SEMINAR REPORT on Ultra Wide Band(UWB)
description
Transcript of SEMINAR REPORT on Ultra Wide Band(UWB)
A SEMINAR REPORT ON
RF transmission based on Microwave UWB
Submitted in partial fulfilment of the requirements for the
award of the degree of
BACHELOR OF TECHNOLOGY
In
ELECTRONICS AND COMMUNICATION
ENGINEERING
Submitted by
VINOD V: 07402144
DEPARTMENT OF ELECTRONICS AND COMMUNICATION
ENGINEERING
SREE CHITRA THIRUNAL COLLEGE OF ENGINEERING
THIRUVANANTHAPURAM 695 018
NOVEMBER 2010
SREE CHITRA THIRUNAL COLLEGE OF ENGINEERING,
THIRUVANANTHAPURAM - 695 018.
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING.
CERTIFICATE
Certified that seminar work entitled “RF transmission based on Microwave UWB”
is a bonafide work carried out in the seventh semester by “VINOD V (07402144)” in
partial fulfilment for the award of Bachelor of Technology in “ELECTRONICS
AND COMMUNICATION ENGINEERING” from University of Kerala during the
academic year 2010-2011, who carried out the seminar work under the guidance and
no part of this work has been submitted or published any where earlier for the award
of any degree.
SEMINAR CO-ORDINATOR HEAD OF THE DEPARTMENT
SUBHA V S.VAIDYANATHAN Lecturer, Professor, Department of ECE Department of ECE SCT College of Engineering SCT College of Engineering Thiruvananthapuram-18 Thiruvananthapuram-18
ACKNOWLEDGEMENT
I owe a great many thanks to a great many people who helped and supported
us during the making of this seminar. My deepest thanks to Ms Subha.V, lecturer in
Electronics and Communication Engineering, Sree Chitra Thirunal College of
Engineering, Trivandrum, the seminar co-ordinator for guiding and correcting various
documents with attention and care. They have taken pain to go through the seminar
and make necessary corrections as and when needed.
I gratefully obliged to thank Prof. S.Balachandran, Principal, Sree Chitra
Thirunal College of Engineering, Trivandrum and Prof. S.Vaidyanathan, Head of
the Department, Department of Electronics & Communication Engineering for their
timely assistance during the course of this seminar.
I would like to thank our institution and our faculty members without whom
this seminar would have been a distant reality. I also extend our heartfelt thanks to our
families and well wishers. Last but not the least I would like to express our gratitude
to God almighty.
Vinod V
ABSTRACT
Ultra-wideband (UWB) transmission has recently received great attention in
both academia and industry for applications in wireless communications. It was
among the CNN’s top 10 technologies to watch in 2004. A UWB system is defined
as any radio system that has a 10-dB bandwidth larger than 20% of its center
frequency, or has a 10-dB bandwidth equal to or larger than 500 MHz, The recent
approval of UWB technology by Federal Communications Commission (FCC) of the
United States reserves the unlicensed frequency band between 3.1 and 10.6 GHz (7.5
GHz) for indoor UWB wireless communication systems. It is expected that many
conventional principles and approaches used for short-range wireless communications
will be reevaluated and a new industrial sector in short-range (e.g., 10 m) wireless
communications with high data rate (e.g., 400 Mbps) will be formed. Further,
industrial standards IEEE 802.15.3a (high data rate) and IEEE 802.15.4a (very low
data rate) based on UWB technology have been introduced.
The design and implementation rules are outlined and described in
http://www.wimedia.org/ & http://www.uwbforum.org/
TABLE OF CONTENTS
LIST OF FIGURES i
LIST OF TABLES ii
CHAPTER TITLE PAGE NO:
1.0 INTRODUCTION 1
1.1. History and Background 2
1.2. FCC Emission limits 3
1.3. UWB Concepts 4
1.4. UWB Signals 5
2.0 WHY UWB 7
3.0 BAND-PASS UWB 11
3.1 Filter Technologies 11
4.0 MULTIBAND-OFDM APPROACH 14
5.0 IR-UWB vs. MB-OFDM 19
6.0 LNA ARCHITECTURE 20
7.0 UWB ANTENNAS 22
8.0 UWB VS. SPREAD SPECTRUM 24
9.0 UWB APPLICATIONS 25
9.1 UWB Radar 27
9.1.1 Measuring method 28
9.1.2 UWB radar over NB radar 29
9.1.3 Position Estimation Techniques 30
10. CHALLENGES TO UWB 33
11. CONCLUSION 34
REFERENCES 35
APPENDIX 36
i
LIST OF FIGURES
FIGURE NAME PAGE NO:
FIG. 1.1 UWB History 2
FIG. 1.2 FCC Emission limits 3
FIG. 1.3 UWB and Narrowband 4
FIG. 1.4(a) UWB Wavelet 5
FIG. 1.4(b) Wavelet generation 6
FIG.2.1 Coexistence with NB 7
FIG. 3 Band-pass UWB 11
FIG. 3.1(a) UWB Filter response 12
FIG. 3.1 (b) Micro-strip filter 13
FIG. 3.1 (c) UWB Notch filter 13
FIG. 4 (a) DS-UWB 3.1 to 5 GHz 15
FIG. 4 (b) DS-UWB 6 to 10.6 GHz 15
FIG. 4 (c) MB-OFDM 16
FIG. 4 (d) MB-OFDM Generation 17
FIG. 4(e) MB-OFDM with CR 18
FIG. 6(a) LNA Architecture 20
FIG. 6 (b) Impedance matching 20
FIG. 6 (c) Interference suppression 21
ii
FIG. 7 UWB Antennas 23
FIG. 8 UWB vs. Spread Spectrum 24
FIG. 9 OPPN 26
FIG. 9.1 SRR 27
FIG. 9.1.3 (a) UWB position estimation 30
FIG. 9.1.3 (b) UWB position estimation- Setup 31
LIST OF TABLES
TABLE NAME PAGE NO:
TABLE.1.3 UWB, WB & NB 4
TABLE.4 MB-OFDM Generator 17
TABLE.5 MB-OFDM vs. DS-UWB 19
TABLE.7 Antenna design 23
TABLE.10 UWB Interference 33
1
1. INTRODUCTION
Every radio technology allocates a specific part of the spectrum; for example,
the signals for TVs, radios, cell phones, and so on are sent on different frequencies to
avoid interference to each other. As a result, the constraints on the availability of the
RF spectrum become more and stricter with the introduction of new radio services.
Ultra-wideband (UWB) technology offers a promising solution to the RF spectrum
drought by allowing new services to coexist with current radio systems with minimal
or no interference. This coexistence brings the advantage of avoiding the expensive
spectrum licensing fees that providers of all other radio services must pay.
This seminar provides a comprehensive overview of ultra-wideband
Communications.
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1.1 History and Background
Ultra-wideband communications is not a new technology; in fact, it was first
employed by Guglielmo Marconi in 1901 to transmit Morse code sequences across
the Atlantic Ocean using the spark gap radio transmitters. However, the benefit of a
large bandwidth and the capability of implementing multiuser systems provided by
electromagnetic pulses were never considered at that time. Approximately fifty years
after Marconi, modern pulse-based transmission gained momentum in military
applications in the form of impulse radars. Some of the pioneers of modern UWB
communications in the United States from the late 1960s are Henning Harmuth of
Catholic University of America and Gerald Ross and K. W. Robins of Sperry Rand
Corporation.
From the 1960s to the 1990s, this technology was restricted to military and
Department of Defense (DoD) applications under classified programs such as highly
secure communications. However, the recent advancement in micro processing and
fast switching in semiconductor technology has made UWB ready for commercial
applications. Therefore, it is more appropriate to consider UWB as a new name for a
long-existing technology. As interest in the commercialization of UWB has increased
over the past several years, developers of UWB systems began pressuring the FCC to
approve UWB for commercial use. In February 2002, the FCC approved the First
Report and Order (R&O) for commercial use of UWB technology under strict power
emission limits for various devices.
FIG. 1.1 UWB History
3
1.2 Fcc Emission Limits
In order to protect existing radio services from UWB interference, the FCC
has assigned conservative emission masks between 3.1 GHz and 10.6 GHz for
commercial UWB devices. The maximum allowed power spectral density for these
devices—that is,–41.3 dBm/MHz, or 75 nW/MHz—places them at the same level as
un-intentional radiators (FCC Part 15 class) such as televisions and computer
monitors. The spectral mask for outdoor devices is 10 dB lower than that for indoor
devices, between 1.61 GHz and 3.1 GHz, as shown in above Figure 1.2. According to
FCC regulations, indoor UWB devices must consist of handheld equipment, and their
activities should be restricted to peer-to-peer operations inside buildings.
The FCC’s rule dictates that no fixed infrastructure can be used for UWB
communications in outdoor environments. Therefore, outdoor UWB communications
are restricted to handheld devices that can send information only to their associated
receivers.
FIG. 1.2- UWB FCC Emission
4
1.3 Uwb Concepts
Traditional narrowband communications systems modulate continuous
waveform (CW) RF signals with a specific carrier frequency to transmit and receive
information. A continuous waveform has well-defined signal energy in a narrow
frequency band that makes it very vulnerable to detection and interception. Above
Figure 1.3 represents both narrowband & wideband signals in the time and frequency
domains. UWB systems use carrier-less, short-duration (picoseconds to nanosecond)
pulses with a very low duty cycle (less than 0.5 percent) for transmission and
reception of the information.
FIG. 1.3- UWB & Narrowband
TABLE.1.3 – UWB, Wide band, & Narrow
5
Low duty cycle offers a very low average transmission power in UWB
communications systems. The average transmission power of a UWB system is on the
order of microwatts, which is a thousand times less than the transmission power of a
cell phone! However, the peak or instantaneous power of individual UWB pulses can
be relatively large, but because they are transmitted for only a very short time, the
average power becomes considerably lower. Consequently, UWB devices require low
transmit power due to this control over the duty cycle, which directly translates to
longer battery life for handheld equipment. Since frequency is inversely related to
time, the short-duration UWB pulses spread their energy across a wide range of
frequencies—from near DC several gigahertz (GHz)—with very low power spectral
density (PSD). The wide instantaneous bandwidth results from the time-scaling
property of theoretical Fourier transforms.
1.4 Uwb Signals
UWB modulates an impulse-like waveform (WAVELET) with Data. A typical
baseband UWB pulse, also called mono-pulse, such as the Gaussian first derivative
pulse can be used. UWB signals must have bandwidths of greater than 500MHz or a
fractional bandwidth larger than 20 percent at all times of transmission. Fractional
(relative) bandwidth is a factor used to classify signals as narrowband, wideband, or
ultra-wideband and is defined by the ratio of bandwidth at –10 dB points to center
frequency.
FIG. 1.4(a) - UWB Wavelet
6
where fh and f1 are the highest and lowest cutoff frequencies (at the –10 dB
point) of a UWB pulse spectrum, respectively. A UWB signal can be any one of a
variety of wideband signals, such as Gaussian, chirp, wavelet, or Hermite-based short-
duration pulses. Above Figure 1.4(a) represents a Gaussian monocycle as an example
of a UWB pulse.
Wavelet Generation
The development of laser-actuated semiconductor fast-acting switches that
can produce impulses or short duration waveforms of one or several cycles has
been of interest for UWB. The traveling wave tube (TWT) can be used. It can be
excited with a narrow impulse, but its energy is limited by the peak power of
the TWT.
FIG. 1.4(b) - Wavelet Generation
7
2. WHY UWB?
The nature of the short-duration pulses used in UWB technology offers several
advantages over narrowband communications systems. Next, we discuss some of the
key benefits that UWB brings to wireless communications.
2.1 Ability to Share the Frequency Spectrum
UWB systems reside below the noise floor of a typical narrow-band receiver
and enables UWB signals to coexist with current radio services with minimal or no
interference as illustrated in FIG. 2.1.
2.2 Large Channel Capacity
One of the major advantages of the large bandwidth for UWB pulses is
improved channel capacity. Channel capacity, or data rate, is defined as the maximum
amount of data that can be transmitted per second over a communications channel.
FIG. 2.1-Coexistence with Narrow band
8
The large channel capacity of UWB communications systems is evident from
Hartley-Shannon’s capacity formula. Where C represents the maximum channel
capacity, B is the bandwidth, and SNR is the signal-to-noise power ratio. As shown in
Equation, channel capacity C linearly increases with bandwidth B. Therefore, having
several gigahertz of bandwidth available for UWB signals, a data rate of gigabits per
second (Gbps) can be expected.
However, due to the FCC’s current power limitation on UWB transmissions,
such a high data rate is available only for short ranges, up to 10 meters. This makes
UWB systems perfect candidates for short-range, high-data-rate wireless applications
such as wireless personal area networks (WPANs). The trade-off between the range
and the data rate makes UWB technology ideal for a wide array of applications in
military, civil, and commercial sectors.
2.3 Ability to Work with Low Signal-To-Noise Ratios
The Hartley-Shannon formula for maximum capacity also indicates that the
channel capacity is only logarithmically dependent on signal-to-noise ratio
(SNR).Therefore, UWB communications systems are capable of working in harsh
communication channels with low SNRs and still offer a large channel capacity as a
result of their large bandwidth.
2.4 Low probability of intercept and detection
Because of their low average transmission power, UWB communications
systems have an inherent immunity to detection and intercept. With such low
transmission power, the eaves-dropper has to be very close to the transmitter (about 1
meter) to be able to detect the transmitted information. In addition, UWB pulses are
time modulated with codes unique to each transmitter/receiver pair. The time
modulation of extremely narrow pulses adds more security to UWB transmission,
because detecting picoseconds pulses without knowing when they will arrive is next
to impossible. Therefore, UWB systems hold significant promise of achieving highly
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secure, low probability of intercept and detection (LPI/D) communications that is a
critical need for military operations.
2.5 Resistance to Jamming
Processing gain (PG) is a measure of a radio system’s resistance to jamming
and is defined as the ratio of the RF bandwidth to the information bandwidth of a
signal. The frequency diversity caused by high processing gain makes UWB signals
relatively resistant to intentional and unintentional jamming, because no jammer can
jam every frequency in the UWB spectrum at once. Therefore, if some of the
frequencies are jammed, there is still a large range of frequencies that remains
untouched. However, this resistance to jamming is only in comparison to narrowband
and wideband systems. Hence, the performance of a UWB communications system
can still be degraded, depending on its modulation scheme, by strong narrow-band
interference from traditional radio transmitters coexisting in the UWB receiver’s
frequency band.
2.6 High performance in multipath channels
The phenomenon known as multipath is unavoidable in wireless
communications channels. It is caused by multiple reflections of the transmitted signal
from various surfaces such as buildings, trees, and people. The straight line between a
transmitter and a receiver is the line of sight (LOS); the reflected signals from
surfaces are non-line of sight (NLOS).
The effect of multipath is rather severe for narrowband signals; it can cause
signal degradation up to –40 dB due to the out-of-phase addition of LOS and NLOS
continuous waveforms. On the other hand, the very short duration of UWB pulses
makes them less sensitive to the multipath effect. Because the transmission duration
of a UWB pulse is shorter than a nanosecond in most cases, the reflected pulse has an
extremely short window of opportunity to collide with the LOS pulse and cause signal
degradation.
10
2.7 Superior penetration properties
Unlike narrowband technology, UWB systems can penetrate effectively
through different materials. The low frequencies included in the broad range of the
UWB frequency spectrum have long wavelengths, which allows UWB signals to
penetrate a variety of materials, including walls. This property makes UWB
technology viable for through-the-wall communications and ground-penetrating
radars (GPRs). However, the material penetration capability of UWB signals is useful
only when they are allowed to occupy the low-frequency portion of the radio
spectrum.
2.8 Simple transceiver architecture
UWB transmission is carrier-less, meaning that data is not modulated on a
Continuous waveform with a specific carrier frequency, as in narrowband and
wideband technologies. Carrier-less transmission requires fewer RF components than
carrier-based transmission. For this reason UWB transceiver architecture is
significantly simpler and thus cheaper to build.
The transmission of low-powered pulses eliminates the need for a power
amplifier (PA) in UWB transmitters. Also, because UWB transmission is carrier-less,
there is no need for mixers and local oscillators to translate the carrier frequency to
the required frequency band; consequently there is no need for a carrier recovery
stage at the receiver end. In general, the analog front end of a UWB transceiver is
noticeably less complicated than that of a narrowband transceiver. This simplicity
makes an all- CMOS implementation of UWB transceivers possible, which translates
to smaller form factors and lower production costs.
11
3. BAND-PASS UWB
Low energy, short duration UWB pulses modulates Input data. Microwave
Spectrum controlled by impulse response of BPF in FIG. 3. Modulation scheme may
be among PPM, OOK, or BPSK.
3.1 Filter Technologies
UWB band-pass filter is a key component of UWB system. It must have an
ultra wide pass-band, but also needs high selectivity to reject signals from existing
systems such as 1.6 GHz global positioning systems (GPS) and 2.4 GHz Bluetooth
systems. In addition, in some cases, the UWB band pass filter needs to introduce
steeply notched frequency bands (FIG 3.1(a)) in order to reduce interference from
existing NB radio systems located within the UWB pass-band. These requirements
increase the challenges for the UWB filter designer.
FIG. 3-Band-pass UWB
12
However, since conventional filter theory is based on the narrowband
assumption and cannot be used to design UWB band pass filters, novel techniques and
technologies need to be developed for UWB band pass filter design.
FIG. 3.1(a)-UWB Filter response
13
Micro-strip Filter
Micro strip filters only become practical above 300MHz. It is a size issue. The
inductance and capacitance of the micro strip line PCB traces to form the filter, rather
than discrete inductors and capacitors.
FIG. 3.1(b)-Micro-strip Filter
FIG. 3.1(c)-UWB Notch Filter
14
4. MULTIBAND-OFDM APPROACH
The ability of UWB technology to provide very high data rates for short
ranges (less than 10 meters) has made it an excellent candidate for the physical layer
of the IEEE 802.15.3a standard for wireless personal area networks (WPANs).
However, two opposing groups of UWB developers are battling over the IEEE
standard. The two competing technologies are single band and multiband. The
single-band technique, backed by Motorola/XtremeSpectrum, supports the idea of
impulse radio that is the original approach to UWB by using narrow pulses that
occupy a large portion of the spectrum. The multiband approach divides the available
UWB frequency spectrum (3.1 GHz to 10.6 GHz) into multiple smaller and non
overlapping bands with bandwidths greater than 500 MHz to obey the FCC’s
definition of UWB signals. The multiband approach is supported by several
companies, including Staccato Communications, Intel, Texas Instruments, General
Atomics, and Time Domain Corporation.
To date, several proposals from both groups have been submitted to the IEEE
802.15.3a working group, and the decision is yet to be made because both
technologies are impressive and have technical credibility.
The following subsections discuss the two leading candidates for the
802.15.3a standard: direct-sequence UWB (DS-UWB) and multiband orthogonal
Frequency division multiplexing (OFDM)
15
Direct-Sequence Uwb
Above figure 4(a) shows DS-UWB with 3.1-to 5-GHz range band plan. And
the below figure 4(b) shows DS-UWB with 6-to 10.6-GHz band plan
Direct-sequence UWB is a single-band approach that uses narrow UWB
pulses and time-domain signal processing combined with well-understood DSSS
techniques to transmit and receive information. Data representation in this approach is
based on simple bi-phase shift keying (BPSK) modulation, and rake receivers are
used to capture the signal energy from multiple paths in a multipath channel.
According to the proposals sent to the IEEE 802.15.3a standardization
committee by the proponents of this technology, the DS-UWB technique is scalable
and can achieve data rates in excess of 1 Gbps. The technical reason behind using DS-
FIG. 4(a)-DS-UWB 3.1 to 5 GHz
FIG. 4(b) - DS-UWB 6 to 10.6
16
UWB is the propagation benefits of ultra-wideband pulses, which experience no
Rayleigh fading. In contrast, narrowband transmissions degrade significantly due to
fading.
Multiband OFDM
The multiband UWB approach uses the 7500 MHz of the RF spectrum
available to UWB communications in a way that differs from traditional UWB
techniques. The UWB frequency band is divided into multiple smaller bands with
bandwidths greater than 500 MHz (FIG. 4(c)). This approach is similar to the
narrowband frequency-hopping technique. Dividing the UWB spectrum into multiple
frequency bands offers the advantage of avoiding transmission over certain bands,
such as 802.11a at 5 GHz, to prevent potential interference. In the multiband
approach, UWB pulses are not as narrow as in traditional UWB techniques; therefore,
synchronization requirements are more relaxed.
A variety of modulation techniques have been proposed by industry leaders
for the multiband approach; however, OFDM, which was initially proposed by Texas
Instruments, offers improved performance for high-data rate applications. In fact, both
technologies are technically valid and impressive.
Supporters of DS-UWB criticize the multiband OFDM systems for their
complexity, which results from using complex Fast Fourier Transforms (FFTs). On
the other side, advocates of multiband OFDM believe that their technique offers better
coexistence with other radio services, and they disapprove of DS-UWB because of
possible interference concerns.
FIG. 4(c)-MB-OFDM
17
The debate will likely continue until the IEEE 802.15.3a standardization
committee reaches a decision.
Mb-OFDM Generation Method
PLL provides center frequencies for first three Groups “A” bands.
FIG. 4(d)-MB-OFDM generation
TABLE.4-MB-OFDM Generator
18
Integration of Multiband and Cognitive Radio (CR)
Cognitive Radio (CR) is an emerging approach for a more flexible usage of
the precious radio spectrum resources. By investigations on the radio spectrum usage,
it has been observed that some frequency bands are largely unoccupied most of the
time, some other frequency bands are only partially occupied, and the remaining
frequency bands are heavily used.
A CR terminal can sense its environment and location and then adapt some of
its features allowing to dynamically reusing valuable spectrum. This could lead to a
multidimensional reuse (dynamical usage) of spectrum in space, frequency and time,
exceeding the severe limitations in the spectrum and bandwidth allocations (FIG.
4(e)).
FIG. 4(e)-MB-OFDM with CR
19
5. IR-UWB VS. MB-OFDM
TABLE.5-MB-OFDM vs. IR-UWB
20
6. LNA ARCHITECTURE
Due to the wide bandwidth, classical narrow band LNA design techniques
cannot be used. Feedback amplifier architecture, described in Figure 6(a), has been
considered as a good candidate for wideband amplification due to its relative
simplicity to provide flat gain and good 50 Ohms matching with respect to low noise.
Wideband Input Impedance Matching
The main challenge in UWB designs is to extend matching to the wide
frequency range of 3.1-10.6 GHz. The LNA has to exhibit good input impedance as in
FIG. 6(b).
FIG. 6(a)-LNA (Low Noise Amplifier)
FIG. 6(b)-Impedance matching
21
NB interference suppression
A tunable center frequency RF “roofing filter” applied to the UWB NB
interference mitigation problem as in FIG. 6(c). This filter will introduce significant
group delay distortion in the pass band, and so spectral shaping of the transmitted
waveform out of the interference band will also be required to minimize the resulting
degradation in system performance.
In the second case, an accurate estimation of the frequency, phase, and
amplitude of the jammer is required to significantly reduce the interference level.
FIG. 6(c)-NB Interference
22
7. UWB ANTENNAS
Antennas are particularly challenging aspect of UWB. If an impulse is fed to
an antenna, it tends to ring, severely distorting the pulse and spreading it out in time.
Also have poor matching and large reflections. Conventional wideband antennas such
as the log-periodic and the spiral are wideband in amplitude, but not in phase;
they distort the UWB signal.
The best antennas for UWB are arrays of TEM horns. The higher the
frequency the antennas can be equally small (FIG. 7). In UWB systems, antenna
design is one of key technologies and has been widely investigated by both academia
and industry. The antenna design considerations are strongly dependent on the
modulation scheme, which the UWB systems are using, and applications.
In general, MB-OFDM UWB wireless communication systems require the
antennas which should have broadband response in terms of return loss, gain at the
directions of interest, and /or polarization. Such requirements are almost the same as
the designs for conventional broadband wireless systems but a required extremely
broad bandwidth of 50% to 100% with a consistent gain response. However,
additional attention must be paid for pulse-based UWB systems where the UWB
antenna usually function as a band pass filter and tailor the spectra of the
radiated/received pulses so that the waveforms of radiated/received pulses are
distorted.
23
TABLE.7-UWB Antenna design
FIG. 7-Antenna shapes
24
8. Uwb Vs Spread Spectrum
Although UWB and spread-spectrum (SS) techniques share the same
advantage of expanded bandwidth as evident from FIG. 8, the method of achieving
the large bandwidth is the main distinction between the two technologies. In
conventional spread-spectrum techniques, the signals are continuous-wave sinusoids
that are modulated with a fixed carrier frequency.
In UWB communications, on the other hand, there is no carrier frequency; the
short duration of UWB pulses directly generates an extremely wide bandwidth.
Another distinguishing factor in UWB is the very large bandwidth. Spread-spectrum
techniques can offer megahertz of bandwidth, while UWB pulses provide several
gigahertz of bandwidth. Above figure 8 shows the time and frequency domain
representation of narrowband, wideband, and UWB signals.
The low transmission power could be a disadvantage for UWB systems,
because the information can travel only short distances. Therefore, for long-range
applications, spread-spectrum techniques are still more appropriate.
FIG. 8-UWB & SS
25
9. UWB APPLICATIONS
The trade-off between data rate and range in UWB systems holds great
promise for a wide variety of applications in military, civilian, and commercial
sectors. The FCC categorizes UWB applications as radar, imaging, or
communications devices. Radar is considered one of the most powerful applications
of UWB technology. The fine positioning characteristics of narrow UWB pulses
enables them to offer high-resolution radar (within centimeters) for military and
civilian applications. Also, because of the very wide frequency spectrum band, UWB
signals can easily penetrate various obstacles. This property makes UWB-based
ground-penetrating radar (GPR) a useful asset for rescue and disaster recovery teams
for detecting survivors buried under rubble in disaster situations.
In the commercial sector, such radar systems can be used on construction sites
to locate pipes, studs, and electrical wiring. The same technology under different
regulations can be used for various types of medical imaging, such as remote heart
monitoring systems. In addition, UWB radar is used in the automotive industry for
collision avoidance systems. Moreover, the low transmission power of UWB pulses
makes them ideal candidates for covert military communications.
UWB pulses are extremely difficult to detect or intercept; therefore,
unauthorized parties will not get access to secure military information. Also, because
UWB devices have simpler transceiver circuitry than narrowband transceivers, they
can be manufactured in small sizes at a lower price than narrowband systems.
Small and inexpensive UWB transceivers are excellent candidates for wireless
sensor network applications for both military and civilian use. Such sensor networks
are used to detect a physical phenomenon in an inaccessible area and transfer the
information to a destination. A military application could be the detection of
biological agents or enemy tracking on the battlefield. Civilian applications might
include habitat monitoring, environment observation, health monitoring, and home
automation.
26
The precise location-finding ability of UWB systems can be used in inventory
control and asset management applications, such as tagging and identification
systems—for example, RFID tags. Also, the good performance of UWB devices in
multipath channels can provide accurate geo-location capability for indoor and
obscured environments where GPS receivers won’t work.
The high-data-rate capability of UWB systems for short distances has
numerous applications for home networking and multimedia-rich communications in
the form of WPAN applications. UWB systems could replace cables connecting
camcorders and VCRs, as well as other consumer electronics applications, such as
laptops, DVDs, digital cameras, and portable HDTV monitors. No other available
wireless technologies—such as Bluetooth or 802.11a/b—are capable of transferring
streaming video.
UWB Outdoor Peer-To-Peer Network (OPPN)
Downloading of video movie purchase or rental, for example, is a very data-
intensive activity that could be enabled by UWB.
FIG. 9-UWB OPPN
27
9.1 Uwb Radar (Short-Range Radar (SRR))
The wide bandwidth of UWB signals implies a fine time resolution that gives
them a potential for high-resolution positioning applications /Localization and
tracking (LT)/ranging, provided that the multipath are dealt with. As of Short Pulse
Width we can Resolve Multipath Components. Above Figure 9.1 demonstrates
external views of this UWB radar model.
The major specifications of the prototype are given be
• Operation range 8 m;
• Pulse power 10 mW;
• Average power 80 ~W;
• Width of the antenna’s pattern: 8° x 8°; and
• Duration of radiated radio pulses 2 ns.
FIG. 9.1-UWB SRR
28
9.1.1 The Measuring Method of Uwb Radar
While constructing UWB radars, as with constructing conventional narrow-
band radars, we use the property of electromagnetic waves to be scattered from a
boundary of two media with different parameters. The short electromagnetic pulses
radiated by radar are scattered by a moving object. The oscillation frequency within
the pulse and the repetition frequency of pulses are changed owing to the Doppler
Effect. The sign of these variations depends on the direction of target movement
relative to the radar and the variation value depends on the object's radial velocity.
According to this direction, the signal spectrum is going wider or narrower and moves
toward high or low frequency areas.
The radars work in conditions of high level of passive noise - the signals,
reflected from walls and stationary objects, which will have large amplitude and will
disguise useful signals. Time slots, opening the receiver at the moment of input of
signal reflected from object at distance defined are formed in receiving path to
eliminate interfering pulses. This task in radar design is executed by a time
discriminator, being gated. It consists of fast-acting electronic switches. The
switching time is on the order of 200-300 picoseconds. The switches connect the
receiving antenna to the UWB amplifier at the moment of signal input. These
moments are defined by a delay magnitude of the control signal at a software-
controlled delay line. All of the rest of the time, the receiver is closed. The signals
received at time slots are detected and amplified in integrating amplifier and the
signal, carrying data of target motion is selected at its output.
The time constant of integration of integrating amplifier is chosen
Independently of the bandwidth of the desired signal. For example, measuring a
person's vital signs, the bandwidth of the desired signal is near 40 - 50 Hz, that
corresponds to an accumulation of 10 - 30 thousands of pulses, approximately. The
accumulation permits us to decrease the average radiated power of the transmitter and
increase the signal-to-noise ratio at the input of the amplifier.
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The selected and amplified low-frequency signal enters the analog-digital
converter (ADC). The microprocessor-controlled unit directs the work of the radar on
given algorithms, monitors the state of major units and modules, and provides data
output for further digital processing in the computer. The selection of moving targets,
fast Fourier transform, and digital filtration are software-programmable at the
computer.
9.1.2 UWB Radar over NB Radar
• Higher range resolution and accuracy .Ultra High Range Resolution
(UHRR)
• enhanced target recognition
• immunity to passive “interference”
• immunity to co-located radar transmissions
• signals scattered by separate target elements do not interfere
• operational security because of the extremely large spectral spreading
• ability to detect very slowly moving or stationary targets
• Multiple targets can be resolved
• With a long pulse NB radar waveform, changes in the target aspect
cause a change only in the amplitude of the echo signal. With UWB
signals, the echo signal will change, which makes efficient signal processing.
• NB signal processing in radar almost always utilizes the envelope. With
UWB waveforms, either the envelope or the RF signal can be used.
• In indoor and dense urban environments the GPS signal is typically
unavailable.
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9.1.3 Position Estimation Techniques
In the below set-up FIG. 9.1.3(b) Short-pulse RF emissions from the tags are
subsequently received by either all, or a subset, of these sensors and processed by the
central hub CPU.
FIG. 9.1.3(a) - Target in piconet
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A set of three or more receivers (four receivers are typically used) are
positioned at known coordinates within, or about the periphery of, the area to be
monitored as in FIG 9.1.3(a).
In order to comprehend the high-precision positioning capability of UWB
signals, position estimation techniques should be investigated first. Position
estimation of a node in a wireless network involves signal exchanges between that
node (Called the target_ node; i.e., the node to be located) and a number of reference
nodes (FIG. 9.1.3(b)). A central unit that gathers position information from the
reference nodes and then estimates the position based on those signal parameters.
Signal parameters, such as TOA (time-of-arrival), angle-of-arrival (AOA), TDOA
(Time Difference of Arrival), RTD (Round Trip Delay) and/or received signal
FIG. 9.1.3(b)-UWB position estimation
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strength (RSS) are estimated. Short-pulse RF emissions from the tags are
subsequently received by receivers and processed by the central hub CPU. A typical
tag emission consists of a short burst, which includes synchronization preamble, tag
identification (ID), optional data field (e.g., tag battery indicator), and FEC bits. Time
differences of arrival (TDOA) of the tag burst at the various receiver sites are
measured and sent back to the central processing hub for processing. Calibration is
performed at system startup by monitoring data from a reference tag, which has been
placed at a known location.
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10. CHALLENGES TO UWB
► suspicious about the NB interference as shown in TABLE.10
► extreme antenna bandwidth requirements
► very accurate timing synchronization need for correlation -based receiver
► Complex RAKE-type receiver to cope with significant amount of energy in
the multipath
► filter matching accuracy
► timely approval from the regulatory bodies
► lack of an universal standard
TABLE.10-Systems degraded by UWB
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11. CONCLUSION
With the recent advances in semiconductor device technology and the FCC’s
approval of the unlicensed use of ultra-wideband systems, UWB development has
moved from research labs and classified military projects to the commercial sector.
UWB technology brings many opportunities as well as challenges to the world of
wireless communications. UWB is a promising technology for the Next Generation
Wireless Systems!
Home audio systems and PCs without the confusing and messy cables, and
even more tech savvy cell phones are the promise of UWB. Some people question
whether UWB really will impact consumer life. A better question is when? There is
a definite demand for the applications that can be developed using UWB. UWB also
has a unique edge over competing technologies in its low cost and low power model.
Unfortunately early regulatory division has split UWB implementers down the
middle. Countries around the world have been reluctant to release radio spectrum for
UWB use. The consequential lack of a universal standard must be addressed so
consumers can reap the benefits of UWB.
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5. Immoreev, ‘Practical Applications of UWB Technology’ ,IEEE A&E Systems 2010
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APPENDIX
AWICS UWB Aircraft Inter communications system
BToUWB- Bluetooth over Ultra Wideband
Bluetooth connection’s data over a software implemented UWB Medium Access Control (MAC) and simulated Physical (PHY) layer radio channel
DRACO UWB Network Transceiver IEEE 802.15.3a UWB HDR WPAN IEEE 802.15.4a UWB LDR WSN
Sensor, positioning, and identification network (SPIN)
IEEE 802.15.6 UWB Wearable LDR WBAN ORION L-band UWB Transceiver Precision Asset Location (PAL) System UWB for detection of on-board items
inside vehicles QUPID- QUick response Perimeter Intrusion Detection
UWB radar used for guarding of objects in the room.
SPIDER GPR used as a backup sensor for a large mining vehicle
UROOF UWB Radio Over Optical Fiber for UWB Network extension
UWB Endoscope real-time diagnosis with high resolution images by UWB
UWB-MIMO UWB-based Virtual-MIMO system for cellular network to provide better spatial diversity and higher system capacity
UWB SATCOM UWB signals are radiated from satellites to the earth by which new satellite applications can be developed
UWB UMV UWB UnManned Vehicle employing Vehicular collision avoidance by SRR
Wireless USB UWB as the technology to achieve high data rates up to 480 Mbps