Ultra Wideband Communication

ACKNOWLEDGEMENT

I would first like to thanks Mr. A. K. Choudhary principal of Apex college for education research and tech. for providing the opportunity to work on this seminar and help me to get necessary accessories.

I take this opportunity to express my deep sense of gratitude to my geode Mr. Manoj Gupta (HOD) & all lecturer of department for their guidance and suggestion at every stage of this seminar. They were a source of inspiration for me to put in my best effort into this seminar

I am very much thankful to all teaching and non teaching staffs, official staffs because their helps & suggestions are really mile stone to complete this seminar report.

This acknowledgement will be incomplete if I fail to express my heartful sense of obligation to all teaching & non teaching staffs of college, my family members and their friends for their constant encouragement and inspiration.

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PREFACE

An engineer has to serve the market, for that one must know about the demands and requirements in the market, the way of tackling the hurdles and find a way of working out for their solutions at the right place.

After the completion of degree course an engineer must have a thorough knowledge about the presentation and communication in industries and compnies For this prepare a topic of seminar report

To make the engineer good at presentational skills and communicational skills the collage provides a seminar and seminar presentation on a selected topic .

We have been lucky to present and prepare aseminar report and this report help me in future time. This report has been prepared on the basis of knowledge of my topic ultra wideband wireless communications

UWB WIRELESS COMMUNICATION1

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Table of contents

1 Abstract……………………………………………………………6

2 Introduction………………………………………………………..8

3 History and Background………………………………………….10

3.1 UWB Concept………………………………………………….13

3.2 UWB Technology Overview…………………………………..15

3.3 UWB and Heterogeneous Networking…………………………17

3.4 Regulation Situation…………………………………………....19

4 Towards Ultra Wide Band……………………………………….20

4.1 UWB compared to current PANs and WLANs………………..20

4.2 The role of UWB………………………………………………21

4.2.1 Why home…………………………………………………22

4.2.2 Telecom applications of UWB ……………………………23

5 Challenges for UWB…………………………………………….25

6 Advantage……………………………………………………….31

7 Wider application Of UWB……………………………………..38

8 Conclusions…………………………………………………….42

9 Bibliography…………………………………………………....44

9.1 References…………………………………………………….44


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FIGURE INDEX

1. Heterogeneous wireless broadband network architecture……………….19

2. High mobility and coverage implies lower data rates……………………21.

3. The role of UWB communications among current heterogeneous communication technologies. ………………………………………………24

4. wireless universal serial bus (WUSB), IEEE 1394, the next generation of Bluetooth, and Universal Plug and Play (UPnP)………………………39


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1 ABSTRACT

Ultra-wideband (aka UWB, ultra-wide band, ultraband, etc.) is a radio technology that can be used at very low energy levels for short-range high-bandwidth communications by using a large portion of the radio spectrum. UWB has traditional applications in non-cooperative radar imaging. Most recent applications target sensor data collection, precision locating and tracking applications.

UWB communications transmit in a way that doesn't interfere largely with other more traditional narrowband and continuous carrier wave uses in the same frequency band. However first studies show that the rise of noise level by a number of UWB transmitters puts a burden on existing communications services. This may be hard to bear for traditional systems designs and may affect the stability of such existing systems.

Ultra-Wideband (UWB) is a technology for transmitting information spread over a large bandwidth (>500 MHz) that should, in theory and under the right circumstances, be able to share spectrum with other users. Regulatory settings of FCC are intended to provide an efficient use of scarce radio bandwidth while enabling both high data rate "personal area network" (PAN) wireless connectivity and longer-range, low data rate applications as well as radar and imaging systeUltra Wideband was traditionally accepted as pulse radio, but the FCC and ITU-R now define UWB in terms of a transmission from an antenna for which the emitted signal bandwidth exceeds the lesser of 500 MHz or 20% of the center frequency. Thus, pulse-based systems—wherein each transmitted pulse instantaneously occupies the UWB bandwidth, or an aggregation of at least 500 MHz worth of narrow band carriers, for example in orthogonal frequency-division multiplexing (OFDM) fashion—can gain access to the UWB spectrum under the rules. Pulse repetition rates may be either low or very high. Pulse-based UWB radars and imaging systems tend to use low repetition rates, typically in the range


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of 1 to 100 megapulses per second. On the other hand, communications systems favor high repetition rates, typically in the range of 1 to 2 giga-pulses per second, thus enabling short-range gigabit-per-second communications systems. Each pulse in a pulse-based UWB system occupies the entire UWB bandwidth, thus reaping the benefits of relative immunity to multipath fading (but not to intersymbol interference), unlike carrier-based systems that are subject to both deep fades and intersymbol interferenc

A significant difference between traditional radio transmissions and UWB radio transmissions is that traditional systems transmit information by varying the power level, frequency, and/or phase of a sinusoidal wave. UWB transmissions transmit information by generating radio energy at specific time instants and occupying large bandwidth thus enabling a pulse-position or time-modulation. The information can also be imparted (modulated) on UWB signals (pulses) by encoding the polarity of the pulse, the amplitude of the pulse, and/or by using orthogonal pulses. UWB pulses can be sent sporadically at relatively low pulse rates to support time/position modulation, but can also be sent at rates up to the inverse of the UWB pulse bandwidth. Pulse-UWB systems have been demonstrated at channel pulse rates in excess of pulses per second using a continuous stream of UWB pulses (Continuous Pulse UWB or "C-UWB"), supporting forward error correction encoded data rates in excess of 675 Mbit/s. Such a pulse-based UWB method using bursts of pulses is the basis of the IEEE 802.15.4a draft standard and working group, which has proposed UWB as an alternative PHY layer.

One of the valuable aspects of UWB radio technology is the ability for a UWB radio system to determine "time of flight" of the direct path of the radio transmission between the transmitter and receiver at various frequencies. This helps to overcome multi path propagation, as at least some of the frequencies pass on radio line of sight. With a cooperative symmetric two-way metering technique distances can be measured to high resolution as well as to high accuracy by compensating for local clock drifts and stochastic inaccuracies.

Another valuable aspect of pulse-based UWB is that the pulses are very short in space (less than 60 cm for a 500 MHz wide pulse, less than 23 cm for a 1.3 GHz bandwidth pulse), so most signal reflections do not overlap the original pulse, and


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thus the traditional multipath fading of narrow band signals does not exist. However, there still is multipath propagation and inter-pulse interference for fast pulse systems which have to be mitigated by coding techniques

Uses

The UWB characteristics are very well suited to short-distance applications. A representative case is for PC Peripherals; see Wireless USB (implemented on top of UWB).

2. INTRODUCTION

The recent rapid growthin technology and the successful commercial

deployment of wireless communications are significantly affecting our

daily lives. The transition from analog to digital cellular communications,

the rise of third- and fourth-generation radio systems, and the replacement

of wired connections with Wi-Fi and Bluetooth are enabling consumers

to access a wide range of information from anywhere and at any time. As

the consumer demand for higher capacity, faster service, and more secure

wireless connections increases, new enhanced technologies have to find

their place in the overcrowded and scarce radio frequency (RF) spectrum.

This is because every radio technology allocates a specific part of the

spectrum; for example, the signals for TVs, radios, cell phones, and so on

are sent on different frequencies to avoid interference to each other. As a

result, the constraints on the availability of the RF spectrum become

Ultra-wideband (UWB) technology offers a promising solution to the RF

spectrum drought by allowing new services to coexist with current radio


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systems with minimal or no interference. This coexistence brings the

advantage of avoiding the expensive spectrum licensing fees that providers

of all other radio services must pay.

It provides a comprehensive overview of ultra-wideband

communications, starting with its history and background. Next the discussion

turns to the concepts behind UWB technology, as well as its

advantages and challenges in wireless communications. The chapter also

eliminates the common misconception about UWB and spread spectrum,

and it examines the strengths and weaknesses of ultra-wideband

compared to narrowband and wideband communications. Further,

the single-band and multiband approaches that are two major UWB

techniques under consideration for IEEE standardization are explained.

Next we discuss the current Federal Communications Commission

(FCC) regulations for UWB deployment in the United States and briefly

address worldwide regulatory efforts. The chapter ends with a concise

overview of UWB applications; we present a detailed discussion of

present and future UWB applications and their potential markets inmore and more strict with the introduction of new radio services


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3. HISTORY AND BACKGROUND

Ultra-wideband communications is fundamentally different from all

other communication techniques because it employs extremely narrow

RF pulses to communicate between transmitters and receivers. Utilizing

short-duration pulses as the building blocks for communications directly

The United Kingdom’s spectrum auction for next-generation wireless applications generated $35.4 billion in April 2000 [1]. generates a very wide bandwidth and offers several advantages, such aslarge throughput, covertness, robustness to jamming, and coexistencewith current radio services (see Section 1.4).

Ultra-wideband communications is not a new technology; in fact, it was

first employed by Guglielmo Marconi in 1901 to transmit Morse code

sequences across the Atlantic Ocean using spark gap radio transmitters.

However, the benefit of a large bandwidth and the capability of implementing

multiuser systems provided by electromagnetic pulses were

never considered at that time.

Approximately fifty years after Marconi, modern pulse-based transmission

gained momentum in military applications in the form of impulse

radars. Some of the pioneers of modern UWB communications in the

United States from the late 1960s are Henning Harmuth of Catholic University

of America and Gerald Ross and K. W. Robins of Sperry Rand


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Corporation [2]. From the 1960s to the 1990s, this technology was

restricted to military and Department of Defense (DoD) applications

under classified programs such as highly secure communications. However,

the recent advancement in microprocessing and fast switching in

semiconductor technology has made UWB ready for commercial applications.

Therefore, it is more appropriate to consider UWB as a new name

for a long-existing technology.

As interest in the commercialization of UWB has increased over the past

several years, developers of UWB systems began pressuring the FCC to

approve UWB for commercial use. In February 2002, the FCC approved

the First Report and Order (R&O) for commercial use of UWB technology

under strict power emission limits for various devices. Sections 1.9

and 1.10 present a detailed recent history of the standardization and

worldwide regulation of UWB technology. Figure 1–1 summarizes the

development timeline of UWB.

with current radio services (see Section 1.4).

Ultra-wideband communications is not a new technology; in fact, it was

first employed by Guglielmo Marconi in 1901 to transmit Morse code

sequences across the Atlantic Ocean using spark gap radio transmitters.

However, the benefit of a large bandwidth and the capability of implementing

multiuser systems provided by electromagnetic pulses were

never considered at that time.


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Approximately fifty years after Marconi, modern pulse-based transmission

gained momentum in military applications in the form of impulse

radars. Some of the pioneers of modern UWB communications in the

United States from the late 1960s are Henning Harmuth of Catholic University

of America and Gerald Ross and K. W. Robins of Sperry Rand

Corporation From the 1960s to the 1990s, this technology was

restricted to military and Department of Defense (DoD) applications

under classified programs such as highly secure communications. However,

the recent advancement in microprocessing and fast switching in

semiconductor technology has made UWB ready for commercial applications.

Therefore, it is more appropriate to consider UWB as a new name

for a long-existing technology.

As interest in the commercialization of UWB has increased over the past

several years, developers of UWB systems began pressuring the FCC to

approve UWB for commercial use. In February 2002, the FCC approved

the First Report and Order (R&O) for commercial use of UWB technology

under strict power emission limits for various devices. Sections 1.9

and 1.10 present a detailed recent history of the standardization and

worldwide regulation of UWB technology. Figure 1–1 summarizes the

development timeline of UWB.

1900 - Spark Gap Transmission, Hertz and Marconi


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1960 -1990 :- Military Radars and CovertCommunications

2002 - FCC Approves the Use of UnlicensedUWB for Commerical Purposes

Traditional business models of mobile communications, ones that are used in the current highly vertical and closed markets, will be challenged in the near future. New unregulated band wireless broadband networks will begin to complement existing and next generation cellular networks and fixed networks in forming a technologically heterogeneous environment. In this environment IP connectivity is available everywhere, only the underlying technology and connection speeds vary. Multimode terminals are needed in order to establish a network connection according to the location of a moving user and the particular service to be used.

In addition to multimode terminals and heterogeneous IP networking also the need for local very high data rate wireless products is emerging. Internet-based streaming video services and high definition wireless video connections within the home are an essential ingredient in the next phase of digital revolution. Ultra Wideband (UWB) impulse radio technology will play a prominent role in enabling these services and products with its high speed (up to 500 Mb/s), low cost (simpler RF architecture) and low power consumption.

3.1 UWB CONCEPT

Traditional narrowband communications systems modulate continuouswaveform


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(CW) RF signals with a specific carrier frequency to transmit

and receive information. A continuous waveform has a well-defined signal

energy in a narrow frequency band that makes it very vulnerable to

detection and interception. Figure 1–2 represents a narrowband signal in

the time and frequency domains.

As mentioned in Section 1.2, UWB systems use carrierless, short-duration

(picosecond to nanosecond) pulses with a very low duty cycle (less

than 0.5 percent) for transmission and reception of the information. A

simple definition for duty cycle is the ratio of the time that a pulse is

present to the total transmission time. Figure 1–3 and Equation 1–1 represent

the definition of duty cycle.

Low duty cycle offers a very low average transmission power in UWB

communications systems. The average transmission power of a UWB system

is on the order of microwatts, which is a thousand times less than the

transmission power of a cell phone! However, the peak or instantaneous

power of individual UWB pulses can be relatively large,2 but because they

are transmitted for only a very short time (Ton < 1 nanosecond), the average

power becomes considerably lower. Consequently, UWB devices

require low transmit power due to this control over the duty cycle, which

directly translates to longer battery life for handheld equipment. Since

frequency is inversely related to time, the short-duration UWB pulses


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Duty Cycle = Ton/(Ton+Toff)

Low duty cycle offers a very low average transmission power in UWB

communications systems. The average transmission power of a UWB system

is on the order of microwatts, which is a thousand times less than the

transmission power of a cell phone! However, the peak or instantaneous

power of individual UWB pulses can be relatively large,2 but because they

are transmitted for only a very short time (Ton < 1 nanosecond), the average

power becomes considerably lower. Consequently, UWB devices

require low transmit power due to this control over the duty cycle, which

directly translates to longer battery life for handheld equipment. Since

frequency is inversely related to time, the short-duration UWB pulses

3.2 UWB Technology Overview

The focal point of the BROCOM project is in the UWB (Ultra Wideband) technology and its applications. This report addresses the role of UWB in communication networks as a technical building block. Other possible applications of UWB technology, such as positioning and radar systems, are not covered in this report.


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UWB is fundamentally different from what we usually think of RF communications. Instead of using a carrier frequency, as traditional systems like FM radio or GSM networks do, UWB technology is based on sending and receiving very high bandwidth carrierless radio impulses using extremely accurate timing (Win and Scholtz, 1998). The radio impulses are transmitted in sub-nanosecond intervals, which inherently leads to very a high bandwidth (typically several GHz) and on the other hand to a very accurate spatial resolution, which can be taken advantage of in positioning applications. Very fast impulse rates enable high connection speeds, even up to 1 Gb/s over short distances. Because UWB signals occupy a very broad spectrum, low transmission powers must be used in order not to interfere with existing RF systems. A common approach is to set UWB power levels so low that the signals cannot be distinguished from external noise by other systems operating in overlapping frequencies.

As an idea UWB is not new, it dates back to the 1980’s (Foerster et al., 2001). However, it has been used mainly in radar-based applications since the timing and synchronization requirements of UWB communications have been too challenging for making reasonable cost consumer products. Recent developments in semiconductor technology have brought the applications closer to realization and the regulatory steps taken in the US also indicate a trend towards accelerating research efforts on the topic.

From a communications point of view, UWB is not well suited to be a cellular technology, but instead an evolution of current WLAN and especially PAN (Personal Area Network) technologies due to the small antenna range. It is impossible or at least infeasible to build full coverage UWB networks with high-speed mobility features, as high speed movement would require an excessive amount of handovers. That is, if a cellular-like basestation paradigm is applicable to UWB at all. Other communication hierarchy models like ad hoc networking must also be investigated. Taking into account techno-economic constraints, UWB technology will be best applied to highly local networks in rooms, buildings, corporation sites, public places and so on. This application field lets UWB excel in


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what it is best at: very high bandwidth short- to medium-range wireless connectivity at very low cost and very low power consumption.

“As opposed to traditional narrowband radios, Ultra-Wideband (UWB) is a wireless digital communication system exchanging data using short duration pulses. The complexity of the analog front-end in UWB is drastically reduced due to its intrinsic baseband transmission. Based on this simplification and the high spreading gain it possesses, UWB promises low-cost implementation with fine time resolution and high throughput at short distances without interfering with other existing wireless communication systems

Low cost and power consumption with very high transmission speed is a combination that will make UWB to be pulled onto the market instead of engineering-driven pushing of a new technology. Video-on-demand and other video related (or otherwise high bandwidth data intensive) consumer products and services are there, they are just waiting for a technology like UWB to make those services fast and easy, convenient enough for the customers.

3.3UWB and Heterogeneous Networking

UWB technology is not mobile but instead it is wireless. A marriage of these two building blocks, mobile and wireless, is needed in order to achieve a single subscription, single bill, variable bandwidth, total coverage IP service. For this service a heterogeneous network model (Figure 1) is needed. Cellular technology combined with wireless high bandwidth hot spot (WLAN) technology forms a network environment in which multimode terminals can be used to obtain generic IP connectivity regardless the place.

Heterogeneous networks consist of different network layers: a cellular layer, a hot spot layer and a personal network layer (De Vriendt et al., 2002). The cellular layer is for full coverage services with moderate data rates, typical services being speech


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and multimedia messaging. This is the area of technologies like GSM with its expansions and UMTS. The hot spot layer is for shorter range, higher data rate, slow mobility services like WLAN. The personal network layer provides connections between computers, PDAs, laptops and printers. Current wireless solutions in this area include IrDA and Bluetooth, wired alternatives are USB and Firewire (IEEE 1394).

In terms of these layers, heterogeneous networking scenarios require a combination of cellular and hot spot layers whereas the scope of UWB technology is in the hot spot layer and especially in the personal network layer. For this reason we must take all three layers into account in the following considerations on future wireless communication business.

A current example of heterogeneous networking hardware is a GPRS & WLAN enabled PCMCIA card for laptop computers like the Nokia D211, released in February 2002. When used in conjunction with Sonera wGate (Nokia Corp., 2001) service it enables the use of WLAN hot spots so that billing is integrated into user’s mobile phone subscription based on SIM authentication. In the future this concept can be gradually updated to support technologies like EDGE or UMTS packet data (on the cellular layer) and next generation WLANs (hot spot layer) and UWB (hot spot and personal layer).

The possible use of UWB technology in communications ranges from WLAN-like networking and Internet access to wireless connectivity at home, office or on the move, in areas where technologies like Bluetooth (wireless), Firewire, and USB (wired) are used today. It might well be that in a decade UWB is the wireless lingua franca between different information-related pieces of equipment, from cell phones and computers to refridgerators, stereo systems and home security systems.


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The heterogeneous network model for all-round communications is presented in the following picture. Note that unlike others UWB is an acronym for a radio access technology.

WLAN

WLAN

UMTS

GPRS / EDGE

GPRS / EDGE

UMTS

UWB

UWB

Figure 1Heterogeneous wireless broadband network architecture.Different connection technologies are used in different geographical areas based on population density.

3.4 Regulation Situation

By September 2002 there are still a few questions open about UWB, regulation being probably the most acute. Federal Communications Commission of the United States (FCC) authorized the use of UWB in February 2002 in frequency band 3.1-10.6 GHz taking a very conservative approach. FCC continues to work on


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the regulations in order to come up with an updated and hopefully less stringent set of rules in a time frame of six to twelve months (FCC, 2002).

As opposed to the frequency band authorized by FCC, earlier UWB systems have made use of frequencies ranging from near DC to a few GHz. If FCC is going to keep the doors shut in the frequencies below 3 GHz, some rework and further research is required.

4. Towards Ultra Wide Band

The different applications of UWB technology for short range communications, metering and sensing are numerous and it is difficult to forecast which applications will diffuse to the market. This report concentrates on evaluating the role of UWB in communications. Personal area networks are the primary–or at least the first–application area of UWB. However, also larger scale IP connectivity solutions can be envisioned, in which a heterogeneous networking model is needed to complement UWB.

From heterogeneous networking point of view, the cellular mobile systems are assumed as they are. That is, they exist already and will evolve according to requirements specific to mobile telecommunications, which include wide geographical coverage and high-speed mobility. The future of the other network layers, hot spot and personal, is more exposed to consumer market dynamics because on these layers the vertical market control is weaker. For this reason it is important to evaluate the role of UWB with care and create globally compatible standards for UWB implementations.

4.1 UWB compared to current PANs and WLANs


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WLANs have only recently started taking off, IEEE 802.11b (commercially known as Wi-Fi) being the dominant standard. Also Bluetooth has started gaining popularity in personal area networks. As both operate in the unlicenced 2.4 GHz frequency range (Table 1), interference problems are likely to occur eventually when both technologies become more and more popular. A gradual migration to 5 GHz WLANs would help this situation, but a contest of standards is going on there. The 802.11a has a significant first-mover advantage over the European standard, IEEE HiperLAN2, and is likely to become the dominant solution if ongoing efforts to converge the 5 GHz WLAN systems fail. Current research on UWB seems to concentrate on personal area networks, but other applications such as small-scale WLAN implemented with medium-range UWB should not be overlooked.

4.2The role of UWB

Derived from the basic laws of radio propagation and business economy, it is logical that we need to make compromises when building mobile or wireless communication systems. As the diagram below (Figure 2) suggests, the more coverage and mobility is wanted, the more has to be given up on the data rate side.

Mobile Fixed

Slow Fast

GSM WLAN UWBUMTS

MOBI L I TY

DATA RATE

LAN


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Figure 2High mobility and coverage implies lower data rates. Note that Bluetooth is not present in the figure: as a personal layer technology Bluetooth has low mobility but it also lacks high data rates being capable of less than 1 Mb/s. This leaves a gap between fixed LANs and WLANs, a niche for short- to medium-range UWB solutions.

As stated earlier, current research efforts concentrate on PAN applications for UWB. Also the first commercial UWB products are likely to be in the personal networking area. According to an article by Roy Mark (2002) companies like Cisco, Intel and Motorola are going to introduce first products in this area as early as by the end of 2003.

The probable killer application for UWB is replacing cables in the home and enabling wireless high quality video. As an example of current state of the art, Northern Virginia based XtremeSpectrum demonstrated in June 2002 a transmission of six simultaneous MPEG-2 video streams (12 Mb/s each) over a UWB connection. Especially wireless video could be the fuel for rapid UWB adoption, example products including DLP projectors with UWB video connections. Also digital cameras, digital video cameras, wireless multi-channel digital audio systems, cell phones, PDAs, laptops, scanners, printers and of course desktop PCs could be interconnected by UWB.

4.2.1 Why home?

In the beginning of UWB technology evolution the home seems to be the natural environment for UWB applications. This is because of limited range and the limited capabilities in handling bursty packet traffic due to relatively slow synchronization of the radio channel. In contrast to the roughly 1 microsecond that for example 802.11 WLAN systems take to synchronize, the synchronization time


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(channel acquisition time) for current UWB systems is typically in the scale of a few milliseconds (Ding et al., 2002). This is problematic when an arbitrary number of users try to acquire the channel and transfer small bursts of data, just as is the case in multi-user wireless Internet environments. As opposed to traffic typical for Internet browsing, home applications usually require more static connections (eg. downloading pictures from digital camera or transferring a video signal), and in this area UWB does well with its high throughput. Also, the regulatory aspects and requirements of low emission and interference to other systems are more easily dealt with within the home than in open air applications.

4.2.2Telecom applications of UWB

The UWB technology itself doesn’t set any fixed limits for the range of applications for UWB. Along with getting more practical experience on UWB systems in the future and the consequently loosening regulations, the scale and scope of UWB systems could be enlarged to cover functions handled by WLAN today. This is, however, a more or less open question.


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UWB

Coverage

Mobility Bitrate

GSM UMTS WLANBluetooth LAN

Figure 3The role of UWB communications among current heterogeneous communication technologies. Note: The presentation is qualitative; parameters are not in a confom scale.

In general UWB has an appealing position due to its high bandwidth (see Figure 3). If only the issues concerning synchronization/MAC and range/interference can be dealt with, UWB can have a tremendously large field of applications.


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A recent study on radio access selection for multi-standard terminals (Kalliokulju et al., 2001) concluded that a combination of WLAN and GERAN/UTRAN (eg. GPRS/UMTS) support in a mobile terminal would provide sufficient quality of service in different usage scenarios of mobile IP-based services. Also Bluetooth was covered in the study, but due to its significantly shorter range it did not appear to be a suitable technology for mobile multimode networking. On these grounds UWB researchers should actively address the issues related to range and channel acquisition in order to make UWB a competitive solution also in heterogeneous networking.

On the other hand, it may turn out that UWB is bound to home and office applications only. After all, the different network layers (cellular, hot spot and personal layer) have different requirements for the wireless technology by nature and perhaps they all need accordingly optimized, different solutions for each. Which, unfortunately, would mean that an omni-compatible terminal would need to be equipped with at least three different radio modes, perhaps even four (GPRS, UMTS, WLAN, and UWB for example) to achieve optimal connectivity in all situations. In a laptop computer this might be reasonable, but in smaller low cost terminals problems concerning space, price and power consumption arise. Software-defined radio (SDR, see www.sdrforum.org) based solutions might help the case with multiple radio interface standards, but it remains to be seen how this technology could be used in conjunction with UWB radio.

5. Challenges for UWB

At this point, September 2002, UWB is still just a lot of promises. While legislation adjustment is still in progress, some fundamental questions about the technology should be answered. Some open questions and suggestions for aiming the technical research are presented in the next subchapters.


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UWB technology for communications is not all about advantages. In fact,

there are many challenges involved in using nanosecond-duration pulses

for communications. Some of the main difficulties of UWB communications

are discussed in the following subsections.

5.1 PULSE-SHAPE DISTORTION

The transmission characteristics of UWB pulses are more complicated

than those of continuous narrowband sinusoids. A narrowband signal

remains sinusoidal throughout the transmission channel. However, the

weak and low-powered UWB pulses can be distorted significantly by the

transmission link. We can show this distortion mathematically with the

widely used Friis transmission formula:

where Pr and Pt are the received and transmitted signal power, respectively;

Gt and Gr are the transmitter and receiver antenna gains, respectively;

c is the speed of light;6d is the distance between the transmitter and

the receiver; and f is the signal frequency.

This formula shows that the received signal power will decrease quadratically

with the increase in frequency. In narrowband signals with a very

narrow frequency band, the change in frequency only minimally changes

the received power and hence can be overlooked. However, due to the


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wide range of frequencies that is covered by the UWB spectrum, the

6. In a vacuum, all electromagnetic waveforms travel at the speed of light, c = 3 × 108

meters per second.

received power drastically changes and thus distorts the pulse shape. This

will limit the performance of UWB receivers that correlate the received

pulses with a predefined template such as classical matched filter

5.2 CHANNEL ESTIMATION

Channel estimation is a core issue for receiver design in wireless communications

systems. Because it is not possible to measure every wireless

channel in the field, it is important to use training sequences to estimate

channel parameters, such as attenuations and delays of the propagation

path. Given that most UWB receivers correlate the received signal with a

predefined template signal, prior knowledge of the wireless channel parameters

is necessary to predict the shape of the template signal that matches

the received signal. However, as a result of the wide bandwidth and reduced

signal energy, UWB pulses undergo severe pulse distortion; thus, channel

estimation in UWB communications systems becomes very complicated

5.3 HIGH-FREQUENCY SYNCHRONIZATION


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Time synchronization is a major challenge and a rich area of study in

UWB communications systems. As with any other wireless communications

system, time synchronization between the receiver and the transmitter

is a must for UWB transmitter/receiver pairs. However, sampling

and synchronizing nanosecond pulses place a major limitation on the

design of UWB systems. In order to sample these narrow pulses, very fast

(on the order of gigahertz) analog-to-digital converters (ADCs) are needed.

Moreover, the strict power limitations and short pulse duration make the

performance of UWB systems highly sensitive to timing errors such as jitter

and drift. This can become a major issue in the success of pulse-position

modulation (PPM) receivers, which rely on detecting the exact position

of the received signal.

5.4 MULTIPLE-ACCESS INTERFERENCE

In a multiuser or a multiple-access communications system, different

users or devices send information independently and concurrently over a

shared transmission medium (such as the air interface in wireless communications).

At the receiving end, one or more receivers should be able

to separate users and detect information from the user of interest. Interference


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from other users with the user of interest is called multiple-access

interference (MAI), which is a limiting factor to channel capacity and the

performance of such receivers. The addition of MAI to the unavoidable

channel noise and narrowband interference discussed earlier can significantly

degrade the low-powered UWB pulses and make the detection process

very difficult. separating each user’s information from the

combination of heavily distorted and low-powered UWB signals from all

users is a very challenging task. A comprehensive study of multiple-access

techniques in UWB systems

5.5 Hot Spot or PAN

Personal Area Networks are quite naturally the first application field of UWB. However, several significant advantages could be obtained if also the hot spot network layer could be covered. From a marketing strategy point of view a dual-function technology such as UWB with both PAN and hot spot (WLAN) functionality would be easier to push into the market.

While other customers would be especially interested in hot spot UWB products, others might prefer home applications and PAN connectivity. The number of sold units in both user groups together would grow much more quickly than in the case


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of single purpose technology, bringing up a strong positive feedback to UWB adoption due to network externalities. Personal area UWB users would find the technology even more attractive with the emergence of UWB hot spots, and vice versa.

As very often in consumer electronics, network externalities play a very big role in technology adoption, especially in telecommunications related products. For this reason, to support the demand side economies of scale also from the hot spot market sector, the hot spot functionality of UWB technology should appear a very appealing topic for research despite current problems with slow synchronization times in multi-user bursty-traffic environments.

5.6 Low Cost

Low cost is an essential ingredient in the success of future UWB systems. There are numerous wireless broadband technologies capable of high speeds and long ranges, but the essence of UWB is in low power consumption and low cost due to simplified RF hardware compared to traditional systems (Foerster et al., 2001). If something needs to be traded off in the development of UWB consumer products let it be the 1 Gb/s speed envisioned by some, not the low cost or power consumption. Even with significantly lower data rates UWB seems to be capable of spatial capacity far better than existing wireless systems (Foerster et al, 2001).

The available spectrum for UWB systems was set to 3.10-10.6 GHz in the “First Report and Order” released by FCC in February 2002. Hopefully the consequence of this is not a higher complexity and cost of required RF hardware, caused by “frequency transposing” of earlier systems using frequencies between near DC and a few GHz.


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5.7 MAC for UWB

One drawback of current UWB technology is the long channel acquisition time, probably several milliseconds, which is tenfold compared to 1 microsecond of IEEE 802.11 systems. Tailored medium access protocols (MAC) are needed in order to get maximal performance out of UWB systems (Ding et al., 2002).

The first company to demonstrate UWB products, Xtreme Spectrum, Inc., has made use of the new 802.15.3 (WiMedia) standard in its UWB system taking a personal area network approach. However, being originally aimed at 2.4 GHz wireless technology, the 802.15.3 is not an ideal solution for UWB. Fast channel acquisition, optimal packet sizes and means to acquire precise positioning and timing information are issues to be dealt with in creating a new, UWB-tuned MAC protocol.

6 ADVANTAGES

The nature of the short-duration pulses used in UWB technology offers

several advantages over narrowband communications systems. In this

section, we discuss some of the key benefits that UWB brings to wireless

communications.

6.1 ABILITY TO SHARE THE FREQUENCY SPECTRUM

The FCC’s power requirement of –41.3 dBm/MHz,5 equal to 75 nanowatts/


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MHz for UWB systems, puts them in the category of unintentional

radiators, such as TVs and computer monitors. Such power restriction

allows UWB systems to reside below the noise floor of a typical narrowband

receiver and enables UWB signals to coexist with current radio services

with minimal or no interference. However, this all depends on the

type of modulation used for data transfer in a UWB system.

some modulation schemes generate undesirable

discrete spectral lines in their PSD, which can both increase the

chance of interference to other systems and increase the vulnerability of

the UWB system to interference from other radio services.

we present a detailed discussion on interference from UWB on narrowband

and wideband radio systems. the general idea

of UWB’s coexistence with narrowband and wideband technologies.

6.2 LARGE CHANNEL CAPACITY

One of the major advantages of the large bandwidth for UWB pulses is

improved channel capacity. Channel capacity, or data rate, is defined as

the maximum amount of data that can be transmitted per second over a

communications channel. The large channel capacity of UWB communications

a system is evident from Hartley-Shannon’s capacity formula:


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where C represents the maximum channel capacity, B is the bandwidth,

and SNR is the signal-to-noise power ratio.

channel capacity C linearly increases with bandwidth B. Therefore, having

several gigahertz of bandwidth available for UWB signals, a data rate

of gigabits per second (Gbps) can be expected. However, due to the FCC’s

current power limitation on UWB transmissions, such a high data rate is

available only for short ranges, up to 10 meters. This makes UWB systems

perfect candidates for short-range, high-data-rate wireless applications

such as wireless personal area networks (WPANs). The trade-off between

the range and the data rate makes UWB technology ideal for a wide array

of applications in military, civil, and commercial sectors.

6.3 ABILITY TO WORK WITH LOW SIGNAL-TO-NOISE RATIOS

The Hartley-Shannon formula for maximum capacity

also indicates that the channel capacity is only logarithmically dependent

on signal-to-noise ratio (SNR). Therefore, UWB communications systems

are capable of working in harsh communication channels with low

SNRs and still offer a large channel capacity as a result of their large

bandwidth.


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6.4 LOW PROBABILITY OF INTERCEPT AND DETECTION

Because of their low average transmission power, as discussed in previous

sections, UWB communications systems have an inherent immunity to

detection and intercept. With such low transmission power, the eavesdropper

has to be very close to the transmitter (about 1 meter) to be able

to detect the transmitted information. In addition, UWB pulses are time

modulated with codes unique to each transmitter/receiver pair. The time

modulation of extremely narrow pulses adds more security to UWB

transmission, because detecting picosecond pulses without knowing

When they will arrive is next to impossible. Therefore, UWB systems hold

significant promise of achieving highly secure, low probability of intercept

and detection (LPI/D) communications that is a critical need for

military operations.

6.5 RESISTANCE TO JAMMING

Unlike the well-defined narrowband frequency spectrum, the UWB spectrum

covers a vast range of frequencies from near DC to several gigahertz

and offers high processing gain for UWB signals. Processing gain (PG) is

a measure of a radio system’s resistance to jamming and is defined as the

ratio of the RF bandwidth to the information bandwidth of a signal:


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The frequency diversity caused by high processing gain makes UWB signals

relatively resistant to intentional and unintentional jamming,

because no jammer can jam every frequency in the UWB spectrum at

once. Therefore, if some of the frequencies are jammed, there is still a

large range of frequencies that remains untouched. However, this resistance

to jamming is only in comparison to narrowband and wideband

systems. Hence, the performance of a UWB communications system can

still be degraded, depending on its modulation scheme, by strong narrowband

interference from traditional radio transmitters coexisting in the

UWB receiver’s frequency band

6.6 HIGH PERFORMANCE IN MULTIPATH CHANNELS

The phenomenon known as multipath is unavoidable in wireless communications

channels. It is caused by multiple reflections of the transmitted

signal from various surfaces such as buildings, trees, and people. The

straight line between a transmitter and a receiver is the line of sight

(LOS); the reflected signals from surfaces are non-line of sight (NLOS).

the multipath phenomenon in narrowband and UWB signal

the effect of multipath is rather severe for narrowband


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signals; it can cause signal degradation up to –40 dB due to the

out-of-phase addition of LOS and NLOS continuous waveforms. On the

other hand, the very short duration of UWB pulses makes them less sensitive

to the multipath effect. Because the transmission duration of a

UWB pulse is shorter than a nanosecond in most cases, the reflected pulse

has an extremely short window of opportunity to collide with the LOS

pulse and cause signal degradation.

Although the short duration of UWB pulses makes them less sensitive to

multipath effects compared to narrowband signals, it doesn’t mean that

UWB communications is totally immune to multipath distortion.

Research on UWB channel modeling has shown that depending on the

UWB modulation scheme used, low-powered UWB pulses can become

significantly distorted in indoor channels where a large number of objects

and scatterers are closely spaced.

For a comprehensive discussion on various UWB modulation techniques

and their performance in multipath channels.

6.7 SUPERIOR PENETRATION PROPERTIES

Unlike narrowband technology, UWB systems can penetrate effectively

through different materials. The low frequencies included in the broad

range of the UWB frequency spectrum have long wavelengths, which


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allows UWB signals to penetrate a variety of materials, including walls.

This property makes UWB technology viable for through-the-wall communications

and ground-penetrating radars. However, the material penetration

capability of UWB signals is useful only when they are allowed to

occupy the low-frequency portion of the radio spectrum.

6.8 SIMPLE TRANSCEIVER ARCHITECTURE

UWB transmission is carrierless,meaning that data is not modulated on a continous waveform with a specificcarrier frequency, as in narrowband and wideband technologies.

Carrierless transmission requires fewer RF components than carrierbased

Transmission. For this reason UWB transceiver architecture is significantly

simpler and thus cheaper to build. the UWB transceiver architecture is considerably

less complicated than that of the narrowband transceiver. The transmission

of low-powered pulses eliminates the need for a power amplifier

(PA) in UWB transmitters. Also, because UWB transmission is carrierless,

there is no need for mixers and local oscillators to translate the carrier

frequency to the required frequency band; consequently there is no

need for a carrier recovery stage at the receiver end. In general, the analog

front end of a UWB transceiver is noticeably less complicated than that of


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a narrowband transceiver. This simplicity makes an all-CMOS (short for

complementary metal-oxide semiconductors) implementation of UWB

transceivers possible, which translates to smaller form factors and lower

production costs.

Advantage Benefit

Coexistence with current narrowband and

wideband radio services

Avoids expensive licensing fees.

Large channel capacity High bandwidth can support real-time highdefinition

video streaming.

Ability to work with low SNRs Offers high performance in noisy environments.

Low transmit power Provides high degree of security with low probability

of detection and intercept.

Resistance to jamming Reliable in hostile environments.

High performance in multipath channels Delivers higher signal strengths in adverse

conditions.

Simple transceiver architecture Enables ultra-low power, smaller form factor,

and better mean time between failures, all at a

reduced cost.


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7 Wider Applications of UWB

The concept of a UWB radio spans many different applications and industries and has been coined the "common UWB radio platform." The UWB radio, along with the convergence layer, becomes the underlying transport mechanism for different applications, some of which are currently only wired. Some of the more notable applications that would operate on top of the common UWB platform would be wireless universal serial bus (WUSB), IEEE 1394, the next generation of Bluetooth, and Universal Plug and Play (UPnP). You can see a diagram of this vision in Figure 1.


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This concept has many potential applications since it creates the first high-speed wireless interconnects. UWB technology offers a combination of performance and ease of use unparalleled by other interconnect options available today.

Presently, wired USB has significant market segment share as the cable interconnect of choice for the PC platform. But the need for the cable itself points to convenience and usability challenges for users. By unleashing peripheral devices from the PC while still providing the performance users have come to expect from wired USB connections, wireless USB running on ultra wideband promises to gain significant volume in the PC peripheral interconnect market segment.

An example application for UWB would be bringing a mobile device like a portable media player (PMP) in proximity to a content source like a PC, laptop, or external hard disk drive. Once authentication and authorization is established, the device and PC can perform bulk data transfer of video files onto the PMP for later viewing.

Within the consumer electronics industry, there is demand for wirelessly connecting various devices such as DVDs, HDTVs, set-top boxes (STBs), PVRs, stereos, camcorders, digital cameras, and other CE devices. Wireless ease of use and data transfer performance is a key factor for adoption in this category.

For example, wireless connectivity would be ideal for a wall-mounted plasma display where, for aesthetic reasons, users prefer not to have cables from an STB or Entertainment PC visible. A variation on this usage model is the ability to stream content to multiple devices simultaneously. This would allow picture-in-picture functionality or viewing of the same or different content on multiple viewing devicesDue to the extremely low emission levels currently allowed by regulatory agencies, UWB systems tend to be short-range and indoors applications. However, due to the short duration of the UWB pulses, it is easier to engineer extremely high data rates, and data rate can be readily traded for range by simply


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aggregating pulse energy per data bit using either simple integration or by coding techniques. Conventional OFDM technology can also be used subject to the minimum bandwidth requirement of the regulations. High data rate UWB can enable wirelessmonitors, the efficient transfer of data from digital camcorders, wireless printing of digital pictures from a camera without the need for an intervening personal computer, and the transfer of files among cell phone handsets and other handheld devices like personal digital audio and video players.

UWB is used as a part of location systems and real time location systems. The precision capabilities combined with the very low power makes it ideal for certain radio frequency sensitive environments such as hospitals and healthcare. Another benefit of UWB is the short broadcast time which enables implementers of the technology to install orders of magnitude more transmitter tags in an environment relative to competitive technologies. U.S.-based Parco Merged Media Corporation was the first systems developer to deploy a commercial version of this system in a Washington, DC hospital.

UWB is also used in "see-through-the-wall" precision radar imaging technology, precision locating and tracking (using distance measurements between radios), and precision time-of-arrival-based localization approaches. It exhibits excellent efficiency with a spatial capacity of approximately 1013 bit/s/m²

UWB has been a proposed technology for use in personal area networks and appeared in the IEEE 802.15.3a draft PAN standard. However, after several years of deadlock, the IEEE 802.15.3a task group[ was dissolved in 2006. Slow progress in UWB standards development, high cost of initial implementations and performance significantly lower than initially expected are some of the reasons for the limited success of UWB in consumer products, which caused several UWB vendors to cease operations during 2008 and 2009

8 Conclusions

UWB holds great promises in high data rate wireless communications over short distances. Primarily UWB is suitable for wireless home applications and personal


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area networks. A secondary target is medium range applications including hot spot networking.

In order for UWB to be beneficial for both consumers and the ICT industry, some aspects need to be taken into account by researchers, corporations involved, regulation authorities, and standard makers. The success of UWB systems needs the support of:

Low cost of hardware – low cost fuels broad adoption which is essential for network externalities to emerge. Especially specific band filtering requirements can be a threat to the simplicity and low cost of UWB equipment.

Open standards – with open standards UWB can become a universal wireless language for an unprecedentedly broad range of hardware

Ubiquitous market presence – a divided market of competing standards and incompatible products is what customers don’t want, so the industry shouldn’t want it either

WLAN range operation – heterogeneous networking with UWB hot spots would enable tiny dual-mode terminals (cellular + UWB) and synergy advantages with computer and home appliance industry. Further research is needed to see whether hot spot UWB is a viable concept.

Deployment of IPv6 – personal area networking with UWB brings up the need for IP addresses for a growing number of gadgets: digital cameras, digital video cameras, home stereo systems, and so forth

Regulation – field testing and accumulating practical experience hopefully helps in setting up regulations appropriate for UWB spectrum usage.


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Despite the challenges on the way, UWB is certainly coming and the technology probably matures to the level of product launches earlier than expected. However, the forecasts expecting retail products in the end of 2003 seem optimistic.

In the US the pace of research and the governmental interest towards the technology seem strong. European legislators should not let the US and Japan markets get too big an advantage by leaving behind with the regulatory process. European researchers must also work hard in order to stay competitive in the race for UWB related patents.

From the point of view of mobile terminal manufacturers and telecom operators UWB technology is not a threat, but just a new technical piece in the puzzle. In mobile terminals UWB can be used for interconnecting terminals and other information equipment and perhaps for establishing Internet access via medium range UWB hot spots.

Telecom operators may not be interested in the PAN functionality of UWB, but the overall growth of equipment capable of IP based communication is a certainly business issue for telecom operators due to economies of scale in high bandwidth service provision. The concept of wireless high bandwidth solutions in everyday use in homes and offices enables new data intensive multimedia services, which could boost both network access and service provision business. .


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9 Bibliography

9.1References

1 .www.wikapedia.com

2 .www.seminar.com

3 .www.scribd.com

4 .www.google.com

5 .www.seminarppt.com

6 .www.arga.net

7 .www.yahoo.com


http://www.yahoo.com/

http://www.arga.net/

http://www.seminarppt.com/

http://www.google.com/

http://www.scribd.com/

http://www.seminar.com/

http://www.wikapedia.com/

Ultra Wideband Communication

Documents

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