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DVANCES IN OMMUNICATIONS AND EDIA ESEARCH

A C M R DVANCES IN OMMUNICATIONS A C

AND EDIA ESEARCH

M R

OLUME

  V

  12

  

A DVANCES IN C OMMUNICATIONS

AND M EDIA R ESEARCH

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  A DVANCES IN C OMMUNICATIONS AND M EDIA R ESEARCH A DVANCES IN C OMMUNICATIONS AND M EDIA R ESEARCH

  V OLUME

  12 A NTHONY

V. S TAVROS E

  

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  ONTENTS C Preface vii

  Chapter 1 From Software to UWB Radio Communications:

  1 A Brief Introduction Vasilis Christofilakis, Giorgos Tatsis,

Constantinos I. Votis and Panos Kostarakis

  Chapter 2 Wideband Slotted Microstrip Antennas

  35

  for Modern Applications

  Amel Boufrioua

  Chapter 3 Device-to-Device Communications

  in 5G Networks: Technical Challenges

  57

  and Security Issues

  Anargyros J. Roumeliotis and Athanasios D. Panagopoulos

  Chapter 4 The Use of Mobile Devices to Support Young 101 People with Disabilities Damian Maher and Kirsty Young Chapter 5 On the Singular Optimal Control 127

  of Switched Systems

  Vadim Azhmyakov and Carlos M. Velezy vi Contents

Chapter 6 A Pedagogical Proposal to Support the Teaching

  of History with Audiovisual Content, Including Video Game Advertising: The Example of Assassin`s Creed IV: Black Flag

  145

  and Privateer Amaro Pargo

  Enrique Carrasco Molina Index

  165

  

REFACE

P

  In a society predicated on information, the media has a pervasive presence. From government policy to leisure television, the information age touches us all. The papers collected in this book constitute some of today's leading analyses of the information industry. Together, these essays represent a needed foundation for understanding the present state and future development of the mass media. Current trends in communications as well as media impact on public opinion are studied and reported on. Topics include a brief introduction on software radio to ultra wideband radio communications; wideband slotted microstrip antennas for modern applications; Device-to- Device (D2D) communication in 5G networks; the use of mobile devices to support young people with disabilities; and singular optimal control of switched systems. The final chapter is a proposal to support the teaching of history with audiovisual content, including video game advertising.

  Chapter 1

• – Sixteen years after the dawn of the new millennium, strong trends in telecommunications drive to adaptable wideband communication systems. This effort is primarily motivated by two technological concepts: software radio (SWR) and ultra wideband (UWB) communications. The design, development and implementation of SWR involve either hardware or software challenges such as analog to digital and digital signal processing speed, power consumption, waveform application portability, software modularity. Upon completing all these challenges and with the enormous advantages of UWB communications, fully programmable, unlicensed, low power radios, minimizing interfering with other systems, will be realized. Furthermore, due to the large spectral coverage, UWB communications show

viii Anthony V. Stavros and UWB technological concepts, and it presents benefits of this combination as well as limitation and bottlenecks arising. Definition, scope, motivation and a brief history of both technologies are also presented.

  Chapter 2 – Today, the state of the art antenna technology allows the use of different types and models of antennas, depending on the area of application considered. With the rapid development of wireless communications, it is desirable to design small size, low profile and wideband multi-frequency planar antennas. The difficulty of antenna design increases when the number of operating frequency bands increases. The slot loaded patch antenna is used to overcome this problem. This chapter is focused on the multi-band application of the microstrip patch antenna, which is analysed by introducing different slots as U and L-shaped slots in rectangular and circular patches. The effects of different physical parameters on the characteristics of the structure are investigated. The results in terms of return loss, bandwidth and radiation pattern are given. The proposed structures can be scaled to meet different frequencies of wireless communication systems just by changing the dimension of the main antenna. Comparisons of return loss and radiation pattern for the same area of the rectangular and circular patches loaded with slot is also given. Moreover, U-slot loaded rectangular patch antenna in a stacked geometry with U-slot loaded circular patch antenna and vice versa are analysed. The results show that dual wide bands can be achieved and a better impedance matching for the upper and lower resonance can be obtained. Also, it is observed that various antenna parameters are obtained as a function of frequency for different values of slot length and width. It is easy to adjust the upper and the lower band by varying these different antenna parameters. The theoretical results using Matlab are compared with the simulated results obtained from Ansoft HFSS which are in close agreement. Furthermore, comparative studies between our results and those available in the literature is done and showed to be in good agreement.

  Chapter 3 – The present chapter deals with the concept of Device-to- Device (D2D) communication networks, their technical implementation and security challenges. The first part is an introduction discussing briefly the basic characteristics of D2D communications and their inclusion in the upcoming 5G cellular systems as well as the importance of secure wireless communications. Afterwards an overview of D2D framework follows and its standardization history with future enhancements are described. Moreover, the

  5G requirements and key enablers are indicated and the importance of the

  Preface ix are presented and the physical layer security techniques are mentioned emphasizing in the secrecy capacity metric. Additionally, the integration of secrecy capacity in D2D systems is surveyed and discussed. Finally, the chapter concludes with future trends of D2D technology towards its integration in the 5G communications.

  Chapter 4

• – Emerging evidence suggests mobile devices have the potential to deliver students with disabilities a more equitable education, which is one of the goals set down by the United Nations. The focus of this chapter is to explore how mobile devices can be used to support young people with communication disabilities and communication difficulties as a result of isolation. The chapter draws upon international legislation and policy documents, research literature and uses a specific case study to highlight the implications and future directions.

  Chapter 5 – This paper studies a singular case of Optimal Control Problems (OCPs) governed by a class of switched control systems. The authors propose a new mathematical formalism for this type of switched dynamic systems and study OCPs with a quadratic cost functionals. The original sophisticated optimization problem is next replaced by an auxiliary “weakly relaxed” OCP. Our main result includes a formal proof of the local convexity property of the obtained auxiliary OCP. The convex structure of the OCP implies a possibility to apply a variety of powerful and relatively simple optimization schemes to the sophisticated singular OCP involving switched dynamics. The conceptual numerical approach the authors finally develop includes an optimal switching times selection ( “timing”) and a simultaneous optimal switched modes sequence scheduling ( “sequencing”).

  Chapter 6 – Based on the analysis of a documentary included in the advertising campaign to promote the game Assassin`s Creed IV: Black Flag

  (2013

  ), this study proposes to take, as a methodological resource, view and analyze various audiovisual resources in order to improve teaching specific aspects of the subjects of History in different education levels. Although such games affect their access to age 18, certain content could be shown to students with slightly lower ages.

  The authors selected as an example a documentary on the life of Spanish privateer born in Tenerife (Canary Islands), Amaro Pargo, a character who lived during the golden age of piracy (XVIII Century) which has been produced by the Spanish delegation of the French multinational Ubisoft.

  The documentary recreates a scientific and archaeological study that x Anthony V. Stavros Santo Domingo (La Laguna), and how the bones of the privateer were exhumed.

  Thanks to the explanation of Pargo`s life and socio-historical context we can understand how marine life was, how were the trips and stopovers in the Canary Islands and other islands, and how new colonial territories overseas were described.

  This chapter attempts to demonstrate the effectiveness of including in the curriculum content and audiovisual pieces that recreate environments such as those proposed by Assassin`s Creed universe, an imaginative entertainment series that discovers interesting details that are inspired by various historical periods as the French Revolution , or the Seven Years’ War, among others, and include the active presence of some characters actually existed, as Amaro Pargo (in the documentary) or pirate Blackbeard (in the videogame). In: Adv. in Communications and Media. Vol. 12

  ISBN: 978-1-53610-979-5 Editor: Anthony V. Stavros © 2017 Nova Science Publishers, Inc.

Chapter 1 ROM OFTWARE TO ADIO F S UWB R OMMUNICATIONS C : RIEF NTRODUCTION A B I

• *

  Vasilis Christofilakis , Giorgos Tatsis,

  Constantinos I. Votis and Panos Kostarakis

  

Physics Department, Electronics-Telecommunications and

Applications Lab, University of Ioannina, Ioannina, Greece

BSTRACT

A

  Sixteen years after the dawn of the new millennium, strong trends in

telecommunications drive to adaptable wideband communication

systems. This effort is primarily motivated by two technological

concepts: software radio (SWR) and ultra wideband (UWB)

communications. The design, development and implementation of SWR

involve either hardware or software challenges such as analog to digital

and digital signal processing speed, power consumption, waveform

application portability, software modularity. Upon completing all these

challenges and with the enormous advantages of UWB communications,

fully programmable, unlicensed, low power radios, minimizing

interfering with other systems, will be realized. Furthermore, due to the

large spectral coverage, UWB communications show little loss of

  2 Vasilis Christofilakis, Giorgos Tatsis, Constantinos I. Votis et al.

  

penetration in the materials, making it a perfect candidate for emergency

applications and harsh environments. This chapter focuses on SWR and

UWB technological concepts, and it presents benefits of this combination

as well as limitation and bottlenecks arising. Definition, scope,

motivation and a brief history of both technologies are also presented.

  

NTRODUCTION

  I The invention of the term

  “Software Radio” in the early 90’s [1] marked the beginning of the transition from digital radios to fully programmable software radio platforms. In the literature we find several definitions for the term

  “Software Radio.” In [2] the concept of SWR is defined as follows: “Software Radio” is an emerging technology, thought to build flexible

   radio systems, multi-service, multi-standard, multi-band, reconfigurable and reprogrammable by software. The following definition is given by [3]: “Software radio” means different things to different people - the common

   ground perhaps is the recognition that the pace of advance in digital and software technologies is not slackening and that these technologies will have a profound impact upon future terminals, not simply mobile phone terminals, but all kinds of consumer devices, ranging from multimedia digital set-top boxes to new Internet-TV products. In [1] Joseph Mitola defines software radio concept as follows:

   “A software radio is a set of Digital Signal Processing primitives, a meta- level system for combining the primitives into communications systems functions and a set of target processors on which the software radio is hosted in real-time communications. ” In fact, all SWR's definitions are covered by the following statement [4]: “The placement of the A/D/A converters as close to the antenna as 

  From Software to UWB Radio Communications

  3 However, even if future state of the art A/D/A converters are capable of capturing/transmitting wideband RF signals, something that should not be ignored is the fact that, in practice, it is inevitable to eliminate hardware- dependent stages [5, 6]. Just for this reason the Software Radio (SWR) is an ideal system, often found in the literature using the term Software Defined

1 Radio (SDR) , which is the functional version of the ideal Software Radio [7].

  Ultra-Wideband (UWB) technology has recently attracted the attention of both academia and industry for applications in wireless telecommunications. This technology has many advantages, such as better immunity to multipath, low power consumption, low interference. UWB systems promise high data rates of the order of 100Mbps, suitable for multimedia applications. Also, due to the large spectral coverage, UWB signals present small penetration loss through materials and, therefore, are appropriate in short-range radar and imaging systems, ground penetration radars, wall radar imaging, vehicular radar systems for collision avoidance, guided parking, etc., surveillance systems and medical imaging. Wireless communication applications are also on the scope, including wireless home networking, UWB wireless computer peripherals such as mouse, keyboard, speakers, printers, wireless USB, wireless sensors networks etc. Back on April 2002 the Federal Communications Commission (FCC) at USA approved the use of UWB technology for wireless applications. The corresponding standards, the IEEE 802.15.3a (short range, high data rate) and the EEE 802.15.4a (low power, low data rates) have been introduced [8].

  The design, development and implementation of UWB-SWRs, capable of operating within 3.1 to 10.6GHz band, with bandwidth at least 500MHz, involves either hardware or software challenges such as wide bandwidth ADC’s, digital signal processing throughput, power consumption, waveform application portability, software modularity [9-13]. Upon completing all these challenges and with the enormous advantages of UWB communications, reconfigurable, unlicensed, low power radios, minimizing interfering with other systems, will be realized. Especially in disaster or crisis areas, where various military, police, fire department and other rescue forces are acting, SWR is the ideal solution since it has the capability to access different bands and frequency ranges of the radio spectrum. Additionally, in disaster or crisis areas, the environment is likely to be altered due to demolished buildings, dust and fire, making UWB communications a perfect candidate for such harsh environments since they show little loss of penetration in the materials.

  4 Vasilis Christofilakis, Giorgos Tatsis, Constantinos I. Votis et al.

  This chapter gives the reader an opportunity to understand Software Radio and ultra wideband technological concepts as well as the tremendous advantages arising from a UWB-SWR platform.

  VERVIEW SWR O

  An ideal software radio system essentially uses only four primitives which are: the Antenna, the A/D/A, the Digital Signal Processing unit and finally the

  User Interface

  (Figure 1). It should be clear to the reader that a multi-hardware radio is not a software radio. As shown in Figure 2(a) a multi-hardware radio system can support different operating standards having discrete hardware for each channel. Each channel has a different carrier frequency and channel bandwidth and is selected through frequency dependent passive components both for heterodyne and homodyne (zero-IF) architectures. Homodyne architectures are better than heterodyne concerning issues of complexity and volume, but suffer from design problems such as I/Q mismatch and DC offset. On the other hand, in the SWR all channels are digitized/transmitted through a wideband A/D/A and the desired channel is digitally selected via the digital signal processing unit (Figure 2(b)).

  From Software to UWB Radio Communications

  5 Figure 2. (a) Multi-hardware Radio System, (b) Software Radio.

  Figure 3. Software radio functions.

  6 Vasilis Christofilakis, Giorgos Tatsis, Constantinos I. Votis et al.

  As shown in Figure 3, the SWR Core consists of several modules including security, frequency band, and modulation schemes. Every module (or sub module) in the SWR core could be declared as a class. For example all digital modulation schemes could be declared as a DModulation class. Instances of this DModulation class are various modulation objects such as fsk() and ask(). The bottom line is that in SWR every radio function can be defined through software running on a fast digital signal processing unit (SWR core).

  The digital signal processing unit could be based on application specific integrated circuit (ASIC), field programmable gate array (FPGA), digital signal processor (DSP) or a combination of the above. In the literature we find additional SWR based on a general processor [14, 15]. Usually, the digital signal processing unit is distinguished according to five criteria [16]. These are:

   Programmability: The ability and method redefining the system to perform all desired functions for different models  Integration: The ability to complete the most functions in a single device, which directs to the reduction of complexity and size of the device.

   Development Cycle: The time from design to implementation of a specific function, depending mainly on software tools and available sources.  Performance: Execution time of specific functions  Power Consumption: Crucial for portable devices An ASIC outperforms others in power consumption and performance, but lacks significantly in programmability which is a primary function of a reconfigurable software radio. The FPGAs have evolved from logical design platforms in digital processing “machines.” An FPGA can achieve higher performance compared to a DSP if properly optimized architecture is implemented. However, to date, FPGAs have been used almost exclusively for fixed point DSP designs. FPGAs have not been viewed as an effective platform for applications requiring high performance floating point computations [17]. Advanced floating-point computations such as matrix inversion, matrix multiply and fast Fourier transform are extremely difficult to

  From Software to UWB Radio Communications

  7 fully or partially reconfiguration with time less than 1ms [20]. On the other hand, run-time reconfiguration time of a DSP is much smaller and primarily depends on DSP cycle time. State of the art DSPs have cycle time less than 1ns [21]. Even now there is not specific digital signal processing unit for SWR architecture. A combination of DSP and FPGA could finally be a natural choice [22-24]. Features, aiming SWR architecture for DSPs and FPGAs, are summarized in the following Table.

  

Table 1. FPGA and DSP features

Feature FPGA DSP Programming Language

  VHDL, Verilog

  C, Assembly, Modeling Tools Performance Depends on architecture Depends on cycle time Consumption Depends on architecture Depends on peripheral Re-configurability Full Full Ease of programming Hardware/Software Software Orientation orientation Figure 4. RF spectrum.

  The A/D/A primitive is also an essential SWR component, especially in the case of the receiver, the implementation of which is at least four times more difficult of the transmitter’s. The question evidently arisen is whether the established technology can succeed the right sampling and quantization of RF signals from 3 KHz to 300

  GHz. For the case of simplicity let’s consider a realistic portion (~3.3%) of the RF Spectrum from 3 KHz to 10GHz (Figure 4). Taking into account that the upper-frequency limit lies at 10 GHz, we conclude that we need A/Ds with sampling rate at least 20 GS/sec, according to the sampling theorem [25]. Based on the latest A/Ds surveys [26, 27], state of the art A/Ds including various technologies and architectures such as Si

  ICs, III-V ICs (semiconductors are synthesized using elements from third and

  8 Vasilis Christofilakis, Giorgos Tatsis, Constantinos I. Votis et al. handle ultra wide band limited signals having frequency components lying even around 20-40GHz [28, 29]. Even if the sampling frequency satisfies the Nyquist criterion and A/D/A converters can handle above 10GHz full power Input/output bandwidths [30, 31, 32] there are other parameters affecting the performance of an A/D/A. Some of these parameters are bit resolution, aperture jitter, differential nonlinearity error (DNL), integral nonlinearity error (INL), full-power analog input bandwidth (FPBW), spurious free dynamic range (SFDR), effective number of bits (ENOB). The parameters just mentioned can play a significant role in real life and can affect the performance of an A/D and thereby the implementation of an ideal SWR [33].

  RIEF

  ISTORY B H

  Software radio’s origins date back to the military communications of the 70’s and 80’s. During that period, besides traditional subjects of cyber warfare, for the first time the focus was on wideband digital techniques which, as mentioned previously, are the beginning of SWR. The concept of SWR began to spread substantially after 1995. A Pioneering military project was the Speakeasy (the military software radio) [34] implemented in two phases from 1992 to 1995 and 1995 to 1997. The main goal of this ambitious project was an operating frequency range from 2 MHz to 2 GHz and interoperability among various waveforms that include STAJ, PACER bounce, Sincgars, Have quick, EPLRS, JTIDS, GPS and technical Narrow Band modulation (AM / FM) but also as spread spectrum direct sequence spread spectrum - DSSS modulation and spread spectrum Frequency Hopping - FH [35]. Eventually, the operating frequency range was between 4 to 400 MHz and the number of waveforms supported much smaller [36]. The military organizations expressed further interest in the SWR technology after the project Speakeasy thus creating a group entitled “Programmable, Modular Communications System – PMCS

  ,” which recommended the creation of the Joint Tactical Radio System (JTRS) [37]. The global interest in this technology led to the creation in 1996 of the Software Defined Radio Forum. The SWR Forum’s aim was to accelerate the spread of technologies relevant to the SWR in wireless telecommunications networks (civil, commercial, military) and participation in the organization of universities, research institutions, companies, industries,

  From Software to UWB Radio Communications

  9 Significant boost to SWR technology was mainly achieved from 1995 to 2005 by research and academic institutions [5, 39-43], but also by international projects such as FIRST (Flexible Integrated Radio Systems Technology), SORT (Software Radio Technology), TRUST (Transparently re- configurable Ubiquitous Terminal), CAST (Configurable radio with advanced software Technology) [44].

  Several manufacturers stepped up their efforts and after 2005 and for the last ten years the SWR concept is applied in the commercial and military market. Anywave Base Station was the first FCC-certified base station system that fully implemented the base transceiver station (BTS) and base station controller (BSC) entirely in software, running on a general-purpose server [45]. Small-form factor (SFF) SDR handheld platform was a joint development between Texas Instruments (TI), Xilinx and Lyrtech as well as a host of leading software tool vendors [46]. Motorola Labs also presented a 100 MHz to 2.5 GHz Direct Conversion CMOS Transceiver for SWR applications [47]. A software defined tactical radio that provides wideband data performance, interoperability with fielded waveforms and covers 30 MHz to 2 GHz was presented by Harris co [48]. Another product was manufactured by Rohde & Schwarz owing to different high-speed data modes and protocols as well as different antijam modes for HF, VHF and UHF [49]. The European Secure Software Defined Radio (ESSOR) is another promising programme which started in 2008. The aim of the ESSOR programme is to develop a European software-defined radio technology in order to improve the capabilities for cooperation in joint inter-country operations. The first phase of the EDA’s ESSOR programme has now successfully ended. In the first phase of the ESSOR program, the parties were Indra from Spain, Radmor from Poland, Saab from Sweden, Selex ES from Italy, Thales Communications & Security from France and Bittium from Finland. The parties are currently in negotiations about the second phase of the program. The most important goal of the second phase is to achieve operational performance for the ESSOR system [50]. Latest research, development and commercial efforts on this promising technology are gathered every year in Wireless Innovation Forum on Communications Technologies and Software Defined Radio [51].

  

COPE AND OTIVATION

S M

  10 Vasilis Christofilakis, Giorgos Tatsis, Constantinos I. Votis et al. applications and leads to solving a variety of restrictions and bottlenecks. The need for a radio system that can support and communicate with all existing types of military radios is the backbone of military applications. A radio system that can not only change the scrambling and encryption but also modulation schemes and channel bandwidth is a highly interesting prospect. A system like that could not only prevent hostile eavesdropping attemps, but also be updated to perform better under certain conditions and different environments.

  Figure 5. 2002: The beginning of broadband (3G), 2008: Global penetration of broadband reaches 10%, 2015: Global penetration of mobile broadband subscribers reaches 47%.

  Regarding the commercial sector, further details, such as size, cost, and user friendliness play a major role. The problem of incompatibility between different standards can also be resolved using SWR technology. As an example, consider the incompatibility of cellular standards from first to the

  From Software to UWB Radio Communications

  11 Japan by NTT DoCoMo. The network had the brand name FOMA and was introduced in May 2001 on a W-CDMA technology. At the time, the overall percentage of other standards such as IS-54, IS-136, usually known as Digital- AMPS (D-AMPS) or TDMA due to the type of multiplexing access, is shown in Figure 5 (2002). IS-95 with 12% percentage was the first CDMA-based digital cellular standard introduced by Qualcomm. All these standards have some common features; on the other hand, each of them requires different technology terminals and base stations (BS). The rapid change after 2006 to broadband has modified the above percentages. In the year 2008, there were 4 billion global mobile-cellular subscriptions. Mobile broadband subscriptions increased almost a thousand times from 2002 to 2008 with global penetration from 0.01% to 10%. (Figure 5 (2008)) [53]. Mobile broadband is the most dynamic market segment; globally, mobile-broadband penetration reaches 47% in 2015, a value that increased 12 times since 2007 [54]. Additionally, new cellular standards and generations, 5G and beyond meant to be created could be run on SWR base stations and mobile terminals. (Figure 6).

  12 Vasilis Christofilakis, Giorgos Tatsis, Constantinos I. Votis et al.

  Furthermore, lack of flexibility and upgrading can create significant security issues. GSM was the prevalent mobile communication technology in 2002, with around 68% of the world-wide market share and over 200 million subscribers. The over-the-air privacy of GSM telephone conversations is protected by the A5 algorithm. The stronger A5/1 version was used by about 130 million customers in Western Europe and North America while another 100 million customers used the weaker A5/2 version. The approximate design of A5/ leaked in 1994, and the exact design of both A5/1 and A5/2 was reverse engineered by Briceno from an actual GSM telephone in 1999 [55]. Only 2 minutes of conversation time (data) and about a few seconds of processing on a PC are fair enough to extract the conversation key [56]. Third Generation cellular communications are protected by the new 128-bit A5/3 algorithm, called Kasumi, a modified version of the MISTY cryptosystem. Although A5/3 block cipher is the most recent version, several weaknesses have already been identified [57]. Security vulnerabilities in mobile communications could be easily resolved through over the air upgradability of SWR platforms.

  UWB O

  VERVIEW

  Ultra-Wideband (UWB) technology is a relatively new entry in the world of telecommunications that has attracted the attention of the scientific community. As its name implies, and according to the definition of the Federal Communication Committee (FCC), a wireless scheme is considered as UWB if the absolute bandwidth occupied is greater than 500 MHz or the fractional bandwidth is over 20%. FCC also has set the limits of the maximum emission power for indoor and outdoor applications in the United States (US), reserving an unlicensed band between 3.1-10.6 GHz in which the maximum radiated power is -41.3 dBm/MHz [58]. The spectral mask released by the FCC in 2002 is depicted in Figure 7. In European Union (EU) accordingly, the ETSI (European Technical Standard Institute) and CEPT (European Conference of Postal and Telecommunications) are still working for these limits. According to the latest at the time report for indoor short-range devices (SRD) the corresponding spectral mask is depicted in Figure 8 [59]. The EU limits are more restricted than those in US, in a manner to avoid interference with other technologies. Special mitigation techniques are required such as Low Duty

  From Software to UWB Radio Communications

  13 power without mitigation band is between 6-8.5 GHz with the same level as the FCC.

  The dominant technique for generating UWB signal in the literature is the use of very short-duration pulses of the order of 1nsec. This scenario is also known as Impulse Radio UWB (IR-UWB) [60], although a multi-band scenario based on Orthogonal Frequency Division Multiplexing (OFDM) is also under study [61, 62]. Typical shapes of the pulses are Gaussian-like or similar to the derivatives of a Gauss pulse. Figure 9 depicts a possible UWB pulse with the form of the first Gaussian derivative and the corresponding spectrum. One may notice how the short duration in time domain spans the frequencies over the spectrum giving the ultra-wideband nature in the signal. Other pulse shapes are also under the scope regarding optimality and spectral compatibility [63]. Also pulsed based UWB systems exploit a variety of modulation types such as Pulse Amplitude Modulation (PAM) including the simplest On-Off Keying (OOK), Pulse Position Modulation (PPM) and Phase Shift Keying (PSK) [64-66].

  Figure 7. FCC spectral mask for UWB.

  14 Vasilis Christofilakis, Giorgos Tatsis, Constantinos I. Votis et al.

  Figure 8. European spectral mask for UWB.

  UWB technology has some significant advantages over conventional narrowband systems.  Low complexity: The UWB signal is by nature a baseband signal, consisting of a sequence of very short baseband pulses. There is no need to use up-down converting stages or mixing with carriers.  Low interference: UWB signal is seen by other coexisting narrowband technologies as a noise-like signal due to its relatively large bandwidth and at the same time the very low transmitting power.

   Resistance to multipath: The enormous bandwidth allows the high multipath resolution, meaning a large number of resolvable paths to the receiver.  High time domain resolution: The use of very short pulses in UWB signals is an asset in the application that requires accuracy in space such as radar, location, posisioning etc.

  From Software to UWB Radio Communications

  15 Figure 9. UWB pulse in time domain (up) and corresponding spectrum (down).

  Several transceiver architectures have been proposed. The implementation of the transmitter is relatively easier than the receiver. The transmitter usually consists of an analog pulse generator that is controlled by software-based devices according to the modulation scheme used. The conventional UWB pulse generator is based commonly on step recovery diodes. A step recovery diode (SRD) can produce a short in time output pulse triggered by a regular square pulse [67-71]. Data modulation can be done using square pulses in digital logic and the SRD circuitry acts as the pulse shaper for the final form of the UWB pulses that are driven finally to an antenna. The receiver on the other side has a more difficult job. Due to the strong impact of the multipath channel the transmitted signal is distorted. The UWB indoor channel impulse response

  16 Vasilis Christofilakis, Giorgos Tatsis, Constantinos I. Votis et al. [72,73]. Figure 10 shows a simulated received waveform through such a channel with strong interference, coming from a single transmitted pulse, having the form of the second Gaussian derivative (Scholtz’s monocycle). One may observe the multiple copies of the initial pulse in different time positions spreading the waveform for several nanoseconds.

  Figure 10. Simulated received UWB waveform in indoor multipath environment.

  Usually, one has to tradeoff the low complexity and simplicity with the performance which tends to be both power and computationally expensive. The energy detector is the simplest approach but with the poorest noise performance. It consists of a square-law device followed by an integrator and the estimation of the symbols is done by the energy output and a predefined threshold. The RAKE receiver on the other hand is an optimized receiver for best performance in multipath channels [74-79]. It exploits the advantage of the high temporal resolution of UWB signals to distinguish different paths. The fingers of the receiver correspond to those paths. The drawback of this system is the complexity. Dense multipath environment may require a large number of fingers that is very difficult to implement. Also, channel estimation is necessary on the receiver side. Another candidate UWB transceiver type is

  From Software to UWB Radio Communications

  17 autocorrelation detection technique. Each pulse actually is correlated with the reference of it which is virtually the same waveform at different time. The advantage of this method is that there is no need to estimate the channel’s response.

  LATFORM ESTRICTIONS AND OLUTIONS UWB-SWR P : R S

  One of the greatest challenges in modern telecommunication systems is a fully software-defined reconfigurable transceiver structures and operations.

  IR-UWB trends to that concept and great effort takes place now days to reach the ideal SDR solution as much as possible. In an ideal SDR transmitter only one Digital to Analog converter (DAC) is able to replace all the analog parts used to generate the transmitted signal, and it just needs to be connected to the software device, processing the logic of the system, and to the antenna, as depicted in Figure 1. In an IR-UWB SDR concept a DAC is used to produce the ultra-short pulse instead of an analog pulse shaper in order to be reconfigurable. Because impulsive UWB technologies essentially are digital in nature — without the attending complexities of RF front-end designs — a variety of such technologies potentially could be realized with the same chipset [87]. In [88] a reconfigurable UWB transceiver is presented. At the transmitter side the authors used a multi-Nyquist DAC (Digital to Analog Converter) that generates the UWB pulse. In order to avoid up-converting stages, the bandpass sampling technique is used [89]. The

  DAC’s sampling rate is 2 GS/s, therefore a pulse of 1 GHz bandwidth is generated, and the RF bandwidth is between 2-3 GHz. The same principle would be implemented for higher frequencies. The limitations of current technology especially in sampling rates of the order of GHz together with the following processing of such enormous data rate lead us to less ideal solutions but yet effective without loss of reconfigurability. A mixed solution with analog components assisted and configured by software (digital part) is a fair compromise between the ideal software radio and a realistic reconfigurable transceiver implementation. The today’s possibilities of components integration into a single chip makes this idea practical. In [90] an IR-UWB reconfigurable transceiver is implemented using distributed circuit techniques, fabricated in a custom 0.18um CMOS chip for this purpose. Both the transmitter and the receiver

  18 Vasilis Christofilakis, Giorgos Tatsis, Constantinos I. Votis et al. authors measured an energy efficiency of 25-pJ/pulse for the transmitter and 190pJ/pulse for the receiver, due to heavy data manipulation that is power consuming, with a maximum of 250 MHz pulse rate. UWB technology is a promising technology with great future and with the capabilities and potential for implementation of a real software radio, although technical obstacles need to be overcome. Regarding A/D and D/A speeds, there has been a remarkable progress in the last years and several GSamples/sec of data rate are already attained [93-95]. The bit resolution is usually about 4-6 bits, and it is notable that even for a resolution of 4 bit is sufficient for a typical UWB pulse detection [96]. On the transmit side it seems that a fully software defined UWB Impulse Radio transmitter is feasible satisfying the low-cost implementation. On the receive side, more effort needs to be made. The pure software-based processing of huge amount of raw A/D data is still a major challenge. A mix of digital and analog components for signal detection that are configured by software is a vital middle ground solution in favor of reconfigurability. Parallel processing techniques, like the ones offered by FPGAs, are needed in order to manage the high data rate that UWB technology handles. [97- 99].

  Digital Real-Time Baseband processing for UWB communications remains a challenging task. Even for real-time modulation/demodulation of typical wireless protocol packets, the digital baseband processor must operate at an efficiency of 100 million operations per second (Mops) per milliwatt (mW). Most embedded DSP and FPGA systems operate at an efficiency of approximately 10 Mops/mW [100]. Low power ultra-wide band digital baseband implementations do exist, but only in a few works are stated to be programmable [101- 103].

  ARDWARE NDEPENDENCE SING MART H U S “I ” NTENNAS UWB A