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David E. Culler University of California, Berkeley Arch Rock Corp. July 13, 2007

Wireless Embedded Systems and Networking Foundations of IP-based Ubiquitous Sensor Networks Micro-Power Systems. David E. Culler University of California, Berkeley Arch Rock Corp. July 13, 2007. Micro-Power System Architecture. Evaluation Metrics Eff solar = P on / P maxP

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David E. Culler University of California, Berkeley Arch Rock Corp. July 13, 2007

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  1. Wireless Embedded Systems and NetworkingFoundations of IP-based Ubiquitous Sensor NetworksMicro-Power Systems David E. Culler University of California, Berkeley Arch Rock Corp. July 13, 2007 AIIT Summer Course - D#

  2. Micro-Power System Architecture • Evaluation Metrics • Effsolar = Pon / PmaxP • Effsystem = (EL1+ … + ELn + Econs) / Esol AIIT Summer Course - D#

  3. An Example Prometheus Design estimates • Solar energy scavenging system for Telos • Super capacitors buffer energy • Lithium rechargeable battery as a backup • Uses MCU to manage charge cycles to extend system lifetime • Manage limited recharges • Simple, carefully developed design • Redesigned for TRIO deployment • Boosting and current limiting • Developed reactive power management software architecture • Demonstrated in REALITY AIIT Summer Course - D# Perpetual Environmentally Powered Sensor Networks, Jiang, Polastre, Culler, IPSN/SPOTS, 2005

  4. Facts • E = P * T AIIT Summer Course - D#

  5. Energy Storage AIIT Summer Course - D#

  6. Energy and Power Density AIIT Summer Course - D#

  7. Battery Chemistry AIIT Summer Course - D#

  8. Energy Stroage • Requirements: • Lifetime, Capacity, Current draw, Size/Weight • Types of storage: • NiMH: capacity and cost • Li+: energy density and capacity • Supercap: lifetime • Storage configuration: • Combination of battery and supercap provides good lifetime as well as capacity. • Charging mechanisms: • HW vs. SW, Complexity vs. Efficiency AIIT Summer Course - D#

  9. The Load AIIT Summer Course - D#

  10. Load (Sensor Node):Estimating Node Consumption • Energy consumption with radio comm: • Iest = R*Iawake + (1-R) * Isleep AIIT Summer Course - D#

  11. The Ambient Source • Solar • Vibration • Movement • Flow • Heat transfer AIIT Summer Course - D#

  12. External Environment:Estimating Solar Radiation • Statistical Model • Mathematical Model AIIT Summer Course - D#

  13. Solar Collector:Solar-cell Characteristics • Solar-cell I-V curve • Regulator AIIT Summer Course - D#

  14. Solar Energy Harvesting Unit Solar Cell Circuit Energy Storage Energy Storage Element Controller Wireless Sunlight Sensor Node Charging Characteristic Set Solar Li - ion DC - DC (Micro - Charge Cell Battery Converter controller 4.400 0.800 & Set 4.200 0.700 Radio) Power Power Regulating Super - 4.000 0.600 Selection Circuit capacitor VCC SW 3.800 0.500 Current (A) Voltage (V) 3.600 0.400 3.400 0.300 3.200 0.200 Cell Voltage (V) 3.000 0.100 Charge Current (A) 2.800 0.000 0.0 20.0 40.0 60.0 80.0 100.0 Time Charging to Energy Storage Element • Supercap for primary, lithium-ion for secondary. • Reduces battery charging frequency. • Software-controlled battery charging. • Unlike other batteries, Li+ battery should be charged only when there is sufficient charge in the supercap. • Pros: Simple hardware: micro-controller, DC-DC converter, analog switch. • Cons: Requires correct software for charging control. AIIT Summer Course - D#

  15. Consideration of other types of storage element • Battery is needed during overcast days. • Supercap-only method doesn’t have sufficient capacity. • Comparison of charging efficiency is not available yet. AIIT Summer Course - D#

  16. Comparative Study:Solar-Collector Operation • Compare Pon with PmaxP • solar-cell operating point • maximum possible value • Trio • Pon – PmaxP = 4.83mW (5.3%) • Heliomote • Pon – PmaxP = -16.75mW (-23.2%) AIIT Summer Course - D#

  17. Comparative Study:Energy flow and efficiency • Compare mote consumption (Econs) and stored energy (Ebat and Ecap) with solar energy income (Esol). • Trio: up to 33.4%, Heliomote: up to 14.6% AIIT Summer Course - D#

  18. Solar-Collector Operation: Trio AIIT Summer Course - D#

  19. Solar-Collector Operation: Heliomote AIIT Summer Course - D#

  20. Energy flow and efficiency (Heliomote)- Energy loss due to regulator • Solar energy income: 08:00 to 17:00. • Clipped after 12:00. • Two-third loss in daily energy income. AIIT Summer Course - D#

  21. RF TX beacon Prometheus Heliomote ZebraNet Trio Related Work on Solar Powered Sensor Network • Trio [DHJ+06] • Real deployment of large sensor nodes. • Multi-hop routing. • Operate only for several hours with full radio cycle. • Other Previous Works • RF transmit beacon [ROC+03], Prometheus [JPC05]Heliomote [RKH+05], ZebraNet [ZSLM04] AIIT Summer Course - D#

  22. Energy Management Architecture AIIT Summer Course - D#

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