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Slide 1: The Mote Revolution: Low Power Wireless Sensor Network Devices University of California, Berkeley Joseph Polastre Robert Szewczyk Cory Sharp David Culler
Slide 2: Outline Trends and Applications  Mote History and Evolution  Design Principles  Telos  “The Mote Revolution: Low Power Wireless Sensor Network Devices” Hot Chips 2004 : Aug 22-24, 2004 2
Slide 3: Faster, Smaller, Numerous  Moore’s Law   Bell’s Law  “Stuff” (transistors, etc) doubling every 1-2 years New computing class every 10 years Streaming Data to/from the Physical World log (people per computer) year “The Mote Revolution: Low Power Wireless Sensor Network Devices” Hot Chips 2004 : Aug 22-24, 2004 3
Slide 4: Applications   Environmental Monitoring Habitat Monitoring  Integrated Biology  Structural Monitoring e ion tim is Life re c & P cy ion e& cale ct S at te n e R & ility ow La onn i ty ple b c s L Mo Dis Sam Den  Interactive and Control Pursuer-Evader  Intrusion Detection  Automation  “The Mote Revolution: Low Power Wireless Sensor Network Devices” Hot Chips 2004 : Aug 22-24, 2004 4
Slide 5: Open Experimental Platform Services Networking TinyOS WeC 99 “Smart Rock” Rene 11/00 Dot 9/01 Mica 1/02 Telos 4/04 Robust Low Power 250kbps Easy to use Small microcontroller 8 kB code 512 B data Simple, low-power radio 10 kbps ASK EEPROM (32 KB) Simple sensors Designed for experimentation -sensor boards -power boards Demonstrate scale Mica2 12/02 38.4kbps radio FSK NEST open exp. Platform 128 kB code, 4 kB data 40kbps OOK/ASK radio 512 kB Flash Spec 6/03 “Mote on a chip” Commercial Off The Shelf Components (COTS) “The Mote Revolution: Low Power Wireless Sensor Network Devices” Hot Chips 2004 : Aug 22-24, 2004 5
Slide 6: Mote Evolution “The Mote Revolution: Low Power Wireless Sensor Network Devices” Hot Chips 2004 : Aug 22-24, 2004 6
Slide 7: Low Power Operation  Efficient Hardware  Integration and Isolation  Complementary functionality (DMA, USART, etc)  Selectable Power States (Off, Sleep, Standby)  Operate at low voltages and low current  Run to cut-off voltage of power source  Efficient Software  Fine grained control of hardware  Utilize wireless broadcast medium  Aggregate “The Mote Revolution: Low Power Wireless Sensor Network Devices” Hot Chips 2004 : Aug 22-24, 2004 7
Slide 8: Typical WSN Application  Periodic Data Collection  Network Maintenance  Majority of operation  processing data acquisition communication  Triggered Events Power  But… must be reported quickly and reliably  Long Lifetime Months to Years without changing batteries  Power management is the key to WSN success  sleep Time “The Mote Revolution: Low Power Wireless Sensor Network Devices” Hot Chips 2004 : Aug 22-24, 2004 wakeup Detection/Notification  Infrequently occurs  8
Slide 9: Design Principles  Key to Low Duty Cycle Operation:  Sleep – majority of the time  Wakeup – quickly start processing  Active – minimize work & return to sleep “The Mote Revolution: Low Power Wireless Sensor Network Devices” Hot Chips 2004 : Aug 22-24, 2004 9
Slide 10: Sleep   Majority of time, node is asleep  >99% Minimize sleep current through  Isolating  and shutting down individual circuits  Using low power hardware Need RAM retention  Run auxiliary hardware components from low speed oscillators (typically 32kHz)  Perform ADC conversions, DMA transfers, and bus operations while microcontroller core is stopped “The Mote Revolution: Low Power Wireless Sensor Network Devices” Hot Chips 2004 : Aug 22-24, 2004 10
Slide 11: Wakeup   Overhead of switching from Sleep to Active Mode  Radio (FSK) Microcontroller 292 ns 10ns – 4ms typical 2.5 ms 1– 10 ms typical “The Mote Revolution: Low Power Wireless Sensor Network Devices” Hot Chips 2004 : Aug 22-24, 2004 11
Slide 12: Active  Microcontroller Fast processing, low active power  Avoid external oscillators   External Flash (stable storage) Data logging, network code reprogramming, aggregation  High power consumption  Long writes   Radio High data rate, low power tradeoffs  Narrowband radios    Radio vs. Flash  Low power, lower data rate, simple channel encoding, faster startup More robust to noise, higher power, high data rates 250kbps radio sending 1 byte   Energy : 1.5J Duration : 32s Energy : 3J Duration : 78s  Wideband radios   Atmel flash writing 1 byte   “The Mote Revolution: Low Power Wireless Sensor Network Devices” Hot Chips 2004 : Aug 22-24, 2004 12
Slide 13: Telos Platform  A new platform for low power research   Standards Based   Monitoring applications:    Environmental Building Tracking IEEE 802.15.4 USB  IEEE 802.15.4     Long lifetime, low power, low cost Built from application experiences and low duty cycle design principles Robustness    CC2420 radio 250kbps 2.4GHz ISM band   TI MSP430  Ultra low power     Integrated antenna Integrated sensors Soldered connections 1.6A sleep 460A active 1.8V operation Open embedded platform with open source tools, operating system (TinyOS), and designs. “The Mote Revolution: Low Power Wireless Sensor Network Devices” Hot Chips 2004 : Aug 22-24, 2004 13
Slide 14: Low Power Operation  TI MSP430 -- Advantages over previous motes 16-bit core  12-bit ADC    16 conversion store registers Sequence and repeat sequence programmable < 50nA port leakage (vs. 1A for Atmels)  Double buffered data buses  Interrupt priorities  Calibrated DCO   Buffers and Transistors  Switch on/off each sensor and component subsystem “The Mote Revolution: Low Power Wireless Sensor Network Devices” Hot Chips 2004 : Aug 22-24, 2004 14
Slide 15: Minimize Power Consumption   Compare to MicaZ: a Mica2 mote with AVR mcu and 802.15.4 radio Sleep Majority of the time  Telos: 2.4A  MicaZ: 30A   Wakeup As quickly as possible to process and return to sleep  Telos: 290ns typical, 6s max  MicaZ: 60s max internal oscillator, 4ms external   Active Get your work done and get back to sleep  Telos: 4-8MHz 16-bit  MicaZ: 8MHz 8-bit  “The Mote Revolution: Low Power Wireless Sensor Network Devices” Hot Chips 2004 : Aug 22-24, 2004 15
Slide 16: CC2420 Radio IEEE 802.15.4 Compliant  CC2420  Fast data rate, robust signal     250kbps : 2Mchip/s : DSSS 2.4GHz : Offset QPSK : 5MHz 16 channels in 802.15.4 -94dBm sensitivity 1.8V minimum supply 128byte TX/RX buffers for full packet support Automatic address decoding and automatic acknowledgements Hardware encryption/authentication Link quality indicator (assist software link estimation)    Low Voltage Operation  Software Assistance for Low Power Microcontrollers     samples error rate of first 8 chips of packet (8 chips/bit) “The Mote Revolution: Low Power Wireless Sensor Network Devices” Hot Chips 2004 : Aug 22-24, 2004 16
Slide 17: Power Calculation Comparison Design for low power  Mica2 (AVR)        MicaZ (AVR)        Telos (TI MSP)       0.2 ms wakeup 30 W sleep 33 mW active 21 mW radio 19 kbps 2.5V min  0.2 ms wakeup 30 W sleep 33 mW active 45 mW radio 250 kbps 2.5V min  0.006 ms wakeup 2 W sleep 3 mW active 45 mW radio 250 kbps 1.8V min  2/3 of AA capacity 2/3 of AA capacity 8/8 of AA capacity Supporting mesh networking with a pair of AA batteries reporting data once every 3 minutes using synchronization (<1% duty cycle) 453 days 328 days “The Mote Revolution: Low Power Wireless Sensor Network Devices” Hot Chips 2004 : Aug 22-24, 2004 945 days 17
Slide 18: Integrated Antenna Inverted-F Microstrip Antenna and SMA Connector  Inverted-F Psuedo Omnidirectional  50m range indoors  125m range outdoors  Optimum at 2400-2460MHz   SMA Connector Enabled by moving a capacitor  > 125m range  Optimum at 2430-2483MHz  “The Mote Revolution: Low Power Wireless Sensor Network Devices” Hot Chips 2004 : Aug 22-24, 2004 18
Slide 19: Sensors  Integrated Sensors   Expansion 6 ADC channels  4 digital I/O  Existing sensor boards        Sensirion SHT11    Humidity (3.5%) Temperature (0.5oC) Digital sensor Photosynthetically active light Silicon diode Total solar light Silicon diode  Hamamatsu S1087    Hamamatsu S1337-BQ   Magnetometer Ultrasound Accelerometer 4 PIR sensors Microphone Buzzer acoustic mag ultrasound dot “The Mote Revolution: Low Power Wireless Sensor Network Devices” Hot Chips 2004 : Aug 22-24, 2004 19
Slide 20: Conclusions  New design approach derived from our experience with resource constrained wireless sensor networks Active mode needs to run quickly to completion  Wakeup time is crucial for low power operation   Wakeup time and sleep current set the minimal energy consumption for an application  Sleep most of the time   Tradeoffs between complexity/robustness and low power radios Careful integration of hardware and peripherals “The Mote Revolution: Low Power Wireless Sensor Network Devices” Hot Chips 2004 : Aug 22-24, 2004 20