1. EM-MAC: A Dynamic Multichannel Energy-Efficient MAC Protocol for Wireless Sensor Networks 2014. 11. 11 Bonhyun Koo Lei Tang*, Yanjun Sun †, Omer Gurewitz ‡, and David B. Johnson* *Department of Computer Science, Rice University, Houston, TX, USA † Systems and Applications R&D Center, Texas Instruments, Dallas, TX, USA ‡ Department of Communication Systems Engineering, Ben Gurion University, Israel MobiHoc’11

2. Contents 1. Introduction (Goal and Contributions) 2. Related Works 3. EM-MAC Protocol Design - Design Overview - Dynamic Channel Selection - Precise and Quick Multichannel Rendezvous 4. Performance Evaluation - Multichannel Rendezvous - Multihop Networks - Wireless Interference 5. Conclusion

3. 1. Goal and Contributions Problem 1) Traffic Loads (Energy Efficient Operation and Robust Support for varying) 2) Wireless Interference (Example. Jamming Attacks) Purpose - Introduction of novel mechanism (EM-MAC) for adaptive receiver-initiated multichannel rendezvous and predictive wake-up scheduling - A predictive and asynchronous duty-cycling MAC protocol (no control channel, dynamic channel selection) Validation  The lowest Sender and Receiver duty cycles and packet delivery latency  100% packet delivery ratio (PDR)

4. 2. Related Works - Comparison with previous MAC Protocols Channel TypeProtocolsProblems Single Radio Channel S-MAC, B-MAC, RI-MAC, PW-MAC, DW-MAC Limitation of Network Throughput Multiple Orthogonal Radio Channel Y-MAC, A-MAC, MMAC, CAM-MAC (Dedicated) Control Channel (interference, jamming attack) Multiple Channel MMSN, TMMAC (Assuming) Precise Time Synchronization MuChMAC Fixed Channel Set (without adapting to Channel Conditions)

5. 3. EM-MAC (Design Overview) Sender S, Receiver R Only three of the channels (i, j, and k) At the time of R’s second beacon, no node has a packet waiting to send to R. Protocol Example MICAz motes N ch = 16, T maxInterval =1500ms (500~1500ms) EM-MAC is a receiver-initiated MAC protocol A node sends a wake-up beacon to notify potential senders (awake and ready to receive data packets)

6. 3.1 EM-MAC Protocol Design EM-MAC uses a pseudorandom function (LCG : Linear Congruential Generator) Applied to (1) Channel and (2) Wake-up Time X n+1 = (aX n + c) mod m m > 0 is the modulus, a : multiplier c : increment X n : current seed X n+1 becomes the next seed m =7, a=3, c=0, X 0 =6 Example) X 1 = (3x6 + 0) mod 7 = 4 X 2 = (3x4 + 0) mod 7 = 5 X 7 = (3x2 + 0) mod 7 = 6 : 6,4,5,1,3,2, 6,4,5… period : m-1(6) X n+1 = (aX n + c) mod m XnXn X n+2 = (aX n+1 + c) mod m X k = (aX k-1 + c) mod m : Node’s MAC address

7. 3.1 EM-MAC Protocol Design (Sender) Prediction Mechanism - Predicts the wake-up times and channels of a receiver based on ‘prediction state’ : Sender (S) Receiver (R) : N ch = 16 T maxInterval =1500 ms T black = 100 s 1 2 3 4 16 1 2 3 4 Ch. Waiting T black + 2 x N ch x T maxInterval DATA I want to send my DATA! B B DATAB B set a flag (in Header) prediction state information (a, c, X n, timestamp) Channel next : (300x10+300) mod16 = 4 Interval next : (300x60+300) mod500= 100 (ms) Example: (300, 300, {10,60}, timestamp) B DATAB B B

8. 3.2 Dynamic Channel Selection 1) Detecting Channel Conditions 2) Multichannel Rendezvous with Blacklisted Channels - Nodes maintains for each channel “badness” metric. Ch.badness 15 21 :: 162 - Every Nodes maintains its own channel blacklist Reset after T black Time (1000 ms) (badness = 0) Assignment 2 bytes to Header

9. 3.3 Precise and Quick Multichannel Rendezvous 1) Adaptive Time Modeling 2) Sender Wake-up Time & Exponential Chase Algorithm y = kx + b  k=1 case, it doesn’t need additional clock sync. y 1 = kx 1 +b y 2 = kx 2 +b DATA B B set a flag (in Header) timestamp y : the current time of R x : the current time of S k : clock rate difference b : initial clock difference Sender (S) Receiver (R) BB #1#2 wake-up advance time Fail reset wake-up advance time >T giveup Decision powered off or out of range

10. 4. Evaluation on MICAz MOTES 1) Performance on Multichannel Rendezvous Experimental Environments (S)(R) R’s clock rate was Increased (until the sender failed) Node wake-up interval : 1 s Wake-up adv. Time : 20 ms 30 times (repeat) R’s clock rate was accelerated by 3000ppm

11. 4. Evaluation on MICAz MOTES 3) Performance with Wireless Interference Performance With Wireless Interference and Jamming 2) Performance on Multihop Networks #flow1 #flow2 #flow3 28-byte data packet (every second)