Sensor and energy-efficient networking

1. Sensor and energy-efficient networking CSE 525: Advanced Networking Computer Science and Engineering Department Winter 2004 Oregon Graduate Institute

2. Energy efficient MAC • An energy-efficient MAC protocol for wireless sensor networks by W. Ye, J. Heidemann, and D. Estrin • An Energy Efficient MAC Protocol for Wireless LANs by E. Jung and N. Vaidya • Energy efficient communications in ad hoc networks using directional antennas by A. Spyropoulos and C. Raghavendra Oregon Graduate Institute

3. Motivation • Challenged Networks are normally battery operated, hence power limited • Other goals: • Self-configuration • good scalability • collision avoidance • Fairness and latency are NOT important Oregon Graduate Institute

4. Conventional MAC Layer • An access mechanism for nodes that ensure that NO two nodes have access to the communication channel concurrently • If air is clear, send; for receiving, wait • How do we know when to receive? • Listen always! • Usually designed to allow for maximum throughput • Hence not energy-efficient Oregon Graduate Institute

5. Sources of energy inefficiency • Collision • Overhearing • Control packet overhead • Idle listening Oregon Graduate Institute

6. #1: S(sensor)-MAC • It is contention based • Tries to reduce wastage of energy from all four sources of energy inefficiency • Collision – by using RTS and CTS • Overhearing – by switching the radio off when the transmission is not meant for that node • Control overhead – by Message Passing • Idle listening – by Periodic Sleep Oregon Graduate Institute

7. There is no FREE dinner! • In exchange there is some reduction in both per-hop fairness and latency • But this does not necessarily result in lower end-to-end application fairness and latency – Which acceptable in Challenged Network Oregon Graduate Institute

8. Periodic Listen and Sleep • Each node go into periodic sleep mode during which it switches the radio off and sets a timer to awake later • To reduce control overhead, neighboring nodes are synchronized (i.e. Listen and sleep together) Oregon Graduate Institute

9. Periodic Listen and Sleep • Broadcasting schedule to all its immediate neighbor • neighbor can have different schedules. • If multiple neighbor want to talk to a node, use 802.11 (RTS/CTS) like contention scheme • After they start data transmission, they do not follow their sleep schedules until they finish transmission. Oregon Graduate Institute

10. Choosing and Maintaining Schedules • Each node maintains a schedule table that stores schedules of all its known neighbors. • To establish the initial schedule (at the startup) following steps are followed: • A node first listens for a certain amount of time. • If it does not hear a schedule from another node, it randomly chooses a schedule and broadcast its schedule immediately. • This node is called a SYNCHRONIZER. Oregon Graduate Institute

11. Choosing and Maintaining Schedules • If a node receives a schedule from a neighbor before choosing its own schedule, it just follows this neighbor’s schedule. • This node is called a FOLLOWER and it waits for a random delay and broadcasts its schedule. Oregon Graduate Institute

12. Border Nodes • If a node receives a different schedule after it selects and broadcasts its own schedule, it adopts both schedules • Border nodes consume more energy Oregon Graduate Institute

13. Maintaining Synchronization • Timer synchronization among neighbors are needed to prevent the clock drift. • Synchronizer needs to periodically send SYNC to its followers. • If a follower has a neighbor that has a different schedule with it, it also needs update that neighbor. Oregon Graduate Institute

14. Maintaining Synchronization • Time of next sleep is relative to the moment that the sender finishes transmitting the SYNC packet • Receivers will adjust their timer counters immediately after they receive the SYNC packet • Listen interval is divided into two parts: one for receiving SYNC and other for receiving RTS Oregon Graduate Institute

15. Timing Relationship of Possible Situations Oregon Graduate Institute

16. Collision/Overhearing Avoidance • Collision Avoidance: 802.11 • RTS/CTS • NAV: virtual carrier sense • Physical carrier sense • Overhearing Avoidance • Go to sleep if overhear RTS/CTS packet • NAV • Avoid overhearing “long” data packet • All immediate neighbors of both sender and receiver go to sleep Oregon Graduate Institute

17. Message Passing • Short packets are used in wireless networks • More robust • Overhead of control packets (RTS/CTS) • In-network processing requires a complete msg • Divide the long message into small fragments and transmit them in a burst. • RTS/CTS/Data1/Ack1/Data2/Ack2/…/DataN/AckN • If a packet is lost, extend the duration and immediately retransmit it • Data and Acknowledge include a field of duration Oregon Graduate Institute

18. Delay includes: Carrier sense Back off Transmission Propagation Processing Queuing Sleeping Energy Savings vs. Increased Latency Oregon Graduate Institute

19. Conclusions and Future work • S-MAC has good energy conserving properties comparing to IEEE 802.11 Future work • Analytical study on the energy consumption and latency • Analyze the effect of topology changes Oregon Graduate Institute

20. #2: EEM for WLAN • Optimize PSM in the DCF in IEEE 802.11 Standard • Dynamic PSM (DPSM) • What is PSM? • PSM for DCF, divide time into intervals called beacon intervals, each node in power save mode periodically wakes up at the beginning of beacon interval for a duration called ATIM [Ad-hoc Traffic Indication Message] window to exchange control information. Oregon Graduate Institute

21. What’s wrong? • Fixed ATIM window does not perform good in all situation • Adaptive mechanism to dynamically adjust ATIM window • Synchronization of beacon interval of initially partitioned network • Not addressed; it assumes, there is a way to synchronize Oregon Graduate Institute

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23. Dynamic - PSM • Each node chose its own ATIM window size based on network traffic condition • Allow to increase and decrease the ATIM window dynamically; ATIMmin is defined as minimum level • Move into doze state, after completing packet transmission, if remaining time is not “too-small” – Save Energy Oregon Graduate Institute

24. Dynamic - PSM • Piggyback own window size on all transmitted packets • Packet marking use to adjust ATIM window Oregon Graduate Institute

25. Dynamic - PSM • Rules to increase ATIM • Pending packet can’t be announce in current window time • Based on piggyback information • Receiving an ATIM frame after ATIM window • Received a marked packet • Rules to decrease ATIM • If node successfully announce ATIM frame and none of the above rule satisfied Oregon Graduate Institute

26. Result • Simulation result shows that DPSM improves energy consumption without degrading performance • Only when energy gain from doze state is more then energy loss [overhead of beacon, ATIM and ATIM-ACK frame] • Energy save in doze mode is 96% compare to idle mode. Oregon Graduate Institute

27. #3: Directional Antenna • Energy efficient routing and scheduling algorithm in ad hoc network where each node has single directional antenna. • Using topology consisting of all the possible link in the network, find shortest cost path to be energy efficient. • Calculate the amount of traffic that has to go over each link and find the maximum amount of time each link can be up. • Schedule node’s transmissions, trying to minimize the total time it takes for all possible Tx-Rx pairs to communicate with each other. Oregon Graduate Institute

28. Conclusion and future work • Benefits of using directional antennas in ad hoc networks. • Energy efficient algorithm for routing. • Scheduling • 45% improvement in network life time that is achieved by using energy-aware routing. • Future work • Multicasting and broadcasting in ad hoc networks with directional antennas • Scheduling algorithm in this context Oregon Graduate Institute

29. Related work • TDMA Based • Naturally have a duty cycle • It is not easy to change the slot assignment dynamically, hence scalability is not as good as contention based • Requires nodes to form real communication clusters and managing inter-cluster communication is difficult • Out-of band solutions [PAMAS]: • Requires extra band for signaling Oregon Graduate Institute

30. Questions? Oregon Graduate Institute