Ultra-Wide Band Communication for the Internet of Things

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16 Φεβ 2014 (πριν από 3 χρόνια και 3 μήνες)

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1
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
2
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 pleaguesindoors
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.
3
Table of Contents
1.The UWB Network of MICS
2.What is UWB ?
3.Impulse Radio UWB
4.Low Power Medical Application
5.Robustness to Interference
6.Ranging
7.Outlook
4
A Network within MICS researching on
Impulse Radio UWB
The network
CSEM, Neuchatel
Prof. Farserotu, HaiZhan
Prof. Decotignie, Jerôme
Rousselot
ETHZ, Zurich
Prof. Wittneben, FlorianTrösch,
ChristophSteiner
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, JéromeVernez
ST Microelectronics, Geneva
Dr. J. Zory
Impulse radioUltra Wide Band
communication
Low power
In presence of multi user
interference
Ranging
Provide fundamental research
and proofs of concept
5
Table of Contents
1.The UWB Network of MICS
2.What is UWB ?
3.Impulse Radio UWB
4.Low Power Medical Application
5.Robustness to Interference
6.Ranging
7.Outlook
6
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
US
EC
(source: FCC 2002, CH-Ofcom, 2007)
7
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 echo
Target 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.gUbisense, Cambridge UK
Low power
E.L.
E.L.
8
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
Robots with ranging needs
for collective intelligence
Source: Prof. Alcherio
Martinoli
9
Strengths and Weaknesses of UWB
High throughputfor 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 Powerfor 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
Rangingwith cm accuracy indoors
Secure ranging
Short range
10 m to 30 m
Source: Mohammad Abualreesh
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Table of Contents
1.The UWB Network of MICS
2.What is UWB ?
3.Impulse Radio UWB
4.Low Power Medical Application
5.Robustness to Interference
6.Ranging
7.Outlook
11
Impulse Radio UWB Uses Short Pulses
Pulses are narrow in time,
wide in frequency
Pulse duration order of 1 ns
Source: Gabriela Quintero
Features
Low power
Duty cycle at 1 Mb/s = 1 %
Robust against multi-user interference
High 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 THS
THS is predictibleto user who knows the key ; e.g.: MAC address
Transforms packet collision into symbol collision
Increaedbit 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
13
Multipath Propagation
Signal propagation subject to reflections
Pulses are attenuated / modified but still distinguishable
Very little destructive interference
Channel response
Received signal
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Table of Contents
1.The UWB Network of MICS
2.What is UWB ?
3.Impulse Radio UWB
4.Low Power: Medical Application
5.Robustness to Interference
6.Ranging
7.Outlook
15
Body Area Network with UWB
Requires very low power
Very bad transmission
channel
UWB body area network
prototype developed at ETH /
Prof A. Wittneben’sgroup
Ear to ear communication
Focus 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 Txand Rx Structures
Mainly Analog Processing
Estimated Power Consumption < 1mW
Analog Part
Rx Chain
Energy Detection
TxChain
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 Cost
Low Power
Low Complexity
Ultra-Wideband Radio
17
Body Area Network UWB
Test Bed
Ear-to-Ear Channel
18
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
transmitreceive
19
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.
20
Table of Contents
1.The UWB Network of MICS
2.What is UWB ?
3.Impulse Radio UWB
4.Low Power Medical Application
5.Robustness to Interference
6.Ranging
7.Outlook
21
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
potentially
scalable,
well
adapted to dense deployments
Throughput per node constant
with number of nodes N
Contrast to narrowband
systems: θ∼N-1/2
In practice, this requires
careful system design
MAC
Signal Acquisition
Accommodate multipath
22
PHY-Aware MAC
Classical organization of a
network
E.g. WiFi, Bluetooth
PHY transmits packets
MAC avoids collisions
i.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
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
IncrementalRed.
THS(A)
BA
C
Our experimental MAC
Interference,
not collision
23
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
CA/CDMA -like
802.11 -like
N nodes in a chain
24
Signal Acquisition
Signal acquisition is difficult for
Impulse Radio UWB
Signal is intermittent
Interferences are allowed
Classical methods based on
gaussiannoise hypotheses do not
apply
Power Independent Detection
(PID) is robust to interference
even if interfering power is larger
than intended signal
uses thresholding
25
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
26
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
27
Accommodate Multipath
Assume modulation is pulse
position
With interferers and multipath,
received signal looks like
28
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
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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 THSsin 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
30
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
Benchmark 2: Perfect capture
Benchmark 1: Destructive collision
802.154a, no interference
802.154a, with interference
31
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
PrakashThoppayegambaram
Jerome Vernez
Jean-François Zürcher
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Interference Testbed(EPFL, HES SO)
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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
34
Table of Contents
1.The UWB Network of MICS
2.What is UWB ?
3.Impulse Radio UWB
4.Low Power Medical Application
5.Robustness to Interference
6.Ranging
7.Outlook
35
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
36
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
Channel response
37
UWB Geo-Regioning Demonstration
Developed by Prof. A. Wittneben’s
group / ETHZ
Channel impulse responses from region 22 to RX
38
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.
39
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
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
Pronyalgo
40
Experimental setting
Quiet room at EPFL (not
anechoic)
Experiment implemented by
HaiZhan (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 Pronyalgorithm
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
Click on figure for video
Video by HaiZhan, CSEM
41
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
42
Table of Contents
1.The UWB Network of MICS
2.What is UWB ?
3.Impulse Radio UWB
4.Low Power Medical Application
5.Ranging
6.Robustness to Interference
7.Outlook
43
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
44
Thank You
Special thanks go to all who
helped prepare this presentation
Jerome Vernez
HaiZhan
Ruben Merz
ChristophSteiner
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
JéromeRousselot
AnjaSkrivervik
PrakashThoppayegambaram
FlorianTrösch
Armin Wittneben
JulienZory