Ultra Wide Band (UWB) Technology and Applications

Young Man Kim

The Ohio State University

What is Ultra Wideband?Radio technology that modulates impulse based waveforms instead of continuous carrier waves

FrequencyModulation

2.4 GHzNa

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0 1 0 1

ImpulseModulation

3 10 GHzfrequency

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Time-domain behavior Frequency-domain behavior

time

1 0 1

(FCC Min=500Mhz)

Information Modulation

Pulse Position Modulation (PPM)

Pulse Amplitude Modulation (PAM)

On-Off Keying (OOK)

Bi-Phase Modulation (BPSK)

Pulse length ~ 200ps; Energy concentrated in 2-6GHz band;

Voltage swing ~100mV; Power ~ 10uW

UWB SpectrumFCC ruling permits UWB spectrum overlay

1.6 1.9 2.4

Bluetooth,802.11bCordless PhonesMicrowave OvensG

PS

PC

S

5

802.11a

-41 dBm/Mhz“Part 15 Limit”

UWB Spectrum

Frequency (Ghz)

EmittedSignalPower

10.63.1

FCC ruling issued 2/14/2002 after ~4 years of study & public debate

Theoretical Data Rates over Range

UWB shows significant throughput potential at short rangeUWB shows significant throughput potential at short range

Performance Analysis with encoding rules

So why is UWB so Interesting?

7.5 Ghz of “free spectrum” in the U.S.FCC recently legalized UWB for commercial useSpectrum allocation overlays existing users, but its allowed power level is very low to minimize interference

Very high data rates possible500 Mbps can be achieved at distances of 10 feet under current regulations

“Moore’s Law Radio”Data rate scales with the shorter pulse widths made possible with ever faster CMOS circuits

Simple CMOS transmitters at very low powerSuitable for battery-operated devicesLow power is CMOS friendly

Ultra Wideband CharacteristicsExtremely low transmission energy ( less than 1mW)Very high bandwidth within short range (200Mbps within 10m)Extremely difficult to intercept

– Short pulse excitation generates wideband spectra – low energy densities– Low energy density also minimizes interference to other services

Multipath immunityCommonality of signal generation and processing architecturesRadar

– Inherent high precision – sub-centimeter ranging– Wideband excitation for detection of complex, low RCS targets

Geolocation/Positioning– Sub-centimeter resolution using pulse leading edge detection– passes through building blocks, walls, etc. (LOS not required)

Low Cost– Nearly “all-digital” architecture– ideal for microminiaturization into a chipset

Frequency diversity with minimal hardware modifications

UWB AdvantagesCapacity

possibility of achieving high throughputLow power & Low cost

Can directly modulate a baseband pulseCan be made nearly all digitalHigh capacity with lower Tx power levels

Fading robustnessWideband nature of the signal reduces time varying amplitude fluctuations (?)Relatively immune to multipath cancellation effects

Path delay ~ 1ns > pulse durationBut don’t we build RAKE just to rebuild the multipath thing ?What about ISI ?

Position location capabilityDeveloped first as radar technology (!)

FlexibilityCan dynamically trade-off throughput for distance

UWB Application 1 : WPANMobileCluster

handheld PCs

tablets

MP3

PDAs

mobile phone

3Ghandsets

camera phones

laptops

printers

speakers

PCCluster

storagedevices

Scanners

scanners

DVDplayers

• Desktop and Laptop PCs– High res. printers, scanners,

storage devices, etc– Connectivity to mobile and

CE devices

• Mobile Devices– Multimedia files, MP3, games, video– Personal connectivity

• CE Devices– Cameras, DVD, PVR, HDTV– Personal connectivity

One PHY for Personal Computing, Consumer Electronic and Mobile, Wireless Personal Area Connectivity

cameras

CECluster

HDTV

STBs

VCRs

PVRs

camcordersconsole games

audiosystems

UWB Application 2

Positioning, Geolocation, LocalizationHigh Multipath EnvironmentsObscured Environments

CommunicationsHigh Multipath EnvironmentsShort Range High Data RateLow Probability of Intercept/ Interference

Radar/Sensor : MIR (motion detector, range-finder, etc.)Military and Commercial: Asset ProtectionAnti-Terrorist/Law EnforcementRescue Applications

Three Principles of Positioning

TOA (Time of Arrival) & RTD (Round Trip Delay)

TDOA (Time Difference of Arrival)

AOA (Angle of arrival)

Related Standards

IEEE 802.15 : Wireless Personal Area Network (WPAN)IEEE 802.15.1 : Bluetooth, 1MbpsIEEE 802.15.3 : WPAN/high rate, 50MbpsIEEE 802.15.3a: WPAN/Higher rate, 200Mbps, UWBIEEE 802.15.4 : WPAN/low-rate, low-power, mW level, 200kbps

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Ultra-Wide Band Communication for the Internet of Things

The MICS UWB Networkuwb.epfl.ch

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Ultra-Wide Band communication is a technology for lowrange, low power sensor and mobile devices whichemploys very low transmission powers (below the levelof unintentional emissions) and high bandwidth.

It possesses a number of unique features that make itvery attractive to many local applications.

• First, ranging with high accuracy is possible evenindoors.

• Second, it is resistant to multipath fading which oftenpleagues indoors communications.

• Third, it scales well in dense deployments.

• Fourth, cryptographic modulation is possible.

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Table of Contents

1. The UWB Network of MICS2. What is UWB ?

3. Impulse Radio UWB4. Low Power Medical Application

5. Robustness to Interference6. Ranging7. Outlook

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Ultra Wide Band (UWB) Communication

Use a very large spectrumup to Several GHzs

Very low powerBelow level of unintentional emission

UnlicensedCo-exists with other technologies

Power LimitsFCC (2002) limits

peak power (0dBm per 50MHz)

mean power (-41.3dBm per MHz)

Europe (and CH-Ofcom, 2007) put more stringent limits

US

EC

(source: FCC 2002, CH-Ofcom, 2007)

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Various Uses of UWB SignalsRadar and Ranging

RadarA very old UWB application, used for maritime or air navigation, and as remote speedometer New apps: automotive security, rescue operationOne active device analyzes echoTarget is passive and unaware of signalNot always low power

RangingFrom device to deviceDevice is active senderBase station is receiver /transmitterE.g Ubisense, Cambridge UKLow power

E.L.

E.L.

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Various Uses of UWB SignalsCommunication

Short Range CommunicationLow powerUp to 30 m indoors

High data rate UWB Communication

Wireless USB / Wireless FirewireUses entire bandwidthVery large bit rate on one single linkPeaky in frequency

Low data rateE.g. Sensor networksImpulse radio signalsVery large aggregate throughput

Robots with ranging needs for collective intelligence

Source: Prof. Alcherio Martinoli

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Strengths and Weaknesses of UWB

High throughput for high data rateShannon-Hartley law: C = B log2 ( 1 + S/N )

with C = bit rate (b/s)B = bandwidth (Hz)

Exploited by Wireless USB / Firewire : 100- 480 Mb/s for Wireless USB over 3-10 m

Low Power for Low Data rate

ScalabilitySensor network with very large bandwidth, total capacity scales with number of nodes

Resistance to Channel Impairments

Multiple paths are distinguishableSuitable for indoors, terrain with obstacles, metallic environment

High Resolution in time domainRanging with cm accuracy indoorsSecure ranging

Short range10 m to 30 m

Source: Mohammad Abualreesh

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Impulse Radio UWB Uses Short Pulses

Pulses are narrow in time, wide in frequency

Pulse duration order of 1 ns

FeaturesLow power

Duty cycle at 1 Mb/s = 1 %Robust against multi-user interferenceHigh precision ranging

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Impulse Radio UWB Uses Time Hopping

Time Hopping Sequence: […, 2, 5, 4, 7 …] Pulses appear random unless you know THSTHS is predictible to user who knows the key ; e.g.: MAC address

Transforms packet collision into symbol collisionIncreased bit error rate instead of packet loss

Software-like flexibility in hardwareWhen a pulse is sent can easily be changed by modifying a few values in the systemChange the time hopping sequenceChange the modulation rate

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Multipath PropagationSignal propagation subject to reflectionsPulses are attenuated / modified but still distinguishable

Very little destructive interference

Channel response Received signal

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Body Area Network with UWB

Requires very low powerVery bad transmission channel

UWB body area network prototype developed at ETH / Prof A. Wittneben’s group

Ear to ear communicationFocus on low power and point to point link

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Wireless BAN Communication for less than 1 mW

Bursts of 500 bits/ms

Average Data Rate of 500 kbit/s

Peak Data Rate of 50 Mbit/s

Simple Tx and Rx Structures

Mainly Analog Processing

Estimated Power Consumption < 1mW

Analog Part

Rx Chain Energy Detection

Tx Chain UWB Pulse Generator

1% duty cycle 500 kbits/s < 0.3 mW

Digital Baseband

ADC Clock Synthesis Synchronization Decoding Error Correction MAC

< 0.7 mW

Sampling at 200 MHz

Low CostLow PowerLow ComplexityUltra-Wideband Radio

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GUI for UWB test-bedAverage transmit power -45 dBmEar-to-ear channel with artificial water-bucket-headBER at -45dBm is 0.04, capacity is 480 Mb/s

transmit receive

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Robustness to InterferenceFrom Theory to Practice

In Theory, UWB transmission is robust to interference from other UWB systems (Due to large bandwidth)

This makes UWB systems potentiallyscalable, well adapted to dense deployments

Throughput per node constant with number of nodes NContrast to narrowband systems: » 1/N1/2

In practice, this requires careful system designMACSignal AcquisitionAccommodate multipath

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Impulse Radio UWB enables low cost ranging at high precision

Short pulses can easily be located by receiverBasis for radarsCan be used at low cost in all sorts of equipments with UWB2 techniques are researched in the MICS UWB Network

Geo-regioningHigh resolution ranging

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Geo-Regioning

A method for location finger-printingIdea: channel impulse response is correlated in spaceMethod:

Learning phase: send test signals to base station from various locations Analyze correlations (e.g. covariance matrix, delay profile)

Tracking PhaseMobile sends beacons to base stationReal time correlation is performed

Channel response

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UWB Geo-Regioning Demonstration Developed by Prof. A. Wittneben’s group / ETHZ

Channel impulse responses from region 22 to RX

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High Resolution Ranging

Accurate ranging = estimation of distance

Based on time of arrival of signal

Idea:mobile sends UWB pulses to one or several base stationsdetect first pulse at receiver

How:Estimate both channel response and time of arrival of first pulse

Not always strongest

Remove noise and interference by modified Prony algo

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Impulse Radio UWB is a key technology for the Internet of Things

Unique featuresIndoors rangingResistance to multiuser interferenceScalable total throughputVery low power

Practical developments are only starting

Standard based implementations can be improved

Potential areas of future research

Secure rangingVery short signal time

High throughput ranging Frequent position updates for distributed robot control