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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
TinyOSTinyOSMate
MANTISMANTISRetOSContikiContikiMagnetOSE OSEyes OSSenOS
ldEmeraldsPicOS