1 Ultra-Wide Band Communication for the Internet of Things The MICS UWB Network uwb.epfl.ch...

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Ultra-Wide Band Communication for the

Internet of ThingsThe MICS UWB Network

uwb.epfl.ch

Jean-Yves Le Boudec (coordinator), EPFL I&C21-23 January 2008

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Abstract:

Ultra-Wide Band communication is a technology for low range, low power sensor and mobile devices which employs very low transmission powers (below the level of unintentional emissions) and high bandwidth. It possesses a number of unique features that make it very attractive to many local applications. First, ranging with high accuracy is possible even indoors. Second, it is resistant to multipath fading which often pleagues indoors communications. Third, it scales well in dense deployments. Fourth, cryptographic modulation is possible. In this talk, we describe the research done in the MICS Ultra-Wide Band network, showing ranging, dense deployment capabilities and medical applications.

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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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A Network within MICS researching on Impulse Radio UWB

The network CSEM, Neuchatel

Prof. Farserotu, Hai ZhanProf. Decotignie, Jerôme Rousselot

ETHZ, Zurich Prof. Wittneben, Florian Trösch, Christoph Steiner

EPFL I&C, Lausanne Prof Le Boudec (coordinator), Ruben Merz, Manuel Flury

EPFL STI, Lausanne Prof. Dehollain, James Colli-Vignarelli, Prakash Thoppayegambaram Prof. Skrivervik, Gabriela Quintero

HES SO, Yverdon Prof. Robert, Jérome Vernez

ST Microelectronics, Geneva Dr. J. Zory

Impulse radio Ultra Wide Band communication

Low powerIn presence of multi user interferenceRanging

Provide fundamental research and proofs of concept

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Table of Contents




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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 rate

Shannon-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

Source: Gabriela Quintero

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 collisionIncreaed 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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Table of Contents


3. Impulse Radio UWB4.Low Power: Medical Application


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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 kbits/s

Peak Data Rate of 50 Mbits/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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Body Area Network UWB Test Bed

Ear-to-Ear Channel

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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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Relevant Publications

F. Troesch, C. Steiner, T. Zasowski, T. Burger, and A. Wittneben, "Hardware Aware Optimization of an Ultra Low Power UWB Communication System," IEEE International Conference on Ultra-Wideband, ICUWB 2007, Marina Mandarin, Singapore, Sept. 2007. C. Steiner and A. Wittneben, "On the Interference Robustness of Ultra-Wideband Energy Detection Receivers," IEEE International Conference on Ultra-Wideband, ICUWB 2007, Singapore, Sept. 2007.

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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: » N-1/2

In practice, this requires careful system design

MACSignal AcquisitionAccommodate multipath

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PHY-Aware MAC

Classical organization of a network

E.g. WiFi, BluetoothPHY transmits packetsMAC avoids collisionsi.e. MAC = mutual exclusion

This is not efficient for UWBMutual exclusion divides throughput linearly…… but most collisions are at pulse level

Rate reduction is small

The optimal is: Allow interference and manage it !Requires MAC to be PHY aware

Data

THS(A), Code = Ri

ACK

THS(A),Code = RN

Data

THS(A),Code = Rj

Idle

THS(B), Code = RN

NACK THS(A),Code = RN

Incremental Red.

THS(A)

B A C

Our experimental MAC

Interference, not collision

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DCC-MAC

A PHY aware MAC protocol, designed to be robust to interference

DCC= dynamic channel coding

Key features of designOne time hopping sequence per destination (private time hopping sequences)Interference mitigation at pulse levelMutual exclusion for a single destination onlyRate adaptation

DCC MAC

CA/CDMA -like

802.11 - like

N nodes in a chain

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Signal Acquisition

Signal acquisition is difficult for Impulse Radio UWB

Signal is intermittentInterferences are allowedClassical methods based on gaussian noise hypotheses do not apply

Power Independent Detection (PID) is robust to interference

even if interfering power is larger than intended signaluses thresholding

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Private Time Hopping Sequences

Common Time Hopping Sequence in preamble

Many useless acquisitions

One Private Time Hopping Sequence per destination

Acquisition is private, only intended receiver decodesRequires source to know sequence of destination

E.g. linear congruence seeded with MAC address of destination

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Private Sequences Avoid the Ad-Hoc Collapse

Ad-hoc collapseMany TCP connections in an ad-hocCollapses with 802.11 and other protocolsDue to collisionsNo good solution known to this problem

With private sequences, the ad-hoc collapse goes away

Nodes acquire only packets destined to self

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Accommodate Multipath

Assume modulation is pulse position

With interferers and multipath, received signal looks like

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Idea: (Rake receiver)Estimate channel during signal acquisition phaseLook for pattern of pulses in the received signal - correlationUse thresholds to avoid near end effects

Similar ideas apply to energy detectors

0

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Performance Evaluation of IEEE 802.15.4a

Standard for Impulse Radio UWB, Low Data Rate

MAC influenced by narrow band tradition

2 THSs in total

Makes some compromises to ease implementation

Bursts of pulses

Q: how does it perform with respect to interference robustness ?

Multiple transmissions in same networkTransmissions from neighbouring, non coordinated network

We simulated the standard in detail, with interferers, and compared its performance against two benchmarks

Benchmark 1: Destructive collision

Packet lost when two transmissions overlapALOHA performanceTypical of narrowband systems

Benchmark 2: Perfect capture

Packets compete during signal acquisition and transmissionOnly one succeedsTypical of ideal UWB system

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IEEE 802.15.4a is not Robust to Interference

Performance is close to destructive collision

Does not exploit UWB benefits well

Possible fixesCompress burstsPrivate time hopping sequences

Benchmark 2: Perfect capture

Benchmark 1: Destructive collision

802.154a, no interference

802.154a, with interference

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Interference Testbed

Goal:Implement and test multi-user impulse radio systemIn presence of multi-user interference

Real hardware, still programmable in matlab

A coordinated effort of the MICS UWB network

Ruben Merz (coordinator)James Colli-VignarelliGabriela QuinteroPrakash Thoppayegambaram Jerome VernezJean-François Zürcher

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Interference Testbed (EPFL, HES SO)

Video by Jerome Vernez, HES SO (Yverdon)

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El Fawal, Alaeddine ; Le Boudec, Jean-Yves, “A Robust Signal Detection Method for Ultra Wide Band (UWB) Networks with Uncontrolled Interference”, In: IEEE Transactions on Microwave Theory and Techniques (MTT), vol. 54, num. 4, part 2, 2006, p. 1769-1781Radunovic, Bozidar ; Le Boudec, Jean-Yves, “Optimal Power Control, Scheduling and Routing in UWB Networks”, In: IEEE Journal on Selected Areas in Communications, vol. 22, num. 7, 2004, p. 1252Merz, Ruben ; Widmer, Jörg ; Le Boudec, Jean-Yves ; Radunovic, Bozidar, “A Joint PHY/MAC Architecture for Low-Radiated Power TH-UWB Wireless Ad-Hoc Networks”, In: Wireless Communications and Mobile Computing Journal, Special Issue on Ultrawideband (UWB) Communications, vol. 5, num. 5, 2005, p. 567-580Flury, Manuel ; Merz, Ruben ; Le Boudec, Jean-Yves, “Managing Impulsive Interference in Impulse Radio UWB Networks”, In: ST Journal of Research, 2007Flury, Manuel ; Merz, Ruben ; Le Boudec, Jean-Yves ; Zory, Julien, “Performance Evaluation of an IEEE 802.15.4a Physical Layer with Energy Detection and Multi-User Interference”, In: IEEE International Conference on Ultra-Wideband (ICUWB 2007), 2007

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Table of Contents



5.Robustness to Interference 6.Ranging7.Outlook

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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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C. Steiner, F. Althaus, F. Troesch, and A. Wittneben, "Ultra-Wideband Geo-Regioning: A Novel Clustering and Localization Technique," EURASIP Journal on Advances in Signal Processing, Special Issue on Signal Processing for Location Estimation and Tracking in Wireless Environments, Nov. 2007.C. Steiner and A. Wittneben, "Clustering of Wireless Sensors based on Ultra-Wideband Geo-Regioning," Asilomar Conference on Signals, Systems, and Computers, Pacific Grove, USA, Nov. 2007.

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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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Experimental setting

Quiet room at EPFL (not anechoic)

Experiment implemented by Hai Zhan (CSME)True distance is 48.8 cm – estimated distance is 50.0 cm

Ranging Through Obstacles and With Interferers

Non severe non light of sight ranging is possible

E.g. through wood or cardboard

The modified Prony algorithm finds the first pulse

Sent signal contains a train of encoded pulsesReceived signal contains many replicas due to multipathStrong pulses help find weak

Click on figure for video

Video by Hai Zhan, CSEM

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Zhan, Hai ; Farserotu, John ; Le Boudec, Jean-Yves “A Novel Maximum Likelihood Estimation Of Superimposed Exponential Signals In Noise And Ultra-Wideband”, PIMRC 07, 2007

Zhan, Hai ; Ayadi, Jaouhar ; Farserotu, John ; Le Boudec, Jean-Yves, “High-Resolution Impulse Radio Ultra Wideband”, In: The 2007 IEEE International Conference on Ultra-Wideband, ICUWB 2007, 2007

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Table of Contents



5.Ranging6.Robustness to Interference

7.Outlook

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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

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Thank You

Special thanks go to all who helped prepare this presentation

Jerome VernezHai ZhanRuben MerzChristoph Steiner

And to all other contributors of the MICS UWB network who make this project such a great fun

Manuel FluryJames Colli-Vignarelli Jean-Dominique DecotignieCatherine DehollainJohn FarserotuGabriela QuinteroStephan RobertJérome RousselotAnja SkrivervikPrakash Thoppayegambaram Florian TröschArmin WittnebenJulien Zory

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