ultra wide band (uwb) technology and applications · so why is uwb so interesting? 7.5 ghz of...
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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
rro
wb
an
dC
om
mu
nic
atio
n
0 1 0 1
ImpulseModulation
3 10 GHzfrequency
Ult
raw
ide
ba
nd
Co
mm
un
icat
ion
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
14
Ultra-Wide Band Communication for the Internet of Things
The MICS UWB Networkuwb.epfl.ch
15
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.
16
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
17
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)
18
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.
19
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
20
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
21
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
22
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
23
Multipath PropagationSignal propagation subject to reflectionsPulses are attenuated / modified but still distinguishable
Very little destructive interference
Channel response Received signal
24
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
25
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
26
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
27
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
28
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
29
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
31
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
32
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
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