Distance Measurements using Ultra Wide-Band (UWB)

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

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.

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.

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

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

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

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

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

12

Chapter 1

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

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.

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

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].

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].

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

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,

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.

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.

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

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

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

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

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.

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)

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! +!!

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].

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).

31

Chapter 2

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].


2.1.1 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 𝜔tr(t) is the UWB pulse waveform, k represents the transmitted bit

(“0” or “1”) and

dk = −1 𝑖𝑓 𝑘 = 0+1 𝑖𝑓𝑘 = 1 (2.2)

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]

dk = 0 𝑖𝑓 𝑘 = 0+1 𝑖𝑓𝑘 = 1 (2.4)

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

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]

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

transmission rate is thus equal to R =𝑙𝑜𝑔!(𝑀)

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

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],

dk = 1 𝑖𝑓 𝑘 = 1−1 𝑖𝑓𝑘 = 0 (2.7)

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

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)

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 𝑇𝑐. 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

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

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.

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]

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

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].

44

Figure 9: RAKE Receiver with J fingers

45

Chapter 3

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.


3.2.1 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.

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.

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

Band Group #5

f

Band

#1

Band

#2

Band

#3

Band

#4

Band

#5

Band

# 6

Band

#7

Band

#8

Band

#9

Band

#10

Band

#11

Band

#12

Band

#13

Band

#14

Band Group #1 Band Group #2 Band Group #3 Band Group #4

3432

MHz

3960

MHz

4488

MHz

9768

MHz

10296

MHz

5016

MHz

5544

MHz

6072

MHz

6600

MHz

7128

MHz

7656

MHz

8184

MHz

8712

MHz

9240

MHz

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

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

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

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.

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

Rates(Mbps)

Modulation Code Rate Frequency

Spreading

Time Spreading

53.3

55

80

106.7

110

160

200

QPSK

QPSK

QPSK

QPSK

QPSK

QPSK

QPSK

1/3

11/32

½

1/3

11/32

½

5/8

Yes

Yes

Yes

No

No

No

No

2

2

2

2

2

2

2

53

320

400

480

QPSK

QPSK

QPSK

½

5/8

3/4

No

No

No

1

1

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].

54

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

-‐1 +1

00 10

01 11

Q

+1

-‐1

QPSK

I

𝑏!𝑏!

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].

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,

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].

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].

59

Figure 15: Viterbi decoder data flow

Decoded stream

Branch metric calculation

Path metric calculation

Traceback Encoded stream

60

Chapter 4

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

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.

Figure 16. (a) Direct positioning (b) Two step positioning

(a)

Received signal

Position estimation

Position Estimation

Received signal

Position estimation

Parameters Estimation

Ranging /Position Estimation

Parameter

Estimate

(b)

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)

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,

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.

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)

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!"# = arg𝑚𝑎𝑥! 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)

68

Figure 18. a) Single path received signal b) Multipath received signal.

Where SNR is representing signal-to-noise ratio, τ is representing unbiased

TOA estimate and β is the effective bandwidth. The TOA approach gives

more accurate results if we increase SNR and effective bandwidth. Accurate

TOA measurement estimate position more close to the original.

4.3.4 Time Difference of Arrival (TDOA)

TDOA is similar to TOA approach. Difference of time is calculated on the

basis of signal arrival on synchronized reference nodes. It is important to keep

synchronization among reference nodes to calculate TDOA [26]. The process

involves first estimation of TOA on target node as well as reference nodes

and then applies subtraction and estimate the difference. As we can see, nodes

are properly synchronized, so the timing offset is same for TOA. The offset

11

Fig. 7A) RECEIVED SIGNAL IN A SINGLE-PATH CHANNEL. B) RECEIVED SIGNAL OVER A MULTIPATH CHANNEL. NOISE IS NOT SHOWN IN THE

FIGURE.

signal model in (11):

!

Var(!) ! 1

2"

2""SNR#

, (13)

where ! represents an unbiased TOA estimate, SNR is the signal-to-noise ratio, and # is the effective bandwidth

[33], [34]. The CRLB expression in (13) implies that the accuracy of TOA estimation increases with SNR and

effective bandwidth. 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

standard deviation of an unbiased range estimate (obtained by multiplying the TOA estimate by the speed of light)

is less than a centimeter at an SNR of 5 dB.

4) Time Difference of Arrival: Another position related parameter is the difference between the arrival times of

two signals traveling between the target node and two reference nodes. This parameter, called time difference of

arrival (TDOA), can be estimated unambiguously if there is synchronization among the reference nodes [23].

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 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].

When the TDOA estimates are obtained from the TOA estimates as described above, the accuracy limits can

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!"# = arg𝑚𝑎𝑥! 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

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

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

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

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.

74

Chapter 5

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].

76

In the following section, we discussed ranging algorithm with different issues

based on TOA in context of range measurement and theoretical analysis to

measure distance between two nodes. Also we will explain in detail the TOA

method that is commonly used for ranging as well as cause of errors in TOA

[37]. At the end, we have analyzed a previous experiment result to find

distance between two nodes in LOS and NLOS environment.

5.2 Ranging algorithm based on TOA

In TOA based ranging, TOA estimate as the delay to the correlation peak

shown in figure 22. The received UWB signal is correlated with different

delay of a template signal by TOA based ranging algorithm. In practical

UWB system, there are a large number of possible signal delays, due to high

resolutions of UWB signal. That’s why, correlations peak need to be find out

from those signals [37]. Correlation peak may not always perfect match with

true TOA. To determine true TOA, a serial search strategy can be employed.

In this strategy, it estimates the delay corresponding to the correlation output

that exceeds a certain threshold [26], [42]. In many cases, this approach can

be take very long time to estimate TOA. Now we need another strategy to

calculate TOA faster. Random search or bit reversal search can use to speed

up the estimation process. For example, to estimate TOA, signal delays are

selected randomly then tested it using random search strategies. To obtain a

rough TOA, this process with multipath propagation can reduce the time.

Then, using backward searching according to time can determine fine TOA

77

from the detected signal component [37].

Figure 22: TOA based receiver architecture for correlation.

Generally, to reduce amount of time to perform ranging, there are two-step

approaches to estimate TOA. Estimate rough TOA in first step then estimate

fine TOA in second step. Low-complexity receivers can use for rough TOA

estimation in the first step, which reduces the possible delay positions. To

determine a rough TOA, simple energy detector is used. In second step,

estimate TOA within a smaller interval. Correlation-based first-path detection

schemes [42], or statistical change detection approaches [43] can be employed

to calculate fine TOA. TOA estimation based on low rate sampling and it

needs low power implementations [37]. These are the theoretical aspects of

ranging algorithm. Now we need to consider practical aspects, such as UWB

ranging signals and hardware aspects for UWB transmitters and receivers in

UWB positioning and ranging system.

Correlator

Decision Unit

Template Signal

Delay Update

Received Signal

TOA Estimate

78

5.2.1 Signal aspects

UWB ranging signals should be designed properly in order to meet certain

performance requirements. It is very important to consider ranging accuracy.

It is commonly determined by root-mean-square error (RMSE) expressed as

[29],

𝑅𝑀𝑆𝐸 = 𝐸 (𝑑 − 𝑑)! (5.1)

Where d is the estimated range and d is the original or true range. As we

know, the definition of root-mean square error (RMSE) is the square root of

the average value of the squared error. In practice, the sample mean of the

squared error approximated the expected value shown in equation (5.1 [37];

i.e.,

𝑅𝑀𝑆𝐸 ≈ !!

(𝑑!−𝑑!)!!!!! (5.2)

Where d! and d! are respectively, the original range and the estimated range

for the 𝑖!! measurement, for i = 1, . . ., N.

Ranging signal is another important parameter to achieve ranging accuracy in

UWB ranging systems [29]. Range estimate can be obtained faster for small

durations of ranging signal. If the system performing both ranging and

communication, more signal recourses can be allocated for data transmission.

More accurate range estimation can be used when duration of signal increase.

This can be observed from the CRLB expression shown in equation (4.9.

79

Now consider a standard ranging signal structure for UWB ranging systems

shown in figure 23 which is expressed as in equation (5.3),

Figure 23: Short pulse UWB signal with low duty cycle. Where T is signal duration and T! frame interval.

𝑠 𝑡 = 𝑎!𝜔(𝑡 − 𝑗𝑇!)!!!!! (5.3)

Where ω(t) is a UWB pulse, T! is the frame interval. a! is a binary −1,+1 ,

or ternary −1, 0,+1 code. It is used for interference robustness and spectral

optimization. Ternary codes are employed in the IEEE 802.15.4a standard in

order to synchronization preamble of each packet. It uses for ranging

estimation process [30], [49], [50].

The maximum amount of average power P!"# can be determined from FCC

limit that are transmitted by UWB transmitter. Then, we can calculate

T!P!"#, where T!P!"# is the pulse maximum energy in the frame. A ranging

system employs N! UWB pulses. N! is the number of pulses representing one

information symbol, which is called the pulse combining gain [50]. The SNR

in the CRLB expression in equation (4.9) becomes directly proportional to

3

100 101−80

−75

−70

−65

−60

−55

−50

−45

−40

Frequency (GHz)

EIR

P Em

issi

on L

evel

(dBm

)

0.96 1.61

1.993.1 10.6

Fig. 2FCC EMISSION LIMITS FOR INDOOR UWB SYSTEMS. PLEASE REFER TO [1] FOR THE REGULATIONS FOR IMAGING, VEHICULAR

RADAR, AND OUTDOOR COMMUNICATIONS SYSTEMS. NOTE THAT THE LIMITS ARE SPECIFIED IN TERMS OF EQUIVALENT

ISOTROPICALLY-RADIATED POWER (EIRP), WHICH IS DEFINED AS THE PRODUCT OF THE POWER SUPPLIED TO AN ANTENNA AND ITS

GAIN IN A GIVEN DIRECTION RELATIVE TO AN ISOTROPIC ANTENNA. ACCORDING TO THE FCC REGULATIONS, EMISSIONS (EIRPS)ARE MEASURED USING A RESOLUTION BANDWIDTH OF 1 MHZ.

Fig. 3AN EXAMPLE UWB SIGNAL CONSISTING OF SHORT DURATION PULSES WITH A LOW DUTY CYCLE, WHERE T IS THE SIGNAL

DURATION, AND Tf REPRESENTS THE PULSE REPETITION INTERVAL OR THE FRAME INTERVAL.

of UWB pulses are transmitted per information symbol and information is usually conveyed by the timings or the

polarities of the pulses1. For positioning systems, the main purpose is to estimate position related parameters of

this IR UWB signal, such as its time-of-arrival (TOA), as will be discussed in Section II.

Large bandwidths of UWB signals bring many advantages for positioning, communications, and radar applications

1In addition to IR UWB systems, it is also possible to realize UWB systems with continuous transmissions. For example, direct sequencecode division multiple access (DS-CDMA) systems with very short chip intervals can be classified as a UWB communications system[8]. Alternatively, transmission and reception of very short duration orthogonal frequency division multiplexing (OFDM) symbols can beconsidered as an OFDM UWB scheme [9]. However, the focus of this paper will be on IR UWB systems.

80

TP!"#, where T = N!T!. So, if the duration of the ranging signal increases,

accuracy will be better. We can say that the duration of ranging signal and the

error variance in lower bound of unbiased range estimators are inversely

proportional [37].

An appropriate selection of the frame interval T! is important requirement of

ranging signal design shown in equation (5.3). As we know from above, pulse

energy and frame interval are proportional in a frame. [37]. Hence, if the peak

power increase, the frame interval will be increase for a given pulse width.

5.2.2 Hardware aspects

Figure 24: Block diagram of a UWB transmitter with a ranging capability.

Firstly Commutation data is coded by channel coding to provide robustness

shown in figure 24. Specific symbol are mapped that coded date to use for

modulation purpose. For example, BPSK symbols are mapped coded data

that take value from the set {−1, +1}. Then, ranging related parameters

information is attached with communication data. Typically, packets are

transmitted between two nodes that contain both communication and ranging

25

Fig. 13BLOCK DIAGRAM OF A UWB TRANSMITTER IN A COMMUNICATIONS SYSTEM WITH RANGING CAPABILITY [2].

UWB system [2]. As shown in the figure, communications data is first coded in order to provide robustness against

the adverse effects of the channel. In other words, some systematic redundancy is added into the data in order to

recover the correct data at the receiver in the presence of errors. Then, the coded data is mapped onto specific

symbols for modulation purposes. As an example, the coded data can be mapped onto binary phase shift keying

(BPSK) symbols, which take values from the set {!1,+1}. After symbol mapping, ranging related information is

inserted at the beginning of the communications data. Typically, transmission is performed in terms of packets, which

contain both communications and ranging signals; i.e., a certain section of transmission is allocated for ranging

signals, and the remaining is allocated for communications signals. Since ranging signals commonly constitute the

beginning section of each packet, they are also called preambles18.

The digital sequence at the output of the preamble insertion block is converted into an analog UWB pulse

sequence by the pulse generation block. UWB pulse generators can be broadly classified into two depending on

the use of an up-conversion unit19. The ones that employ an up-conversion unit first generate a pulse at baseband,

and then translate the frequency contents of the signal (i.e., “up-convert” it) around a desired center frequency

[83]-[85]. On the other hand, some UWB pulse generators can directly generate the pulses in the desired frequency

band without employing any up-conversion unit. Among such pulse generators are the ones that generate UWB

pulses, such the fifth derivative of a Gaussian pulse, without any filtering operations [86], [87], the ones that use

antenna for shaping UWB pulses [88], [89], and the ones that employ filtering for pulse shaping [90]-[95].

After generating UWB pulses, a power amplifier (PA) can be used to increase the power of the signal delivered to

the antenna. For UWB systems operating under extremely low power regulations, such as the Japanese regulations

for unlicensed use of UWB systems, use of a PA may not be needed [96]. Commonly, PAs can constitute a large

portion of the transmitter power consumption. Hence, it is desirable to have efficient20 PAs in order to minimize

18In a system that performs both communications and ranging, preamble signals are used not only for ranging, but also for timingacquisition, frequency recovery, packet and frame synchronization and channel estimation.

19An up-conversion unit commonly consists of a mixer and a local oscillator. The incoming signal and the signal generated by the localoscillator is multiplied using the mixer in order to perform frequency translation.

20Efficiency of a PA is defined as the ratio between the signal power delivered to the load and the total power consumed by the amplifier.

81

signals. Pulse generation block converts digital sequence to an analog UWB

pulse. Purpose of Power amplifier (PA) is increasing the power of the UWB

signal. Then it is delivered to the antenna. Finally, The UWB signal is

transmitted into space by antenna shown in figure 24 [37].

Figure 25: Block diagram of a UWB receiver.

UWB antenna should have large bandwidth, because signal loss should not be

more than 10% due to the mismatch the transmitter circuitry and the antenna

[29]. To achieve no significant pulse distortion occurs; the antenna should

radiate small pulses. To achieve no significant power loss, radiation efficiency

should be quite high. In ranging systems, the efficiency of the radiation

should be considered properly according to the traveling distance of signal.

Most widely used antennas those are used in UWB systems are polygonal and

elliptical monopole antennas, planar antennas (bow tie), and diamond and

26

Fig. 14BLOCK DIAGRAM OF A UWB RECEIVER. THE UNIT IN THE DOTTED BOX EXISTS ONLY WHEN ANALOG CORRELATION OR ENERGY

DETECTION IS TO BE PERFORMED [2].

the power consumed at a transmitter [97]-[101].

Finally, an antenna unit transmits the UWB signal into space, as shown in Fig. 13. Related to large bandwidths

of UWB signals, UWB antenna design should take a number of issues into account. First, a UWB antenna should

have a wide impedance bandwidth, which is defined as the frequency band over which there is no more than 10%

signal loss due to the mismatch between the transmitter circuitry and the antenna [2]. Ideally, when there is perfect

matching, incoming signal towards the antenna is completely radiated into space. In order to obtain large impedance

bandwidths for UWB antennas, various bandwidth broadening techniques are commonly employed. Among those

techniques are using specific antenna geometries such as helix, biconical, and bow-tie structures [102], beveling or

smoothing [103]-[106], resistive loading [107], slotting (or adding a strip) [108], [109], notching, and optimizing

location or structure of the antenna feed [110]-[112]. Another important issue in UWB antenna design is that a

UWB antenna should radiate a pulse that is very similar to the pulse at the feed of the antenna (or its derivative)

so that no significant pulse distortion occurs [107]. In addition, radiation efficiency, which is defined as the ratio of

the radiated power to the input power at the terminals of the antenna [102], should be quite high so that there is no

significant power loss. Since UWB signals operating under regulatory constraints can transmit low power signals

only, high radiation efficiency of UWB antennas is needed for ranging/communications at reasonable distances.

Commonly, planar antennas, such as bow-tie, diamond and square dipole antennas, and polygonal and elliptical

monopole antennas, are well-suited for UWB systems as they are compact and can be printed on PCBs ([113]

and [114], and references therein). In addition, they can have wide impedance bandwidths and reasonable pulse

distortion if their geometries and feeding structures are designed in an appropriate fashion [113].

Considering the receiver part, UWB signals are collected by a UWB antenna as shown in Fig. 14 [2]. Then, the

signal is passed through a band-pass filter (BPF) and a low-noise amplifier (LNA) for out-of-band noise/interference

mitigation and signal amplification, respectively. At this point, two groups of UWB receivers can be considered.

82

square dipole antennas. Bow tie considered as the best UWB antenna [37].

A UWB antenna as shown in Figure 25 collects UWB signals from space. To

reduce out-of-band noise or interference and signal amplification, first the

signal will pass through band-pass filter (BPF) and then through low-noise

amplifier (LNA). Based on the UWB receiver’s type, it performs correlation,

which detects energy in the analog domain. Then it converts from analog

domain to digital domain [45]. UWB signal is adjusted its level according to

ADC specification by the automatic gain control (AGC). The ADC unit

performs analog-to-digital conversion. To estimate position or ranging related

parameters such as TOA and TDOA, the digital signal samples are processed

by digital signal processing unit and then these parameters are further more

processed to measure the desired node position. The target node itself

determines the position in self-positioning systems while in remote position a

central node or Root node locate the node. In both positioning systems, the

signal processing requirements are sets by the position estimation algorithm

on the related node [37].

5.3 Theoretical analysis of UWB distance measurements

A distance measuring experiment in UWB ranging systems implemented in

different environment with inferences and obstacles. Firstly, implemented in

an indoor environment to investigate the case of line of sight (LOS) with

multi-path, and also the case of non loss line of sight (NLOS) with different

83

materials, for instance, chair, counter, door and walls; secondly, the outdoor

open field case is evaluated with reflections are presented at the receiver.

Relevant UWB signal characterization, pulse response and transmitting power

are measured [38].

Figure 26: Timeline for a packet exchange showing delays in the system

Our approach to TOA relies on accurate measurements of the total elapsed

time for a two- packet exchange to within a few nanoseconds. Figure 26

illustrates this approach where two radios (node A and node B) exchange

packets. In that case, to measure the total elapsed time for that exchange, node

A maintains a high-precision timer. Elapsed time consists of various time

intervals that can be determined and subtracted to obtain the desired round-

trip propagation time [46]. A classical time of arrival based method called

Data Packet

Data Packet

ACK

ACK

Node A

Node B

Total elapsed time

Packet Exchange timeline

!T due to excess delay

!T due to direct path propagation

Delay in Rx before ACK is transmitted

II. PEER-TO-PEER RANGING

A. Ranging

The system employs time-of-arrival (TOA) techniques that derive a range value using an estimate of signal propagation time between two nodes. Our approach to TOA relies on accurate measurements of the total elapsed time for a two-packet exchange to within a few nanoseconds.

Figure 1 illustrates this approach where two radios (node A and node B) exchange packets while node A maintains a high-precision timer that measures the total elapsed time for the exchange.

Fig. 1 Timeline for a packet exchange showing delays in the system

Elapsed time consists of various time intervals that

can be determined and subtracted to obtain the desired round-trip propagation time. Analysis of the performance of this algorithm was initially performed using computer simulations with both measured and simulated UWB channels and verified via field measurements.

III. RELATIVE LOCATION The classical approach to radiolocation is based

on measuring characteristics of the radio signal from/to an individual device to/from fixed access points and then essentially using geometric principles to estimate the location of the device. In

contrast to the classical approach, relative location distills location estimates from a collection of pair wise range measurements between devices and their neighbors [5]. A relative location system features two types of devices: reference devices, which are devices that have a-priori knowledge of their absolute location, and blindfolded devices whose location needs to be estimated.

Relative location provides two key advantages. It can provide increased accuracy and range extension. A simple example can be used to appreciate the first issue. Let us assume a one-dimensional system with two reference devices at each end (their fix location represented as nails) and two “floating” blindfolded nodes. The pairwise ranges between the network devices are denoted d1 thru d5. This system is displayed in Figure 2.

A C D B0 x1 x2 1

d1 d2 d3

d5d4

A C D B0 x1 x2 1

d1 d2 d3

d5d4

Fig. 2 One-dimensional network with 2 reference devices and 2 blindfolded devices.

With the classical approach, to compute the location of device C, only the distances d1 and d5 would be used. Similarly for device D only distances d4 and d3 would be employed. Under the assumption that the TOA errors are iiid N(0,"d) random variables, the average error for the classical approach would be d"" 707.0= . With a relative location system, by including the peer-to-peer distance d2 in the error minimization process the location error is reduced to d"" 61.0= .

IV. SIMULATION RESULTS Computer based simulations were used to

investigate system performance for a two story 20x20x 6 meter building structure. The TOA errors

84

two-way ranging was originally proposed in [40]. Time based practical

ranging mechanism is shown in Figure 27.

Node A Node B

Figure 27: Time based ranging method. From the figure 27 we can calculate the round trip time. First considering the

node B, node B observes a round trip time B!" = T!! − T!" and a turn

around time B!" = T!" − T!! where T!",T!! and T!" are the node send-

time, receive-time and future send time respectively. On the other side node

A!" = T!" − T!" and a turn around time A!" = T!" − T!" where

T!", T!" and T!" are the node send-time, receive time and future send time

respectively.

impulse UWB based transceiver for both indoorand outdoor environments. A two way ranging al-gorithm based on TOA employed as part of thiswork is described in detail. A theoretical analysisof impulse UWB radio for wireless communicationand ranging is provided employing the ShannonHartley theorem [5] and Cramer-Rao lower bound(CRLB) [6] method.

To fully test the reliability of the UWB rangingsystem, a distance measuring experiment is firstlyimplemented in an indoor environment to inves-tigate the case of LOS with multi-path, and alsothe case of NLOS with di↵erent materials, for in-stance, chair, counter, door and walls; secondly,the outdoor open field case is evaluated with re-flections are presented at the receiver. RelevantUWB signal characterization, pulse response andtransmitting power are measured. A realistic twoway ranging model of the system in operation isdescribed. Finally some conclusion are included.

II Theoretical analysis of UWB ranging

A classical time of arrival based method calledtwo-way ranging (TWR) was originally proposedin [3]. The practical ranging demonstration is de-scribed in Fig.1. The leader observes a round trip

Fig. 1: TW-Ranging Method

time LRT

= TRR

� TSB

and a turn around timeL

TA

= TSF

� TRR

, where TSB

, TRR

and TSF

arethe leader send-time, receive-time and future send-time respectively. The follower observes a roundtrip time F

RT

= TRF

� TSR

and a turn aroundtime F

TA

= TSR

�TRB

, where TRB

, TSR

and TRF

are the follower receive-time, send-time and futurereceive-time respectively. The value of transmis-sion time T is computed at both leader (T

l

) andfollower (T

f

):

2Tl

= (TRR

� TSB

)� (TSR

� TRB

) (1)

2Tf

= (TRF

� TSR

)� (TSF

� TRR

) (2)

The follower or leader can then combine these tworesultant round trip times (by averaging) to re-move by e↵ects of clock di↵erences. The result isthen divided by 2 to get one way trip time.

T =2T

l

+ 2Tf

2⇥ 2(3)

Thus the distance between the two prototypes is:

d = T ⇥ C (4)

Here C is the speed of light.When implementing this ranging method in a

practical operation, reliable ranging depends onthe system being able to accurately determine thetransmitting and receiving times of the signal mes-sages at the antenna. The IEEE 802.15.4a specifi-cally defines the time stamps reflecting the instanttime of the first ultra wide band pulse of the firstbit of the physical layer header (PHR)of a rang-ing frame. Moreover, there are a number of chal-lenges that remain before accurate ranging can beachieved in a harsh environment including multi-path, radio interference, and the NLOS propaga-tions. Thus, the TWR requires that the radio fre-quency (RF) signal should have a good channel ca-pacity and be robust to interference to enable thedetection of the first path of the received signal.

For any given RF radio, Shannon’s theory [5] ex-amines the characterization of the signal channel.

C = B ⇥ log2(1 + SNR) (5)

In equation (5), C is the maximum channel ca-pacity, B is the channel bandwidth, and SNR isthe signal to noise ratio. This equation indicatesthat for high frequency bands, large channel capac-ity is available despite a reduction in transmissionpower. An UWB signal is defined by the FCC tohave either a signal bandwidth exceeding 500MHzor a fractional bandwidth exceeding 0.2. If bothUWB (500MHz) and narrow band signal such asIEEE 802.11n [7] (40MHz) have the same SNR,the channel capacity of UWB is approximately 12times larger than IEEE 802.11n.

UWB signal is broadly categorized into impulseUWB and multi-carrier UWB. The UWB pulsecan be easily generated from a Gaussian pulse andits derivatives. A Gaussian pulse in the time do-main is described in [8] as:

P (t) = ±p

2↵

e�2⇡t2

↵2 (6)

Here

↵2 = 4⇡�2 (7)

where ↵ is the pulse form factor and �2 is thevariance. The Gaussian pulse and its first 15

85

Transmission time T computed by both node A (T!) and node B (T!),

2𝑇! = 𝑇!! − 𝑇!" − (𝑇!" − 𝑇!") (5.4) 2𝑇! = 𝑇!" − 𝑇!" − (𝑇!" − 𝑇!!) (5.5)

As we know from TOA that only one node should have clock. Node A and

node B can then combine these two resultant round trip times (by averaging)

to remove by effects of clock differences. To get one-way trip time, the result

is divided by 2 [38].

𝑇 = ! !!!! !!!∗!

(5.6)

Thus the distance between two nodes is

𝑑 = 𝑇 ∗ 𝐶 (5.7)

Here C is the speed of light. There are a number of challenges such as, harsh environment including multi-

path, radio interference, and the NLOS propagations remain before accurate

ranging. That’s why; the two way ranging requires that the radio frequency

(RF) signal should have a good channel capacity. Also it should be robust to

interference to enable the detection of the first path of the received signal

[38]. For any given RF radio, Shannon’s theory determines the

characterization of the signal channel.

𝐶 = 𝐵 log!(1 + 𝑆𝑁𝑅) (5.8)

Where C is the channel capacity in bits/second, B is the channel bandwidth in

86

Hz, SNR is the signal to noise ratio [7].

UWB signal is broadly categorized into impulse UWB and multi-carrier

UWB. The UWB pulse can be easily generated from a Gaussian pulse and its

derivatives. A Gaussian pulse in the time domain is expressed as follows [47];

𝜔 𝑡 = ± !∝𝑒!

!!!!

∝! (5.9)

Here ∝!= 4𝜋𝜎!

Time-Hopping (TH) modulation and Direct Sequence (DS) modulation are

used to modulate the impulse UWB signal. The DS modulation is selected to

generate a UWB signal whose transmitting signal is defined in equation (5.3)

Based on the TOA method, the system captures the transmitting time in

ranging applications. Accuracy limits for TOA estimation can be determined

by CLRB, expressed as by the following equation [44],

𝑣𝑎𝑟(𝜏) ≥ !! !! !"#!

(5.10)

Where τ is representing the unbiased TOA estimate, SNR is the signal-to-

noise ratio and β is representing the effective bandwidth.

The accuracy of TOA approach increases with the increase in SNR and

effective bandwidth. Therefore, the more accurate the ranging precision can

be achieved by the high signal bandwidth or the better SNR.

Implementation of ranging method in a practical operation, reliable ranging

depends system being able to accurately determine time or not. Determine the

87

transmitting and receiving time of a signal message at the antenna is the most

important factor in ranging mechanism. The IEEE 802.15.4a specifically

defines the time stamps reflecting the instant time of the first UWB pulse of

the first bit of the physical layer header (PHR) of a ranging frame. Due to its

high quality communication and accurate ranging, UWB is promising

technology for location aware wireless sensor networks. Finally we can say

that, the fine time resolution on the order of sub-nanosecond pulses, accuracy

of a few centimeters in distance measurement can be obtained [38].

5.4 Experimental ranging results

Here we are using a previous experimental result. The goal of this experiment

is to validate the characterization, reliability and ranging of the UWB

transceiver technology in indoor and outdoors environments. The

measurements were made using two FCC-compliant UWB radios obtained

from Decawave, a company based in Dublin, Ireland [48].

To validate the reliability of the UWB transceiver ranging in cluttered indoor

and outdoor environments, according to the different channel models, three

scenarios are defined and implemented in some offices, hallways, and yards

in the Tyndall National Institute as shown in Figure 28. The two motes are

mounted on the floor; one is located at the fixed origin, while the other moves

to perform point-to- point measurement. The distance between the two radios

is varied from 1m up to 45m to capture a variety of operating conditions. In

88

each measurement location, the values such as the pulse response, instant

distance estimates, SNR, as well as the actual distance from a tape are

measured [38].

Figure: 28: LOS, Soft-NLOS, Hard-NLOS Ranging Scenarios

5.4.1 LOS area test results

The line of sight ranging experiments are measured in a library, an indoor

hallway, an outdoor hallway and in the open field such as Figure 28(a, b)

where is no obstructions between the two motes. The goal this experiment in

LOS area is to validate the performance of the UWB ranging system in an

environment with significant multi-path propagation, thermal noise and

narrowband interference. Figure 29 shows the average LOS ranging results in

the library which has some counters and chairs around the motes, the outdoor

hallway in which the two boards are located between the outside walls and

bicycle shed, the indoor hallway with some doors, and walls on the both sides

shown in Fig.7, in which the red line (c) is theplot of the real pulse response, the green line (d)is the imaginary response and the blue line (b)is the computed magnitude values. The verticalcyan line (a) is the leading path which is used tofind the first in time arriving receive signal. Thesystem SNR (44.4dB), first path SNR (38.4dB),and the real time distance (1.31m) is tested andrecorded. This distance is firstly measured in ano�ce with no obstructions and subsequently lessreflections. Compared with the true value 1.30mmeasured physically using a tape, the measured in-stant and average distances are very accurate withonly 1cm error. The round trip time value L, R, ofboth local and remote prototypes and their aver-age value C are calculated in device time units [3].The device time units follow the definition of timecontained in the IEEE Std 802.15.4a, which statesthe LSB of a time value represents 1/128 of a chiptime at the mandatory chipping rate of 499.2MHz.After dividing C by 128 and multiplying by thespeed of light, the distance is finally calculated.

Fig. 7: Received UWB Signal Response

IV experimental ranging results

To validate the reliability of the UWB transceiverranging in cluttered indoor and outdoor environ-ments, according to the di↵erent channel models, 3scenarios are defined and implemented in some of-fices, hallways, and yards in the Tyndall NationalInstitute as shown in Fig.8. The two motes aremounted on the floor, One is located at the fixedorigin, while the other moves to perform point-to-point measurement. The distance between the tworadios is varied from 1m up to 45m to capture a va-riety of operating conditions. In each measurementlocation, the values such as the pulse response, in-stant distance estimates, SNR, as well as the actualdistance from a tape are recorded.

a) LOS Test

The line of sight ranging experiments are con-ducted in a library, an indoor hallway, an outdoorhallway and in the open field such as Fig.8(a,b)where is no obstructions between the two motes.This experiment is to validate the performance ofthe UWB ranging system in an environment withsignificant multi-path propagation, thermal noise

and narrowband interference such as WIFI signals.Testing Points are placed randomly but are re-stricted to the tape measured points.

Fig. 8: LOS, Soft-NLOS, Hard-NLOS Ranging Campaigns

Fig. 9: Ranging Results of LOS Area Measurement

Fig.9 shows the average LOS ranging results inthe library which has some counters and chairsaround the motes, the outdoor hallway in whichthe two boards are located between the outsidewalls and bicycle shed, the indoor hallway withsome doors, WIFI sites and walls on the both sidesand in the open field where there are no obstruc-tions, and the only sources of signal reflection arethe operators, the equipment and the ground. Theaverage ranging errors of these tested points areless than ±20cm regardless of the system error.The errors measured in the open field are less than10cm, which is more accurate than the results ofother conditions with more reflections and sourcesof interference in between. The outdoor hallwayresult is less than the positive value measured viaa tape, that is likely because the PHY header checkbits of some frames were in error.

b) Soft-NLOS Test

This experiment aims to validate the reliability ofthe UWB ranging system through a Soft-NLOSchannel which occurs when the LOS path is ob-structed by materials with relatively low attenua-tion or by a combination of these materials suchas glass, chairs, counters and doors. A 3m test-ing point is selected for each experimental clusterand di↵erent obstructions are deployed betweenthe two motes as in Fig.8 (c). Some obstructions

89

and in the open field where there are no obstructions, and the only sources of

signal reflection are the operators, the equipment and the ground [38].


After analyzing the measured data from this experiment, we can observe, the

average ranging errors are less than 20cm regardless of the system error.

Ranging error in the open field are measured less than 10cm, which is more

accurate than the results of other conditions with more reflections and sources

of interference in between. The outdoor hallway result is less than the positive

value measured because the PHY header check bits of some frames were in

error.

shown in Fig.7, in which the red line (c) is theplot of the real pulse response, the green line (d)is the imaginary response and the blue line (b)is the computed magnitude values. The verticalcyan line (a) is the leading path which is used tofind the first in time arriving receive signal. Thesystem SNR (44.4dB), first path SNR (38.4dB),and the real time distance (1.31m) is tested andrecorded. This distance is firstly measured in ano�ce with no obstructions and subsequently lessreflections. Compared with the true value 1.30mmeasured physically using a tape, the measured in-stant and average distances are very accurate withonly 1cm error. The round trip time value L, R, ofboth local and remote prototypes and their aver-age value C are calculated in device time units [3].The device time units follow the definition of timecontained in the IEEE Std 802.15.4a, which statesthe LSB of a time value represents 1/128 of a chiptime at the mandatory chipping rate of 499.2MHz.After dividing C by 128 and multiplying by thespeed of light, the distance is finally calculated.

Fig. 7: Received UWB Signal Response

IV experimental ranging results

To validate the reliability of the UWB transceiverranging in cluttered indoor and outdoor environ-ments, according to the di↵erent channel models, 3scenarios are defined and implemented in some of-fices, hallways, and yards in the Tyndall NationalInstitute as shown in Fig.8. The two motes aremounted on the floor, One is located at the fixedorigin, while the other moves to perform point-to-point measurement. The distance between the tworadios is varied from 1m up to 45m to capture a va-riety of operating conditions. In each measurementlocation, the values such as the pulse response, in-stant distance estimates, SNR, as well as the actualdistance from a tape are recorded.

a) LOS Test

The line of sight ranging experiments are con-ducted in a library, an indoor hallway, an outdoorhallway and in the open field such as Fig.8(a,b)where is no obstructions between the two motes.This experiment is to validate the performance ofthe UWB ranging system in an environment withsignificant multi-path propagation, thermal noise

and narrowband interference such as WIFI signals.Testing Points are placed randomly but are re-stricted to the tape measured points.

Fig. 8: LOS, Soft-NLOS, Hard-NLOS Ranging Campaigns


Fig.9 shows the average LOS ranging results inthe library which has some counters and chairsaround the motes, the outdoor hallway in whichthe two boards are located between the outsidewalls and bicycle shed, the indoor hallway withsome doors, WIFI sites and walls on the both sidesand in the open field where there are no obstruc-tions, and the only sources of signal reflection arethe operators, the equipment and the ground. Theaverage ranging errors of these tested points areless than ±20cm regardless of the system error.The errors measured in the open field are less than10cm, which is more accurate than the results ofother conditions with more reflections and sourcesof interference in between. The outdoor hallwayresult is less than the positive value measured viaa tape, that is likely because the PHY header checkbits of some frames were in error.

b) Soft-NLOS Test

This experiment aims to validate the reliability ofthe UWB ranging system through a Soft-NLOSchannel which occurs when the LOS path is ob-structed by materials with relatively low attenua-tion or by a combination of these materials suchas glass, chairs, counters and doors. A 3m test-ing point is selected for each experimental clusterand di↵erent obstructions are deployed betweenthe two motes as in Fig.8 (c). Some obstructions

90

5.4.2 Soft-NLOS area test results

When the LOS path is obstructed by materials with relatively low attenuation

such as glass, chairs, counters and doors, then this environment consider as

soft-NLOS area. In this experiment, UWB ranging system through a Soft-

NLOS channel, a 3m testing point is selected for each experimental cluster

and different obstructions are deployed between the two motes as in Figure 28

(c). Some obstructions are combined. All the results of clusters in Figure 30

show that the error from different obstructions varies from 6cm (Glass) to

29cm (Door) [38]. In indoor ranging measurement, the average results of less

than 30cm accuracy are acceptable to validate that the UWB signal can be

utilized.

Figure 30: Ranging Results of Soft-NLOS Area at 3m Point

are combined as this would likely be the case in ac-tual conditions. All the results of clusters in Fig.10show that the error from di↵erent obstructionsvaries from 6cm (Glass) to 29cm (Door). Theseexperimental conditions represent the most com-mon channel model over the distances of interestin most European o�ces, the average results of lessthan 30cm accuracy are acceptable to validate thatthe UWB signal can be utilized in indoor rangingmeasurements.

Fig. 10: Ranging Results of Soft-NLOS Area at 3m Point

c) Hard-NLOS Test

This experiment (Fig.8 (d)) attempts to validatethe capability of the UWB ranging system in ahard-NLOS channel with multiple concrete wallsor multi-obstructions in the environment. Resultsin Fig.11 indicate that hard obstructions severelyattenuate the UWB signal propagation and gener-ate large positive bias in the range estimates. Thedistance error varies widely from 26cm for one wallto 87cm for 4 walls. While at the 38m point, the re-ceiver is unable to receive the signal. It is clear thatlocalization in this hard NLOS rooms can not ob-tain high precision by only using TWR algorithm.Some method and algorithms [3] are proposed toimprove or solve the hard NLOS ranging problems,but ranging in an NLOS area is still a challengingproblem for indoor locations.

Fig. 11: Ranging Results of Hard-NLOS Area

V Conclusion

In this paper, we theoretically analyzed and realis-tically validated the reliability of an impulse UWB

transceiver based point-to-point ranging systemusing a two way ranging algorithm in both indoorand outdoor environments. In theory, the UWBsignal is very resistant to multi-path and reflec-tions, the CRLB method proves that the UWBsignal has a high precision on the order of severalcentimeters. In practical operation, the two UWBtransceivers were evaluated in this study satisfyingthe FCC limits. A realistic two way ranging modelwas generated with antenna-to-system delay, firstpath detection delay and time o↵set and imple-mented in the ranging system. Results recordedof LOS, Soft-NLOS and Hard-NLOS ranging ex-periments show that UWB transceivers are capa-ble of capturing accurate transmission time be-tween two radios which can be used in turn tocompute the real distance. With features such aslarge channel capacity, robustness to interferenceand multi-path, energy e�ciency and fine resolu-tion, UWB transceiver technology is a dependablewireless communications mechanism for WSN lo-calization applications.

References

[1] M.G. diBenedetto, T. Kaiser, A.F. Molish,I. Oppermann, C. Plitano, and D. Porcino(eds.). “UWB Communications Systems: AComprehensive Overview”. EURASIP Publish-ing,2005.

[2] IEEE Working Group 802.15.4a. “Draft speci-fications for IEEE 802.15.4a standard”.

[3] IEEE Std 802.15.4aTM -2007, IEEE Standardfor information Technology

[4] http://www.idtechex.com/events/

presentations/scensor_an_ieee802_15_

4a_uwb_compliant_chip_ripe_for_energy_

harvesing_001824.asp

[5] Kazimierz Siwiak and Debra McKeown.“Ultra-Wideband Radio Technology”. JohnWiley and Sons,2006.

[6] S.M. Kay. “Fundamentals of Statistical Sig-nal Processing Estimation Theory”. EnglewoodCli↵s, New Jersey:Prentice-Hall,1993.

[7] IEEE Std 802.11n-2009,IEEE Standard forinformation Technology–Telecommunicationsand information exchange between systems

[8] Maria-Gabriella Di Benedetto and Branimir R.Vojcic. “Ultra Wide Band Wireless Communi-cations : A Tutorial”. Journal of communica-tions and networks, Vol.5, No.4, , December2003.

[9] http://www.decawave.com/index.html

91

5.4.3 Hard-NLOS area test results

The goal of this experiment is to validate the capability of the UWB ranging

system in a hard NLOS channel. Figure 28 (d) shows that’s hard NLOS

environment with multiple concrete walls or multi obstructions. After analyze

the results from figure 31, we can observe, hard obstructions severely

attenuate UWB signal propagation and generate large positive bias in the

range estimates. The distance error varies widely from 26cm for one wall to

87cm for 4 walls. The receiver is unable to receive the signal at 38m point.

After measuring data in hard NLOS channel, it is clear that localization in this

hard NLOS rooms cannot obtain high precision by only using two-way

ranging algorithm. Some different method and algorithms are proposed to

improve or solve the hard NLOS ranging problems, but ranging in an NLOS

area is still a challenging problem for indoor locations [38].

Figure 31: Ranging Results of Hard-NLOS Area

are combined as this would likely be the case in ac-tual conditions. All the results of clusters in Fig.10show that the error from di↵erent obstructionsvaries from 6cm (Glass) to 29cm (Door). Theseexperimental conditions represent the most com-mon channel model over the distances of interestin most European o�ces, the average results of lessthan 30cm accuracy are acceptable to validate thatthe UWB signal can be utilized in indoor rangingmeasurements.

Fig. 10: Ranging Results of Soft-NLOS Area at 3m Point

c) Hard-NLOS Test

This experiment (Fig.8 (d)) attempts to validatethe capability of the UWB ranging system in ahard-NLOS channel with multiple concrete wallsor multi-obstructions in the environment. Resultsin Fig.11 indicate that hard obstructions severelyattenuate the UWB signal propagation and gener-ate large positive bias in the range estimates. Thedistance error varies widely from 26cm for one wallto 87cm for 4 walls. While at the 38m point, the re-ceiver is unable to receive the signal. It is clear thatlocalization in this hard NLOS rooms can not ob-tain high precision by only using TWR algorithm.Some method and algorithms [3] are proposed toimprove or solve the hard NLOS ranging problems,but ranging in an NLOS area is still a challengingproblem for indoor locations.

Fig. 11: Ranging Results of Hard-NLOS Area

V Conclusion

In this paper, we theoretically analyzed and realis-tically validated the reliability of an impulse UWB

transceiver based point-to-point ranging systemusing a two way ranging algorithm in both indoorand outdoor environments. In theory, the UWBsignal is very resistant to multi-path and reflec-tions, the CRLB method proves that the UWBsignal has a high precision on the order of severalcentimeters. In practical operation, the two UWBtransceivers were evaluated in this study satisfyingthe FCC limits. A realistic two way ranging modelwas generated with antenna-to-system delay, firstpath detection delay and time o↵set and imple-mented in the ranging system. Results recordedof LOS, Soft-NLOS and Hard-NLOS ranging ex-periments show that UWB transceivers are capa-ble of capturing accurate transmission time be-tween two radios which can be used in turn tocompute the real distance. With features such aslarge channel capacity, robustness to interferenceand multi-path, energy e�ciency and fine resolu-tion, UWB transceiver technology is a dependablewireless communications mechanism for WSN lo-calization applications.

References

[1] M.G. diBenedetto, T. Kaiser, A.F. Molish,I. Oppermann, C. Plitano, and D. Porcino(eds.). “UWB Communications Systems: AComprehensive Overview”. EURASIP Publish-ing,2005.

[2] IEEE Working Group 802.15.4a. “Draft speci-fications for IEEE 802.15.4a standard”.

[3] IEEE Std 802.15.4aTM -2007, IEEE Standardfor information Technology

[4] http://www.idtechex.com/events/

presentations/scensor_an_ieee802_15_

4a_uwb_compliant_chip_ripe_for_energy_

harvesing_001824.asp

[5] Kazimierz Siwiak and Debra McKeown.“Ultra-Wideband Radio Technology”. JohnWiley and Sons,2006.

[6] S.M. Kay. “Fundamentals of Statistical Sig-nal Processing Estimation Theory”. EnglewoodCli↵s, New Jersey:Prentice-Hall,1993.

[7] IEEE Std 802.11n-2009,IEEE Standard forinformation Technology–Telecommunicationsand information exchange between systems

[8] Maria-Gabriella Di Benedetto and Branimir R.Vojcic. “Ultra Wide Band Wireless Communi-cations : A Tutorial”. Journal of communica-tions and networks, Vol.5, No.4, , December2003.

[9] http://www.decawave.com/index.html

92

6. Conclusion

In this paper, we have described an overview of UWB technology. Single

band UWB systems have simple transceiver architecture, and so are

potentially lower costs. MB-OFDM systems are potentially good technical

solutions for the diverse set of high performance, short -range UWB

applications. In addition, they may support many modulation schemes

including orthogonal and antipodal schemes. However, this modulation must

be combined with some form of spectrum randomization techniques to

enhance the detection performance and to enable multiple access capability.

Both TH and DS spectrum spreading techniques were presented.

Here, we theoretically analyzed and realistically validated the reliability of an

impulse UWB transceiver based point-to-point ranging system using a two

way ranging algorithm in both indoor and outdoor environments. We mainly

focused on two-step positioning approach. In first step we discussed how to

estimate the parameters using TOA, AOA, TDOA and RTT. In second step

we discussed about position estimation based on parameters obtained in first

step. The study review shown that TOA based approach is easy, less

expensive and more accurate in practical scenario. In theory, the UWB signal

is very resistant to multi-path and reflections; the CRLB method proves that

the UWB signal has a high precision on the order of several centimeters. In

practical results recorded of LOS, Soft-NLOS and Hard-NLOS ranging

experiments show that UWB transceivers are capable of capturing accurate

93

transmission time between two radios, which can be used in turn to compute

the real distance. It has been overcome the two main difficulties for indoor

localization. Using UWB signals resolves problems due to multipath fading.

The remaining issue (NLOS propagation) adds a positive bias to the range

measurement, which degrades the localization accuracy and robustness if

nothing is done.

We need to address some difficulties, when nodes are continuously moving

between indoor and outdoor environments, solving synchronization problems,

reducing the impact of noise interference, and improving energy efficiency.

Innovative research efforts are expected to tackle these issues in the near

future.

94

7 References [1] Ultra-Wideband (UWB Technology) Enabling high-speed wireless

personal area networks. Intel, 2005

[2] Jinyun Zhang, Philip Orlik, Zafer Sahinoglu, Andreas Molisch, Patrick

Kinney. UWB Systems for Wireless Sensor Networks. TR2009-007 March

2009

[3] Mohit Lad “Ultra-Wideband: The Next Generation Personal Area

Network Tecnology “Patni Computer Systems Limited, Frburary 2004

[4] Jin-Shyan Lee, Yu-Wei Su, and Chung-Chou Shen, A Comparative Study

of Wireless Protocols: Bluetooth, UWB, ZigBee, and Wi-Fi, Information &

Communications Research Labs Industrial Technology Research Institute

(ITRI) Hsinchu, Taiwan

[5]. Jeff Foerster, Corp.Evan Green, Srinivasa Somayazulu, David Leeper,

Ultra-Wideband Technology for Short- or Medium-Range Wireless

Communications Intel Corp.

[6] Chia-Chin Chong, Fujio Watanabe, and Hiroshi Inamura , Potential of

UWB Technology for the Next Generation Wireless Communications (Invited

Paper) NTT DoCoMo USA Labs 181, Metro Drive, Suite 300 San Jose, CA

95110 USA.

[7] Seyed Mohammad-Sajad SADOUGH, A Tutorial on Ultra Wideband

Modulation and Detection Schemes, April 2009

[8] Xuemin (Sherman) Shen, Mohsen Guizani, Robert Caiming Qiu, Tho Le-

Ngoc, ULTRA-WIDEBAND WIRELESS COMMUNICATIONS

AND NETWORKS, 2006 John Wiley & Sons, Ltd. ISBN: 0-470-01144-0

95

[9] Leonard E. Miller, Why UWB? A Review of Ultra-wideband

Technology, Wireless Communication Technologies Group, National Institute

of Standards and Technology, April 2003

[10] Weihua Zhuang, Xuemin (Sherman) Shen and Qi Bi, Ultra-wideband

wireless communications, WIRELESS COMMUNICATIONS AND

MOBILE COMPUTING, 2003

[11] Wimedia Ultra-Wideband : efficiency of the efforts of protocol overhead

on data throughput, Wimedia alliance, january 2009

[12] AvW. Pam Siriwongpairat, K. J. Ray Liu, Ultra-wideband

communications systems: multiband OFDM approach John Wiley & son,

Inc., 2008, Canada.

[13] , M. Mezzour, Direct Spread Spectrum (DS) / Time Hopping (TH) UWB

Performances comparison in a multi-user Ad Hoc environment, Federal

Institute of Technology of Lausanne , Ecublens 1015 Switzerland

[14] M. G. Di Benedetto, T. Kaiser, A. F. Molish, I. Opperman, C. Politano,

and D. Porcino, UWB Communication Systems A Comprehensive Overview,

Series on Signal Processing and Communications. EURASIP, 2006.

[15] Saúl Rodríguez Dueñas, Design of a DS-UWB Transceiver, Stockholm,

March 2005

[16] M. Z. Win and R. A. Scholtz, “Ultra-wide bandwidth time-hopping

spread-spectrum impulse radio for wireless multiple-access communications,”

IEEE Trans. Commun., pp. 679–691, April 2000.

[17 ]Anuj Batra,Member, IEEE, Jaiganesh Balakrishnan, Member, IEEE, G.

Roberto Aiello, Member, IEEE, Jeffrey R. Foerster, Member, IEEE, and

Anand Dabak, Member, IEEE, Design of a Multiband OFDM System for

96

Realistic UWB Channel Environments, IEEE TRANSACTIONS ON

MICROWAVE THEORY AND TECHNIQUES, VOL. 52, NO. 9,

SEPTEMBER 2004

[18] Viterbi Algorithm for Decoding of Convolutional Codes, CORE

Technologies, 24 Radio str., Moscow, Russia, 105005

[19] G. D. Forney, “The Viterbi algorithm,” Proceedings of the IEEE, vol. 61,

no. 3, pp. 268–278, March 1973.

[20] Markku Pukkila, Channel Estimation Modeling, Nokia Research Center,

December 2000

[21] Ultra Wideband (UWB), A Background Brief, Spectrum Planning Team,

Radiofrequency Planning Group, Australian Communications Authority,

Date: May 2003

[22] A. Batra, J. Balakrishnan, G. R. Aiello, J. R. Foerster, and A. Dabak,

“Design of multiband OFDM system for realistic UWB channel

environments,” IEEE Trans. Microwave Theory and Techniques, vol. 52, pp.

2123–2138, Sep. 2004.

[23] A. Batra, J. Balakrishnan, and A. Dabak, “Multiband OFDM physical

layer proposal for IEEE 802.15 task group 3a,” July 2003.

[24] WiMedia Alliance, ,” http://www.wimedia.org

[25] J. G. Proakis, Digital Communications, McGraw-Hill, third edition,

1995.

[26] J. J. Caffery, Wireless Location in CDMA Cellular Radio Systems.

Boston: Kluwer Academic Publishers, 2000.

[27] S. Gezici, “A survey on wireless position estimation,” Wireless Personal

Communications, vol. 44, no. 3, pp. 263–282, Feb. 2008.

97

[28] J. J. Caffery and G. L. Stuber, “Subscriber location in CDMA cellular

networks,” IEEE Trans. Veh. Technol., vol. 47, no. 2, pp. 406–416, May

1998.

[29] Z. Sahinoglu, S. Gezici, and I. Guvenc, Ultra-Wideband Positioning

Systems: Theoretical Limits, Ranging Algorithms, and Protocols.

Cambridge University Press, 2008.

[30] IEEE P802.15.4a/D4 (Amendment of IEEE Std 802.15.4), “Part 15.4:

Wireless medium access control (MAC) and physical layer (PHY)

specifications for low-rate wireless personal area networks (LRWPANs),”

July 2006.

[31] S. Gezici, Z. Tian, G. B. Giannakis, H. Kobayashi, A. F. Molisch, H. V.

Poor, and Z. Sahinoglu, “Localization via ultra-wideband

radios: A look at positioning aspects for future sensor networks,” IEEE Signal

Processing Mag., vol. 22, no. 4, pp. 70–84, July 2005.

[32] K. Siwiak and J. Gabig, “IEEE 802.15.4IGa informal call for application

response, contribution#11,” Doc.: IEEE 802.15-04/266r0,

July, 2003. [Online]. Available: http://www.ieee802.org/15/pub/TG4a.html

[33]IEEE standard for information technology, telecommunications and

information exchange between systems, “Local and metropolitan area

networks specific requirements, Part 15.4: Wireless medium access control

(MAC) and physical layer (PHY) specifications for low-rate wireless personal

area networks (LR-WPANs),” May 2003. [Online]. Available:

http://standards.ieee.org/getieee802/download/802.15.4-2003.pdf

[34] F. Gustafsson and F. Gunnarsson, “Mobile positioning using wireless

98

networks,” IEEE Signal Processing Mag., vol. 22, no. 4, pp. 41–53, July

2005.

[35] Da Zhang, Feng Xia, Zhuo Yang, Lin Yao, Wenhong Zhao, Localization

Technologies for Indoor Human Tracking, Dalian University of Technology ,

Zhejiang University of Technology, Chaina,

[36] Y. Qi, “Wireless geolocation in a non-line-of-sight environment,” Ph.D.

Dissertation, Princeton University, Dec. 2004.

[37] Sinan Gezici, Member, IEEE, and H. Vincent Poor, Position Estimation

via Ultra-Wideband Signals, Fellow IEEE.

[38] Tingcong Ye, Michael Walsh, Peter Haigh, John Barton, Alan

Mathewson, Brendan O’Flynn, Experimental Impulse Radio IEEE 802.15.4a

UWB Based Wireless Sensor Localization Technology: Characterization,

Reliability and Ranging, Tyndall National Institute University College

Ireland, UCC, Cork, ISSC 2011, Trinity College Dublin, June 23–24

[39] IEEE Working Group 802.15.4a. “Draft specifications for IEEE 802.15.4a standard”.

[40] IEEE Std 802.15.4aTM-2007, IEEE Standard for information

Technology

[41] http://www.idtechex.com/events/ presentations/scensor_an_ieee802_15_

4a_uwb_compliant_chip_ripe_for_energy_ harvesing_001824.asp

[42] I. Guvenc and Z. Sahinoglu, “Threshold-based TOA estimation for

impulse radio UWB systems,” in in Proc. IEEE Int. Conf. UWB (ICU),

Zurich, Switzerland, Sep. 2005, pp. 420–425.

[43] S. Gezici, Z. Sahinoglu, H. Kobayashi, H. V. Poor, and A. F. Molisch,

99

“A two-step time of arrival estimation algorithm for impulse radio

ultrawideband systems,” in Proc. 13th European Signal Processing

Conference (EUSIPCO), Antalya, Turkey, Sep. 2005.

[44] “IEEE 802.15 WPAN low rate alternative PHY task group 4a (TG4a).”

[Online]. Available: http://www.ieee802.org/15/pub/TG4a.html

[45]A. F. Molisch, Y. P. Nakache, P. Orlik, J. Zhang, Y. Wu, S. Gezici, S. Y.

Kung, H. Kobayashi, H. V. Poor, Y. G. Li, H. Sheng, and A. Haimovich, “An

efficient low-cost time-hopping impulse radio for high data rate

transmission,” EURASIP Journal on Applied Signal Processing (Special Issue

on UWB - State of the Art), vol. 2005, no. 3, pp. 397–412, Mar. 2005.

[46] Neiyer S. Correal, Spyros Kyperountas, Qicai Shi and Matt Welborn, An

UWB Relative Location System.

[47] Maria-Gabriella Di Benedetto and Branimir R. Vojcic. “Ultra Wide Band

Wireless Communi- cations : A Tutorial”. Journal of communications and

networks, Vol.5, No.4, , December 2003.

[48] “Decawave”, Ireland, http://www.decawave.com/index.html

[49] S. Gezici, H. Kobayashi, H. V. Poor, and A. F. Molisch, “Performance

evaluation of impulse radio UWB systems with pulse-based polarity

randomization,” IEEE Trans. Signal Processing, vol. 53, no. 7, pp. 2537–

2549, July 2005.

[50] S. Gezici, A. F. Molisch, H. V. Poor, and H. Kobayashi, “The trade-off

between processing gains of an impulse radio UWB system in the presence of

timing jitter,” IEEE Trans. Commun., vol. 55, no. 8, pp. 1504–1515, Aug.

2007.

Distance Measurements using Ultra Wide-Band (UWB)

Technology

uwb technology

uwb regulations

uwb features

single band uwb modulation

impulse uwb basedtransceiver

abstractultra wideband

directsequence uwb

multiband uwb modulations463