Wireless Embedded Systems and Networking Foundations of IP-based Ubiquitous Sensor Networks Micro-Power Systems

1
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

2
Micro-Power System Architecture

• Evaluation Metrics
• Effsolar Pon / PmaxP
• Effsystem (EL1 ELn Econs) / Esol

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

Duty Cycle Light Required System Lifetime
1 5 hrs / 1 mo 43 years
10 5 hrs / 4 days 4 years
100 10 hrs / 1 day 1 year
Perpetual Environmentally Powered Sensor
Networks, Jiang, Polastre, Culler, IPSN/SPOTS,
2005
4
Facts

• E P T

5
Energy Storage
6
Energy and Power Density
7
Battery Chemistry
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

9
The Load
10
Load (Sensor Node)Estimating Node Consumption

• Energy consumption with radio comm
• Iest RIawake (1-R) Isleep

11
The Ambient Source

• Solar
• Vibration
• Movement
• Flow
• Heat transfer

12
External EnvironmentEstimating Solar Radiation

• Statistical Model
• Mathematical Model

13
Solar CollectorSolar-cell Characteristics

• Solar-cell I-V curve

• Regulator

14
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.

15
Consideration of other types of storage element

• Battery is needed during overcast days.
• Supercap-only method doesnt have sufficient
  capacity.
• Comparison of charging efficiency is not
  available yet.

(1) Trio DHJ06 (2) HeliomoteRKH05 (3) EverlastSSC05
Storage One Li batterywith one 22F cap Two AA NiMH batteries One 100F capacitor
Capacity Ebat 2625mWh Ebat 4320mWh Ecap 86.8mWh
Bday 14.5 days at 106.7 days at 25 23.9 days at 1011.0 days at 25 0.48 days at 100.22 days at 25
Chargingcontrol Software, pulse charging Hardware,trickle charging Hardware,trickle charging
overcast days? YES YES NO
16
Comparative StudySolar-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)

17
Comparative StudyEnergy 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

18
Solar-Collector Operation Trio
19
Solar-Collector Operation Heliomote
20
Energy flow and efficiency (Heliomote)- Energy
loss due to regulator

• Solar energy income 0800 to 1700.
• Clipped after 1200.
• Two-third loss in daily energy income.

21
Related Work on Solar Powered Sensor Network

• Trio DHJ06
• Real deployment of large sensor nodes.
• Multi-hop routing.
• Operate only for several hours with full radio
  cycle.
• Other Previous Works
• RF transmit beacon ROC03, Prometheus
  JPC05Heliomote RKH05, ZebraNet ZSLM04

TrioDHJ06 RF TX beaconROC03 PrometheusJPC05 HeliomoteRKH05 ZebraNetZSLM04
Multi-hop Yes No No No No
SustainableOperation No No(No battery) Yes Yes Yes
Duty-cycling On-offduty-cycle On-offduty-cycle On-offduty-cycle On-offduty-cycle GPS assistedtime-sync
Deployment 500 Lab bench Lab bench Lab bench 10
22
Energy Management Architecture