1. Medium Access Control With Coordinated Adaptive Sleeping for Wireless Sensor Networks Debate 1 - Defense Joseph Camp Anastasios Giannoulis

2. Problem Statement Wireless sensor nodes have vastly different energy requirements than 802.11-type nodes Require long periods of being idle Less stringent demands on per-node fairness, latency, and throughput Network has global objective in contrast to selfish objectives Need for scalability (unlike TDMA)

3. Energy Waste 802.11 and TDMA MACs Sources of Energy Waste Idle listening (50%-100% of energy consumed for receiving) Collision/Retransmission Overhearing Control Packet Overhead Need for redesign of MAC for sensor networks -- Sensor-MAC (S-MAC)

4. Existing MACs Contention-based 802.11 high energy consumption [SK97] PAMAS reduces overhearing, but needs 2 radios Does not reduce idle listening TDMA-based (i.e. Bluetooth and LEACH) Not scalable--hard to change frame length and time slot assignment Low bandwidth utilization (FDMA, CDMA) Adaptive rate control for fairness (not objective here) Piconet had low-duty-cycle operation, but not coordinated Power-Save (PS) 802.11 for single hop networks

5. Energy Reduction Techniques Periodic Listen and Sleep Coordinate sleep schedules Maintain synchronization Collision/Overhearing Avoidance Physical carrier sensing Virtual carrier sensing (RTS/CTS and keep track of NAV) Overhearing avoidance Message passing--fragment bursts

6. Technique 1: Periodic Listen and Sleep Each node has schedule table about neighbors Node first listens for synchronization period If hears neighbor’s schedule, follows that schedule Else it sets its own schedule; If it then hears a schedule One schedule -> follows new schedule Multiple schedules -> adopts all schedules

7. Technique 1: Periodic Listen and Sleep Maintaining synchronization Counter clock drift by… Relative time stamps instead of absolute Receiver subtracts transmission time Listening period >> clock drift Adaptive listening Wake at end of neighbor’s tx to forward data Known from control packets

8. Technique 1: Periodic Listen and Sleep Latency Analysis Common delays to both 802.11 and S-MAC Propagation and processing (ignored) Backoff and Queueing (none for light traffic) Carrier Sense and Transmission SMAC-specific delay -- sleep delay Average Latency Without sleeping With sleeping, without adaptive listening With sleeping and adaptive listening

9. Technique 1: Periodic Listen and Sleep Without sleeping (t cs + t tx ) Sleeping, no adaptive listening (T f ) Sleeping and adaptive listening (T f / 2) * T f >> (t cs + t tx )

10. Technique 2: Overhearing Avoidance Overhearing Avoidance After RTS directed for another, go to sleep Neighbors of both sender and receiver Message Passing Technique to transmit long message Transmitting entire message high probability of corruption/wasted air time -> wasted energy Burst fragments of packet after one RTS/CTS (less control overhead)

11. Protocol Implementation Initial Implementation on Rene Motes 802.11-like MAC S-MAC without sleep S-MAC with sleep Current Implementation on Mica Motes Duty-cycle selection Fully active mode Disable adaptive listen Modes: Rx (14.4 mW), Tx (36 mW) and Sleep (15uW)

12. Results: Measurement of Energy Consumption Two-Hop Network 802.11 (no sleep) S-MAC (no sleep) Overhearing avoidance and message passing S-MAC (with sleep - 50% duty cycle) 802.11 uses > twice the energy as S-MAC Periodic sleep gains at greater than 4 s Rene Motes

13. Results: Measurement of Energy Consumption No sleep vs. sleep similar result for multihop Mica Motes Adaptive listen not as beneficial for energy savings as latency…

14. Results: Adaptive Listen and End-to-End Latency Save equal energy with 10% duty cycle (previous slide) yet achieve performance close to no sleep 1/5 latency with adaptive listening Without adaptive listening message has to wait one sleep cycle each hop

15. Results: More on Latency Similar results for average packet latency for highest traffic load Highlights variance of latency: Adaptive Listen reduces variance of latency

16. Results: E2E Throughput Less throughput than no sleep 10% duty w/ adaptive listen - 1/2 10% duty w/out adaptive listen - 1/8 Results inversely hold for throughput At 10 s inter-arrival period, all schemes have enough throughput 1/2 1/8

17. Energy Time Cost Per Byte All factors incorporated with Energy-time cost per byte 10% duty cycle with adaptive listen performs best for all traffic loads Heavy Load (< 4 s) Work with duty cycles

18. Unique Contributions Implement low-duty-cycle scheme for multihop sensor network Employ adaptive listening to reduce latency In-channel signaling to avoid energy waste Message passing to reduce control overhead Measurement and evaluation of S-MAC (tradeoff of energy, latency, and throughput)

19. Summary Well-written, well-motivated paper Identify objective, origins of problem, relate to existing work, and contribute solutions to the identified problems Combine theory and practice to validate solution Clearly define where the solution would have the most benefit Neutralize tradeoff between energy, latency, and throughput

20. High Impact Motivated work in the future 107 citations in three years! First released as a technical report in September, 2002 and submitted to journal in January, 2003 Additional work in MAC for sensor networks (pioneering paper for sensor networks) Ten of the papers that cited this work have 9 or more citations, one of which has 71 citations INFOCOM’02 Paper (almost same text) has 638 citations 30 papers that cited this work w/ 50 citations or more!