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Medium Access Control With Coordinated Adaptive Sleeping
for Wireless Sensor Networks
Debate 1 - Defense
Joseph Camp
Anastasios Giannoulis
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)
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)
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
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
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
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
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
Technique 1:Periodic Listen and Sleep
Without sleeping (tcs + ttx)
Sleeping, no adaptive listening (Tf)
Sleeping and adaptive listening (Tf / 2)
* Tf >> (tcs + ttx)
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)
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)
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
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…
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
Results: More on Latency
Similar results for average packet latency for highest traffic load
Highlights variance of latency: Adaptive Listen reduces variance of latency
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
1/21/8
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
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)
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
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!