Challenges and Opportunities for Energy Reduction in Wireless Sensor Networks

Transcription

1 Challenges and Opportunities for Energy Reduction in Wireless Sensor Networks Olivier Sentieys University of Rennes I INRIA 1 Research Institute olivier.sentieys@inria.fr 1 French National Institute for Research in Computer Science and Control Agenda! Principle, requirements and challenges! Generic architecture of a WSN node Processor and radio transceiver performance! Energy efficient protocols MAC layer! Energy optimization Power models Error control (LINK layer) Cooperation strategies (PHY layer) Architectural optimizations, FPGA co-processing ISSC

2 Wireless Sensor Network (WSN)! What is a Wireless Sensor Network?! Dense network of small nodes sensing the physical world and communicating through wireless links sensing, actuating, control processing, storage communication, relaying o ad hoc network Relay Sensor and relay Base station and gateway Wireless Sensor Network ISSC Wireless Sensor Network (WSN)! Sensing the physical world Modern sensing parameters include: temperature, humidity, seismic activity, building occupation, airflow, particulate detection, medical and biological parameters, etc.! Monitors environmental parameters and transmit the data to the network for automatic control or human evaluation Process could also include data compression, fusion or processing to reduce the amount of transmitted data! Enables digital abstraction of the physical world ISSC

3 Tremendous Space of Applications! Monitoring space: ocean water, pollution,! Monitoring things: robots, human body, Fire detection Target monitoring Monitoring in agriculture [Fischione, UCB, 2007] ISSC Emerging Applications! Indoor environment Industrial control, machine health monitoring, condition based maintenance of equipment in factory Indoor localization Home automation, intelligent lightning and heating Health care! Outdoor environment Monitor natural habitats, remote ecosystems, agriculture, forest fires Structural Health Monitoring (e.g. bridges, buildings) Automotive Disaster sites Security & military surveillance ISSC

4 WSN System Requirements! Simplified deployment, fault tolerance No maintenance and battery replacement! Network characteristics Low mean distance Limited amount of data Multi-hop routing! Low cost, small size! Long autonomy Towards autonomous self-powered sensor nodes mw on active period low energy consumption ISSC Challenges in WSNs (1/2)! Protocols Physical Layer MAC protocols o Power saving, collision avoidance,... Routing protocols Cross-layer optimizations! Network management! Application: computing in a distributed system Data fusion, distributed signal processing, source coding, positioning, tracking, etc. ISSC

5 Challenges in WSNs (2/2)! Energy reduction of HW/SW Computing o Low power processors/accelerators Radio front-end, analog processing o Small radios with small bandwidth & transmission ranges Light and efficient software o No complex operating systems o Mainly hardware-dependant software! Process or transmit? Limited processing power but communicating wirelessly is power-hungry ISSC Agenda! Principle, requirements and challenges! Generic architecture of a WSN node Processor and radio transceiver performance! Energy efficient protocols MAC layer! Energy optimization Power models Error control (LINK layer) Cooperation strategies (PHY layer) Architectural optimizations, FPGA co-processing ISSC

6 Generic Architecture of a Wireless Node A typical embedded system Main features: sense, process, store, communicate, power management Generator Battery DC/DC conv. Sensor A/D Processor Coprocessor Radio RAM Flash ISSC Generic Architecture of a Wireless Node SW Infrastructure APPLICATION NET LINK MAC PHY HW Infrastructure ISSC

7 Typical WSN Platform! Modern low-power microcontrollers Atmel Freescale Device Year Arch. Vdd (V) AT128L AT256l HCS08 MC RISC 8b b Ram (kb) 4 8 Flash (kb) Active 1 (ma) Sleep (ua) 5 1 Wake (us) Jennic JN b TI MSP430 F1612 F RISC 16b TI CC NXP LPC1114 CortexM ARM 32b Active current at 3V and 1MHz #6mW@8MHz [Dutta, Sensys, 2008] ISSC Typical WSN Platform! Radio transceivers IEEE compatible Device Year Vdd (V) RxSens (dbm) TxPwr (dbm ) Rx (ma) Tx (ma) Sleep (ua) Atmel RF Wake (ms) Freescale MC Jennic JN >2.5 TI CC2420 CC to 0-20 to #50mW ISSC

8 PowWow HW Platform (PWNode) PowWow: power optimized hardware/software framework for wireless motes! Open source hardware developed at INRIA/Cairn Mother board with MSP430 Daughter boards for o V1: CC2420, Sensors o V2: FPGA, DVFS! FPGA for hardware acceleration! Voltage and frequency scaling! Power management (sleep, wake-up) PWNode V1 ISSC Agenda! Principle, requirements and challenges! Generic architecture of a WSN node Processor and radio transceiver performance! Energy efficient protocols MAC layer! Energy optimization Power models Error control (LINK layer) Cooperation strategies (PHY layer) Architectural optimizations, FPGA co-processing ISSC

9 MAC Protocols! MAC protocol determines next node to use the medium (air)! Carrier Sense Multiple Access (CSMA) Compete for medium Simple, scalable e.g Avoid collisions Overhearing! Optimized CSMA Sensor-MAC (S-MAC) Timeout-MAC (T-MAC)! Time Division Multiple Access (TDMA) Schedule of medium access Avoid collision e.g. GSM Complexity of scheduling and synchronization [Bachir et al., MAC essentials for WSN, 2010] ISSC MAC Protocols! Preamble-sampling protocol Asynchronous rendezvous scheme initiated by receiver: RICER (Receiver-Initiated CyclEd Receiver) Receiver wait Node j (transmitter) Wake-up period (T) Data transmission Node k (receiver) Wake-up frames Waiting time Acknowledge Radio transceiver in reception/listening mode Radio transceiver in transmission mode [Lin, ICC, 2005] ISSC

10 Power Measurements on PowWow HW! Wake-up and channel sensing Rx Tx Rx All measurements realized with Agilent N6705A DC Power Analyzer ISSC Power Measurements on PowWow HW! Wake-up and channel sensing (with packet Tx) 6, 8, 16, 32, 64, 128 packet size in bytes ISSC

11 Power Measurements on PowWow HW! Wake-up and channel sensing with collision ISSC PowWow SW Stack! Open source software developed at INRIA/Cairn Event-driven, multi-threaded, C code Based on Protothread library from Contiki! HAL, PHY, LINK, MAC, NETW layers and API FEC/ARQ, geographical routing, positioning, Tx power and low-power mode management Modes: broadcast, flooding, direct/multi-hop with/without ACK Configurable packet structure! Memory efficiency 6 Kbytes (protocol layers) + 5 Kbytes (application)! Over-the-air re-programmation (and soon reconfiguration)! More than 12x less power than /ZigBee for the same application scenario o Temperature sensing, s sensing period, TI MAC vs. PowWow ISSC

12 Agenda! Principle, requirements and challenges! Generic architecture of a WSN node Processor and radio transceiver performance! Energy efficient protocols MAC layer! Energy optimization Power models Error control (LINK layer) Cooperation strategies (PHY layer) Architectural optimizations, FPGA co-processing ISSC Power Model of a WSN Node! PTB/PRB: power in baseband digital signal processing circuit of transmitter/receiver! PTRF/PRRF: power in front-end circuit of transmitter/receiver! PA: power of the Power Amplifier! PL: power of the Low Noise Amplifier ISSC

13 Power Model of a Transmission! Total power consumption Tx: PT(d) for a transmission of distance d Rx: PR d ISSC Power Model of a Transmission! Relation between PT(d) and the required RF output power for reliable transmission PTx(d) Gt, Gr: transmitter and receiver antenna gain PRx: desired receive power at destination!: drain efficiency!: carrier wavelength L: system loss factor ISSC

14 Chipcon Radio Tranceivers! CC2420 radio transceiver: P T (P Tx ) ~50% power reduction ISSC Output Radio Power Management Energy (mj) as a function of radio output power (dbm) Current (ma) Energy (mj) Current of a transmission for different radio output power ISSC 2010 Time (ms) 28

15 Main Issues in Energy Optmization! How can we design an energy-efficient software and hardware platform for wireless sensor networks?! (1) Decrease transmission (Tx) power Power-aware signal processing Error detection and correction! (2) Optimize radio activity and MAC Wake-up interval tuning! (3) Power optimization of the hardware Co-processing, DVS, power-gating, etc. ISSC Power optimization of a wireless node SW Infrastructure APPLICATION NET LINK MAC PHY HW Infrastructure ISSC

16 ARQ/FEC Error Control! Energy per successfully transmitted bit Energy per successfully transmitted bit[j] as a function of distance and Tx power with and without error correction d D=10 m, Pnoise=-90 dbm, 53 bytes packets Transmission Power (PTx) [dbm] ISSC 2010 [Min et al., 2002, Sentieys et al., 2007] 31 ARQ/FEC Error Control! Energy per successfully transmitted bit as a function of distance and Tx power with and without error correction " Dynamic adaptation of output radio power depending on channel conditions, distance, etc. " RSSI or CRC as quality metrics d " Interesting challenge when considering the whole network ISSC 2010 [Min et al., 2002, Sentieys et al., 2007] 32

17 Power optimization of a wireless node SW Infrastructure APPLICATION NET LINK MAC PHY HW Infrastructure ISSC Cooperative techniques! Multiple antennas at the transmitter and/or the receiver improve communication performance and therefore transmission power! Cooperative diversity with distributed antennas Cooperative strategies between wireless nodes Take advantage of channel spatial and temporal diversity to decrease the radio output power! Techniques Cooperative MIMO (or Virtual MIMO) o Space-time coding Relay o Time diversity [Cui et al., 2004] ISSC

18 Cooperative MIMO! Three phases of C-MIMO communications Phase 1: Local data exchange and space-time coding Phase 2: Virtual MIMO transmission Phase 3: Cooperative reception d S MIMO transmission N r D d m N t d m <<d d m = m ISSC Cooperative MIMO! Total energy = Transmission Energy + Digital Energy + Cooperation Energy d=100m, MISO 2-1 d=100m, SISO ISSC

19 Energy consumption of C-MIMO! Cooperative MIMO technique is more energy efficient than SISO and multi-hop SISO techniques for long distance transmission [Nguyen, Berder, Sentieys, ICC, 2008] ISSC Power optimization of a wireless node SW Infrastructure APPLICATION NET LINK MAC PHY HW Infrastructure ISSC

20 HW Platform Energy Optimization! (1) Co-processing! (2) Dynamic Voltage Scaling! (3) Radio transceiver, etc.! (4) Power Gated FSM Generator Battery DC/DC conv. Sensor A/D Processor Coprocessor Radio RAM Flash ISSC PowWow HW Platform (PWNode)! FPGA co-processing! Power Mode Management (PMM)! Dynamic Voltage and Frequency Scaling (DFVS) Watch Dog DC/DC Vdd scaling Wake-Up CC2420 Igloo FPGA Control Data MSP430 Sensors Px Co-processing mode ISSC

21 Co-Processing with a Low Power FPGA ISSC Dynamic Voltage Scaling DVS (and frequency) 1.6V, 1.8V, 2V, 2.5V, 3V, 3.3V ISSC

22 Radio Transceiver Optimization! LetiBee chip (CEA LETI) Expected power consumption (2nd release) Function RX (ma) TX RF LO 4 7 PLL Analog Digital Biasing o Tx " dbm o Rx " dbm! Trends Wake-up radio, Ultra-Wide Band ISSC 2010 [Bernier, ESSIRC, 2008] 43 Summary! Energy optimization in WSN Complex cross-layer problem Power/performance joint models! Reduction of Tx Power Signal processing, error correcting code, cooperation! Reduction of Rx activity MAC, routing, wake-up radio! Power optimization of heterogeneous platforms Power management, dedicated hardware, power gating, etc.! Power optimization of analog and radio ISSC

23 A challenging field for embedded systems Signal Processing Control! Hybrid systems! Networked control! Source coding! Modulation! MAC! Routing! Channel coding! MIMO, relay Communications WSN Computer Science! Verification! Distributed computing! Embedded software! Middleware! Operating Systems! Micro-architecture! CAD tools Microelectronics! Digital! Analog! RF ISSC References [Alam10] M. Alam, O. Berder, D. Menard, T. Anger, O. Sentieys, A Hybrid Model for Accurate Energy Analysisfor WSN, Technical Report INRIA, [Min02] R. Min et al., Power-aware Wireless Microsensor Networks, in Power-aware Design Methodologies, [Bac10] A. Bachir, M. Dohler, T. Watteyne, and K. K. Leung, MAC Essentials for Wireless Sensor Networks, IEEE. Communication surveys &Tutorials, vol. 12, no. 2, pp , [Cui04] S. Cui, A. Goldsmith, Energy_efficiency of MIMO and cooperative MIMO Techniques in Sensor Networks, IEEE JSAC, [Cartron 2006] M. Cartron, Vers une plate-forme efficace en énergie pour les réseaux de capteurs sans fil, PhD Thesis, University of Rennes 1, [Li07] Y. Li, B. Bakkaloglu and C. Chakrabarti, A System Level Energy Model and Energy-Quality Evaluation for Integrated Transceiver Front-Ends, IEEE Trans. on VLSI, [Nguyen07] Tuan-Duc Nguyen, Olivier Berder and Olivier Sentieys, Cooperative MIMO schemes optimal selection for wireless sensor networks, IEEE VTC-Spring, [Sentieys07] O. Sentieys, O. Berder, P. Quemerais and M. Cartron, Wake-up Interval Optimization for Sensor Networks with Rendez-vous Schemes, Workshop on Design and Architectures for Signal and Image Processing (DASIP), [Wang06] Q. Wang, M. Hempstead and W. Yang, A Realistic Power Consumption Model for Wireless Sensor Network Devices, IEEE SECON, [Pasha09] M. A. Pasha, S. Derrien, and O. Sentieys. Ultra low-power fsm for control oriented applications. IEEE International Symposium on Circuits and Systems, ISCAS 2009, pages , Taipei, Taiwan, May [Pasha10] M. A. Pasha, S. Derrien and O. Sentieys, A Complete Design-Flow for the Generation of Ultra Low-Power WSN Node Architectures Based on Micro-Tasking, Proc. of the IEEE/ACM Design Automation Conference (DAC) Anaheim, CA, USA, June [Nguyen08a] T. Nguyen, O. Berder, and O. Sentieys, Impact of transmission synchronization error and cooperative reception techniques on the performance of cooperative MIMO systems, IEEE ICC, [Nguyen08b] T. Nguyen, O. Berder, and O. Sentieys, Efficient space time combination technique for unsynchronized cooperative MISO transmission, IEEE VTC-Spring, [Lin05] E.Y Lin, J. Rabaey, S. Wiethoelter, and A. Wolitz. Receiver Initiated Rendez-vous Schemes for Sensor Networks. In Proc. of IEEE Globecom, [Lin04] E.Y. Lin, J. M. Rabaey, and A. Wolisz. Power-Efficient Rendez-vous Schemes for Dense Wireless Sensor Networks. In IEEE ISSC 2010 International Conference on Communications ICC,

24 Questions? Thanks for their contributions to: Thomas Anger, Jérôme Astier, Arnaud Carer, Olivier Berder, Duc Nguyen, Vinh Tran, Adeel Pasha, Steven Derrien, Hai-Nam Nguyen, Daniel Ménard, Vivek T.D., Mahtab Alam and others