1. Realisierungskonzepte für drahtlose Sensornetzwerke – Ein Überblick
Stefan von der Mark, Georg Böck

2. Overview What are Wireless Sensor Networks?
Similarities and differences to RFID
Some published approaches
PicoRadio/PicoBeacon (Berkeley)
WiseNET (CSEM)
MUSE and ORBIT (WINLAB)
The AVM eGrain project
Concept
WakeUp
Demonstrator

3. What are Sensor Networks?
Smart Dust:
University of Geneva in Switzerland

4. Applications Logistics, Locationing Environmental monitoring
Goods in a warehouse or shopping center
Books in a library
Environmental monitoring
Indoor: Temperature, humidity, intruders
Outdoor: Pollution, agricultural research
Structural monitoring
Bridges, skyscrapers, large halls
Ageing, stress from snow, earthquakes
Military

5. Properties of Sensor Networks
Tiny little low cost sensor nodes
Wireless peer to peer communication
Self-sustained operation for prolonged time
Preferably completely integrated (CMOS)
Ad Hoc Networking:
Only some sensors communicate with base stations
Data is routed through the sensors

6. State of the Art Existing sensor arrays are usually wired
Classical: Analog wire from each sensor
More modern: Digital bus systems
Existing wireless sensors usually communicate with dedicated access points
Sensor communication mostly proprietary, but IEEE standard /ZigBee exists
New IEEE „plug&play“ standard for
Sensor ID
Type of measurement (Units!)
Calibration data

7. Sensor Networks vs. RFID
Transponder and interrogator
All nodes equal
Tags reply only on request of Interrogator
All nodes can initiate transmission
High transmission power available from interrogator
Very low transmission power
Transponder usually powered by incoming RF
Own power source necessary

8. Similarities Low data rates Only occasional communication
Receivers can be similar
But transmission is completely different

9. Realisation approaches
Nothing coming close to the vision has been realized so far
Different approaches are being pursued:
Big and power hungry, but functional nodes (for protocol develompment, application research)
Demonstration of particular technologies (low power circuits, sensing, energy scavenging)
Attempts towards complete low power hardware (with reduced functionality)
And anything in between
Kleine Auswahl, bei Weitem nicht vollständig

10. PicoNode I (UC Berkeley)
„PicoRadio Project“ at Berkeley Wireless Research Center, University of California at Berkeley (UCB)
Strong ARM CPU
Xilinx FPGA
Proxim RangeLAN or Bluetooth HW with own protocols
24 hr operation out of 2 x 1200mAh Li-Ion
Variety of sensor boards (modular concept)
January 2002

11. PicoBeacon (UCB) Energy scavenged from light and vibration
180 W out of 1 cm3 from vibrations
1.9 GHz transmission (no receiver)
10m range
2.4 x 3.9 cm2
Agilent Film Bulk Acoustic Resonator (FBAR) for 1.9 GHz Oscillator

12. WiseNet (CSEM) Swiss Center for Electronics and Microtechnology (CSEM)
2 mW RX, 32 mW TX
433 / 868 MHz ISM
25 kbps
25 W for 56 bytes every 100 seconds
WiseMAC specialized MAC protocol
External Antenna

13. Mote (Crossbow Inc.)
Commercial sensor nodes based on UCB design and TinyOS operating system

14. Mote (cont.) Variety of different nodes
MICA2 or /ZigBee protocols
315/433/868/916 MHz options (MICA) or 2.4 GHz (ZigBee)
1 yr operation out of AAA batteries

15. MUSE (WINLAB)
Wireless Information Network Laboratory, Rutgers University, New Jersey
Commercial embedded computers and WLAN transceiver
Target is complete integration

16. ORBIT (WINLAB) 400 nodes Pure software testbed
No development of sensor hardware

17. The AVM eGrain Project AVM – „Autarke Verteilte Mikrosysteme“
3 year BMBF project with these partners:
MWT - ANT - TKN
AVM
BMBF grant No. 16SV1658

18. Concept
Development of completely autarkic ultra low power pico cell network
Nodes are self organizing, no master/slave principle
Highly integrated, node size ~1 cm3
RF frequency 24 GHz
Development of low power system architecture
Development of ultra low power RF components

19. Wakeup Strategies
Nodes need to be in a sleep mode most of the time, but how and when to activate them?
Periodic Wakeup
Wakeup Receiver
 No extra components
 Network synchronization necessary
 Waste of power through unnecessary wakeups
 Delay in communications
 Immediate response
 No reference clock
 Standby power consumption

20. Block Diagram of the Wakeup Circuit

21. Detector Principle Zero bias Schottky Diodes
FET size increases from first to third stage

22. „MOS Diode“
Diode-like behavior of an NMOS Transistor:

23. Alternative Principle
MOS rectifier
CMOS compatible, no BiCMOS necessary
But: less sensitivity, more standby power

24. Wake-Up Address Decoder
Main requirement: low power consumption
Block diagram:
Detector
PWM-signal
serial Input
Shift registers
Adress
correlator
A1-A8
Discriminators
&
Logic
serial
data (0/1)
clock
reset
Adress preset
Wakeup
parallel
data
valid

25. Prototype of Address Decoder
CMOS-technology
Low complexity: ca. 470 transistors
No oscillator
Low data rate: e.g. 50 kb/s
Address
preset
RF Input
PWM signal
Wakeup-Output
Bias
Vcc: + 3V

26. RF Frontend Overview Frontend characteristics
Frequency: GHz
Range: ca. 1 m
Transmit power: ca. 1 mW
Flip-Chip-Assembly and integrated Antenna
IC-Technology: GaAs-HBT-MMICs (FBH)
TU Berlin (MWT, ANT), FBH

27. Heterodyne Concept Standard approach
Upconversion and downconversion mixers
Good channel selectivity
Oscillator needed for Tx and Rx

28. Zero IF Concept No oscillator needed in the receiver
Power consumption determined by LNA
Low complexity, low power consumption

29. Baseband demonstrator
Concept
Real data transmission at 24 GHz
Patch antenna realised on multilayer PCB
Minimum component count

30. Transmitter On-Off-Keying (OOK) modulation
No power consumption in standby mode
No power consumption for „0“ bits

31. Receiver Zero IF No mixer => no LO necessary (power saving!)
LF amplifier has very low current consumption (ca. 100 µA)
Total battery current < 15 mA
Dielectric Resonator as BPF

32. Detector Detector Diode type HSCH-3486 (Agilent) Single stage detector
Other topologies are less efficient (bridge, cascade)
PTX = 0 dBm, Pathloss GHz) = 76 dB => PRX = –76 dBm, Gain LNA = 13 dB => Pin, Detector = –63 dBm => Uout = 3 µV
Matching

33. LNA Measured LNA performance 14 mA DC @ 2 V 13.3 dB gain @ 24.8 GHz
Bandwidth 4.2 GHz
NF 5.8 dB (simulated)
Chipsize 1.1x1.3 mm

34. Assembly Aperture coupled patch antenna
Industry standard multilayer PCB
RF Chip Flip-Chip mounted
LF electronics in SMD
Housing soldered
=> only standard assembly technologies

35. Patch Antenna Principle
Whole module size is antenna base
Great beam collimation
Directivity 19.6 dB
Gain 8.5 dB (theo. Max. 9 dB)
Coax feed

36. Aperture coupled feed Greater bandwidth than for coaxial feed
Lower directivity of 15.6 dB
Gain 7.8 dB
Fabrication much easier than coax feed

37. Photo
1 cm3
2 button cell batteries
24 GHz
2400 bps

38. Future Work
CMOS LNA to further reduce power consumption of the receiver (7 1.2 V)
Integration of detector with LNA
BiCMOS with schottky diodes
Pure CMOS with MOS rectifier
Complete integration as SoC

39. Summary Today the vision is still far from reality
But many efforts and progress are made in
Hardware design (digital and RF)
Integration and miniaturization
Energy scavenging and storage
Software design
Some day the vision will become reality!

40. References
T. T. Hsieh Using sensor networks for highway and traffic applications IEEE Potentials, vol. 23, no. 2, pp. 13 – 16, Apr-May 2004
Christian C.Enz, Amre El-Hoiydi, Jean-Dominique Decotignie, Vincent Peiris WiseNET: An Ultralow-Power Wireless Sensor Network Solution IEEE Computer, August 2004, p
Shad Roundy, Brian P. Otis, Yuen-Hui Chee, Jan M. Rabaey, Paul Wright A 1.9GHz RF Transmit Beacon using Environmentally Scavenged Energy IEEE Int.Symposium on Low Power Elec. and Devices 2003
Stefan von der Mark, Meik Huber, Mathias Wittwer, Wolfgang Heinrich, and Georg Boeck System Architecture for Low Power 24 GHz Front-End Frequenz -Zeitschrift für Telekommunikation, Special Issue Autarkic Distributed Microsystems in Sensor Networks, 3-4/2004, p
M. Huber, S.v.d. Mark, N. Angwafo and G. Boeck Ultra low power Wakeup Circuits for Pico Cell Networks, A conceptional View Technical Report of the 1st European Workshop on Wireless Sensor Networks (EWSN), Jan 2004
Stefan von der Mark, Roy Kamp, Meik Huber and Georg Boeck Three Stage Wakeup Scheme for Sensor Networks IEEE/SBMO International Microwave and Optoelectronics Conference IMOC 2005; Brasilia, Brazil, July 25-28
University of Geneva in Switzerland
BWRC at UCB: PicoRadio, PicoNode, PicoBeacon
CSEM: WiseNet
Crossbow: Mote
WINLAB: Muse, Orbit
Technische Universität Berlin Microwave Engineering: AVM