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Wireless Sensor Network (WSN)Platforms
Christian Decker
Universität Karlsruhe
Institut für TelematikTelecooperation Officewww.teco.uni-karlsruhe.de
TecO 2Wireless Sensor Network Platforms
A Brief History
! 1978 DARPA-sponsored Distributed Sensor Nets Workshop (CMU), tracking for military applications
! 1993 WINS (UCLA): system design, networking, sensing, signal processing
! mid-1990s DARPA low power wireless integrated microsensors (LWIM)
! 1998 SensIT: distributed military sensor systems (29 research projects, 25 institutions)
! 1998 first spin-off Sensoria from WINS
! 1998 Smart Dust, MEMS based motes
! 1999 PicoRadio (UCB): ad hoc wireless network for low-cost, low energy sensor and monitoring nodes
! 2000 !AMPSFocus on sensor network comm. Protocols, LEACH
! 2001 Terminodes, MANET: low-power routing under mobilityand TCP/IP usage
! 2003 EU IST FP7 work program on Ambient Intelligence (AmI)
! 2007 EU Framework 7, „Cooperating Objects“
TecO 3Wireless Sensor Network Platforms
Early Platforms (1)
ISSS (1990-1994)
! 250 sensors (temperature, pressure, flow)
! 45 control points (valves, power)
! 22 distributed processing nodes
Implementation
! Mock-up (nuclear) power plant
! Boiler, heat exchangers, pumps, by-pass circuits
! Primary water coolant
TecO 4Wireless Sensor Network Platforms
Early Platforms (2)
SKIDS (1986-1991)
! EU FP1 project
! Distributed Tracking of people
! Cameras with embedded processing
! optical barriers, acoustic sensors
WSN like communication issues
! Non-fully connected networks
! Time varying and ad-hoc networks
! Communications management
! Distributed processing and data fusion
TecO 5Wireless Sensor Network Platforms
WSN Platform overview I just picked some....
Germany
! Some companies started, mostly university‘s spin-offs
! Lots of research platforms
World wide
! Several dozens commercial platforms from Start-ups, Spin-offs and other organisations
! Huge diversity of research platforms
TecO 6Wireless Sensor Network Platforms
Platform Diversity ... and it‘s growing
TecO 7Wireless Sensor Network Platforms
Drawing a lot of Comparisons
15.4 (BT/802.11)300-900MHz802.15.4802.15.4BTRadio
250 (720/11,000)15250250720Bandwidth [kb/s]
TinyOSTinyOSTinyOSTinyOSTinyOSOS support
YNAES-128AES-1284LFSR-128Security HW
1-100196271-250Power sleep [uA]
40/20/188 / 10 / 271 / 20 / 188 / 20 / 1815 / 24 / 24Power C/R/T [mA]
32,000128 + 51248 KB / 1024 KB128 + 512512FLASH [kB]
256/32,000410464SRAM [kB]
32b XS@13(104)8bit Atmel @816bit TI @88bit Atmel @832bit ARM @12CPU type @[MHz]
Imote 2Mica2TelosMicazImoteFeature
TecO 8Wireless Sensor Network Platforms
How to proceed?
Goal
! Learn a systematic way to the design and evaluation of wireless sensor network platforms
Method
! Decompose sensor network platforms
! Find design criteria
! Identify design choices
! Explain trade-offs
TecO 9Wireless Sensor Network Platforms
Lecture Outline
!Platform Design
!Radio Communication
!Sensors
!Energy
TecO 10Wireless Sensor Network Platforms
Design Criteria (1)
! Application computational requirements
" RAM, ROM, MIPS
! Ability to use host resources
" Host integration, e.g. PDAs, cell phones, controller,takes over some functionality
! Market flexibility
" Energy scavenging, radio frequency support (315 MHz, 433 MHz, 868 MHz, 2.4 GHz)
! Physical size
" Size of battery, antenna, integration with other systems
! Time to market
" Level of use of standard components vs. Integrated approach
TecO 11Wireless Sensor Network Platforms
Design Criteria (2)
! Networking capabilities
" Single vs. Multi-hop, multi-tier network architecture
" FFD vs. RFD in IEEE 802.15.4
! Chip-to-Chip Connectivity
" Noise, higher capacitance, higher power consumption
! Power source diversity
" power conditioning for energy scavenging techniques,rechargeable batteries, low power operations
! Packaging
" Material costs, design amortization
And there a certainly more...
TecO 12Wireless Sensor Network Platforms
Separation of Concerns
! Concept of breaking a computer program in distinct functionalities
! Probably coined by Edsger W. Dijkstra in "On the role of scientific thought" (1974)
" “..."the separation of concerns", which, even if not perfectly possible, is yet the only available technique for effective ordering of one's thoughts, that I know of.”
" “focusing one's attention upon some aspect“
! Seems to be a recurrent design pattern also for WSN
Examples
! Processor – transceiver
! Communication protocol – transceiver
! Sensor board – communication board
! Power source – power consumer
TecO 13Wireless Sensor Network Platforms
Lecture Outline
!Platform Design" Components & Partitions
" Microprocessors
!Radio Communication
!Sensors
!Energy
TecO 14Wireless Sensor Network Platforms
Platform Components
Source:Callaway, Wireless Sensor Networks
TecO 15Wireless Sensor Network Platforms
Separation Decisions (1)
! All-in-one, SoC
RF TranceiverProtocol Handler
App. Processor
Data
RF TranceiverProtocol Handler
App. Processor
Data
! Separates transceiver from the rest of the node
Example: Jennic, JN5139
Example: TecO Particle
TecO 16Wireless Sensor Network Platforms
Separation Decisions (2)
! Separate comm. protocol and application
RF Tranceiver Protocol HandlerDataApp.
Processor
RF TranceiverProtocol Handler
App. Processor
Data
! Separate power conditioning from
Power
Conditioning
Example: BTNode rev3
TecO 17Wireless Sensor Network Platforms
Separation Decisions (3)Integration with Host
! Use regular sensor node
! Connector to embedded or PC system
! Serial line or USB interface dominant
Node
Components
DataHost
Interface
(serial, usb)
Network
TecO 18Wireless Sensor Network Platforms
Application ProcessorDesign Choices
Application-Specific Integrated Circuit (ASIC)
! Fast, low power
! Hardwired functionality, single purpose, high development costs
Field-Programmable Gate Array (FPGA)
! Transistor overhead # waste power!
! Used for prototyping
! But: Gets better, becomes more important
Microprocessors, -controller
! Slower (software), performance/watt low
! Flexibility compensates: control power consumption (powersaving modes), software is energy aware
! Multi-purpose device: same hardware runs multiple applications
! Fast and low-cost development, i.e. upgrades, patches, and reuseing, simplifies design of families of products
TecO 19Wireless Sensor Network Platforms
Application ProcessorMicroprocessors
Taxonomy
! Embedded processors
" RISC orr RISC-“like“ microcontrollers (MCU), 5-10 MIPS
" Integrated RAM, Program-ROM, A/D, I/O, WDT, ...
! Dedicated processors
" Digital signal processors (DSP), >30 MIPS
" basieren inzwischen oft auf eingebetteten Prozessoren
! System-on-Chip, SOC
" Wireless microcontroller, MCU + RF transceiver
" Often two cores in one housing
Processor architecture
! von Neumann
! Harvard
TecO 20Wireless Sensor Network Platforms
Harvard vs. Von Neuman
Von Neuman
! Volatile, energy consuming RAM (SRAM 1MB ca. 15mA) for program + data
! flexible
Harvard
! Data volatile, Progr. fix (ROM, Flash, EEPROM)
! Fast boot
! Data do not corruptprogram
! Keine Energie für Speichern Programme
! typ. energy consumption <10mA
! Faster, 2 Busses
Memory
CPUAddr.
Data Program Counter
Data
Memory CPUAddr.
Data
Program CounterPrg.
Memory
Addr.
Instructions
TecO 21Wireless Sensor Network Platforms
Popular Processors
Embedded Processors
! Arizona Microchip PIC Reihe (8-bit, 16-bit, Harvard)
" Huge number of derivates (several hundreds), contain busses and networks (CAN, RF,...)
" 1k-128k Flash Program memory, 32byte-8k RAM, bis 33 MIPS
" Low energy consumption (<8mA @5 MIPS), compatibility (similarcore) between derivates
! ATMEL AVR (8bit, Harvard)
" Market leader, several dozen derivates
" 1k-128k Flash, 32byte-4k RAM, max 20 MIPS
" Low energy consumption (<10mA @ 5MIPS)
! TI MSP430 (16 bit, von Neumann)
" several dozen derivates
" Bis 64 k Flash, 10 k RAM
" 5 Power Modi, extremly low energy consumption (few mA bis uA)
! 8051 verwandte Architekturen (Kern inzwischen frei!)
TecO 22Wireless Sensor Network Platforms
PIC 16F876
! Harvard architecture, RISC (35 Instruktionen), up to 20 MHz, 5 MIPS, power supply 2-5.5V
! ROM: 8K, RAM: 68 bytes
! Low Cost (2 Euro), Low Power
" < 0.6 mA typical @ 3V, 4 MHz
" 20 !A typical @ 3V, 32 kHz
" < 1 !A typical standby current
! Compact core, many I/O interfaces
! E.g. A/D, SPI, serial, I2C,...
! (almost) no further components required
! Programming: C,Assembler
Example: Arizona Microchip PIC
ProgramMemory
RAM
Processor
Port A (A/D)
Port B (INT)
Port C (I/O, SPI, I2C, Ser)
Timer
Power-Up
WDT
Brown Out
TecO 23Wireless Sensor Network Platforms
Jennic, MCU+Zigbee (SOC)
Jennic JN5139, wireless microcontroller
! 32-bit RISC, 32MIPs, low power
! 192kB ROM for system code, protocol stack
! Up to 96kB RAM for data and bootloader
! 48-byte OTP eFuse: MAC ID, AES based code encryption
! On-chip power regulation for 2.2V to 3.6V
Communication
! 802.15.4 MAC and Zigbee protocol stack, 250 Kbit/s
! supporting co-ordinator, routerand end device
! Power consumption
! RX / TX: 34mA
! Deep Sleep: 0,2 uA
Interfaces
! 12-bit ADC, 11-bit DACs,
! 2 UARTs, 1 SPI, 2-wire serialinterface, up to 21 GPIO
Source:jennic.com
TecO 24Wireless Sensor Network Platforms
Lecture Outline
!Platform Design
!Radio Communication" Components and Design Choices
" Antenna
" Power Consumption
!Sensors
!Energy
TecO 25Wireless Sensor Network Platforms
Radio Subsystem
Components
! Transceiver
" (De-)Modulation, filtering, frequency generation, RSSI provision, gain control, frame synchronization data(de-)encoding, optional CRC
! Protocol
" Data format, payload packet structure
! Antenna
" Forms, material, characteristics
RF Tranceiver Protocol HandlerData
Antenna
TecO 26Wireless Sensor Network Platforms
Popular Radio Transceivers
Source:http://www.btnode.ethz.ch/Projects/RadioSystems
TecO 27Wireless Sensor Network Platforms
Radio Choices
! Too early to commit to a single radio for WSN
! Lots of RF chips available
" Providing carrier and modulation scheme, e.g. RFM TR1001
" RF modem solutions: wire replacements, e.g. radiometrix
" Standardized solutions: Phy, Mac, Network, Data format, e.g. Bluetooth, Zigbee
! Different applications might need different radios
" 802.15.4 (Zigbee Mac):medium data rate, low power
" Bluetooth: ubiquitous
" Wifi 802.11: installed infrastructure available
# Separation of Concerns
! Other requirements: antenna, bandwidth, range, power consumption
TecO 28Wireless Sensor Network Platforms
Example: BTNode
Dual radio approach
! High performance inter-node comm. (Back-bone)
" Bluetooth subsystem: Zeevo ZV4002, supporting AFH/SFH
" Scatternets with max. 4 Piconets/7 Slaves, BT v1.2compatible
! Low bandwidth inter-node comm.
" Low-power radio: Chipcon CC1000 operating in ISM band 433-915 MHz
" Compatible with Mica2
Zeevo ZV4002
CC1000
Source: BTNodes Hardware Reference
TecO 29Wireless Sensor Network Platforms
Example: Intel Imote!
! Imote" has an onboard ChipCon CC2420 (802.15.4)
! Other radio options via SDIO cards and UART/USB! SDIO connector too big (30x30 mm) and costly ($1.74) ! Only pins exposed through basic connector! SDIO connector board on your own
802.11b
Bluetooth
36
mm
48 mm
Advanced I/O
connector
Advanced I/O
connector
Crystal
Antenna
Optional SMA
connector
Mini USB
Connector
CC2420
Source:Lama Nachman, Intel Corporation Research
TecO 30Wireless Sensor Network Platforms
Antenna
Printed antenna
! Inexpensive
! Depends on dielectric and thickness of the board
! Inductor for tuning
SMD (chip) antenna
! SMD, Compact, cost-effective
! 868MHz,915MHz,2.45GHz
! Omnidirectional (horizontal)
! Separate from layout
Whip antenna
! Very simple, just a wire
! Omnidirectional (horizontal)
! Requires a large ground plate
Source: antennafactor.com Source: ETH
BTNode rev.3
Layout!
Particle 1/81
Source: RFM.com
TecO 31Wireless Sensor Network Platforms
Monopole Antenna (Whip)Radiation Pattern
Side View Top View
Communication
range
Symmetric Region Antenna orientation
independent regions
Communication
range
Source: Andreas Savvides"Sensor Network Hardware Platform Design"
TecO 32Wireless Sensor Network Platforms
Effects of Antenna Orientation
! RSSI: Receiver signal strength indicator
! Provided by radio hardware
! Foundation for location estimation
Source: Andreas Savvides"Sensor Network Hardware Platform Design"
Eqn: Log-normal location model
Best angleWorst angle
No Comm.
Setup:
TX Power -15dBm
TecO 33Wireless Sensor Network Platforms
Effects in 3D
! Radio operates best in 2D plane
! Antenna effects become dominant at different heights
Conclusion
! In 2D
! good models for radio propagation (log-normal shadowing model)
! Most models applicable in symmetric propagation region
! In 3D:
! strong antenna effects (orientation, height)
! Increase rate of asymmetric links Source: Andreas Savvides
"Sensor Network Hardware Platform Design"
Setup:
TX Power -15dBm
TecO 34Wireless Sensor Network Platforms
Power Consumption
! Example: Chipcon CC2420 (IEEE 811.15.4) Radio Power Levels
-25
-15
-10
-7
-5
-3
-1
0
TX Power(dBm)
15.3
17.82
20.16
22.5
25.02
27.36
29.7
31.32
PowerConsumed(mW)
8
7
6
5
4
3
2
1
Level
)mW(1mW
P(mW)20logP(dBm) =
Avg. MCU consumption24mW
Source: Andreas Savvides"Sensor Network Hardware Platform Design"
TecO 35Wireless Sensor Network Platforms
Lecture Outline
!Platform Design
!Radio Communication
!Sensors" Sensor boards
" Analog and digital sensors
" Sensor interfaces
!Energy
TecO 36Wireless Sensor Network Platforms
Design criteria
! Flexibility: separate communication from sensors (separation of concerns)
" Easy integration of new (specialized) sensors
" Complex: connector, mechanical robustness, housing
" Example: Motes, Particles
! Price: all on one board
" Compact design, small
" low flexibility
" Example: ESB, uPart
Sensor Boards
ESB, Source: SchilleruPart
Mote and sensorboard, Source:Xbow.com
TecO 37Wireless Sensor Network Platforms
Case study: Particle Sensors
Example: Generic Sensor board (Particle)
! Low power design
! Separate Co-processor for sensor processing (separation of concerns
! Sensors:
" Microphone, light, temperature, force, acceleration, movement
! Serial, I2C, SPI, A/D, PWM interfaces
TecO 38Wireless Sensor Network Platforms
Case study: uPart
! Idea: all-in-one, tiny, inexpensive
Technology
! MCU: 12F675 @ 4 MHz
! Memory: Program-Flash 1.4 kByte, RAM 64 Byte, EEPROM 128 Byte
! Communication: transmitter only
" 869 Mhz / 315 Mhz
" 2-FSK, ALOHA protocol
" 15m indoor, up to 30m outdoor
! Sensors
" Light, temperature, movement,voltage
! Power supply
" CR1632 coin cell
" Several months (~35s duty cycle)
uPart 1/40
TecO 39Wireless Sensor Network Platforms
Analog & Digital Sensors
Analog sensors
! Sensor output voltage encodes the sensor value
! ADC translates in digital value
Digital sensors
! Sensor value encoded as “1“ and “0”
! Example: Pulse-width modulation (PWM)
Internal Sensors
! MCU contains sensor, e.g. temperature
! Read out via memory mapped register, or specific ADC channel, e.g. MSP430
MCUSensor
GND
Vdd
Source: ADXL Datasheet
TecO 40Wireless Sensor Network Platforms
Analog-Digital Converter (ADC)
! From Analog to Digital
V(t)
The Digital Signal: 0010 0100 0100 0001…
ADC
Properties
! Sampling rate
! frequency of ADC usage
! limited by conversion time
! few us up to 10s of us
! Resolution
! vendor specific, e.g. 10bit (PIC18F), 12bit (MSP430)
Implementations
! Flash, Successive-Approximation, Sigma-Delta, Ramp-Compare, Pipeline
Source: http://entertainment.howstuffworks.com/analog-digital3.htm
MCUADC
SMD Mic
Example:Microphone
TecO 41Wireless Sensor Network Platforms
ExampleRamp-Compare ADC
Function
! Counter resets to 0 and counts up
! Comparator compares measured value andDACed counter
! V_measure == V_counter # stop counting, conversion done
Sourc
e:
http://h
yperp
hysic
s.p
hy-
astr
.gsu.e
du/h
base/e
lectr
onic
/adc.h
tml#
c2
TecO 42Wireless Sensor Network Platforms
MSP430Internal Temperature Sensor
Features
! Low power
! Good accuracy, 12bit A/D conversion
! A bit noisy # 0.5°C accuracy (empirical value)
! Needs device specific calibration: V_SENSOR(0°C) = 986+/-5% mV # +/- 14°C
Calculation
! T [°C] = (V_SENSOR(T) – V_SENSOR(0°C)) / TC_SENSOR
Source: MSP430 Datasheet
TecO 43Wireless Sensor Network Platforms
Digital Sensors:Movement Sensor
Features
! Binary sensor, ballswitch (on/off state)
! Motion detection, orientation dependent
! No current, really low power sensor!
Encapsulated ball,
Shake it, you hear it!
• count #states (on/off)
• continous state length
• on/off cycle
Signal (ideal) :Switch opened Vdd
Switch closed GND
GND Vdd
ADXL acceleration sensor
and ball switch
TecO 44Wireless Sensor Network Platforms
Digital SensorsAcceleration sensor
Example: ADXL202/210
! Micro-Electro-Mechanical Systems (MEMS)
! High accuracy
! Needs calibration
Sensor signal: Pulse-width modulation (PWM)
! g value encoded as ratio T1/T2 (=Duty cylce)
! 0 g = 50 % duty cycle
! Scale factor 4% per g
Source: ADXL Datasheet
Source: Microchip.com
Source: Grace Kim, itp.nyu.edu
TecO 45Wireless Sensor Network Platforms
Digital SensorsSensor Bus
Sensors
! Usually more complex: Sensor + interpretation electronic+ protocol + bus driver
! Typical bus interfaces: I2C, One-Wire
http://www.maxim-ic.com/appnotes.cfm/an_pk/4024
TecO 46Wireless Sensor Network Platforms
Popular Sensors
! Light (usually analog or PWM and some I2C) " Thermopile (mostly analog, some PWM) " Ultraviolet (analog or PWM) " IR (analog, PWM, and a few I2C) " Visible Light (analog, PWM, and a few I2C) " Color sensors (PWM)
! Magnetic (analog, I2C) ! Sound (analog)
" Ultrasound (analog, PWM) ! Accelerometers (SPI, I2C, analog and PWM) ! Temperature sensors (I2C, analog and PWM) ! Pressure sensors (analog, SPI) ! Humidity (custom I2C) ! Touch sensors (analog or PWM)
TecO 47Wireless Sensor Network Platforms
Problems with Sensors
! Systematic problems
" Sensors must be aligned to an application
! Orientation of sensors is crucial
" placement of movement sensor is an interesting research question!
! Sampling intervals too large
" Inaccurate results
" Missed events
" Idea: increase sampling rate (and therewith transmit rate)
Source: Albrecht Schmidt, Summer School 2005
TecO 48Wireless Sensor Network Platforms
Lecture Outline
!Platform Design
!Radio Communication
!Sensors" Sensor boards
" Analog and digital sensors
" Sensor interfaces
!Energy
TecO 49Wireless Sensor Network Platforms
Serial Line Communication
RS232
! Voltage level between -15V and +15V
! Alternative: 0-5V „TTL“ Level
! 2 lines: Transmit+Receive (TxD, RxD),
! Optional: 2 handshake lines (RTS/CTS)
http://www.maxim-ic.com/appnotes.cfm/appnote_number/83/
Bit 0
Bit 1
TecO 50Wireless Sensor Network Platforms
Example: RS232
! Regular transmission format: 8N1, i.e. 8 data bits, no parity, 1 stop bit
! Start bit is mandatory, baud rate must be known or is detected
! This example: 7e2
http://www.arcelect.com/rs232.htm
TecO 51Wireless Sensor Network Platforms
Sensor InterfaceInter-Integrated Circuit I2C, I!C
! A.K.A. 2-wire bus (due to Philips patent)
! Lots of devices – sensors, memory, actuators, e.g. Motherboardfor temperature measurement, battery control
! 2 Lines + GND for all devices:
" SDA (data line)
" SCL (clock line)
" Terminated: Open Collector with pull-up resistor
! Synchr. Master-Slave operation, Multi-master possible, MCU often provides HW driver
! Max. 112 slaves, address often fix in peripheral HW (7bit)
! 100kbit/s, 400kbit/s, 3.4 Mbit/s (brutto)
TecO 52Wireless Sensor Network Platforms
Sensor Interface I2C Protocol
http://www.maxim-ic.com/appnotes.cfm/an_pk/4024
Slave ack/nack master data
Slave can keep SCL low, if not ready (clock stretching)
TecO 53Wireless Sensor Network Platforms
Serial Peripheral Interface (SPI)
Serial Peripheral Interface, Microwire
! 1 master, 1 or more slaves
! Standardfall: Ein Master
! 3 lines+GND+Chip Select (CS):
" Serial Data In (SDI)
" Serial Data Out (SDO)
" Serial Data Clock (SCKL)
! High Speed (several MBit/s)
! Synchronous, duplex
! SD-Card, Memory-Chips (Flash, SRAM), RF chips (CC2430, TR1001)
http://www.mct.net/faq/spi.html
TecO 54Wireless Sensor Network Platforms
Advantages / Disadvantages
1. No bus, 1:1.
2. Slow (115kBit-1.2Mbit)
3. No clock (async)
1. Simple
2. No master
3. Handshake
4. Duplex
Serial
1. Speed: limited to 3.4MHz
2. Half-duplex operation
3. Open-drain bus lines require pullup resistors
4. Reduced noise immunity
1. Fewer bus lineconnections
2. Multiple devices share the same bus
3. Data is acknowledged
I2C
1. Larger number of bus lineconnections
2. Individual chip-select lines required to communicate with more than one slave at a time
3. No acknowledgment ofreceived data
1. Speed
2. No pullup resistors required
3. Full-duplex operation
4. Noise immunity
SPI
DisadvantagesAdvantagesInterface
Sourc
e:
htt
p:/
/ww
w.m
axim
-ic.c
om
/appnote
s.c
fm/a
n_pk/4
024
TecO 55Wireless Sensor Network Platforms
Lecture Outline
!Platform Design
!Radio Communication
!Sensors
!Energy" Batteries
" Power conditioning
" Energy management & scavenging
TecO 56Wireless Sensor Network Platforms
Batteries
Primary Cells / Alkaline
! Non-rechargeable, no capacity given
! 1.5V, long lifetime
Rechargable Cells
! NiMh, Lithium
! High current
! 1.2V, 2800 mAh capacity (AA)
Coin Cells
! ~200 mAh
! Often not rechargable
! Low continuous current (max. 200 uA)
! Higher current burns out the cell
Source: greenbatteries.com
Source: wikipedia
TecO 57Wireless Sensor Network Platforms
Battery Behavior (1)
Rate-Capacity effect
! High discharge / current
! Useable overall capacity decreases
Recovery effect
! After discharge, cell voltage recovers
Source: T. L. Martin. Balancing Batteries, Power, and Performance:System Issues in CPU Speed-Setting for Mobile Computing.
TecO 58Wireless Sensor Network Platforms
Battery Behavior (2)
Discharge curves
! Voltage decreases
! Sensor node has lower supply limit (cut-off voltage)
! # not all capacity is useable
Other effects
! Self discharge, age
! Temperature while under load, during storing, while loading
TecO 59Wireless Sensor Network Platforms
Power Conditioning
Motivation
! Multiple components: processor, radio, sensors, ...
! Multiple power sources: battery, coin cell, solar cells, ...
# Requires Separation of Concerns
! power conditioning by voltage regulation
Features
! 1. Provide operating voltage
! 2. Maintain operating voltage
! 3. Guarantee load performance (watt)
TecO 60Wireless Sensor Network Platforms
Power Converter
Linear regulator
! Down converter, Vin > Vout
! Low noise # preferable for noise sens. RF circuits
! Voltage difference (drop out) 20-50mV (power waste!)
! Minimize drop out in low power nodes
Switching regulator
! Step-up and/or step-down converter, 1.2V battery # 3V sensor node
! Inductor, diode and filter capacitor, switch (IC)
! Switching creates ripple
" # needs high quality capacitors, expensive
" # noise for RF and sensor circuits (additional filter caps)
TecO 61Wireless Sensor Network Platforms
Example: Inductive Boost Converter
Source:Callaway, Wireless Sensor Networks
TecO 62Wireless Sensor Network Platforms
Energy Saving Potential
Technology
! Low power components
" Minimal chip size
" Low voltage, low current, low frequency
! Radio modules down to 0.9V (Source: Abidi, Low-power radio
frequency ICs for portable communication)
Node Architecture
! High loss through busses, driver, multiplexer
! Reduce components and interconnections
! Power-off I/O
! No external memory
TecO 63Wireless Sensor Network Platforms
Energy ManagementMulti-Cell Operation
Multi-cell
! Use several (heterogeneous) battery cells
! Switch between cells
! Exploit discharge and recovery effects
Sequential discharge
! Discharge one battery after an other
Uniform switching discharge
! Switch uniformly between cells
Proportional switching discharge
! Switch according to load and remaining capacity
! # all cells are equally drained
Node
V1
V2
Switch
V1
Source: Benini et al. Discharge Current Steering for Battery Lifetime Optimization
TecO 64Wireless Sensor Network Platforms
Energy Scavenging (1)
MEMS Power generator through vibration
Thermal scavenging (Seiko)
Movement
TecO 65Wireless Sensor Network Platforms
Energy Scavenging (2)
Source: Paradiso, Starner
TecO 66Wireless Sensor Network Platforms
Conclusion
Summary
! WSN occupy a vast design space
! Some dimensions
" Processors, radio, sensors, energy
Lessons learned
! Various design choices and criteria
! There is always a trade-off.
! # Separation of Concerns seems to be a recurrent design principle
Outlook
! More standards will emerge (IEEE 802.15.4 was the beginning, upcoming: WirelessHART)
! More spin-offs will drive quasi-standard platforms (the next Mote), but for specific application area # standards of diversity
TecO 67Wireless Sensor Network Platforms
Next cool things in WSN...
Nanotube Radio
! Radio and receiver using carbon nano tubes (CNT)
Source: K. Jensen, J. Weldon, H. Garcia, and A. Zettl, "Nanotube Radio"
Source: Chris Rutherglen and Peter Burke"Carbon Nanotube Radio"
TecO 68Wireless Sensor Network Platforms
Credits
! Edgar H. Callaway, Jr. „Wireless Sensor Networks –Architectures and Protocols“
! Michael Beigl, TU Braunschweig: Bus systems
! H.F. Durrant-Whyte, ARC Sidney: SKIDS and ISSS
! Andreas Savvides „Sensor Network Hardware PlatformDesign“: Antenna, RSSI investigations