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ILLINOIS INSTITUTE OF TECHNOLOGY Frequency Agility in a ZigBee Network for Smart Grid Application Peizhong Yi, Abiodun Iwayemi, Chi Zhou Optical Wireless Integration Lab Electrical and Computer Engineering Department Illinois Institute of Technology IEEE PES Conference on Innovative Smart Grid Technology Jan,20,2010 1

Frequency Agility in a ZigBee Network for Smart Grid Application - Peizhong Yi, Abiodun Iwayemi, Chi Zhou Agenda  Motivation • Objective • Performance of ZigBee and WiFi Coexistence • Interference Avoidance Scheme—Frequency Agility • Test Result and Performance Evaluation • Conclusion • • Future Work 2

Frequency Agility in a ZigBee Network for Smart Grid Application - Peizhong Yi, Abiodun Iwayemi, Chi Zhou Motivation Smart Grid is an intelligent power generation, distribution and control system which seeks to maximize energy efficiency and foster greater adoption of renewable energy sources. IIT Perfect Power Project , a five-year project sponsored by DoE, aims to develop, demonstrate, promote, and commercialize a Perfect Power system that cannot fail to meet the electric needs of the individual end-user. 3

Frequency Agility in a ZigBee Network for Smart Grid Application - Peizhong Yi, Abiodun Iwayemi, Chi Zhou Motivation ZigBee is the most suitable wireless technology to monitor, collect, and analyze data on energy usage in real time for smart grid application.  Low cost  Low power Consumption  Flexible and extendable  Easy and inexpensive to deploy  Global with use of unlicensed radio bands Problem : IEEE 802.11 Wireless Local Area Networks (WLAN) shares the same license-free 2.4GHz Industrial, Scientific and Medical (ISM) frequency band with ZigBee. 4

Frequency Agility in a ZigBee Network for Smart Grid Application - Peizhong Yi, Abiodun Iwayemi, Chi Zhou Objective  Design an efficient interference avoidance scheme which is simple and practicable to ensure the performance of ZigBee with WiFi present  require minimal adjustments to the existing IEEE 802.15.4 standard  avoid a performance penalty  Minimum the usage of system resources. 5

Frequency Agility in a ZigBee Network for Smart Grid Application - Peizhong Yi, Abiodun Iwayemi, Chi Zhou Performance of ZigBee and WiFi Coexistence  Bit Error Rate (BER) and Packet Error Rate (PER)  Assume signal transmission in an Additive White Gaussian Noise (AWGN) channel, with blind transmissions for both IEEE 802.15.4 and IEEE 802.11b π  4 d ≤ 20log ( ) , d d  λ  10 0  =  L ( ) d π p 4 d d  + > 20log ( ) 10 log n , d d  λ 10 10 0  d 0 where path loss exponent n equals to 3.3 and d 0 is 8 meter = BER Q ( 2 SINR ) 6

Frequency Agility in a ZigBee Network for Smart Grid Application - Peizhong Yi, Abiodun Iwayemi, Chi Zhou Performance of ZigBee and WiFi Coexistence T Z T SIFS T ACK,Z L Z U Z T CCA Zigbee Packet ACK T SIFS T DIFS T C T C x A A WLAN WLAN WLAN C C packet packet packet K K T ACK, L W L W U W W T W Fig. 2. IEEE 802.11b and IEEE 802.15.4 Interference Model [2] − = − − × − N T b / I T b / PER 1 [(1 P ) (1 P ) ] z c c b b 7

Frequency Agility in a ZigBee Network for Smart Grid Application - Peizhong Yi, Abiodun Iwayemi, Chi Zhou Performance of ZigBee and WiFi Coexistence 0 10 •Main interference power 2MHz offset 3MHz offset -1 10 concentrate in the WiFi 7MHz offset 8MHz offset central frequency which -2 10 create heavy interference. BER -3 10 -4 10 •Distance is other important factor which can impact -5 10 BER. -6 10 0 1 2 3 4 5 6 7 Distance (m) 8

Frequency Agility in a ZigBee Network for Smart Grid Application - Peizhong Yi, Abiodun Iwayemi, Chi Zhou Performance of ZigBee and WiFi Coexistence P E R w i t h i nt er f er ance 0 10 •Offset frequency is 2MHz, the PER is highest and the distance - 1 10 between the Zigbee and WIFi - 2 access point must be at least 7 10 R E meters. P - 3 10 •Offset frequency is 8MHz , the - 4 2M H z of f set 10 3M H z of f set interference from WiFi is 7M H z of f set 8M H z of f set - 5 negligible. 10 0 1 2 3 4 5 6 7 D i st ance 9

Frequency Agility in a ZigBee Network for Smart Grid Application - Peizhong Yi, Abiodun Iwayemi, Chi Zhou Interference Avoidance Scheme Frequency Agility Start • Interference Send a Packet Detection Scheme NACK Yes ACK received? counter=0 No Done NACK Counter = NACK Counter+1 No NACK Counter >threshold Yes ED on current channel NACK = 0 No RSSI > threshold ? Yes Channel change 10

Frequency Agility in a ZigBee Network for Smart Grid Application - Peizhong Yi, Abiodun Iwayemi, Chi Zhou Interference Avoidance Scheme Frequency Agility •Interference avoidance 22 MHz Channel 1 Channel 6 Channel 11 2437 MHz 2462 MHz 2483.5 MHz 2400 MHz 2412 MHz IEEE 802.11b North American Channel Selection 2 MHz Channel 2405 2410 2420 2425 2430 2435 2440 2445 2450 2455 2460 2465 2470 2475 2415 2480 2400 MHz 2483.5 MHz IEEE 802.15.4 Channel Selection (2.4GHz PHY) 11

Frequency Agility in a ZigBee Network for Smart Grid Application - Peizhong Yi, Abiodun Iwayemi, Chi Zhou Interference Avoidance Scheme Frequency Agility Interference detected •Interference avoidance Yes i=1 i>3 ? No ED on channel class i No Find available i = i+1 channel? Yes available channel i 1 ,i 2 ...i k m=1 Active scan m = m+1 channel i m No Yes Yes Channel m = k? occupied? No Channel change 12

Frequency Agility in a ZigBee Network for Smart Grid Application - Peizhong Yi, Abiodun Iwayemi, Chi Zhou Test Result and Performance Evaluation 13

Frequency Agility in a ZigBee Network for Smart Grid Application - Peizhong Yi, Abiodun Iwayemi, Chi Zhou Test Result and Performance Evaluation • PER = (Number of failed messages / Number of attempted measurements)*100 Experimental PER 40 35 30 25 PER (%) 20 15 10 5 0 2 7 8 13 Offset Frequency (MHz) 14

Frequency Agility in a ZigBee Network for Smart Grid Application - Peizhong Yi, Abiodun Iwayemi, Chi Zhou Test Result and Performance Evaluation • Link Quality Indicator (LQI): indicate the strength or quality of received packet, PER decreases as LQI increases . LQI 250 200 150 LQI 100 50 0 2 7 8 13 Offset Frequency (MHz) 15

Frequency Agility in a ZigBee Network for Smart Grid Application - Peizhong Yi, Abiodun Iwayemi, Chi Zhou Conclusion • Frequency Agility Interference Avoidance algorithm: 1. NACK-based interference detection 2. Energy Detection as an energy saving and accurate interference detection scheme 3. Classified channels’ energy detection in sequence 4. Active scan makes sure the channel is not occupied 16

Frequency Agility in a ZigBee Network for Smart Grid Application - Peizhong Yi, Abiodun Iwayemi, Chi Zhou Future Work •Interference avoidance algorithm will be implemented on real Zigbee board and performance will be measured in real work, especially in cluster-tree topology in the presence of interference from multiple WLAN APs. •Design and develop self-forming and self-healing cluster-tree ZigBee systems •Design and develop MAC Layer protocol to achieve energy-efficient access for cluster-tree networks •Develop a plan to install ZigBee routers in Siegel Hall and design energy- efficient routing algorithm for communications among cluster heads and routers 17

Frequency Agility in a ZigBee Network for Smart Grid Application - Peizhong Yi, Abiodun Iwayemi, Chi Zhou Thank You ! 18