Sensor node, an implementation approach. ENSIL-ENSCI Cinquième année ELT, Module 6 Vahid Meghdadi

Transcription

1 Sensor node, an implementation approach ENSIL-ENSCI Cinquième année ELT, Module 6 Vahid Meghdadi

2 Wireless sensor network Number of sensors can be just a few but also tens of thousands The gateway (base station) receives the information of all sensors. It stocks and processes the date. Mesh network, multi-hop, routing

3 Wireless sensor network The deployment can be single hop Easier to implement However more power consumption High but limited range Up to 20km

4 Power vs range

5 General structure of a node A sensor node needs following blocks A transmitter A receiver Some sensors Possibly an analog to digital convertors Processing unit Internal memory External memory

6 Node Block Diagram Power source Sensor 1 Sensor n ADC Processor (controller) External memory Transceiver (TX/RX)

7 Sensors Sensors are hardware devices that produce electrical signals related to a physical phenomenon like temperature, humidity, etc The sensor output can be an analog voltage, that is digitized by an on-board A/D Some sensors produce directly a digital signal using a specific standard like I2C or RS232. A sensor should be small in size, consume extremely low energy, operate unattended.

8 Sensor examples Capteur de température Capteur de présence Capteur de lumière Capteur de mouvement Capteur de gaz (C, CO2, fumée, etc)

9 Controller The following devices can be used µcontroller DSP FPGA ASIC PC In WSN, because of the power consumption constraint, normally a simple micro-controller is used. Other kind of digital circuit is used if higher signal processing is required and if there is no power constraint (powered by AC outlet or by large batteries)

10 Memory On-chip microcontroller memory is used for the program and the data Some times off-chip flash memory is used to store collected data

11 Power source It is very rare that sensors use main supply (220 v) to be powered. The sensor node is normally battery operated. The consumption must be very low in order to avoid battery replacement frequently. The energy consumption is due to sensing, processing and communication. An important part of the energy consumption is due to communication: The energy cost of transmitting 1 Kb to a distance of 100 m is comparable to the execution of 3 million instructions Energy harvesting sensor nodes are already on the market.

12 Transceiver The block Transceiver includes the transmitter and the Receiver WSN usually uses ISM band (industrial, scientific and medical); there is no need for licenses when transmitting on this band

13 European ISM band constraints (ERP: Effective Radiated Power)

14 ISM License free Frequency bands used for IoT

15 Communications Normalement Un débit assez limité Des capteurs à basse consommation d énergie Des standards courte-porté IEEE (WiFi) Sans la contrainte d énergie IEEE (Zigbee) Débit limité, porté limité, très basse consommation, très utilisé dans le monde industriel, produit domotique, KNX Débit limité, porté limité, très basse consommation, utilisé dans le monde industriel, produit domotique Des standards longue-porté SigFox, LoRa,

16 Technologie sans fil

17 Transceiver characteristics Carrier frequency Regularity compliance Data rate Coding, CRC What kind of information it gives to upper layer Ex: RSSI (Received Signal Strength Indication) Power consumption When receiving, when transmitting, when processing, when idle Power control possibility

18 Transceiver characteristics (continue ) Radio Modulation (FSK, PSK, ASK, ) CDMA, OFDM Reception sensitivity Range (output power) Multiple channel possibility BER performance Carrier sensing and RSSI Interface with the upper layer

19 Transceiver characteristics (continue ) Functional mode Transmit Receive Idle The chip is listening but not receiving Some functions can be switched off Sleep In very low consumption mode Many parts are turned off Normally takes time to wake up

20 Example of transceiver CC1000 from Texas Instrument Low Power RF Transceiver ISM band (Industrial, Scientific and Medical) Can be programmed in the MHz SRD (Short Range Device) Programmable output power (-20 dbm to 10 dbm) Low supply voltage (2.1 to 3.6 v) RSSI output FSK up to 76.8 kbaud

21 CC1000 Simplified block diagram Super heterodyne receiver Digital interface PLL (synthesizer)

22 Typical circuit

23 Timing used to interface with µc Programming Address Latch Enable Configuration registers write operation

24 CC2520 from Texas Instrument 2.4 GHz ZigBee/IEEE RF transceiver 250 kbps, 2 Mchip/s ISM Band Supply range: 1.8 V 3.8 V Low Power RX (receiving frame, -50 dbm) 18.5 ma TX dbm TX dbm Three power modes: low power 1, low power 2, active mode

25 Features Provides also hardware support for frame handling, data buffering, burst transmissions, data encryption, data authentication, clear channel assessment, link quality indication (LQI) is a cumulative value used in multi-hop networks. Received Signal Strength (RSSI) These features reduce the load on the host controller.

26 System diagram Microproc Interface Used to give instructions to CC and to exchange data DPU: Digital Processing Unit Baseband signal complying with IEEE Digital I/O Up/Down Convertor FSM: Finite State Machine AAF: Anti Aliasing Filter FS: Frequency Synthesizer 32 MHz Cristal

27 CC2520 typical circuit

28 Interconnection with MSP430 MSP430 un processeur fabriqué par TI recommandé pour s interfacer avec CC25xx

29 SPI timing requirement SCLK input to CC2520; Data is read on the rising edge of SCLK, then should be fixed by µp on the falling edge of SCLK; Data is put on the falling edge of SCLK, then the µp can read it on the falling edge if SCLK Tsclk min = 125 ns, data rate max = 8 Mb/s

30 CC2520 programming CC2520 executes the instruction that it receives from SPI Each instruction is a single byte that may be completed by parameters given in the following byte(s) The TX frame is constructed automatically SFD Start of Frame Delimiter MHR MAC Header FCS Frame Check Sequence (CRC)

31 Exemple 1 MICA2 Autonomie 1 an UHF bande (315, 433, 868/916 MHz) Capteurs: lumière, température pression, accéléromètre, Processeur Atmel Atmega 128L RF Power jusqu à 10 dbm Portée: max 300m FSK modulation

32 Xbee Protocole zigbee (IEEE ) 250 kb/s Deux modèles : 1mW et 100 mw

33 Exemple de capteur 2,4 GHz ZigBee IEEE , prix 20 euros

34 Exemple TelosB

35 Texas Instrument CC2530

36 Texas Instrument CC2420

37 Start up espagnol Libelium Over the Air Programming (OTAP) 16 radio technologies: Long range: 4G / 3G / GPRS / GPRS+GPS / LoRaWAN / LoRa / Sigfox / 868 MHz / 900 MHz Medium range: ZigBee / / DigiMesh / WiFi Short range: RFID/NFC / Bluetooth 2.1 / BLE

38 Energy harvesting captors

39 Motes implementation

40 Smart mesh network (Zigbee based) a self-forming network Multihop mesh network exchanges data with a host application uses time slotted channel hopping (TSCH) All the motes are synchronized within 1 ms Each node has two parents (assuring self healing if one of the parents fails) The use of TSCH allows SmartMesh devices to sleep in between scheduled communications and draw very little power in this state (duty cycle of < 1%).

41 LTC e Wireless Mote-on- Chip SmartMesh network Embedded ARM Cortex-M3 32-bit microprocessor (Architecture ARM est connu pour sa simplicié et sa faible consummation, donc très utilize dans l embarqué)

42 LTC5800

43 Active topics MAC layer Routing problems Periodic listen and sleep Message passing

44 Long range networks Network based on cellular téléphonie/sms: 2G, 3G, 4G Good coverage but power consuming Two most used standards (ISM license free bands) SigFox Busyness model: you pay an abonnement The infrastructure is ready for you Just buy the modules and transmit LoRa Like SigFox, there exists un operator But also you can have your own private network

45 Low-power and long-range, so, low data rate

46 Some SigFox Radio modules From Congduc PHAM, université de Pau

47 Some LoRa module from Semtech Sx127x chips From Congduc PHAM, université de Pau

48 ISM band constraints License free, shared frequency bands lots of interference Activity time is constrained from 0.1%, 1% 10% duty-cycle depending on frequency: 3.6s, 36s/hour to 360s/hour For example SigFox s constraint is 140 messages per day LBT: Listen Before Talk, AFA: Adaptive Frequency Agility

49 LBT + AFA Listen Before Talk and Adaptive Frequency Agility can relax the duty-cycle constraints but still 100s / hour on every 200kHz BW no more than 1s for a single transmission so may not be that interesting! From Congduc PHAM, université de Pau

50 Conclusion Low-power, long-range (LR) transmission is a break-through technology for IoT and large-scale deployment of wireless (sensor) devices With a large variety of applications, products & actors the low-power WAN (LPWAN) eco-system is becoming mature New technologies will certainly emerge but the LPWAN «philosophy» is now settled firmly: out-of-the-box connectivity is now the standard. Is multi-hop routing for low-power device still interesting in the IoT domain? Mostly driven by industrials, research & development around long-range technologies should also attract the academic research community