k l f dSensor Network Platforms and Tools

1

Tools

A N O V E R V I E W O F S E N S O R N O D E S A N D T H E I R C O M P O N E N T S

References…2

Sensor Node Architecture 3

Main components of a sensor node…p4

A t llA controllerCommunication device(s)Sensor(s)/actuator(s)StoragegPower supply

Storage

Controller Sensor(s)/actuator(s)

Communicationdevice actuator(s)device

Power supply Power supply

Controller…5

Options: Options: Microcontroller—general purpose processor, optimized for embedded applications, low power consumptionpp , p pDSPs—optimized for signal processing tasks, not suitable hereFPGAs—may be good for testingASICs—only when peak performance is needed, no flexibility

Example microcontrollersT I MSPTexas Instruments MSP430

16-bit RISC core, up to 4 MHz, versions with 2-10 Kbytes RAM, several DACs, RT clock, cheap (prices start at US$ 0.49)p p

Atmel ATMega8-bit controller, larger memory than MSP430, slower

Communication device…6

Whi h t i i di ?Which transmission medium?Electromagnetic at radio frequencies El t ti li htElectromagnetic, lightUltrasound

R di t i t it bit b t t Radio transceivers transmit a bit- or a byte-stream as radio waves

O i it d t it b k i t bit /b t tOr, receive it and convert it back into bit-/byte-stream

Transceiver characteristics…7

T k d bilitiTasks and capabilitiesService to “upper layer”

Usuall to MAC la er; packet oriented; b te or bit interface to the Usually to MAC layer; packet-oriented; byte- or bit-interface to the microcontroller

Carrier frequency and multiple channelsq y pRegulatory restrictions; FDMA, multi-channel CSMA

Data ratesCarrier frequency and the bandwidth together with modulation and coding determines the gross rate

RangeRangeIn the absence of interference!

Transceiver characteristics…28

EEnergyPower consumption

During transmissionDuring transmissionDuring state change

Transmission power controlTransmission power control

Transceiver characteristics…339

RadioRadioModulation? (ASK, FSK, …)Noise figure? Noise figure?

NF = SNRI/SNRO; degradation due to the operation of the element in dB

G i ? Gain? Ratio of the output signal power to the input signal power in dB

Power efficiency?Power efficiency?Ratio of the output signal’s power to the power consumed by the amplifier

R i iti it ? Receiver sensitivity? Minimum S to achieve a given Eb/N0; a prescribed bit/packet error rate

Transceiver characteristics…4410

R di ( t )Radio (cont.)Blocking performance

Achie ed BER in presence of frequenc offset interfererAchieved BER in presence of frequency-offset interfererOut of band emissions

Limiting the disturbanceLimiting the disturbanceCarrier sensing and RSSI characteristicsFrequency stability (e.g., towards temperature changes)q y y ( g , p g )Voltage range

Transceiver structure… 11

R di f f t dRadio frequency front endAnalog signal processing

B b d Base band processorDigital signal processing and communication with the processor and other (digital) circuitryprocessor and other (digital) circuitry

Transceiver states…12

T itTransmitReceiveIdle—ready to receive, but not doing so

Some functions can be switched off, reducing energy consumption a little

Sleep—significant parts of the transceiver are i h d ffswitched off

Need some time to wake up receive something; recovery ti d t t t l l t t b time and startup energy to leave sleep state can be significant

Example transceivers…p13

RFM TR1000 family Chipcon CC 2400y916 or 868 MHz400 kHz bandwidthUp to 115 2 kbps

p 4Implements 802.15.42.4 GHz, DSSS modem 250 kbpsUp to 115,2 kbps

On/off keying or ASK Dynamic/tuneable output

250 kbpsHigher power consumption than above transceivers

powerMaximum power about 1.4 mWLow power consumption

Infineon TDA 525x familyE.g., 5250: 868 MHzASK or FSK modulationp p

Chipcon CC1000Range 300 to 1000 MHz, programmable in 250 Hz steps

ASK or FSK modulationRSSI, highly efficient power amplifierIntelligent power down “selfprogrammable in 250 Hz steps

FSK modulationProvides RSSI

Intelligent power down, self-polling” mechanism Excellent blocking performance

Wakeup receivers…p14

R h i W k iResearch issue: Wakeup receiversCan be woken via radio when in sleep state (seems a contradiction!)contradiction!)

Major energy problem: RECEIVINGIdling and being ready to receive consumes considerable Idling and being ready to receive consumes considerable amounts of power

When to switch on a receiver is not clearWhen to switch on a receiver is not clearContention-based MAC protocols: Receiver is always on TDMA-based MAC protocols: Synchronization overhead TDMA based MAC protocols: Synchronization overhead, inflexible

Wakeup receivers…2p15

D i bl R i th t ( l ) h k f Desirable: Receiver that can (only) check for incoming messages

Wh i l d t t d k i i f t l When signal detected, wake up main receiver for actual receptionIdeally: Wakeup receiver can already process simple Ideally: Wakeup receiver can already process simple addressesNot clear whether they can be actually built, however

Sensors…16

M i t iMain categoriesAny energy radiated?

Passi e s acti e sensorsPassive vs. active sensorsSense of direction?

Omidirectional?Omidirectional?Passive, omnidirectional

Example: light, thermometer, microphones, hygrometer, …p g p ygPassive, narrow-beam

Example: CameraActive

Example: Radar

Sensors…217

I t t t A f Important parameter: Area of coverageWhich region is adequately covered by a given sensor?

Actuators…18

A di As diverse as sensorsUsually paired with a “controlling sensor”In principle have a simple functionality with when paired with a sensor—open or close a switch or a relay or set a value

Storage…g19

Sensors usually accompanied with a small storage:Sensors usually accompanied with a small storage:4-16kB RAM (EEPROM)16-128kB program flashp g256-2048kB external flash (NAND, NOR)

Examples:ktMote sky

10kb RAM48kB program flash4 p g1024kb external flash

micaZ4kb EEPROM4kb EEPROM128kB program flash512kB external flash

Power supply…pp y20

Goal: provide as much energy as possible at smallest Goal: provide as much energy as possible at smallest cost/volume/weight/recharge time/longevity

In WSN, recharging may or may not be an optionOptionsOptions

Primary batteries—not rechargeable Secondary batteries—rechargeable, only makes sense in combination with some form of energy harvestingwith some form of energy harvesting

Requirements include Low self-discharge

h lf liLong shelf liveCapacity under load Efficient recharging at low currentGood relaxation properties (seeming self-recharging)Voltage stability (to avoid DC-DC conversion)

Power consumption…p21

Way out: Do not run sensor node at full operation all Way out: Do not run sensor node at full operation all the time

If nothing to do switch to power safe modeIf nothing to do, switch to power safe modeQuestion: When to throttle down? How to wake up again?

Typical modesyp ca odesController: Active, idle, sleepRadio mode: Turn on/off transmitter/receiver, both

Multiple modes possible, “deeper” sleep modesStrongly depends on hardware

TI MSP 430; four different sleep modesAtmel ATMega; six different modes (idle, ADC Noise Reduction, Power-save, Power-down, Standby, Extended Standby)y y

Switching between modes…g22

Si l t id G dil it h t l d Simplest idea: Greedily switch to lower mode whenever possible

bl i d i i d Problem: Time and power consumption required to reach higher modes not negligible

d h dIntroduces overhead Switching only pays off if Esaved > Eoverhead

E h d

Pactive

EsavedEoverhead

Psleep

timeteventt1 τdown τup

Sensor Node Examples 23

Current sensor nodes…24

MiMica2micaZCricketImote2TmotesunSpotsunSpotSentilla JCreate

Operating S stem and E ec tion Operating System and Execution Environments

25

Operating Systemsp g y26

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