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Ultra-Wide Band Communication for the Internet of Things. The MICS UWB Network uwb.epfl.ch Jean-Yves Le Boudec (coordinator), EPFL I&C 21-23 January 2008. Abstract:

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ultra wide band communication for the internet of things

Ultra-Wide Band Communication for the Internet of Things

The MICS UWB Networkuwb.epfl.ch

Jean-Yves Le Boudec (coordinator), EPFL I&C

21-23 January 2008

1

slide2

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.

2

table of contents
Table of Contents
  • The UWB Network of MICS
  • What is UWB ?
  • Impulse Radio UWB
  • Low Power Medical Application
  • Robustness to Interference
  • Ranging
  • Outlook

3

a network within mics researching on impulse radio uwb
The network

CSEM, Neuchatel

Prof. Farserotu, Hai Zhan

Prof. 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 power

In presence of multi user interference

Ranging

Provide fundamental research and proofs of concept

A Network within MICS researching on Impulse Radio UWB

4

table of contents5
Table of Contents
  • The UWB Network of MICS
  • What is UWB ?
  • Impulse Radio UWB
  • Low Power Medical Application
  • Robustness to Interference
  • Ranging
  • Outlook

5

ultra wide band uwb communication
Use a very large spectrum

up to Several GHzs

Very low power

Below level of unintentional emission

Unlicensed

Co-exists with other technologies

Power Limits

FCC (2002) limits

peak power (0dBm per 50MHz)

mean power (-41.3dBm per MHz)

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

Ultra Wide Band (UWB) Communication

US

EC

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

6

various uses of uwb signals radar and ranging
Radar

A very old UWB application, used for maritime or air navigation, and as remote speedometer

New apps: automotive security, rescue operation

One active device analyzes echoTarget is passive and unaware of signal

Not always low power

Ranging

From device to device

Device is active sender

Base station is receiver /transmitter

E.g Ubisense, Cambridge UK

Low power

Various Uses of UWB SignalsRadar and Ranging

E.L.

E.L.

7

various uses of uwb signals communication
Short Range Communication

Low power

Up to 30 m indoors

High data rate UWB Communication

Wireless USB / Wireless Firewire

Uses entire bandwidth

Very large bit rate on one single link

Peaky in frequency

Low data rate

E.g. Sensor networks

Impulse radio signals

Very large aggregate throughput

Various Uses of UWB SignalsCommunication

Robots with ranging needs for collective intelligence

Source: Prof. Alcherio Martinoli

8

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

Scalability

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

Resistance to Channel Impairments

Multiple paths are distinguishable

Suitable for indoors, terrain with obstacles, metallic environment

High Resolution in time domain

Ranging with cm accuracy indoors

Secure ranging

Short range

10 m to 30 m

Strengths and Weaknesses of UWB

Source: Mohammad Abualreesh

9

table of contents10
Table of Contents
  • The UWB Network of MICS
  • What is UWB ?
  • Impulse Radio UWB
  • Low Power Medical Application
  • Robustness to Interference
  • Ranging
  • Outlook

10

impulse radio uwb uses short pulses
Pulses are narrow in time, wide in frequency

Pulse duration order of 1 ns

Features

Low power

Duty cycle at 1 Mb/s = 1 %

Robust against multi-user interference

High precision ranging

Impulse Radio UWB Uses Short Pulses

Source: Gabriela Quintero

11

impulse radio uwb uses time hopping
Impulse Radio UWB Uses Time Hopping
  • Time Hopping Sequence: […, 2, 5, 4, 7 …]
    • Pulses appear random unless you know THS
    • THS is predictible to user who knows the key ; e.g.: MAC address
  • Transforms packet collision into symbol collision
    • Increaed bit error rate instead of packet loss
  • Software-like flexibility in hardware
    • When a pulse is sent can easily be changed by modifying a few values in the system
    • Change the time hopping sequence
    • Change the modulation rate

12

multipath propagation
Signal propagation subject to reflections

Pulses are attenuated / modified but still distinguishable

Very little destructive interference

Multipath Propagation

Received signal

Channel response

13

table of contents14
Table of Contents
  • The UWB Network of MICS
  • What is UWB ?
  • Impulse Radio UWB
  • Low Power: Medical Application
  • Robustness to Interference
  • Ranging
  • Outlook

14

body area network with uwb
Body Area Network with UWB
  • Requires very low power
  • Very bad transmission channel
  • UWB body area network prototype developed at ETH / Prof A. Wittneben’s group
    • Ear to ear communication
    • Focus on low power and point to point link

15

wireless ban communication for less than 1 mw
Wireless BAN Communication for less than 1 mW

Low Cost

Low Power

Low Complexity

Ultra-Wideband Radio

  • 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

16

body area network uwb test bed
Body Area Network UWB Test Bed

Ear-to-Ear Channel

17

slide18

transmit

receive

  • GUI for UWB test-bed
  • Average transmit power -45 dBm
  • Ear-to-ear channel with artificial water-bucket-head
  • BER at -45dBm is 0.04, capacity is 480 Mb/s

18

relevant publications
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.

19

table of contents20
Table of Contents
  • The UWB Network of MICS
  • What is UWB ?
  • Impulse Radio UWB
  • Low Power Medical Application
  • Robustness to Interference
  • Ranging
  • Outlook

20

robustness to interference from 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 N

Contrast to narrowband systems: » N-1/2

In practice, this requires careful system design

MAC

Signal Acquisition

Accommodate multipath

Robustness to InterferenceFrom Theory to Practice

21

phy aware mac
Classical organization of a network

E.g. WiFi, Bluetooth

PHY transmits packets

MAC avoids collisionsi.e. MAC = mutual exclusion

This is not efficient for UWB

Mutual 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

PHY-Aware MAC

B

A

C

Data

Data

THS(A), Code = Ri

THS(A),Code = Rj

NACK

THS(A),Code = RN

Incremental Red.

THS(A)

Interference, not collision

ACK

THS(A),Code = RN

Idle

THS(B), Code = RN

Our experimental MAC

22

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

DCC= dynamic channel coding

Key features of design

One time hopping sequence per destination (private time hopping sequences)

Interference mitigation at pulse level

Mutual exclusion for a single destination only

Rate adaptation

DCC-MAC

DCC MAC

CA/CDMA -like

802.11 - like

N nodes in a chain

23

signal acquisition
Signal acquisition is difficult for Impulse Radio UWB

Signal is intermittent

Interferences are allowed

Classical 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 signal

uses thresholding

Signal Acquisition

24

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 decodes

Requires source to know sequence of destination

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

Private Time Hopping Sequences

25

private sequences avoid the ad hoc collapse
Ad-hoc collapse

Many TCP connections in an ad-hoc

Collapses with 802.11 and other protocols

Due to collisions

No good solution known to this problem

With private sequences, the ad-hoc collapse goes away

Nodes acquire only packets destined to self

Private Sequences Avoid the Ad-Hoc Collapse

26

accommodate multipath
Assume modulation is pulse position

With interferers and multipath, received signal looks like

Accommodate Multipath

27

slide28
Idea: (Rake receiver)

Estimate channel during signal acquisition phase

Look for pattern of pulses in the received signal - correlation

Use thresholds to avoid near end effects

Similar ideas apply to energy detectors

0

28

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 network

Transmissions 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 overlap

ALOHA performance

Typical of narrowband systems

Benchmark 2: Perfect capture

Packets compete during signal acquisition and transmission

Only one succeeds

Typical of ideal UWB system

Performance Evaluation of IEEE 802.15.4a

29

ieee 802 15 4a is not robust to interference
Performance is close to destructive collision

Does not exploit UWB benefits well

Possible fixes

Compress bursts

Private time hopping sequences

IEEE 802.15.4a is not Robust to Interference

Benchmark 1: Destructive collision

802.154a, with interference

Benchmark 2: Perfect capture

802.154a, no interference

30

interference testbed
Goal:

Implement and test multi-user impulse radio system

In presence of multi-user interference

Real hardware, still programmable in matlab

A coordinated effort of the MICS UWB network

Ruben Merz (coordinator)

James Colli-Vignarelli

Gabriela Quintero

Prakash Thoppayegambaram

Jerome Vernez

Jean-François Zürcher

Interference Testbed

31

interference testbed epfl hes so
Interference Testbed (EPFL, HES SO)

Video by Jerome Vernez, HES SO (Yverdon)

32

relevant publications33
Relevant Publications
  • 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. 1769-1781
  • Radunovic, 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. 1252
  • Merz, 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. 567-580
  • Flury, Manuel ; Merz, Ruben ; Le Boudec, Jean-Yves, “Managing Impulsive Interference in Impulse Radio UWB Networks”, In: ST Journal of Research, 2007
  • Flury, 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

33

table of contents34
Table of Contents
  • The UWB Network of MICS
  • What is UWB ?
  • Impulse Radio UWB
  • Low Power Medical Application
  • Robustness to Interference
  • Ranging
  • Outlook

34

impulse radio uwb enables low cost ranging at high precision
Impulse Radio UWB enables low cost ranging at high precision
  • Short pulses can easily be located by receiver
  • Basis for radars
  • Can be used at low cost in all sorts of equipments with UWB
  • 2 techniques are researched in the MICS UWB Network
    • Geo-regioning
    • High resolution ranging

35

geo regioning
A method for location finger-printing

Idea: channel impulse response is correlated in space

Method:

Learning phase:

send test signals to base station from various locations

Analyze correlations (e.g. covariance matrix, delay profile)

Tracking Phase

Mobile sends beacons to base station

Real time correlation is performed

Geo-Regioning

Channel response

36

relevant publications38
Relevant Publications
  • 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.

38

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 stations

detect firstpulse 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

High Resolution Ranging

39

ranging through obstacles and with interferers
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

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 pulses

Received signal contains many replicas due to multipath

Strong pulses help find weak

Ranging Through Obstacles and With Interferers

Click on figure for video

Video by Hai Zhan, CSEM

40

relevant publications41
Relevant Publications
  • 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

41

table of contents42
Table of Contents
  • The UWB Network of MICS
  • What is UWB ?
  • Impulse Radio UWB
  • Low Power Medical Application
  • Ranging
  • Robustness to Interference
  • Outlook

42

impulse radio uwb is a key technology for the internet of things
Unique features

Indoors ranging

Resistance to multiuser interference

Scalable total throughput

Very low power

Practical developments are only starting

Standard based implementations can be improved

Potential areas of future research

Secure ranging

Very short signal time

High throughput ranging

Frequent position updates for distributed robot control

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

43

thank you
Special thanks go to all who helped prepare this presentation

Jerome Vernez

Hai Zhan

Ruben Merz

Christoph Steiner

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

Manuel Flury

James Colli-Vignarelli

Jean-Dominique Decotignie

Catherine Dehollain

John Farserotu

Gabriela Quintero

Stephan Robert

Jérome Rousselot

Anja Skrivervik

Prakash Thoppayegambaram

Florian Trösch

Armin Wittneben

Julien Zory

Thank You

44