Distributed Medium Reservation Scheme for Wireless Sensor Networks

1. Distributed Medium Reservation Scheme for Wireless Sensor Networks Parag Garg EE202A Fall 2008 Prof. Mani Srivastava Mentor. Rahul Balani

2. Agenda • Motivation • Distributed Medium Reservation Scheme • DMRS – Messaging Protocol • DMRS – LR Allocation Protocol • Pros and Cons • Demo Setup • Conclusion

3. Agenda • Motivation • Distributed Medium Reservation Scheme • DMRS – Messaging Protocol • DMRS – LR Allocation Protocol • Pros and Cons • Demo Setup • Conclusion

4. Current WSN • Play a part in every aspect of modern living. • Applications are varied e.g. agriculture, health care, assisted living, industrial robots … • Broad functions of sensing, computation and communication. • A smart coordinator node performs complex functions (medium reservation). • Other nodes are simple. • This is very efficient for closely knit small sized network.

5. The Problem • As the network scales, the centralized reservation scheme results in latencies. • Coordinator node not fully aware of local conditions at a node leading to inefficient bandwidth utilization. • Single point of failure problems.

6. The Solution • A scheme which • Performs medium reservation in a decentralized manner. • Performs medium reservation based on current local medium conditions. • Has smarter nodes which are aware of their surroundings. • Provides alternatives in case of network failure.

7. Agenda • Motivation • Distributed Medium Reservation Scheme • DMRS – Messaging Protocol • DMRS – LR Allocation Protocol • Pros and Cons • Demo Setup • Conclusion

8. Distributed Medium Reservation Scheme • DMRS defines • Messaging protocol to increase awareness of each node of its surrounding. • Link resource allocation protocol which makes efficient use of the bandwidth while offering performance guarantees.

9. DMRS objective • Provide Scalability while ensuring • Low Packet latency • Low power consumption • High aggregate network throughput • Efficient bandwidth utilization

10. DMRS overview • Consists of two protocols • DMRS Messaging Protocol • DMRS Link Resource Allocation Protocol • Restricted to the MAC layer. • Executes at every node in the network. • Works in a topology transparent manner.

11. Agenda • Motivation • Distributed Medium Reservation Scheme • DMRS – Messaging Protocol • DMRS – LR Allocation Protocol • Pros and Cons • Demo Setup • Conclusion

12. DMRS – Messaging Protocol overview Specifies the • Superframe structure • Messaging at different phases of LR establishment.

13. DMRS – Messaging Protocol details (1) Specifies three communication windows • Beacon window • “Self-coexistence” beacons are transmitted by the nodes in this window. • Contention based medium access. • Negotiation window • Used to transmit Negotiation frames while establishing Link Resource. • Contention based medium access. • Data transfer window • Used for data packet communication. • Contention free medium access.

14. DMRS – Messaging Protocol details (2) • Module interaction • Translates the Traffic requirements into LR requirements.

15. DMRS – Messaging Protocol details (3) • Messaging during Link resource establishment

16. DMRS – Messaging Protocol details (4) LRA Bitmap used by • LR allocation protocol • Power management module • Transmitter/Receiver module

17. DMRS – Messaging Protocol details (5) Power management

18. Agenda • Motivation • Distributed Medium Reservation Scheme • DMRS – Messaging Protocol • DMRS – LR Allocation Protocol • Pros and Cons • Demo Setup • Conclusion

19. DMRS – LR Allocation Protocol overview • Categorizes available channels based on traffic types • Uplink • Pipeup • Downlink • Pipedown • Specifies Link Resource allocation protocol based on pipelining of multi-hop packets

20. DMRS – LR Allocation Protocol details (1) • Channel categorization • Ensures against scenario where a traffic of a particular type hogs all the available channels

21. DMRS – LR Allocation Protocol details (2) • LR allocation protocol

22. DMRS – LR Allocation Protocol details (3) • Pipelining • LR route information in the packet serves as a guidance for the next node to allocate LR in a manner so as to maximize timeslot overlap.

23. Agenda • Motivation • Distributed Medium Reservation Scheme • DMRS – Messaging Protocol • DMRS – LR Allocation Protocol • Pros and Cons • Demo Setup • Conclusion

24. Pros • Improves the scalability of the network by decentralizing the link resource allocation protocol. • Improves throughput and conserves power by eliminating any time incurred in sensing and collision. Beacon enables virtual CSMA scheme. • Minimizes latencies with respect to packet transfer and link resource establishment. • Maximizes power conservation by low duty cycle of the nodes • Does not mandate beacon transmission in every superframe • Does not mandate listening for the whole beacon or negotiation windows • Addresses the hidden node problem and collocated networks • Both the protocols proposed function in a topology transparent fashion. • Minimizes bandwidth fragmentation. • Based on nominal traffic requirements.

25. Cons • Makes nodes complex • No central entity to allocate link resources, complexity of messaging and LR allocation now also in nodes. • More power consumption • Power gets wasted when node is awake during the beacon window, if no beacon gets transmitted. • Execution of the two protocols. • Wasted bandwidth • Beacon and negotiation windows could have been used for data transfer.

26. Agenda • Motivation • Distributed Medium Reservation Scheme • DMRS – Messaging Protocol • DMRS – LR Allocation Protocol • Pros and Cons • Demo Setup • Conclusion

27. Demo Setup • Network topology • Radio range of nodes

28. Demo Software • Microsoft Visual C++ Express edition IDE • DMRS – Messaging Protocol (Simulation) • DMRS – LR Allocation Protocol (Actual implementation)

29. Agenda • Motivation • Distributed Medium Reservation Scheme • DMRS – Messaging Protocol • DMRS – LR Allocation Protocol • Pros and Cons • Demo Setup • Conclusion

30. Conclusion • Two protocols were proposed in order to improve the Network scalability while • Minimizing packet latency • Minimizing power consumption • Maximizing throughput • Efficient bandwidth utilization • Decentralizing the medium reservation is the only way to enable further proliferation of dense and large scale wireless sensor networks.

31. Q & A

32. References Wireless Sensor Network diagram

33. Further Work • Occasional scanning of medium to sense if particular LRs are unavailable due to collocated device of another type (microwave etc.) and mark these LRs busy. • End-to-end medium reservation requires some global knowledge. How can we fit that in the DMR scheme? • Is it better if we do DMRS only at some nodes and leave others as simple devices? Hierarchy of coordinator nodes and how to synchronize them? • When collocated networks exist how do we synchronize Superframe Start Time? How should networks coalesce? • Is it feasible to change channel structure at run-time? How to communicate this to all the nodes? • How to make sure that there is at least one beacon in a beacon window, so that the collocated network knows about the network? • What happens when the Node B rejects the Allocation request with alternatives? Does A mark its LRA bitmap “busy for B” for those LRs? • Is medium reservation the only hindrance in network scalability? Explore an implementation to ensure that.

34. Assumptions • Routes in the WSN are fixed. • There are no overlapping networks. • There is no need of a channel hopping scheme. • There is minimal penalty for channel switch between transmissions or receptions. • The packet deadline is a soft requirement for the current project. This issue involves multi-hop LR allocation which is not in scope.