1. Energy-Efficient and Reliable Medium Access in Sensor Networks Authors: Vivek Jain, Ratnabali Biswas and Dharma P. Agrawal Department of Computer Science University of Cincinnati {jainvk, biswasr, dpa}@ececs.uc.edu Presenter: Dr. Younghwan Yoo Department of Computer Science University of Cincinnati ymomo@ececs.uc.edu

2. Outline Wireless Sensor Network Reliable Sensor MAC Hidden Node Problem Energy Efficient Sensor MAC Protocol Design Performance Evaluation Summary Future Work

3. Wireless Sensor Network (WSN) Usually a set of small immobile nodes referred as motes Generally static topology Cheap alternative to monitor inaccessible or inhospitable terrains Applications Medical Applications – wireless bio-sensors Nuclear and chemical plants Environmental monitoring Industrial Automation Ocean monitoring Battlefields

4. Good Reliable MAC Control Overhead Collision Congestion Transmission Rate Control Idle Listening Hidden Node Overhearing Error Recovery Latency Node receives more than one packet at same time Leads to packet loss due to buffer overflow Wastes energy listening to idle channel Wastes energy receiving packets for other nodes Recover packets corrupted at physical layer Wastes energy transmitting control packets Carrier-sense, backoff, transmission, propagation, processing, queuing Reliable Sensor MAC

5. Hidden Node Problem Data ABCD Random Backoff Collision Random Backoff Hidden node problem exists between every other pair nodes along a route RTS/CTS packets constitute large overhead Transmission rate control mechanism employed

6. Efficient-Efficient Sensor MAC Energy-Efficient MAC Adaptive Duty Cycling Wakeup On-Demand Overemitting: Node transmits when receiver not ready for reception Reduces Throughput Increases Latency

7. E2RMAC - Design Two radio solution A Main radio for actual data transmission/reception A low power pico radio to detect and transmit busy tones CSMA/CA based Skip Backoff mechanism: Intermediate receiving node skips random backoff after successful reception Implicit/Explicit Ack Transmission rate control: After receiving implicit Ack refrain from transmitting for 2 communication_duration Adaptive retransmission attempts Retransmission Attempts = Tx_Attempts +, where p e is packet error rate Protocol for always-on requirement, e.g. automotive, telematics

8. E2RMAC – Basic Operation ABCD Wakeup Random Backoff Filter Data Backoff Skipped Processing Delay Transmission Backoff (2xCommunication_Duration + Random_Duration) Wakeup Implicit Ack Propagation and Processing Delays Filter Data Wakeup Filter Data Wakeup Explicit Ack

9. E2RMAC – Handling False Wakeups Wakeup Filter Set ReceiveTimer = 2xCommunication_Duration Data Wakeup Set ReceiveTimer = Communication_Duration Filter Set ReceiveTimer = 2xCommunication_Duration Data Set ReceiveTimer = Communication_Duration A B C X Y Z

10. E2RMAC – Simulation Parameters ParameterValue Packet size77 bytes Filter/CTS size19 bytes RTS size27 bytes Ack size11 bytes Transmission rate250 kbps slotTime1200 µs T SIFS 200 µs CW min 1 CW max 4 Tx_Attempts5 P sensing = P Tx = P Rx 41 mW P sleep 0.015 mW P Tx_on = P Tx_off 35 mW T Tx_on 580 µs P wakeup_sensing = P wakeup_Tx = P wakeup_Rx 0.015 mW

11. Performance Evaluation – Linear Topology All schemes are equally reliable Latency of E2RMAC is higher than RMAC due to latency involved in transmitting filter packets and switching on/off the main radio STEM and E2RMAC are the only energy efficient protocols p e =0.4

12. Performance Evaluation – 8- hop Linear Topology PDR of RTS-CTS based protocols is higher than E2RMAC as it alleviates the hidden terminal problem p e =0.4

13. Performance Evaluation Transmission of control messages by STEM leads to better PDR, poor latency and more energy consumption Due to adaptive retransmissions, E2RMAC tries to deliver old packets first, leading to buffer overflow at source nodes and thus dropping newly generated packet less PDR when p e =0.4

14. Performance Evaluation Energy expended by the common intermediate node Energy Expended by the route nodes E2RMAC consumes less energy by avoiding control overhead, and false wakeup

15. Performance Evaluation E2RMAC and STEM protocol have comparable performances. We can conclude that transmission rate control and other optimizations successfully mitigates the hidden terminal problem

16. Summary – E2RMAC Best suited for dual radio architecture Energy savings largely depends on power consumption of low- power pico radio Minimizing energy consumption Minimum control messages Implicit Ack by wakeup radio Timers to avoid false wakeup Ensuring reliability Adaptive retransmission attempts Implicit/explicit Ack Transmission rate control Minimizing latency Skip backoff mechanism Minimum control overhead

17. Future Work Energy Consumption Analysis for the proposed and existing protocols To be energy-efficient than single radio solution (no sleep cycles), preliminary results suggests that pico-radio should consume less than 25% of Main radio power for E2RMAC 17% of Main radio power for STEM-T 8% improvement over STEM-T

18. Thank You!!! For further queries, please contact the authors

19. Backup Slides

20. Energy Consumption Analysis

21. RMAC – Design Data ABCD Random Backoff Transmission Backoff Implicit Ack Ack Propagation and Processing Delays Backoff Skipped Explicit Ack Processing Delay CSMA/CA based Intermediate receiving node skips random backoff after successful reception Implicit Ack After receiving implicit Ack refrain from transmitting for transmission backoff duration = 2 communication_duration

22. RMAC – Performance Evaluation Linear topology, Packet arrival rate = 5 and 10 pkts/sec respectively Ack-based schemes have better PDR MultiPath and MultiPacket schemes have constant latency per hop as no retransmissions are involved at any node p e =0.2

23. RMAC – Performance Evaluation Even at higher packet error rate, RMAC delivers more than 80% of packets Also, latency per hop of RMAC is less than its Ack-based counterpart p e =0.4

24. RMAC – Performance Evaluation RMAC and CSMA-Ack schemes are compared for 6-hop linear topology by varying p e from 0 to 0.6 RMAC performs better than CSMA- Ack in all scenarios

25. RMAC – Performance Evaluation Two 6-hop routes intersecting at the center node At p e =0.6, RMAC uses slightly more retransmission attempts than CSMA-ACK but delivers more packets with same latency