Trade-off

16. Reliability The reliability of PBBF protocol can be analyzed using percolation model. Percolation model, [3] Bond percolation Site percolation

17. Site Percolation Theory

19. Bond Percolation Theory

21. Percolation Theory [3] G(V,E) : an infinite connected graph C o : the set of nodes, which can be reached by a specific node n o Θ bond (P edge ) : the probability of the component C o being of infinite size so that Θ bond (P edge )=0 if P edge <P c bond (G)

22. Reliability (PBBF) The probability of A  B is p·q+(1-p) p·q : A broadcasting the message immediately after reception and that B being awake at the time (1-P) : a rebroadcast when B is awake Each edge in the network is open with this probability. Remark 1 (p and q for high reliability): If P edge =1-p·(1-q) ≧ P c bond (G), the broadcast is received at infinitely many node.

23. Reliability (PBBF) - simulator Fig.4. Threshold behavior for 90% reliability Fig.5. Threshold behavior for 99% reliability

24. Reliability (PBBF) - simulator Fig.6. P c bond for various grid sizesFig.7. Relationship between p and q for a given reliability level in a 30*30 grid network

25. Energy Fig.8. Average energy consumption.

26. Latency L: the expected time between A sending the broadcast and B receiving it from A,[4][10]

27. Latency - simulator Fig.9. Average hops traveled by an update to reach a node 20 hops from the source Fig.10. Average hops traveled by an update to reach a node 60 hops from the souce

28. Latency - simulator Fig.11. Average per-hop update latency.

29. Energy-Latency Trade-off Fig.12. Energy-Latency trade-off for 99% reliability.

30. Simulation Results Environment parameter assume perfect synchronization in the network Ns-2 The values of our parameters are based on Mica2 Mote hardware Run time:500 sec Each data point is averaged over ten runs ParameterValue N5625(75*75) P TX 81mW PIPI 30mW PSPS 3μW λ0.01 pakcets/s L1L1 ≈1.5s T frame 10s T active 1s q0.25 ∆ (node density)10.0 Total Packet Size64bytes Data Packet Payload30bytes

31. The impact of the q parameter Fig.13. Average energy consumption

32. The impact of the q,p parameter Fig.14. 2-hop average update latencyFig.15. 5-hop average update latency

33. The impact of the q,p parameter Fig.16. Average updates received

34. The impact of △ Fig.17. Average update latencyFig.18. Average updates received

35. Conclusion PBBF is an efficient broadcast mechanism PBBF provides an application designer the opportunity to tune the system to an appropriate operating point along the reliability-resource-performance spectrum.

36. Future Work Explore how PBBF can be augmented to improve performance The p and q parameters could be adjusted dynamically by nodes Compare its performance with other adaptive sleep protocols.

37. Thank you