EM-MAC: A Dynamic Multichannel Energy-Efficient MAC Protocol for - - PowerPoint PPT Presentation

EM-MAC: A Dynamic Multichannel Energy-Efficient MAC Protocol for Wireless Sensor Networks

Lei Tang, Yanjun Sun, Omer Gurewitz, and David B. Johnson

Presentation at ACM MobiHoc 2011, May 2011

The Objectives of EM-MAC

Jammer

• Spread traffic to multiple channels - reduce collisions.
• Efficiently deliver packets under interference (e.g. Wi-Fi) or

even under jamming attack.

• High energy efficiency.

Wi-Fi

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Outline 1. Introduction 2. Related Work

• Control Channel-based, e.g., Y-MAC
• No Control Channel, e.g., MuChMAC

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Control Channel+1

Control Channel-based: Y-MAC

Control Channel node1 First transmit at control channel node2 node4 node3 node2 node4 Downsides:

• 1. Control channel becomes system bottleneck.
• 2. Unable to deliver packets if control channel is bad.
• 3. Require global time synchronization.

Time

…

slot

No Control Channel: MuChMAC

Pseudorandom channel switching Channel i Channel j node1 Time Downsides:

• 1. Utilize a fixed set of channels, irrespective of their conditions.
• 2. Node can only receive packets in its own slots.
• 3. Synchronization of time slots.

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node1

Outline 1. Introduction 2. Related Work 3. EM-MAC 3.1 Predictive Multichannel Wake-up 3.2 Precise and Quick Multichannel Rendezvous 3.3 Dynamic Channel Selection

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EM-MAC: Efficient Multichannel MAC

S:

S wakes up right before R’s predicted wakeup DATA B A S sends DATA packet in response to wakeup beacon DATA B A i j k

R:

i j k B DATA B DATA A B

Pseudorandom time

R wakes up on pseudorandomly chosen (channel, time) Time Channel

• Minimize energy consumption by predicting receiver wakeup.
• Asynchronous multichannel wakeup: no global time synchronization,

flexible, and spread traffic to channels. A

Pseudoranom channel

Receive ACK

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Send Receive Node awake

Precise and Quick Multichannel Rendezvous

• Critical to energy efficiency and packet delivery.
• Challenging: two freedoms (time and channel).
• EM-MAC introduces:
• adaptive receiver time modeling technique, and
• exponential chase algorithm

Picture from “Catch Me If You Can” movie wallpaper. 8

Exponential Chase Algorithm

S:

S’s prediction of R’s wakeup time i j k

R:

i j k B DATA A B Time S misses receiving R’s beacon B S double its wakeup advance time S doubles advance again S misses R’s wakeup again DATA B A S remains awake to send data

• Quickly re-rendezvous by exponentially increasing waiting window.
• Maintain high energy efficiency even upon sender missing receiver.

EM-MAC Adaptive Time Modeling

S:

DATA B A DATA B A i j k

R:

i j k B DATA A B DATA A B

Detect if need to re-compute receiver clock rate

Time

If needed, request update and re-compute clock rate of R S’s Time S’s model of R’s Time Adaptively compute the relative clock rate between S and R

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Dynamic Channel Selection

• Each node senses and adapts to channel conditions.
• Dynamically avoid any bad channels such as with heavy

traffic, interference, or jamming.

i j k B BAD Time m B B B B

This node has sensed channel j as bad and so avoids waking up on it.

BAD BAD BAD BAD BAD BAD

• Node maintains a badness metric for each channel.
• Channel is blacklisted if its badness metric exceed a threshold
• Channel badness metric increases on observations:

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Measuring Channel Conditions

In EM-MAC, channel condition is obtained for free as a byproduct of wakeup and packet transmission.

i j k B B Channel busy before wakeup beacon Channel busy after wakeup beacon but no valid packet received Time No ACK received after sending data DATA B

Outline 1. Introduction 2. Related Work 3. EM-MAC 4. Evaluation on MICAz motes 4.1 Performance under Interference/Jamming 4.2 Performance in Multihop Networks 4.3 Performance of Multichannel Rendezvous

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Performance Under ZigBee Interference

Interferer 1 Interferer 2 Interferer 3 Interferer 4 Sender Receiver

Performance Under ZigBee Jamming

Jammer Sender Receiver

• Under jamming, Y-MAC and PW-MAC are unable to deliver any packets.
• EM-MAC maintains high energy efficiency, low latency, and 100% PDR.

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Performance Under Wi-Fi Interference

Sender Receiver Under Wi-Fi interference, EM-MAC maintains high energy efficiency, low latency, and 100% PDR.

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Multihop Network Performance

Up to 3 multihop traffic flows of hop-length from 1 to 4 1 packet/s per flow, average wakeup interval 1 s.

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Sender Duty Cycle with Increasing Hop-Length and Num-Flows

EM-MAC achieved the lowest duty cycle in all experiments

Delivery Ratio with Increasing Hop-Length and Num-Flows

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EM-MAC maintained 100% PDR in all experiments

Delivery Latency with Increasing Hop-Length and Num-Flows

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EM-MAC achieved lowest delivery latency in all experiments

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Performance Under Large Clock Rate Difference

Even when receiver clock rate is much faster than sender’s clock, EM-MAC achieves small duty cycle and delivery latency Receiver clock accelerated by 3000 ppm (normal < 100 ppm)

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Performance of Exponential Chase

• Each time prediction error doubles, only one extra

exponential chase iteration is needed.

• During exponential chase procedure, sender still maintains a

low duty cycle (e.g., 6.7% in our experiments).

Deliberately created prediction error on sender to test how quickly sender re-rendezvous with receiver

Exponential chase

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Conclusion

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• EM-MAC is the first asynchronous dynamic predictive

multichannel energy efficient MAC protocol.

• EM-MAC adapts to changing channel conditions

through dynamic channel selection.

• EM-MAC presents an efficient solution for precise

and quick predictive multichannel rendezvous.

• EM-MAC achieved 100% PDR, small delivery latency

and high energy efficiency, under multihop, ZigBee interference and jamming, and Wi-Fi interference experiments.

• The higher the network traffic or interference is, the

larger the performance margin of EM-MAC over other tested protocols.

Questions?

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