1. Masters Thesis
Distance Measurement Using Ultra
Wideband
Md. Iqbal Hossain
Talat Karim Minhas
Supervisor and Examiner: Thomas Lindh
Stockholm February 2012
Masters in Computer Networks
School of Technology and Health
Kungliga Tekniska Högskolan

2. 2

3. Acknowledgements
Praise to Almighty Allah, the origin of knowledge, who enables us to
undertake and accomplish this thesis. We are very thankful to Allah, creator
of this universe whose guidance always remained with us at every moment of
our lives, especially during this work in the form of knowledge, courage and
hopes. May Allah bless our Prophet Hazrat Muhammad (Peace be Upon Him)
whose teachings show us right path in every darkness of our lives.
Our special gratitude goes to our supervisor, Thomas Lind whose precious
guidance accompanied us during our research and study at Royal Institute of
Technology (KTH). Also, I would like to thank Bo Åberg for his help and
kind cooperation during our studies. We feel ourselves very much obliged to
our parents, brothers and sisters whose prayers have enabled us to reach up to
this stage. The efforts of us, and inspirations of many, have led to a successful
completion of this final thesis.
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4. 4

5. Abstract
Ultra wideband (UWB) is vastly under consideration of research industry that
promises high data rata, low power consumption and economic solution.
UWB was in use of military since 1950’s. In 2002 Federal communication
commission (FCC) approved the use of 3.1-10.6 GHz band for unlicensed
UWB applications. UWB is a suitable choice for sensing and position objects
because of high bandwidth and fine time resolution.
The goal of this work is to explore the UWB technology in context of
distance measurement between two nodes. We have described the
characterization; reliability and ranging precision of an impulse UWB based
transceiver for both indoor and outdoor environments. This thesis discuss in
detail about UWB technology. Chapter 1 discusses about UWB applications,
regulation and bandwidth properties. Chapter 2 and 3 discuss about single
band and multi band modulation and detection techniques. Chapter 4 gives a
complete description how to measure position through ranging and
positioning parameters. Finally, to estimate the ranging and positioning, a two
way ranging algorithm based on TOA employed as part of this work is
described in detail in chapter 5. A theoretical analysis of impulse UWB radio
for wireless communication and ranging is provided employing the Shannon
Hartley theorem and Cramer-Rao lower bound (CRLB) method.
5

6. 6

7. Contents
Chapter 1…………………………………………………………………..12
1 Introduction……………………………………………………………13
1.1 Ultra Wideband……………………………………………..……13
1.2 UWB features.……………….…………………………………..16
1.3 UWB and Narrowband technologies…………………………….19
1.4 Applications of UWB……………………………………………21
1.5 UWB Regulations………………………………………………..24
1.6 Bandwidth property of UWB signals…………………………....26
1.6.1 Definition………………………………………………...26
1.6.2 Advantages of large relative bandwidth…………….......27
1.6.2.1 Processing gain potentiality…………………....27
1.6.2.2 Penetration of obstacles………………………..27
1.6.2.3 Propagation loss……………………………….28
1.7 Modulation techniques……………………………………………29
Chapter 2……………………………………………………………………31
2 Single band UWB modulation…………………………………………..32
2.1Modulation Techniques….……………………………………….32
2.1.1 Pulse Amplitude Modulation……………………………32
2.1.2 On-off Keying…………………………………………...33
2.1.3 Pulse Position Modulation………………………………33
2.1.4 Pulse Shape Modulation………………………………...35
2.1.5 Phase Shift Keying……………………………………...36
2.2 Multiple accesses in single band UWB…………………………37
2.2.1 Time-Hopping UWB……………………………………37
2.2.2 Direct-sequence UWB…………………………………..39
2.3 Detection Techniques…………………………………………....40
2.3.1 Correlation Receiver…………………………………….41
2.3.2 Rake Receiver……………………………………….......43
7

8. Chapter 3……………………………………………………………………45
3 Multiband UWB Modulations…………………………………………46
3.1 Introduction………………………………………………………...46
3.2 Modulation Techniques…………………………………………….46
3.2.1 Impulse Radio MB-IR…………………………………….46
3.2.2 MB-OFDM……………………………………………. …47
3.3 Architecture of OFDM Transmitter………………………………..48
3.3.1 Channel Encoding…………………………………………50
3.3.2 Bit Interleaving……………………………………………51
3.3.3 Time and Frequency Domain Spreading………………….52
3.3.4 Subcarrier Constellation Mapping………………………...53
3.4 MB-OFDM Receiver Architecture………………………………...54
3.4.1 System Model……………………………………………..54
3.4.2 Channel Estimation………………………………………..56
3.4.3 Frequency Domain Channel Equalization………………...56
3.4.4 Channel Decoding…………………………………………58
Chapter 4…………………………………………………………………....60
4 Ultra Wideband Position Estimation………………………….……....61
4.1 Introduction to Position Estimation………………………………...61
4.2 Position Estimation Applications…………………………………..61
4.3 Ranging and positioning parameters.………………………………62
4.3.1 Received Signal Strength…………………………………63
4.3.2 Angle of arrival (AOA)…………………………………...64
4.3.3 Time of Arrival (TOA)……………………………………66
4.3.4 Time Difference of Arrival (TDOA)……………………...68
4.3.5 Round Trip Time (RTT)…………………………………..69
4.4 Position Estimation…………………………………………………70
4.4.1 Geometric and statistical Approach……………………….70
4.4.2 Mapping or fingerprinting…………………………………73
Chapter 5……………………………………………………………………74
5 UWB Distance Measurements..………………………………………..75
5.1 Introduction………………………………………………………...75
8

9. 5.2 Ranging algorithm based on TOA……...…………………………..76
5.2.1 Signal aspects………..……………………………………78
5.2.2 Hardware aspects..………………………………………...80
5.3 Theoretical analysis of UWB distance measurements..……………82
5.4 Experimental ranging results………………………………………87
5.4.1 LOS area test results…….………………………………...88
5.4.2 Soft-NLOS area test results.………………………………90
5.4.3 Hard-NLOS area test results….…………………………...91
6 Conclusion………………………………………………………………92
7 References……………………………………………………………….94
9

10. List of Acronyms
AOA Angle of Arrival
AWGN Additive White Gaussian Noise
AP Access Point
ADC Analog-to-digital Convertor
BPSK Binary Phase Shift Keying
BPF Band-Pass Filter
CP Cyclic Prefix
CRLB Cramer-rao Lower Bound
CSS Chirp Spread Spectrum
CEPT Conference of Postal and Telecommunications
Administration
DAC Digital to Analog Conversion
DLP Digital Light Processor
DS Direct Sequence
ETSI European Telecommunications Standards Institute
FCC Federal Communication Commission
FFT Fast Fourier Transform
GPS Global Positioning System
IFFT Inverses Fast Fourier Transform
ISI Inter Symbol Interference
IF Intermediate Frequency
LAN Local Area Networks
LNA Low-noise Amplifier
LOS Line of Sight
10

11. MB-OFDM Multiband orthogonal Frequency-division Multiplexing
MMSE Minimum Mean-Square Error
NLOS Non Line of Sight
OOK On-Off keying
PC Personal Computer
PG Processing Gain
PPM Pulse Position Modulation
PSM Pulse Shape Modulation
PAM Pulse Amplitude Modulation
PR Pseudo Random
RF Radio Frequency
RSS Received Signal Strength
RTT Round Trip Time
RMSE Root-Mean-Square error
SNR Signal-to-Nose Ratio
TH-PPM Time Hopping Pulse Positioning Modulation
TH Time Hopping
TFC Time Frequency Code
TOA Time Of Arrival
TDOA Time Difference of Arrival
UWB Ultra Wideband
WPAN Wireless Personal Area Network
Wi-Fi Wireless Fidelity
ZMCSCG Zero-Mean Circularly Symmetric Complex Gaussian
ZF Zero-Forcing Equalization
11

12. Chapter 1
12

13. 1. Introduction
1.1 Ultra Wideband
Ultra-Wideband (UWB) is a high data rate, low power short-range wireless
technology that is generating a lot of interest in the research community and
the industry, as a high-speed alternative to existing wireless technologies such
as IEEE 802.11 WLAN, HomeRF, and HiperLANs [3]. Although, it
considered as a recent technology in wireless communications, ultra-
wideband (UWB) has actually experienced over 40 years ago. In fact, UWB
has its origin in the spark-gap transmission design of Marconi and Hertz in
the late 1890s. In other words, the first wireless communication system was
based on UWB. Owing to technical limitations, narrowband communications
were preferred to UWB. In the past 20 years, UWB was used for applications
such as radar, sensing, military communication and localization. A substantial
change occurred in February 2002, when the Federal Communication
Commission (FCC) issued a report allowing the commercial and unlicensed
deployment of UWB with a given spectral mask for both indoor and outdoor
applications in the USA. This wide frequency allocation initiated a lot of
research activities from both industry and academia. In recent years, UWB
technology has mostly focused on consumer electronics and wireless
communications. The United States Federal Communications Commission
(FCC) uses the following two-part requirement to identify UWB emissions:
• -10 dB fractional bandwidth greater than 0.20, or
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14. • -10 dB bandwidth equal to or greater than 500 MHz, regardless of the
fractional bandwidth. The fractional bandwidth is based on the frequency
limits of the emission bandwidth using the formula [21],
!! !!!
𝐵! = 2× (1.1)
!! !!!
Where, f! upper frequency, f! lower frequency.
Ultra-Wideband (UWB) technology is loosely defined as any wireless
transmission scheme that occupies a bandwidth of more than 25% of a center
frequency, or more than 1.5GHz. A UWB system can also be determined by
a duty cycle less than 0.5 %. Equation 1.2 illustrates the duty cycle of a UWB
pulse. T! Stands for the symbol duration and T! for the UWB pulse width.
!
Duty Cycle = !! (1.2)
!
UWB characteristics can be analyzed according to the Shannon capacity
formula. For an AWGN channel of bandwidth B, the maximum data that can
be transmitted can be expressed as
𝐶 = 𝐵𝑙𝑜𝑔! 1 + 𝑆𝑁𝑅 𝑏𝑖𝑡/𝑠𝑒𝑐𝑜𝑛𝑑 (1.3)
SNR is representing the signal-to-noise ratio. From this equation it is clear, if
we increase the bandwidth of the system, the capacity of the channel will
increase. If we see in the context of UWB, the bandwidth is very high and
very low power is required for transmission. So we can gain a very high
channel capacity using UWB with lower power that can make batter life
longer and reduce the interference with existing systems.
14

15. UWB is a Radio Frequency (RF) technology that transmits binary data, using
low energy and extremely short duration impulses or bursts (in the order of
picoseconds) over a wide spectrum of frequencies. It delivers data over 15 to
100 meters and does not require a dedicated radio frequency, so is also known
as carrier-free, impulse or base-band radio. UWB systems use carrier-free,
meaning that data is not modulated on a continuous waveform with a specific
carrier frequency, as in narrowband and wideband technologies.
Figure 1: FCC spectral mask for indoor UWB transmission
15

16. 1.2 UWB features
UWB technology has the following significant characteristics.
High Data rate
UWB can handle more bandwidth-intensive applications like streaming video,
than either 802.11 or Bluetooth because it can send data at much faster rates.
UWB technology has a data rate of roughly 100 Mbps, with speeds up to 500
Mbps, This compares with maximum speeds of 11 Mbps for 802.11b (often
referred to as Wi-Fi) which is the technology currently used in most wireless
LANs; and 54 Mbps for 802.11a, which is Wi-Fi at 5MHz. Bluetooth has a
data rate of about 1 Mbps [3].
Figure 2: Maximum range and data rate of different wireless technologies [7].
16

17. Low power consumption
UWB transmits short impulses constantly instead of transmitting modulated
waves continuously like most narrowband systems do. UWB chipsets do not
require Radio Frequency (RF) to Intermediate Frequency (IF) conversion,
local oscillators, mixers, and other filters. Due to low power consumption,
battery-powered devices like cameras and cell phones can use in UWB [3].
Interference Immunity
Due to low power and high frequency transmission, USB’s aggregate
interference is “undetected” by narrowband receivers. Its power spectral
density is at or below narrowband thermal noise floor. This gives rise to the
potential that UWB systems can coexist with narrowband radio systems
operating in the same spectrum without causing undue interference [3].
High Security
Since UWB systems operate below the noise floor, they are inherently covert
and extremely difficult for unintended users to detect [3].
Reasonable Range
IEEE 802.15.3a Study Group defined 10 meters as the minimum range at
speed 100Mbps However, UWB can go further. The Philips Company has
used its Digital Light Processor (DLP) technology in UWB device so it can
operate beyond 45 feet at 50 Mbps for four DVD screens [3].
17

18. Low Complexity, Low Cost
The most attractive of UWB’s advantages are of low system complexity and
cost. Traditional carrier based technologies modulate and demodulate
complex analog carrier waveforms. In UWB, Due to the absence of Carrier,
the transceiver structure may be very simple. The techniques for generating
UWB signals have existed for more than three Decades. Recent advances in
silicon process and switching speeds make UWB system as low-cost. Also
home UWB wireless devices do not need transmitting power amplifier. This
is a great advantage over narrowband architectures that require amplifiers
with significant power back off to support high-order modulation waveforms
for high data rates [3].
Large Channel Capacity
The capacity of a channel can be express as the amount of data bits
transmission/second. Since, UWB signals have several gigahertz of
bandwidth available that can produce very high data rate even in
gigabits/second. The high data rate capability of UWB can be best understood
by examining the Shannon’s famous capacity equation:
!
𝐶 = 𝐵 log ! (1 + ) (1.4)
!
Where C is the channel capacity in bits/second, B is the channel bandwidth in
Hz, S is the signal power and N is the noise power. This equation tells us that
the capacity of a channel grows linearly with the bandwidth W, but only
logarithmically with the signal power S. Since the UWB channel has an
18

19. abundance of bandwidth, it can trade some of the bandwidth against reduced
signal power and interference from other sources. Thus, from Shannon’s
equation we can see that UWB systems have a great potential for high
capacity wireless communications [7].
Resistance to Jamming
The UWB spectrum covers a huge range of frequencies. That’s why, UWB
signals are relatively resistant to jamming, because it is not possible to jam
every frequency in the UWB spectrum at a time. Therefore, there are a lot of
frequency range available even in case of some frequencies are jammed.
Scalability
UWB systems are very flexible because their common architecture is software
re-definable so that it can dynamically trade-off high-data throughput for
range [6].
1.3 UWB and Narrowband technologies
Wireless technologies are growing faster with great flexibility and mobility.
Wireless technology reduces the use of cables and more easy to install.
Currently there are four wireless technology protocols are working around the
globe. Bluetooth (over IEEE 802.15.1), ultra-wideband (UWB, over IEEE
802.15.3), ZigBee (over IEEE 802.15.4) and Wi-Fi (over IEEE 802.11).
These all protocols can be compared with each other on the basis of cost,
19

20. complexity and power, so that it will be easier to select specific protocol for
network engineers for wireless network deployment. Following section gives
a short overview of narrowband technologies [4].
Bluetooth is a short-range radio system, designed for devices operating
within a short distance, for example to connect computer peripherals such as
mouse, keyboard, printers. Blue tooth is used also in mobile handsets to
connect to mobiles for sharing music and files. Piconet and Scatternet are two
topologies used by Bluetooth for connection management. The maximum
signal rate is 1Mb/s with power from 0-10dbm.
ZigBee also known as IEEE 802.15.4 is a low rate wireless technology
operating in simple devices that consumes less power and in range of 10m.
ZigBee is a mesh networking with long battery lifetime. The maximum signal
rate is 256kb/s with power from (-25) - 0 dBm.
Wireless Fidelity (Wi-Fi) is IEEE802.11a/b/g standards for local area
networks. It allows users to use internet at broadband speed connect to an
access point (AP). Wi-Fi operates in range of 100 meter. The maximum signal
rate is 54Mb/s with power from 15 - 20 dBm. Figure 3 gives a graphical view
of power output of different technologies. UWB uses very less emitted power
according to all other technologies. The maximum signal rate is 110Mb/s.
UWB is the suitable choice for WPAN due to low power, high speed and easy
to use.
20

21. Figure 3: Compression between different technologies
1.4 Application of UWB
Wireless technology is playing now main role in our daily lives. In recent
years, demand of higher quality and faster delivery of data is increasing day
by day. The need of more speed and quality brought up many wireless
solutions for short rang communication. The family of Wi-Fi standards
(IEEE802.11), Zigbee (IEEE802.15.4) and the recent standard 802.15.3,
which are used for wireless local area networks (WLAN) and wireless
personal area networks (WPAN), can’t meet the demands of applications that
needs much higher data rate. UWB connection function as cable replacement
with date rate more than 100 Mbps. Applications of UWB can be categorized
in following section.
21

22. Imaging Systems
UWB was firstly used by military purpose to identify the buried installations.
In imaging system emission of UWB is used as illuminator similar to radar
pulse. The receiver receives the signal and the output is processed using
complex time and frequency functions to differentiate between materials at
varying distance. The lower part of radio spectrum < 1 GHz have ability to
penetrate the ground and solid surfaces. This property makes UWB a best
choice for detection of buried objects and public security and protection
organizations.
UWB plays an important role in medical imagine and human body analysis.
Now a day’s ultra wideband radars are used for heart treatment. All of inner
body parts of human being can be imaged by adjusting the emitting pulse
power [21].
Radar Systems
In early days military used UWB technology in radar system to detect the
object in high-density media like ground, ice and air targets. Research and
studies in this area found, radar can be used everywhere where we need
sensing of moving objects. Radar systems can be installed in vehicle to avoid
accident during driving and parking. UWB radars can be used in guarding
systems as alarm sensors to detect unauthorized entrance into the territory.
These radars can be used to find objects or peoples in collapsed buildings by
detecting the movement of person; but in case person is not moving, it can
22

23. still be detected by heart beat and thorax beats. Police department can use
such radars to find criminals hidden in shelters. These radars are able to
measure the patient’s cardiac and breathing activity in hospitals as well as at
home [21].
Home Networks
In a home environment, variety of devices are operating such as DVD players,
HDTVs, STBs, Personal video recorders, MP3 players , digital cameras,
camcorders and others. The current popular usage of home networking is
sharing date from PC to PC and from PCs to peripherals. Customers are
demanding multiplayer gaming and video distributions in home network.
These all devices are connected using wires to share contents at high speed.
UWB is a wire replacement technology provides high bandwidth more than
100 Mbps. These all devices can be connected in a home network to share
multimedia, printers, scanners and etc. UWB can connect a plasma display or
HDTV to a DVD or STB without using any cable. UWB also enables
multiple streaming to multiple devices simultaneously, that allows viewing
same or different content on multiples devices. For example, movie content
can be shared on different display devices in different rooms [1] [3].
The home networks are directly connected to a broadband through a
residential gateway. This approach is cost effective but is ineffective for
whole house coverage. Cables are installed to connect different devices with
Internet in a home environment. With a right UWB solution Internet traffic
23

24. from multiple users in a home can be routed to single broadband connection.
UWB enable devices can be connected in an ad-hoc manner like Bluetooth to
share contents. For example a camera can be connected to a printer directly to
print pictures; MP3 player can be connected to another MP3 player and
shared music.
Sensor Networks
Wireless sensor networks are an important area of communication. Sensor
networks have many applications, like building control, surveillance, medical,
factory automation etc. Sensor networks are operated under many constraints
such as energy consumption, communication performance and cost. In many
applications sensor size is also considered to be smaller. UWB use pulse
transmission, with very low energy consumption. This property enables us to
design very simple transmitters and thus long time battery operated devices.
These sensors can be used in locating hospitals, tracking and communication
systems. These systems enable us to locate and track objects including
facilities, equipment’s, nurses, doctors and patients in a hospital [2].
Furthermore these systems can be used in factories to track equipment’s,
employees and visitors.
1.5 UWB Regulation
Number of wireless systems is working around the globe. Every system
operates under a defined bandwidth range by FCC. Interference was also an
24

25. issue to consider while allowing the UWB for commercial use. To avoid
interference with other systems, UWB have many restrictions to operate
under FCC approved UWB commercial license in March 2002. The approved
range of band for UWB is in between 3.1-10.6 GHz for short-range indoor
wireless networks. This limitation keeps UWB noise out of the sensitive
areas occupied by GPS, cellular phone and WLAN systems. This approval
gave companies to develop high-speed wireless solutions for home and
consumer electronics.
The European Telecommunications Standards Institute (ETSI) and European
Conference of Postal and Telecommunications Administrations (CEPT) have
been working closely to establish a legal framework for the deployment of
unlicensed UWB devices. Within ETSI, there are two TGs to develop UWB
regulation and standards for the European Union. The ETSI TG31A is
responsible for identifying a spectrum requirement and developing radio
standards for short range devices using UWB technologies, while the ETSI
TG31B is responsible for developing standards and system reference
documents for automotive UWB radar applications. Lastly, CEPT SE24 is
responsible for regulatory issues and spectrum management e.g., studying
spectrum sharing for < 6 GHz [6].
The Japanese Ministry of Telecommunications has shown some interest in
adopting UWB technology for communications applications. It plans through
its agencies to develop with industry an indoor UWB system to network
personal devices such as video cameras and computers. In August 2002, a
25

26. UWB technology group was set up by the Communications Research Centre
to work with industry on UWB research, development and standardization
through Japan’s Communications Research Laboratory [21].
1.6 Bandwidth Property of UWB signals
1.6.1 Definition
Bandwidth is the most important characteristic of UWB communication
systems. The definition of ultra-wideband is a signal with greater than 25%
relative bandwidth. UWB signals need large absolute bandwidths. The
relative bandwidth definition of UWB is stated as follows [9]:
!! !!! !! !!! !
𝐵!"# = = 2. ≈ (1.5)
!!"# !! !!! !!
Where, f! = upper band frequency
f! = Lower band frequency
W= Absolute bandwidth
f! = Center frequency
Any signal will considered as a UWB signal that have a relative bandwidth
property.
26

27. 1.6.2 Advantages of large relative bandwidth
1.6.2.1 Processing Gain Potentiality
The ratio of the noise bandwidth at the front and end of the receiver is known
as processing gain (PG). Usually, this ratio is calculated as the ratio of the
channel symbol rate R ! , to the bit rate R ! :
!"#$% !"#$%&$'! !" !!
𝑃𝐺 = = (1.6)
!"#$% !"#$%&'! !"# !!
UWB devices using large scale of bandwidth that’s why, most of the
application desired high data rate and a margin of processing gain can be
achieved simultaneously [9].
1.6.2.2 Penetration of obstacles
In order to implement wider bandwidth, conventional narrowband
communications must use higher carrier frequencies. When frequencies of
these signals increase, the propagation losses and bandwidth becomes larger.
On the other hand, UWB signals can achieve high data rates with lower center
frequencies.
!
𝑓! = ⇒ 𝑓!! < 𝑓!! for 𝐵!"#! > 𝐵!"#! (1.7)
!!"#
27

28.
It follows that UWB signals have the potential for greater penetration of
obstacles such as walls than do conventional signals while achieving the same
data rate. From FCC 2002 rules, if relative bandwidth is 3.55 GHz and the
absolute bandwidth is 900 MHz. If the actual data symbol rate is 100 MHz,
then a conventional communications waveform can be designed with a center
frequency of 3.15 GHz. In this case, the conventional signal will penetrate
materials slightly better than the UWB signal. This example highlights that
the material penetration advantage of UWB signals applies when they are
permitted to occupy the lower portions of the RF spectrum [9].
1.6.2.3 Propagation Loss
UWB signal can be used to estimate propagation loss can be estimate by
UWB signal without incurring a significant error in the calculation of
received power: Let the signal spectrum be denoted Gs (f);
Gs (f)≈ Const. W (1.8)
Propagation loss for UWB signals can be obtained using conventional
methods and the nominal center frequency of the signal.
! !"#$%. !"#$%.
𝑝! ≈ 𝑐𝑜𝑛𝑠𝑡.× ! ! = = ! (1.9)
!! ! !! !! !! !!
Where, 𝑝! = Recieve power
! !
𝑓! = 𝑓! − , 𝑓!" = 𝑓! +
! !
28

29. 𝑓! = 𝑓! 𝑓! is the geometric mean of the lower and upper band-edge
frequencies.
Thus the received power is estimated correctly using the geometric mean as
the nominal frequency [9].
1.7 Modulation Techniques
Early implementation of UWB communication systems was based on
transmission and reception of extremely short duration pulses (typically sub
nanosecond), referred to as impulse radio. Each impulse radio has a very wide
spectrum, which leads to the very low power levels permitted for UWB
transmission. These schemes transmit the information data in a carrier less
modulation; where no up/down conversion of the transmitted signal is
required at the transceiver. The time hopping pulse position modulation (TH-
PPM) introduced in 1993 by Schultz and better formalized later by Win and
Schultz.
Until February 2002, the term UWB used only impulse radio modulation.
According to the new UWB ruling of FCC from 2002, New frequency
spectrum from 3.1 to 10.6 GHz is allocated for unlicensed application.
Furthermore, any communication system that has a bandwidth larger than 500
MHz is considered as UWB. As a result, well known and more established
wireless communication technologies (e.g., OFDM, DS-CDMA) can be used
for UWB transmission [7].
29

30. In last few years, UWB system design has experienced a shift from the
traditional single-band to a multiband design approach. Multiband consists in
dividing the available UWB spectrum into several sub bands, each one
occupying approximately 500 MHz. This bandwidth reduction relaxes the
requirement on sampling rates of analog-to-digital converters (ADC),
consequently enhancing digital processing capability. One example of
multiband UWB is multiband orthogonal frequency-division multiplexing
(MB-OFDM).
30

31. Chapter 2
31

32. 2 Single band UWB modulation
Single band UWB modulation is also called impulse radio modulation. This is
based on very short-time impulse of transmission radio, which are typically
the derivative of Gaussian pulses. This type of transmission does not require
the use of additional carrier modulation, as the pulse will propagate well in
the radio channel. The technique is a baseband signal approach. The most
common modulation technique in UWB is introduced in figure 4 [7].
2.1 Modulation Techniques
2.1.1 Pulse Amplitude Modulation
Pulse amplitude modulation (PAM) is implemented using two antipodal
Gaussian pulses as shown in Figure 4(a). The transmitted binary pulse
amplitude modulated signal str (t) can be represented as,
str(t) = dk 𝜔tr(t) (2.1)
Where 𝜔 tr(t) is the UWB pulse waveform, k represents the transmitted bit
(“0” or “1”) and
−1 𝑖𝑓 𝑘 = 0
dk = (2.2)
+1 𝑖𝑓𝑘 = 1
32

33. Is used for the antipodal representation of the transmitted bit k. The
transmitted pulse is commonly the first derivative of the Gaussian pulse
defined as [12]
!!!
!
𝜔tr(t)=-­‐ 𝑒 !!! (2.3)
!!! !
Where σ is related to the pulse length Tp by σ = Tp/2π.
2.1.2 On-off Keying
The second modulation scheme is the binary on-off keying (OOK) and is
depicted in Figure 4 (b). The waveform used for this modulation is defined as
in (2.1) with [12]
0 𝑖𝑓 𝑘 = 0
dk = (2.4)
+1 𝑖𝑓𝑘 = 1
The difference between OOK and PAM is, no signal is transmitted in OOK
while k=0.
2.1.3 Pulse Position Modulation
Pulse position modulation (PPM) signal is encoded by the position and the
information of the data bit to be transmitted with respect to a normal position.
More precisely, while bit “0” is represented by a pulse originating at the time
instant 0, bit “1” is shifted in time by the amount of δ from 0. Let us first
33

34. assume that a single impulse carry the information corresponding to each
symbol. The PPM signal can be represented as
Figure 4: Single band (impulse radio) UWB modulation schemes [7]
34

35. !
𝑠!" (𝑡) = 𝜔!" !!!!
𝜔!" (𝑡 − 𝑘𝑇𝑠 − 𝑑! 𝛿) (2.5)
Where ω!" (t) = transmitted impulse radio
δ = The time between two states of the PPM modulation
The value of δ may be chosen according to the autocorrelation characteristics
of the pulse. For instance, to implement a standard PPM with orthogonal
signals, the optimum value of δ (δopt) which results in zero auto correlation
ρ(𝛿!"# ) is such as:
!
𝜌 𝛿!"# = !!
𝜔!" 𝜏 𝜔!" 𝛿!"# + 𝜏 = 0 (2.6)
Normally, the symbol is encoded by the integer 𝑑! (0 ≤ 𝑑! ≤ M) where M is
the number of states of the modulation. The total duration of the symbol is
𝑇! , 𝑤ℎ𝑖𝑐ℎ 𝑖𝑠 𝑓𝑖𝑥𝑒𝑑, and chosen greater than Mδ+TGI where TGI is a guard
interval inserted for inter symbol interference (ISI) mitigation. The binary
(𝑀)
transmission rate is thus equal to R =𝑙𝑜𝑔! 𝑇! . Figure 4 (c) shows a two-
state (binary) PPM where a data bit “1” is delayed by a fractional time
interval δ whereas a data bit “0” is sent at the nominal time [7].
2.1.4 Pulse Shape Modulation
Pulse shape modulation (PSM) is an alternative to PAM and PPM
modulations. As shown in Figure 4(d), in PSM the information data is
encoded by different pulse shapes. This requires a suitable set of pulses for
35

36. higher order modulations. The orthogonality of signals used in PSM uses
orthogonal signal that’s why it has desirable property. This attribute permits
an easier detection at the receiver. The application of orthogonal signal sets
also enables multiple access techniques to be considered. This can be attained
by assigning a group of orthogonal pulses to each user, who uses the assigned
set for PSM. The transmission will then be mutually orthogonal and different
user signals will not interfere with each other [7].
2.1.5 Phase Shift Keying
In binary PSK (BPSK) or bi phase modulation, the binary data are carried in
the polarity of the pulse. The waveform used in BPSK defined in equation 2.1
with [12],
1 𝑖𝑓 𝑘 = 1
dk = (2.7)
−1 𝑖𝑓𝑘 = 0
A pulse has a positive polarity if k=1, whereas it has negative polarity if k=0.
A BPSK signal shown in figure 5.Since the different pulse level is twice the
pulse amplitude; the BPSK signal has better performance than OOK [12].
Figure 5: Binary PSK signal
36

37. 2.2 Multiple accesses in single band UWB
Until now, we assumed that each symbol was transmitted by a single pulse.
This continuous pulse transmission can lead to strong lines in the spectrum of
the transmitted signal. In practical system, due to the very restrictive UWB
power limitations, UWB system shows a high sensitivity to interference from
existing systems. The modulation schemes that are described above, they
don’t provide multiple access capability.
To reduce the potential interference from UWB transmissions and provide
multiple access capability, a randomizing technique is applied to the
transmitted signal. This makes the spectrum of the UWB signal more noise-
like. The two main randomizing techniques used for single band UWB
systems are time hopping (TH) and direct-sequence (DS). The TH technique
describes the position of the transmitted UWB impulse in time and the DS
approach is based on continuous transmission of pulses composing a single
data bit. The DS-UWB scheme is similar to conventional DS spread-spectrum
systems where the chip waveform has a UWB spectrum [7].
2.2.1 Time-Hopping UWB
The multiple access and power limit considerations motivate the use of an
improved UWB transmission scheme where each data symbol is encoded by
the transmission of multiple impulse radios shifted in time. A pseudo-random
(PR) code determined the position of each pulse in Time-Hopping (TH)
37

38. scheme. To increase the range of transmission, more energy is allocated to a
symbol. Unique TH code distinguishes different users; they can transmit at
the same time. A TH-PPM signal format for 𝑗!! user can be written as,
! ! !! !! (!) (!)
𝑆!" 𝑡 = !!!! !!! 𝑤!" (𝑡 − 𝑘𝑇! − 𝑙𝑇! − 𝑐! 𝑇! )𝑑! (2.8)
(!)
Where d! is the k-th data bit of user j. 𝑁! is the number of impulses
transmitted for each symbol. The total symbol transmission time 𝑇! is
divided into 𝑁! frames of duration T! and each frame is itself sub-divided into
slots of duration 𝑇 𝑐 . Each frame contains one impulse in a position
(!)
determined by the PR. TH code sequence c! (unique for the j-th user) and
The symbol to be encoded shown in Figure 6 for TH-PPM binary modulation.
TH spreading can be combined with PAM, PPM and PSM [7].
Figure 6: TH-PPM binary Modulation
38

39. 2.2.2 Direct-sequence UWB
DS-UWB employs sequences of UWB pulses. Each user is distinguished by
its specific pseudo random sequence, which performs pseudo random
inversions of the UWB pulse train. DS transmission is modulated by a
pseudo-random (or specific) binary sequence that serves to spread the
waveform spectrum; a correlator at the receiver evaluates the energy at the
binary sequence-defined frequencies and dispreads the signal prior to
decoding it. Instead of transmitting bit per bit, such system will transmit a
sequence for every bit. Since the chip rate is higher than the bit rate, the
bandwidth used has increased. W-CDMA has been accepted as the 3rd
generation cellular standard. This system provides multiple-access, that is,
many users can share the same bandwidth and each has its unique spreading
sequence [13].
The DS-UWB spreading technique is combined with PAM, OOK, PSM and
BPSK modulations. Since PPM is a time-hopping technique, it is not used for
DS-UWB transmission. DS spreading approach for PAM and OOK signal
format for 𝑗!! user can be written as [14],
! ! !! !! (!) (!)
𝑆!" = 𝐴! !!!! !!! 𝑤!" (𝑡 − 𝑘𝑇! − 𝑙𝑇! )𝑐! 𝑑! (2.9)
(!)
Where d! is the 𝑘 !! data bit
(!)
c! is the 𝑙 !! chip of PR code
39

40. Figure 7: Time domain representation of (a) TH-UWB and (b) DS-UWB spreading
techniques.
𝑤!" (t) is the pulse waveform of duration 𝑇!
𝑇! is the chip length and 𝑁! is the number of pulse per data bit.
J is user index. The PR sequence is {-1,+1} and bit length is 𝑇! = 𝑁! 𝑇!
2.3 Detection Techniques
In single band UWB systems, two widely used demodulators are correlation
receivers and Rake receivers.
40

41. 2.3.1 Correlation Receiver
The correlation receiver is the optimum receiver for binary TH-UWB signals
in additive white Gaussian noise (AWGN) channels. TH format is typically
based on PPM. TH-PPM was the first physical layer proposed for UWB
communications. We consider TH-PPM signal for correlation receiver [16].
Let us consider that multiple access active in TH-PPM transmitter. The
received signal r(t) at the receiver is modeled as
!! (!)
r(t)= !!! 𝐴! 𝑆!"# (t-­‐ 𝜏! )+n(t) (2.10)
Figure 8: Correlation receiver block diagram for TH-PPM Signal [7]
41

42. Where, N! is number of users, A! means the attenuation over the propagation
path of the received signal. τ! Represent the time asynchronies between clock
of received signal and the receiver clock. n(t) is the additive receiver noise.
The propagation channel modifies the shape of the transmitted impulse 𝑤!" (𝑡)
to 𝑤!"# (𝑡). We consider the detection of the data from the first user, i.e., d(1).
As shown in Fig. 8, the data detection process is performed by correlating the
received signal with a template v(t) defined as,
V(t)=𝑤!"# 𝑡 − 𝑤!"# (t-­‐𝛿) (2.11)
Where 𝑤!"# (t) and 𝑤!"# (t − 𝛿) represent a symbol with duration Ts. The
received signal in a time interval of duration 𝑇! = 𝑁! 𝑇! is given by
!! !!
𝑟 𝑡 = !!! 𝑤!"# (𝑡 − 𝑇! − 𝑙𝑇! − 𝑐!! 𝑇! − 𝑑 1 𝛿 + 𝑛!"! (𝑡) (2.12)
Where n!"! (t) is the multi-user interference and noise. It is assumed that the
!
receiver knows first transmitter’s TH sequence {c! }and the delay T! .When
the number of users is large, the approximate the interference-plus noise
n!"! t is as a Gaussian random process. Although TH-PPM has interesting
feature, but the data rate is reduced by a factor of Ns. Modification introduced
by the UWB channel on the shape of the transmitted signal is another
disadvantage. Thus, the receiver has to construct a template by using the
shape of the received signal. The construction of an optimal template is an
important concern for practical PPM based systems. Besides, due to
extremely short duration pulses employed, timing mismatches between the
42

43. correlator template and the received signal can result in serious degradation in
the performance of TH-PPM systems. For this reason, accurate
synchronization is of great importance for UWB systems employing PPM
modulation.
2.3.2 Rake Receiver
A typical Rake receiver is shown in Fig. 9. The idea of the RAKE receiver is
to combine the energy of the different multipath components of a received
pulse in order to improve the performance. It is composed of a number of
correlators followed by a linear combiner. Each correlator is synchronized to
a multipath component and the results of all correlators are added. Finally, a
Decision device decides which symbol was transmitted after analyzing the
output of the adders.
The Rake receiver takes advantage of multipath propagation by combining a
large number of different and independent replicas of the same transmitted
pulse, in order to exploit the multipath diversity of the channel. In general,
Rake receivers can support both TH and DS modulated systems Rake
correlators also called as fingers. The major consideration in the design of a
UWB Rake receiver is the number of paths to be combined, that’s why the
complexity increases with the number of fingers [15].
43

44. Figure 9: RAKE Receiver with J fingers
44

45. Chapter 3
45

46. 3 Multiband UWB modulation
3.1 Introduction
In single band system whole spectrum is used simultaneously and different
techniques are implemented to provide multi band environment. Single band
is traditional approach to use the whole spectrum as one. In multiband UWB,
the spectrum is divided into many sub bands of 500 MHz bandwidth. This
approach makes use of spectrum in more efficient way and reduces
interference with other system working in same environment. Different
multiple access and modulation options can be applied to each sub-band.
There are two kind of Multiband UWB modulation, Multiband impulse radio
(MB-IR) and multiband OFDM (MB-OFDM). The following sections
elaborate both classes in sequence.
3.2 Modulation Techniques
3.2.1 Impulse Radio MB-IR
In MB-IR system, the allocated spectrum of UWB is divided in to non-
overlapping small channels with a minimum bandwidth of 500 MHz
Modulations techniques from single band UWB, PAM, PPM or PSM are
applied to each sub-band. A pulse repetition scheme is used to avoid ISI.
These systems are less complex to implement. The Rake receiver is used with
few fingers. The drawback of MB-IR system is that, for each sub-band a Rake
receiver is required separately.
46

47. 3.2.2 MB-OFDM
Orthogonal frequency division multiplexing is a mature technique is being
used in narrow band technologies. The data is transmitted on multiple
carriers. These carriers are spaced with precise frequencies. OFDM approach
has many good properties what makes OFDM a best choice. OFDM increase
Spectral efficiency, inherent ability to avoid RF interference. Multi-path
energy is captured efficiently. The drawback of OFDM technique is that, the
architecture of transmitter and receiver is complex as compared to MB-IR.
Batra et al. in 2004 proposed a scheme to IEEE802.15.3a [22], [23] In this
proposal, spectrum of UWB is divided into non-overlapping sub-bands of 528
MHz each and five band groups are defined within 3.1-10.6 ranges as shown
in figure 10.
Band Group #1 Band Group #2 Band Group #3 Band Group #4 Band Group #5
Band Band Band Band Band Band Band Band Band Band Band Band Band Band
#1 #2 #3 #4 #5 #6 #7 #8 #9 #10 #11 #12 #13 #14
3432 3960 4488 5016 5544 6072 6600 7128 7656 8184 8712 9240 9768 10296 f
MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz
Figure 10: Division of the UWB spectrum from 3.1 to 10.6 GHz into band groups
containing sub-bands of 528 MHz in MB-OFDM systems [24].
The first four groups further have tree sub-bands while last group have only
two sub-bands. Transmission of data over first three groups is known as
mandatory mode I. Information within each sub-band is transmitted using
47

48. conventional coded OFDM modulation. The presence of time-frequency code
(TFC) differentiates MB-OFDM from conventional OFDM system. The
purpose of time-frequency code (TFC) is to provide a different carrier
frequency at each time-slot and also used to distinguish between multiple
users.
Figure 11: Example of time-frequency coding for the multiband OFDM system in mode I,
TFC = {1, 3, 2, 1, 3, 2, … }.
3.3 Architecture of OFDM Transmitter
MB-OFDM transmitter architecture is complex to design as compared to
signal band OFDM and MB-IR. Sub-bands transmit information in a time-
slot fashion. One sub-band at a time transmits information in a particular
time-slot. Binary date is inputted into transmitter that is encoded by non-
recursive non-systematic convolution (NRNSC) code before interleaving.
Bits interleaving is used to provide more diversity to transmit over multipath
fading channels and reduce burst errors. QPSK symbols using Gray labeling
48

49. was used in basic MB-OFDM proposal. Figure 12 presents the architecture of
OFDM transmitter.
Figure 12: Transmitter architecture for the MB-OFDM system.
In OFDM scheme, whole bandwidth is divided into channels each with 528
MHz, each sub-bands contains 𝑁! = 128 subcarriers and each subcarrier is
separated by Δf= 4.125 [13]. Transmitter at each time-slot applies 128 point
inverse fast Fourier transform (IFFT) with a OFDM symbol duration of
𝑇!!" = 1/Δf = 242.42ns. Output signal is added with a cyclic prefix (CP)
TCP=60.6 ns to avoid ISI and guard interval (GI) 𝑇!" =9.5ns. The purpose of
GI is to switch transmitter and receiver form one sub-band to next. Next
stage is for digital-to-analog conversion. OFDM signal with CP and GI is
passed by DAC, which produce an analog baseband OFDM signal. The
49

50. duration of this symbol is the sum of all interval times. 𝑇!"# = 𝑇!!" + 𝑇!" +
𝑇!" =312.5 ns as in figure 12. This process can be mathematically expressed
as,
!! !! !
𝑥! (𝑡)= !!! 𝑆! exp{𝑗2𝜋𝑘∆𝑓(𝑡 − 𝑇!" )} (3.1)
This equation represents the baseband signal to be transmitted. Where t ∈
[𝑇!" , 𝑇!!" + 𝑇!" ] and j = √−1. 𝑥! (t) Represent the copy of last OFDM symbol
and is zero at interval (𝑇!!" +𝑇!" , 𝑇!"# ) corresponding to the GI duration. The
baseband OFDM signal is filtered and generated RF signal that is sent to
transmitting antenna. The transmitted signal can be defined by this equation.
!!"# !!
𝑟!" (𝑡 )= !!! 𝑅𝑒 (𝑥! 𝑡 − 𝑛𝑇!"# exp {𝑗2𝜋𝑓!! 𝑡}) (3.2)
𝑁!"# Represent total number of symbols in the frame and 𝑓 ! represent the
!
carrier frequency over which signal is transmitted.
3.3.1 Channel Encoding
Signals traveling through an environment are subject to fading. OFDM
signals are sent on different carriers, which may suffer fading, which can
cause erroneous decisions. To overcome these kinds of fading effects, forward
error correction coding scheme is used in MB-OFDM. Mother codes with
different coding rate are used. Puncturing procedure is used to generate
different coding rates from the rate R=1/3. In this process, some bits are
50

51. omitted at transmitter and dummy bits are added on receiver side at the place
of omitted bits [25].
3.3.2 Bit Interleaving
Bit interleaving is used when transmission is over multiple fading channels. It
provides high diversity and is of two types [13]. Inter-Symbol interleaving:
This permutes the bits across 6 consecutive OFDM symbols, enables the PHY
to exploit frequency diversity within a band group. Intra-symbol tone
interleaving: This permutes the bits across the data subcarriers within one
OFDM symbol, exploits frequency diversity across subcarriers and provides
robustness against narrow-band interferers. In Intra-symbol tone interleaving
𝑁!"#$ blocks are made by grouping coded bits. 𝑁!"#$ represent number of
coded bits per OFDM symbol. Coded bits are than ordered by Block
interleaver of size Nbi= 6 * 𝑁!"#$ . If {U (i)} is sequence, {S(i)},
(i=0…..6𝑁!"#$ -1) are input and output bits of interleaver than we have
equation representation as
!
𝑆 𝑖 = 𝑈{𝐹𝑙𝑜𝑜𝑟 + 6𝑀𝑜𝑑(𝑖, 𝑁!"#$ )} (3.3)
!!"#$
Floor is used which give largest integer value less or equal to its arguments
value and reminder is returned by Mod function. Blocks of 𝑁!"#$ bits are
constructed by interleaver output and organized by using a regular block
intra-symbol.
51

52. 3.3.3 Spreading Techniques
Bandwidth expansion can be achieved by two schemes.
Frequency Domain Spreading
In this spreading scheme, copy of information is sent on a single OFDM
symbol, information is sent twice. The subcarriers are divided in two half.
Date is sent on first half of subcarriers and conjugate symmetric are sent on
second half of subcarriers.
Time Domain Spreading
In this scheme, different frequency sub-bands is used to transmit same OFDM
symbol. This approach introduces inter-sub-band diversity as well as
maximizes frequency-diversity. Performance is also improved in the presence
of other non-coordinated devices.
Data Modulation Code Rate Frequency Time Spreading
Rates(Mbps) Spreading
53.3 QPSK 1/3 Yes 2
55 QPSK 11/32 Yes 2
80 QPSK ½ Yes 2
106.7 QPSK 1/3 No 2
110 QPSK 11/32 No 2
160 QPSK ½ No 2
200 QPSK 5/8 No 2
52

53. 320 QPSK ½ No 1
400 QPSK 5/8 No 1
480 QPSK 3/4 No 1
Table 1: Rate-dependent parameters in multiband OFDM systems.
Table1 shows different data rates achieved by combining the different channel
codes with time and frequency spreading. Both time and frequency techniques
are used for data rate below 80Mbps. For date rate 106.7 and 200 Mbps, time
domain spreading is used with gain 2. Date rate more than 200 Mbps exploit
neither of these techniques and spreading gain is 1.
3.3.4 Subcarrier Constellation Map
QPSK constellation is used. After coding and interleaving process,
two bits groups of binary date are made and then converted to one
of four complex points of QPSK constellation. Gray labeling is used
for conversation [23].
53

54. Q
QPSK
𝑏! 𝑏!
+1
01
11
-­‐1
+1
I
00
-­‐1
10
Figure 13. Gray mapping QPSK Constellation.
3.4 MB-OFDM Receiver Architecture
3.4.1 System Model
The receiver proposed for MB-OFDM [17] is shown in Figure 14. As shown
in figure, the channel estimation process and data detection are performed
independently. Let us consider a single-user MB-OFDM transmission with
𝑁!"#" =100 data subcarriers per sub-band, through a frequency selective
multipath fading channel, described in discrete-time baseband equivalent
form by the channel impulse response coefficients {ℎ! }!!! . Furthermore, we
!!!
assume that the cyclic prefix (CP) is longer than the maximum delay spread
54

55. of the channel. After removing the CP and performing FFT at the receiver, the
received OFDM symbol over a given sub-band can be written as [7][17]
y = 𝐻! 𝑠 + 𝑧 (3.4)
where (N!"#" × 1) vectors y and s denote the received and transmitted
symbols, respectively; the noise vector z is assumed to be a zero-mean
circularly symmetric complex Gaussian (ZMCSCG) random vector and 𝐻! =
diag(H) is the (N!"#" ×N!"#" ) diagonal channel matrix with diagonal elements
given by the vector H = [H! , … . , H!!"#" !! ]! , where
!!!!"#
!!!
𝐻! = !!! ℎ! 𝑒 !! (3.5)
In MB-OFDM, the channel is assumed to be time invariant over the
transmission of one frame and changes to new independent values from one
frame to the next.
Figure 14: The basic receiver architecture proposed for MB-OFDM in [17].
55

56. 3.4.2 Channel Estimation
In order to estimate the channel, a MB-OFDM system sends some OFDM
pilot symbols at the beginning of the information frame. Here, we consider
the estimation of the channel vector H with NP training symbols S!,! (i = 1,
....., N! ). According to the model (20), the received signal for a given channel
training interval is
𝑌! = 𝐻! 𝑆! + 𝑍! (3.6)
Where each column of the (𝑁!"#" × 𝑁! ) matrix 𝑆! = [𝑆!,! , ..., 𝑆!,!! ]
contains one OFDM pilot symbol. The entries of the noise matrix 𝑍! have the
same distribution as those of z [7].
3.4.3 Frequency Domain Channel Equalization
In order to estimate the transmitted signal vector s from the received signal
vector y, the effect of the channel must be mitigated. To this end, the MB-
OFDM uses a frequency domain channel equalizer, as shown in FEQ block in
Figure 14. It consists of a linear estimator as
ŝ = 𝐺! 𝑦 (3.7)
The two design criteria usually considered for the choice of the linear filter G
are,
56

57. Zero-forcing equalization (ZF): ZF equalization uses the inverse of the
channel transfer function as the estimation filter. In other words, we have G ! =
!!
H! . Since in OFDM systems, under ideal conditions, the channel matrix H!
is diagonal, the ZF estimate of the transmitted signal is obtained
independently on each subcarrier as
!
ŝ!",! = 𝑦! k=0, …..., 𝑁!"#" − 1 (3.8)
!!
Minimum mean-square error equalization (MMSE): To minimize the
mean-squared error between the transmitted signal and the output of the
equalizer, applying the orthogonality principle, we obtain
𝐺 ! !!"# = (𝐻! 𝐻 ! ! + 𝜎! ⫿𝑁! )!! 𝐻 ! ! (3.9)
!
Due to the diagonal structure of H! , equalization can again be done on a
subcarrier basis as
∗
!!
ŝ!!"#,! = ! 𝑦! k=0,......., 𝑁!"#" − 1 (3.10)
⃓!! ⃓! !!!
The main drawback of the ZF solution is that for small amplitudes of H! , the
equalizer enhances the noise level in such a way that the signal-to-noise ratio
(SNR) may go to zero on some subcarriers. The computation of the MMSE
equalization matrix requires an estimate of the current noise level. Notice that
when the noise level is significant, the MMSE solution mitigates the noise
enhancement problem even when H! ’s close to zero while for high SNR
regime, the MMSE equalizer becomes equivalent to the ZF solution [7] [20].
57

58. 3.4.4 Channel Decoding
After frequency domain equalization and de-interleaving, the MB-OFDM
usually uses a hard or soft Viterbi decoder in order to estimate the transmitted
data bits. The maximum-likelihood path is reconstructed by using Viterbi
algorithm according to the input sequence. Bits information containing
reliable estimates are received by soft decision decoder while only bits are
received by hard decision decoder. A branch metric represents the distance
between the bits pair received and “ideal” pairs (“00”, “01”, “10”, “11”) while
path metric is representing the sum of metrics of all branches in the path.
The role of distance is totally based on the decoder type. If we consider hard
decision decoder, hamming distance is used while Euclidean distance is used
for soft decision decoder. Path with minimal path metric is chosen as the
maximum-likelihood path. Viterbi algorithm performs three calculations as
follows;
1. Branch metric calculation performs distance calculation on the basis of
input pair and the ideal pair (“00”, “01”, “10”, “11”).
2. Path metric calculation is metric calculation for survivor path for every
state of encoder. Here survivor path is representing the minimum metric path.
3. Traceback purpose is to store one bit information when a path is selected
out of two. Traceback doesn’t keep track of full information about the path
[18], [19].
58

59.
Branch
metric
Path
metric
Traceback
Decoded
Encoded
stream
calculation
calculation
stream
Figure 15: Viterbi decoder data flow
59

60. Chapter 4
60

61. 4. Ultra Wideband Position Estimation
4. 1 Introduction to Position Estimation
Ultra wideband transmit small pulses with high bandwidth. UWB signal can
easily penetrate through walls and grounds. Due to low energy, high
bandwidth, and fine temporal resolution characteristics, UWB is an ideal
candidate technology for position and ranging applications. The process
involves exchange of signals between nodes and measures the parameters to
estimate the position or range. The process of measuring the distance between
two nodes is called ranging. The measured distance is than processed further
more to estimate the position of the node is called positioning. The accuracy
of measuring distance plays an important role for better position estimation.
UWB is an ideal choice for application where more precise accuracy is
demanded. Different techniques are used to measure the parameters, like
TOA, AOA, TDOA, RTT and RSS. This section mainly discuss in detail
about the parameters measurement between the nodes
4.2 Position Estimation Applications
UWB can be implemented in many areas to get more precise estimations
about objects or nodes. It can be used in medical sector to monitor the patient
conditions and measure the position of patient inside hospital. Additionally it
can be used to locate medical equipment inside hospital. UWB position
measurement can be used to provide information about military security
personals and identify their authorization. It can also be used by military to
61

62. locate the weapons. Positioning can be used to locate employee, machinery
and resources in a manufacturing plant, tracking of children’s, tracking the
shipments with a precision of less than 1 inch.
4.3 Ranging and positioning parameters
Process of ranging and position can be categorized as Direct Positioning or
two-step positioning [37]. In direct positioning actual signal transmitted
between nodes is processed to estimate the position of the node as showing in
figure 16(a), while in two-step positioning parameters are measured and then,
on the basis of measured parameters range or position is estimated. The
following section elaborates in detail about the parameters estimation
approaches.
Received
Position
Position
signal
Estimation
estimation
(a)
Parameters
Parame Ranging
/Position
Received
Position
Estimation
ter
Estimation
signal
estimation
Estimat
e
(b)
Figure 16. (a) Direct positioning (b) Two step positioning
62

63. 4.3.1 Received Signal Strength
When a signal is transmitted in an open environment, it is affected by many
obstacles in its way to target node. The most common cause of signal loss is
Path-loss. These obstructions causes decrease in signal energy. The distance
can be calculated by analyzing the power transmitted, attenuation and the
power received on target node. The relation between signal energy and
distance must be known. The energy or power of the signal decreases during
propagation is known as Path-loss. The Path-loss can be shown by following
equation expressed in [37].
!
𝑝 𝑑 = 𝑝 𝑑! − 10𝑛𝑙𝑜𝑔( ) (4.1)
!!
Where d represent the distance between source and destination, 𝑑! is
reference distance while P(d) and P(𝑑! ) represent the signal strength received
at d and 𝑑! . Additionally signal is affected by reflection, scattering and
diffraction that cause variation in RSS. Signal power is estimated by the
following equation for precise range estimation.
! ! !
𝑝 𝑑 = 𝑟(𝑡, 𝑑) 𝑑𝑡 (4.2)
! !
In this relation r(t,d) is representing the received signal at a distance d while T
is representing the integration interval. Shadowing is another factor that
causes signal energy degradation and expressed in log scale by zero-mean
Gaussian random variable as.
!
𝑝(𝑑)~𝑁(𝑝 𝑑 , 𝜎!! ) (4.3)
63

64. From this discussion it is clear that precise measurement Path-loss and
shadowing is highly important for precise range estimation. For accuracy
measurement of range obtained, Cramer-Rao Lower Bound approach is used
as shown in the following equation [35].
(!" !")!!! !
𝑣𝑎𝑟 𝑑 ≥ (4.4)
!"!
𝑑 is the representation of an unbiased estimate for distance d. If the
shadowing affects are decreased, more accurate results can be are obtained in
range estimation .RSS method is not providing accurate range results because
of dependency on the parameters.
4.3.2 Angle of arrival (AOA)
Angle of arrival is another approach used to measure the position of
destination node on the basis of angle measured. For this approach, numbers
of antenna are used in an array fashion. [27]. Antenna elements are receiving
signals at different times. According to space coordinate, the angle of straight
line that connect target node with reference node is measured. As expressed
in [37], if we arrange the antenna elements in the form of uniform linear array
(ULA) as shown in figure 17, signal received in this configuration have time
difference of l sin α/c. If we consider these parameters, l is inter spacing,
64

65. angle is α and c is the speed of light.
Figure 17. Uniform Linear Array of antenna with different signals arrival with angle 𝛼.
CRLM lower bound can be used to investigate the AOA estimates.
!!
𝑣𝑎𝑟 ∝ ≥ (4.5)
! ! !"# ! !
!! !!!! ! !"#$
In this equation α is representing AOA, c is representing the speed of light,
SNR is representing signal-to-noise ratio for each element, l is representing
inter-element spacing and β is representing the effective bandwidth. From the
equation (4.5), it can be seen that, if SNR, bandwidth, antenna elements and
inter-element spacing is increased, the accuracy of AOA estimation will
increase linearly as well.
65

66. 4.3.3 Time of Arrival (TOA)
This is the most widely used approach for positioning and ranging. The whole
idea behind the TOA approach is the measurement of propagation delay
between sender and receiver. To obtain this, nodes must have a common
clock or share the timing information. In a simple way distance can be
measured if we know the speed of signal traveling between source and
destination and total time taken from source to target or transmission time
delay [35].
𝑑 = 𝑠𝑝𝑒𝑒𝑑 ∗ 𝑡𝑖𝑚𝑒 (4.6)
Where speed represent the speed of signal traveling between nodes, while
time represents the total time spent by signal during transmission between
transmitter and receiver. As a result we obtained d as distance between source
and target. Speed here is constant value. This method is efficient indoor
distance measurement.
As mentioned about TOA measure the propagation delay in order to measure
the distance. TOA uses Matched filter or Correlator for various delay
estimation. If we transmit a signal s(t) and target receive it as r(t) than we can
represent mathematically as
𝑟 𝑡 = 𝑠 𝑡 − 𝜏 + 𝑛(𝑡) (4.7)
66

67. 𝜏 is the time of arrival, 𝑛(𝑡) Represents the noise. This received signal is
matched against different templates s 𝑡 − 𝜏 for various delays 𝜏 as
𝜏 !"# = arg 𝑚𝑎𝑥! 𝑟(𝑡)𝑠 𝑡 − 𝜏 𝑑𝑡 (4.8)
If there is no noise than correlator output is maximized at τ=τ while in case of
noise results can be erroneous. The process involves matching of transmitted
signal using MF receiver and measuring the instant with peak value which
results in equation (4.8). These two approaches, Correlator and MF, are best
for signal in (4.7) (Figure18 (a)). In a practical scenario signals are arriving
from multiple paths as represented in figure 18 (b) [36]. In this case, it is
difficult to obtain the required parameters about TOA. To overcome this
problem and measure the accurate TOA in multipath, algorithms are used to
identify the first signal arrived instead of stronger signal peak [37]. To
measure the Accuracy of the estimation CRLB can be represented
mathematically as [44],
!
𝑣𝑎𝑟(𝜏) ≥ (4.9)
! !! !"#!
67

68. 11
Fig. 7
Figure 18. a) Single path received signal b) Multipath received signal.
A) R ECEIVED SIGNAL IN A SINGLE - PATH CHANNEL . B ) R ECEIVED SIGNAL OVER A MULTIPATH CHANNEL . N OISE IS NOT SHOWN IN THE
FIGURE .
Where SNR is representing signal-to-noise ratio, τ is representing unbiased
signal modelTOA estimate
in (11): and β is the effective bandwidth. The TOA approach gives
more accurate results if we increase SNR and effective bandwidth. Accurate
1
Var(ˆ) ≥ √
τ √ , (13)
TOA measurement estimate position2π SNR β to the original.
2 more close
where τ represents an unbiased TOA estimate, SNR is the signal-to-noise ratio, and β is the effective bandwidth
ˆ
[33], [34]. The CRLB expression in (13) implies that the accuracy of TOA estimation increases with SNR and
effective bandwidth. Time Difference of Arrival (TDOA)
4.3.4 Therefore, large bandwidths of UWB signals can facilitate very precise TOA measurements.
As an example, for the second derivative of a Gaussian pulse [35] with a pulse width of 1 ns, the CRLB for the
TDOA is similar to TOA approach. Difference of time is calculated on the
standard deviation of an unbiased range estimate (obtained by multiplying the TOA estimate by the speed of light)
basis of signal arrival on synchronized reference nodes. It is important to keep
is less than a centimeter at an SNR of 5 dB.
synchronization among reference nodes to calculate TDOA [26]. The process
4) Time Difference of Arrival: Another position related parameter is the difference between the arrival times of
involves first estimation of TOA on target node as well as reference nodes
two signals traveling between the target node and two reference nodes. This parameter, called time difference of
and then applies subtraction and estimate the difference. As we can see, nodes
arrival (TDOA), can be estimated unambiguously if there is synchronization among the reference nodes [23].
are properly synchronized, so the timing offset is same for TOA. The offset
One way to estimate TDOA is to obtain TOA estimates related to the signals traveling between the target node
and two reference nodes, and then to obtain the difference between those two estimates. Since the reference 68
nodes
are synchronized, the TOA estimates contain the same timing offset (due to the asynchronism between the target
node and the reference nodes). Therefore, the offset terms cancel out as the TDOA estimate is obtained as the
difference between the TOA estimates [17].

69. term are cancelled when calculating difference of TOA and the result is
TDOA.
TDOA can also be calculated based on cross-correlations of the signals. In
this approach, cross-correlation is applied between signals traveling between
source and target. In this case delay is measured that is caused by largest
value of cross-correlation. The mathematical model for delay is
!
𝜏 !"# = arg 𝑚𝑎𝑥! 𝑟 (𝑡)𝑟! (𝑡
! !
+ 𝜏)𝑑𝑡 (4.10)
Where T is representing the observation interval whiler! (t), for i=1,2, is
representing the signal transmission between target and 𝑖 !! reference node.
4.3.5 Round Trip Time (RTT)
RTT is simple handshake between source and target node. During handshake
transmission time from source to target and from target to source is measured.
With RTT, the distance is calculated as follows:
!!" !∆! ×!"##$
𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑑 = (4.11)
!
Where t !" is representing the total time spent by the signal during travel from
source to destination plus destination to source, while ∆𝑡 is the processing
time, taken by the source and destination nodes to process the packet. Speed
is a predetermined constant that represent the speed of signal. There is no
need to synchronize the clocks on both sender and receiver. One node is
69

70. enough to calculate the time according to own local clock. Using RTT the
necessity of perfect synchronization is not anymore needed. [35].
4.4 Position Estimation
Position estimation means, locating a node according to geometrical area.
UWB is a perfect choice to measure the distance between nodes. In previous
section we have discussed different methods to measure the important
parameters to estimate the position of the node. After measuring the necessary
parameters, the next step is to analyze those parameters and estimate the
range or position of the destination node. Different approaches are used to
analyze the parameters will be the main focus of the following section.
To estimate the position of target node on the basis of already present
database, following two schemes are used [27].
a) Geometric and statistical Approach
b) Mapping or fingerprinting
We discuss these two approaches one by one in following section.
4.4.1 Geometric and statistical Approach
This approach uses the measured parameters and estimates the position of
node on the basis of geometric relationships. If we consider the TOA or RSS,
these two give the range between reference and target nodes that make a
circle for possible node position. If we have three measurements so with the
70

71. intersection of three circles, we can estimate the position of desired node
using trilateration method as showing in following figure 19.
Figure 19: Position estimation via trilateration.
Figure 20: Position estimation via triangulation
In other case of AOA, the main idea of using Triangulation method for
position estimation is shown in figure 20. When we measure parameters using
TDOA, it gives hyperbola for the position of desired node. If we have three
reference nodes, considering one-reference node two TDOA measurements
can be determined. Finally intersection of two hyperbolas according to TDOA
71

72. measurements, gives the desired node estimation as showing in the following
figure 21[26].
Figure 21: Position estimation based TDOA measurement.
Geometric method can be used in a noise free environment while in case of
noise this method is not suitable. In real scenario parameters measurement
consist of noise that can cause the intersection of lines at multiple points
instead of one. So there is no insight which intersection point should be
chosen to measure the position of desired node. Also if reference nodes are
added more, intersection occurrence will increase more. This approach is not
efficient way to estimate the position [37].
On the other hand statistical approach makes use of multiple position related
parameters including noise or noise free as showing in the following model
[27].
𝑧! = 𝑓! 𝑥, 𝑦 + 𝜂! , 𝑖 = 1, … … … , 𝑁! (4.12)
N! is number of parameters estimates and f! x, y is the ith signal parameter,
which is function of desired node position (x, y), and η! is noise. Statistical
72

73. method bases on the reliability of the each parameter to measure the position
of the desired node.
4.4.2 Mapping or fingerprinting
This method uses available database or training data set to estimate the
position. On the basis of training data, this method determine pattern-
matching algorithm and then according to estimate parameters, target node
position is measured. There are different mapping techniques but most
common are k-NN, SVR, and neural networks. Consider the following
training data model [37].
𝒯= 𝑚! , 𝑙! , 𝑚! , 𝑙! , … … . (𝑚!! , 𝑙!! ) (4.13)
m! is representing the estimated parameter, l! is representing the position of
!
training data that is l! = x! , y! for two dimensional positioning, N! total
number of training vector elements. Mapping approach defines rule or
algorithms according to training set and then measure the position of the
desired node. Mapping method depends on the environment as well as system
parameters as compared to geometric and statistical technique. The most
important factor is the representation of training data and accuracy of
regression technique. In geometric and statistical method, accurate signal
measurement is important to get accurate position estimation.
73

74. Chapter 5
74

75. 5. UWB Distance Measurements
5.1 Introduction
A precise ranging measurement of the wireless sensor systems determines
accurate range-based localization. Wireless signal travelling between two
nodes some ranging and position estimation parameters received, which are
related to energy, direction and the timing of those wireless signals. RSS is
one of UWB ranging estimation technique, which is strongly dependent on
the channel parameters. That’s why it makes the received energy more
sensitive to distance changes in indoor areas. When UWB signal bandwidth is
high that time AOA can estimate accurate position and it needs multiple
antenna that’s make the system more costly. TOA parameter based methods
provide more accurate range estimates. Also this technique is lower cost
compared to the RSS and AOA [38]. TOA ranging mechanism on an impulse
UWB signal based on IEEE802.15.4a standard. [40]. IEEE 802.15.4a
employs fully compliant transceiver technology. The world’s first IEEE
802.15.4a UWB wireless packet was transmitted and successfully coherently
received in real time in March 2009 [41]. For the next generation wires sensor
network, UWB 802.15.4a transceiver technology is a perfect requirement.
To use in Personal area networks (PANs), IEEE has established the 802.15.4a
standard a new UWB physical layer for wireless sensor networks (WSN) [39].
75