Realisierungskonzepte für drahtlose Sensornetzwerke – Ein Überblick

1Stefan von der Mark

Technische Universität Berlin Microwave Engineering

Realisierungskonzepte für drahtlose Sensornetzwerke – Ein Überblick

Stefan von der Mark, Georg Böck



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



What are Sensor Networks?

University of Geneva in Switzerland

Smart Dust:



Applications

• Logistics, Locationing– 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



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:



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 802.15.4/ZigBee exists

• New IEEE 1451.4 „plug&play“ standard for– Sensor ID– Type of measurement (Units!)– Calibration data



Sensor Networks vs. RFID

RFID Sensor Networks

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



Similarities

• Low data rates• Only occasional communication• Receivers can be similar• But transmission is completely different



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



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 withown protocols

• 24 hr operation out of2 x 1200mAh Li-Ion

• Variety of sensor boards (modular concept)



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



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



Mote (Crossbow Inc.)

• Commercial sensor nodes based on UCB design and TinyOS operating system



Mote (cont.)

• Variety of different nodes• MICA2 or 802.15.4/ZigBee protocols • 315/433/868/916 MHz options (MICA)

or 2.4 GHz (ZigBee)• 1 yr operation out of

AAA batteries



MUSE (WINLAB)

• Wireless Information Network Laboratory, Rutgers University, New Jersey

• Commercial embedded computers and WLAN transceiver

• Target is completeintegration



ORBIT (WINLAB)

• 400 nodes• Pure software testbed• No development of sensor hardware



The AVM eGrain Project

• AVM – „Autarke Verteilte Mikrosysteme“• 3 year BMBF project with these partners:

AVMMWT - ANT - TKN

BMBF grant No. 16SV1658



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



Wakeup Strategies

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

Nodes need to be in a sleep mode most of the time, but how and when to activate them?



Block Diagram of the Wakeup Circuit



Detector Principle

• Zero bias Schottky Diodes• FET size increases from first to third stage



0.5 1.0 1.50.0 2.0

20

40

60

0

80

U [V]

I [m

A]

Diode-like behavior of an NMOS Transistor:

„MOS Diode“

U

I



Alternative Principle

• MOS rectifier• CMOS compatible, no BiCMOS necessary• But: less sensitivity, more standby power

Load

Vout



Wake-Up Address Decoder

• Main requirement: low power consumption• Block diagram:

Detector

PWM-signal

serial Input

Shift registersAdress

correlator

A1-A8

Discriminators&

Logic

serialdata (0/1)

clock

reset

Adress preset

A1-

A8

Wakeupparallel

data

datavalid



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



RF Frontend Overview

• Frontend characteristics– Frequency: 24.125 GHz– Range: ca. 1 m– Transmit power: ca. 1 mW

• Flip-Chip-Assemblyand integrated Antenna

• IC-Technology: GaAs-HBT-MMICs (FBH)• TU Berlin (MWT, ANT), FBH



Heterodyne Concept

• Standard approach• Upconversion and downconversion mixers• Good channel selectivity• Oscillator needed for Tx and Rx

LNA

BandFilter Mixer

VCO

Demodulator

PARF FilterIF Filter Mixer

VCO



Zero IF Concept

• No oscillator needed in the receiver • Power consumption determined by LNA• Low complexity, low power consumption

Data

BatteryOscillator

LNA Detector LF-Amplifier

Discriminator

Data

Band filter



Baseband demonstrator

• Concept

• Real data transmission at 24 GHz• Patch antenna realised on multilayer PCB• Minimum component count

RS232 12V

3V

TX Demonstrator

12V

3V

RX Demonstrator

RS232

2 2



Transmitter

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

Data

BatteryOscillator

Antenna



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

LNA Detector LF-Amplifier

Discriminator

Data

Band filter



Detector• Detector

– Diode type HSCH-3486 (Agilent)– Single stage detector – Other topologies are less efficient (bridge, cascade)

– PTX = 0 dBm, Pathloss (1m@24 GHz) = 76 dB=> PRX = –76 dBm, Gain LNA = 13 dB=> Pin, Detector = –63 dBm => Uout = 3 µV

-70 -60 -50 -40 -30-80 -20

1E-7

1E-6

1E-5

1E-4

1E-3

1E-8

1E-2

P_in

HB

.V_out_

e[::,0]

Matching



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) DC

IN

OUT

Bias Bias

Chipsize 1.1x1.3 mm



Assembly

• Aperture coupled patch antenna

• Industry standard multilayer PCB

• RF Chip Flip-Chip mounted

• LF electronics in SMD• Housing soldered

• => only standard assembly technologies

Battery

RF ChipGroundplane

Patch-AntennaApertureFeedlineTeflon

Multilayer- PCB

1cm

LF Components

FR4

Solder



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



Aperture coupled feed

• Greater bandwidth than for coaxial feed

• Lower directivity of15.6 dB

• Gain 7.8 dB• Fabrication much easier

than coax feed



Photo

• 1 cm3

• 2 button cellbatteries

• 24 GHz• 2400 bps



Future Work

• CMOS LNA to further reduce power consumption of the receiver (7 mA @ 1.2 V)

• Integration of detector with LNA– BiCMOS with schottky diodes– Pure CMOS with MOS rectifier

• Complete integration as SoC



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!



ReferencesT. 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. 62-70

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. 70-73

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

http://tcs.unige.ch/doku.php/web/wirelesssensornetworks University of Geneva in Switzerland

http://bwrc.eecs.berkeley.edu BWRC at UCB: PicoRadio, PicoNode, PicoBeacon

http://www.csem.ch CSEM: WiseNet

http://www.xbow.com Crossbow: Mote

http://www.winlab.rutgers.edu WINLAB: Muse, Orbit

http://www-mwt.ee.tu-berlin.de Technische Universität Berlin Microwave Engineering: AVM

Documents

Realisierungskonzepte für drahtlose Sensornetzwerke – Ein Überblick