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  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 Jammer 2

Outline 1. Introduction 2. Related Work  Control Channel-based, e.g., Y-MAC  No Control Channel, e.g., MuChMAC 3

Control Channel-based: Y-MAC … node2 node4 Control Channel+1 Time node1 node2 node3 node4 Control Channel slot First transmit at control channel Downsides: 1. Control channel becomes system bottleneck. 2. Unable to deliver packets if control channel is bad. 3. Require global time synchronization. 4

No Control Channel: MuChMAC node1 Channel i Channel j Time node1 Pseudorandom channel switching 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. 5

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 6

EM-MAC: Efficient Multichannel MAC Send Receive Node awake S wakes up right before R ’s predicted wakeup Channel S sends DATA packet in response to wakeup beacon i Receive ACK S: j B DATA A Pseudoranom channel k B DATA A Time i B Pseudorandom time R: j B DATA A k B DATA A R wakes up on pseudorandomly chosen ( channel, time )  Minimize energy consumption by predicting receiver wakeup.  Asynchronous multichannel wakeup: no global time synchronization, 7 flexible, and spread traffic to channels.

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

Exponential Chase Algorithm S ’s prediction of R ’s wakeup time S misses receiving R ’s beacon S double its wakeup advance time S remains awake S doubles advance again to send data i S misses R ’s wakeup again S: j B DATA A k Time i B R: j B DATA A k B  Quickly re-rendezvous by exponentially increasing waiting window.  Maintain high energy efficiency even upon sender missing receiver.

EM-MAC Adaptive Time Modeling S ’s model of R ’s Time Adaptively compute the relative clock rate between S and R S ’s Time If needed, request update and Detect if need to re-compute re-compute clock rate of R receiver clock rate i S: j B DATA A k B DATA A Time i B R: j B DATA A k B DATA A

Dynamic Channel Selection  Each node senses and adapts to channel conditions.  Dynamically avoid any bad channels such as with heavy traffic, interference, or jamming. This node has sensed channel j as bad and so avoids waking up on it. i B j BAD BAD BAD BAD BAD BAD BAD k B B m B B Time 11

Measuring Channel Conditions In EM-MAC, channel condition is obtained for free as a byproduct of wakeup and packet transmission.  Node maintains a badness metric for each channel.  Channel is blacklisted if its badness metric exceed a threshold  Channel badness metric increases on observations: No ACK received after sending data Channel busy before wakeup beacon i B DATA j B Time k B Channel busy after wakeup beacon but no valid packet received 12

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 13

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. 15

Performance Under Wi-Fi Interference Sender Receiver Under Wi-Fi interference, EM-MAC maintains high energy efficiency, low latency, and 100% PDR. 16

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. 17

Sender Duty Cycle with Increasing Hop-Length and Num-Flows EM-MAC achieved the lowest duty cycle in all experiments 18

Delivery Ratio with Increasing Hop-Length and Num-Flows EM-MAC maintained 100% PDR in all experiments 19

Delivery Latency with Increasing Hop-Length and Num-Flows EM-MAC achieved lowest delivery latency in all experiments 20 20

Performance Under Large Clock Rate Difference Receiver clock accelerated by 3000 ppm (normal < 100 ppm) Even when receiver clock rate is much faster than sender’s clock, EM-MAC achieves small duty cycle and delivery latency 21

Performance of Exponential Chase Deliberately created prediction error on sender to test how quickly sender re-rendezvous with receiver 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). 22

Conclusion  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. 23

Questions? 24