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Ultra-Widebandcommunication technology

for sensor network

applicationsJulien Ryckaert

IMECJulien.Ryckaert@imec.be

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The vision of Ambient Intelligence

An environment where technology isembedded, hidden in the background

Fred BoekhorstPhilips Research, ISSCC 02

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Health Care of the Future

Fitness for you!

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Increase Productivity

Home of the Future

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Energy

S e n s

i n g

clock

A sensor node is a completelyautonomous device

P r o c e s s

i n g

C o m m u n

i c a

t i o n

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Three major challenges in thecommunication module

Ultra-low power : >2 years autonomy Ultra-small size : non-invasive Ultra-low cost : disposable

Energy

S e n s i n g

clock

P r o c e s s i n g

C o m m

u n i c a t i o n

Low communication performance :

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POWER CONSUMPTION

PERFORMANCE

?

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In reality, the total Energyconsumption must be minimized

What does it cost to transfer a bit of information?

Power consumption (Energy/time)

Data rate (bits/time)= Energy/bit

Power Energy/bit

but Data rate Energy/bit

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How does it look like today?

50 Mbps

After CEA-LETI

E n e r g y

/ b i t ( n J / b i t )

10E0

10E1

10E2

10E3

10E4

1Mbps 250kbps 10 to 150 kbps

Increasing data rate

The active time of the radio must be minimized!!!

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POWER CONSUMPTION

PERFORMANCE

?UWB

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Traditional Communicationsystems use continuous waves

NarrowBand Communication

time frequency

Each user/application has its own

spectrum band

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Impulse Radio UWB uses shortpulses

Pulse-based Ultra WideBand communication

time frequency

Emitted power must be low

enough to avoid jamming

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Active Active

Sleep

Power

Activate the radio only whenneeded

The active time of the radio is reduced:

Radio duty - cycling

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FCC: UWB communication must bedone in the 3.1-10GHz band

10.6

-41dBm/MHz

3.11 F [GHz]

Full-7GHz Band

10.6

-41dBm/MHz

3.11 F [GHz]

Minimum 500MHz band

More users

FCC

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IEEE standard for low data-ratesensor networks

1 s

1 s

Burst

Activate the transmitter only whenneeded to achieve low-power

3% Active! 97% Inactive

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The standard imposes someconstraints on the signals

Pulses are BPSK modulated1

0

Fcarrier = N x Fpulse

Pulse repetition frequency multiple of carrier frequency

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DigitallyControlled

Oscillator (DCO)

ProgrammableDivider (DIV)

7:20Div 16

DCO register

E-LDetector

RFout

Chip

Burst Code

Data

Trigger

Clock31.2MHz Enable

DigitalModulator

(DMO)

499.2MHz chip rate

RF LO3-10GHz

Control loop

FPGA

31.2MHz

Data

E/LDCO fine frequencyconfiguration bits

499.2MHz

4

CONTROL LOOP

Overall transmitter architecture

(ISSCC 07)

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Time-domain measurement of the output signal

1 0 0 1 1 1 0 1 1 1 0 0 1 1 0 1

Same energy efficiency as first transmitter!

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Correlation can be done eitherin Analog or in Digital domain

ADC

Analog

Correlation

Decision

ADCDigital

Correlation(Matched Filter)

Decision

High Sampling rate Power Hungry

Very precise timing Power Hungry

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Full system block diagram

LOTiming circuit

DigitalController(System

Configurationand

Interfacing)

ADC

ADC

Q

I

LNA

DL

Clk/Rst

Serial/ParOut

I/O bus

CAL

CAL

Analog Output

Clk

RFin

(ISSCC 06)

DL DL DL

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What about power consumption?

State-of-art narrowband solutions (Zigbee): TX: 10mW RX: 2mW

UWB solutions: TX: 0.5-1mW RX: 0.3mW

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UWB has other advantages

Positioning by measuring the time of arrival

Security : UWB power spectrum below thebackground noise

TX RX

TXD T

D L

Background noise (kT)

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Other impulse Radioimplementations exist

Example: MIT (US) proposes a similar concept:

But uses a proprietary UWB communication interface

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Therefore the question: shouldsensor networks be standardized?

Pros: Interoperability (add nodes in the network) Market pressure decreases cost

Cons: Solution biased by the big ones Security Less interferences (?)

Sandardization aspect is an old controversialdebate for healthcare wireless systems

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Conclusions

UWB offers today a 10x improvement onpower consumption.

UWB has other interesting advantages inthe context of sensor networks: security,positionning,

An IEEE standard exists today (IEEE802.15.4a), but its use in wirelesshealthcare systems is still a debate.