Teses / dissertações sobre o tema "Ultra wide band optical systems"

Les systèmes ultra-large bande(UWB) sont considérés comme une stratégie rentable pour augmenter le débit par fibre dans les communications optiques en repoussant les limites de la bande passante opérationnelle au-delà de la bande C. Des expériences récente sont présenté des résultats prometteurs avec des transmissions à haute capacité UWB fonctionnant à travers les bandes S+C+L, et même au-delà. Ces avancées soulèvent la question des avoir si cette technologie peut être efficacement mise à l'échelle pour répondre aux demandes croissantes de trafic de données. Cette thèse fournit une étude approfondie sur les opportunités et les défis des systèmes UWB. À travers l'analyse de modèles qui tiennent compte des dégradations dépendant de la longueur d'onde, le cœur de cette thèse consiste en le développement et la validation de techniques d'optimisation de puissance basées sur ces modèles, conçues pour améliorer la performance des systèmes UWB. L'étude réalisée comprend des évaluations numériques et expérimentales des systèmes S+C+L. De plus, la précision des prédictions obtenues dans cette étude offre des aperçus précieux sur la qualité de transmission, parmi lesquels une analyse des implications associées à d'éventuelles défaillances du système UWB. Enfin, cette thèse envisage une vision pour l'avenir de cette technologie, discutant de la faisabilité de l'adoption des systèmes UWB par rapport au déploiement de systèmes parallèles en fibre
Ultra-wideband systems (UWB)are considered a cost-effective strategy to boostthe per-fiber through put in optical communications by pushing the boundaries of operational bandwidth beyond the conventional C-band. Recent experiments have showcased promising results with UWB high-capacity transmissions operating across the S+C+L bands, and evenfurther. These advancements raise the question of whether this technology can be effectively used to meet the growing demands for data traffic.This thesis provides an extensive investigation in to the opportunities and challenges ofUWB systems. Through the analysis of models that address the challenging wavelength dependent impairments, the core of this thesis consists in the development and validation of model-based power optimization techniques designed to enhance UWB system performance. The investigation is performed in numerical and experimental assessments in S+C+L systems. Moreover, the accurate model-based predictions obtained in this study offer invaluable insightsinto the transmission quality. These include ananalysis of the implications associated with potential UWB system failures. Finally, this thesis casts a vision for the future of this technology,discussing the feasibility of adopting UWBsystems over the deployment of parallel fibersystems

Depuis quelques années le nouveau paradigme d'internet des objets, qui se traduit par la connexion des objets de la vie quotidienne à internet grâce à des dispositifs électroniques intégrés, est devenu plus qu'un simple concept et a commencé à entrer dans la réalité. Il en est ainsi des systèmes d'identification par radiofréquence (RFID), qui font partie des technologies disponibles. Lorsque le coût et la taille des tags deviennent des exigences prépondérantes, l'adoption de tags (semi-)passifs fondés sur la modulation d'un signal rétrodiffusé représente une solution attractive. En outre, l'utilisation de techniques ULB apporte des avantages propres à favoriser le remplacement d'une partie des systèmes RFID actuels qui souffrent de certains défauts tels qu'une trop forte consommation ou une faible robustesse en présence d'interférence. La thèse de doctorat se place dans ce contexte: elle a pour objectif l'étude des systèmes ULB RFID semi-passifs et se situe dans le cadre du projet européen SELECT, qui vise à développer et à évaluer un tel système. La prise de conscience qu'il était fondamental de comprendre les mécanismes électromagnétiques intrinsèques à la communication lecteur-tag, préalablement à la conception du système, s'est traduite par la mise en oeuvre d'une collaboration franco-italienne dans le cadre d'une cotutelle de thèse. C'est donc au départ autour d'une analyse fine et d'une modélisation des aspects antennaires et du canal radio entre le lecteur et le tag que la 1re partie du travail s'est construite. La 2nde partie a exploité ces travaux pour l'élaboration des schémas de modulation et de codage du lecteur et du tag pour les systèmes semi-passifs
In the recent years, the idea of the Internet of Things, that is a pervasive presence of electronics devices embedded in every-day objects, is facing a rapid adoption and will create a new era in the Internet scenario. Among all the technologies, radio frequency identification (RFID) seems one of the most promising. In addition, when tag cost, size and power consumption become stringent requirements, (semi-) passive solutions based on the modulation of the backscatter signal represent a good choice. Thus, this work was developed with the intent to study UWB RFID systems based on the modulation of the backscattered signal considering different related issues. The European Project SELECT gave the motivation to investigate the combination of UWB and RFID technologies, which are expected together to overcome many limitations of current narrowband RFID devices. The consciousness that, before the design of proper system architectures for backscatter communication, it was fundamental to understand the basic EM mechanisms underlying the interaction between readers and tags, was reflected in a wide investigation ranging from EM characterization of backscatter links to the definition and design of signal structures and transmission schemes. This dual need motivated a joint french-italian agreement between two laboratories for the supervision of the thesis. In particular, in the course of the work carried out in France, the analysis of the tag backscattering has been analyzed in several ways, both in ideal and real conditions. The results and competences were then exploited in Italy, in order to study an architecture able to ensure a reliable communication between reader and tag

This thesis presents a study of Distributed Cognitive Power Allocation for multicarrier based Ultra Wide Band (UWB) wireless systems in a point to point configuration as a way of reducing the coexistence interference for low power emission wireless systems in close proximity, as well as combating the increased path loss and fading at longer range by means of a Distributed Cognitive Power Allocation (DCPA) scheme. The Multiband Orthogonal Frequency Division Multiplexing (MB-OFDM) standard for Ultra Wide Band (UWB) wireless data communication is used as the basis in this research. A novel gradient power allocation is developed for channel sharing and partitioning among multiple user with no direct information exchange. A novel game strategy is used to assist the gradient power allocation and guide the behaviour of the homogenous users in order to acquire their target data rate. We show the superiority of our game based approach in terms of convergence and power efficiency through the comparison between our Game based and iterative water-filling based approaches. The strength of our scheme is also gained from a theoretical proof of convergence (demonstrating of the existence of a Nash Equilibrium). Performance analysis is carried out for both frequency selective and frequency none selective channels. Also, performance is evaluated for both interference dominated and noise dominated environments, where the severe interference is caused by the homogenous systems deployed in close vicinity. It is shown that the achievable target date rate is largely constrained by the interference while the performance is not impaired by frequency selective channel in terms of convergence and convergent speed. The methodology is adapted for an extended range scenario, where the protection of the licensed user (Primary user) is taken into consideration as well as the target data rate requirement. A new performance measure called the Power Impact Factor is used to quantify the impact of the power allocation scheme compared with the FCC spectrum mask. This measure is used to quantify the interference generated by cognitive UWB devices in relation to the existing agile services.

Basic properties and new design principles of ultra wideband Vivaldi antennas are presentedand discussed in this paper. The focus will be on the modeling of Vivaldi antenna design curves, by which it is constructed; its simulation results, realization and the measurements.

According to the aim of this research the discussion starts with the review of the previous researches done for Vivaldi antennas. Introductory part of the report also contains the problem description for the current project and the classification of the goals to be achieved. As a theoretical review, the discussion initiates with the definitions anddescription of basic parameters of the antennas and covers a short presentation of UWBpulse-based radar system. The attention will be focused on UWB signals behavior and characterization, their propagation principles and basic troubles stands nowadays. As anapplication the wall penetrating Radar systems will be considered. The major part of thereport holds on the investigation of the design principles of Vivaldi Antenna andoptimization of the key parameters for achieving the best performance for radar. Theending part of the report shows the simulations and measurement results and theircomparisons following with conclusions/discussions.

The report will be supportive for the antenna designers, who work for UWB systems andparticularly for Vivaldi antennas, as long as there are showing up detailed descriptions ofVivaldi antenna characteristics depending on its shape and substrate properties. The modelfor designing Vivaldi antennas, given in this project, can successfully be applied for almostall the cases used in practice nowadays.

Indoor positioning systems have been widely studied in the last decade due to the need of humans for them especially in the large building such as malls, airports, hospitals...etc. Still, there is no suitable precise indoor positioning system which can be implemented for different indoor environments and situations. We should mention military urban and emergency situations. In military urban and emergency response operations, the time is a crucial issue, and a precise positioning system with a clear indoor covering is a highly prerequisite tool to enhance safety. It should be seamless, low, frugal, power efficacious, low cost and supply less meter-level accuracy. In emergency scenarios, we don't have enough flexibility and time to install all anchor nodes in a proper situation that may help to obtain an appropriate accuracy for locating a mobile station, but command centers require observing their operational forces, and rescuers demand to detect potential victims to perform proper care. The most common users for these situations are the firefighters, police, military, and civilians. The main goal of this Ph.D. dissertation is to create an accurate indoor positioning (IP) system that could be used in different indoor environments and situation, especially for the emergency situation. So, we create this system through different steps as explained below. First, we have considered the study of different radio technologies to choose the suitable radio technology called Ultra wide band (UWB) radio technology. The reasons of selection the UWB and the commercial device that implements such technology are explained in details in chapters 3 and 4. Afterward, due to some impacts of the UWB in indoor environments (see chapters 4 and 5), we continue the study of NLOS identification and mitigation methods. In these chapters, we create two different NLOS identification and mitigation methods using a commercial UWB device experimentally. The first method used two parameters extracted from the UWB device to identify the propagation channel and map information of the building that the method is experimentally done in it to mitigate the NLOS channel. The second method of NLOS identification and mitigation used three parameters extracting from the UWB device to be an input set of the Fuzzy logic technique used to identify the propagation channels. In this identification method, it is not only to identify the prorogation channel to NLOS and LOS but also to divide the NLOS channel into hard and soft channels. Then, we created a database that includes the three parameters and the distance Bias to mitigate the NLOS channel for obtaining an accurately estimated distance to be used for creating an accurate IP system. Finally, with the aim of applying our designs to mass market applications, we move to create a novel IP system using the UWB technology called anchor selection (AS). In this technique, we focus on using fewer sensors (anchor nodes) to locate a mobile station under harsh circumstances such as scenarios where the installation area of the anchor nodes is narrow and/or the installation time should be very short. The proposed approach is based on grouping anchor nodes in different sets and evaluating the positioning error of each of these groups by means of a novel mean squared error (MSE)-based methodology. A virtual node approach is also proposed to consider the case where position must be computed with only two anchor nodes.

Wearable technologies need a smooth and unobtrusive integration of electronics and smart materials into textiles. The integration of sensors, actuators and computing technologies able to sense, react and adapt to external stimuli, is the expression of a new generation of wearable devices. The vision of wearable computing describes a system made by embedded, low power and wireless electronics coupled with smart and reliable sensors - as an integrated part of textile structure or directly in contact with the human body. Therefore, such system must maintain its sensing capabilities under the demand of normal clothing or textile substrate, which can impose severe mechanical deformation to the underlying garment/substrate. The objective of this thesis is to introduce a novel technological contribution for the next generation of wearable devices adopting a multidisciplinary approach in which knowledge of circuit design with Ultra-Wide Band and Bluetooth Low Energy technology, realization of smart piezoresistive / piezocapacitive and electro-active material, electro-mechanical characterization, design of read-out circuits and system integration find a fundamental and necessary synergy. The context and the results presented in this thesis follow an “applications driven” method in terms of wearable technology. A proof of concept has been designed and developed for each addressed issue. The solutions proposed are aimed to demonstrate the integration of a touch/pressure sensor into a fabric for space debris detection (CApture DEorbiting Target project), the effectiveness of the Ultra-Wide Band technology as an ultra-low power data transmission option compared with well known Bluetooth (IR-UWB data transmission project) and to solve issues concerning human proximity estimation (IR-UWB Face-to-Face Interaction and Proximity Sensor), wearable actuator for medical applications (EAPtics project) and aerospace physiology countermeasure (Gravity Loading Countermeasure Skinsuit project).

Modern smartphone technology has created a myriad of opportunities in the field of RF and Microwave. Specifically, Chipless RFID sensor, compact microwave filter, antenna based on a microstrip structure, and many more. In this thesis, innovative ideas for the industrial and biomedical device has been explored. The work presents the reconfigurable filter design, Switch-beam antenna, Microwave interferometer, X-band Rotman Lens antenna, Ultra-wideband antenna based on SIW resonator, L-band Stepped Frequency Continuous Wave antenna, development of a wireless sensor system for environmental monitoring, Indoor Air Quality monitoring, and Wildfire Monitoring based on the modulated scattering technique (MST). The MST sensor probes are based on the scattering properties of small passive antennas and radiate part of the impinging electromagnetic field generated by an interrogating antenna, which also acquires the backscattered signal as information. The MST probes are able to deliver data without a radio frequency front end. They use a simple circuit that alternatively terminates the antenna probe on suitable loads to generate a low modulation signal on the backscattered electromagnetic wave. The antenna presented in this work has been designed in ADS Software by Keysight Technologies. The designed antenna has been assessed numerically and experimentally. The experimental measurement data demonstrate the effectiveness of the individual system. Simultaneously, the MST sensor system has been proposed to obtain the best performance in communication range, load efficiency, and power harvesting. The MST sensor has been fabricated and assessed in practical scenarios. The proposed prototype, able to provide a communication range of about 15 m, serves as a proof-of-concept. The acquired measurements of MST demonstrate the accuracy of the data without radio frequency front end or bulky wired connection with the same efficiency of standard wireless sensors such as radio frequency identifier (RFID) or wireless sensor networks (WSN).

Modern smartphone technology has created a myriad of opportunities in the field of RF and Microwave. Specifically, Chipless RFID sensor, compact microwave filter, antenna based on a microstrip structure, and many more. In this thesis, innovative ideas for the industrial and biomedical device has been explored. The work presents the reconfigurable filter design, Switch-beam antenna, Microwave interferometer, X-band Rotman Lens antenna, Ultra-wideband antenna based on SIW resonator, L-band Stepped Frequency Continuous Wave antenna, development of a wireless sensor system for environmental monitoring, Indoor Air Quality monitoring, and Wildfire Monitoring based on the modulated scattering technique (MST). The MST sensor probes are based on the scattering properties of small passive antennas and radiate part of the impinging electromagnetic field generated by an interrogating antenna, which also acquires the backscattered signal as information. The MST probes are able to deliver data without a radio frequency front end. They use a simple circuit that alternatively terminates the antenna probe on suitable loads to generate a low modulation signal on the backscattered electromagnetic wave. The antenna presented in this work has been designed in ADS Software by Keysight Technologies. The designed antenna has been assessed numerically and experimentally. The experimental measurement data demonstrate the effectiveness of the individual system. Simultaneously, the MST sensor system has been proposed to obtain the best performance in communication range, load efficiency, and power harvesting. The MST sensor has been fabricated and assessed in practical scenarios. The proposed prototype, able to provide a communication range of about 15 m, serves as a proof-of-concept. The acquired measurements of MST demonstrate the accuracy of the data without radio frequency front end or bulky wired connection with the same efficiency of standard wireless sensors such as radio frequency identifier (RFID) or wireless sensor networks (WSN).

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Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior
The microstrip antennas are largely used in wireless communication systems due to their low cost, weight, less complex construction and manufacturing, in addition to its versatility. UWB systems have emerged as an alternative to wireless communications over short distances because they offer of higher capacity and lower multipath distortion than other systems with the same purpose. Combining the advantages of microstrip antennas to the characteristics of UWB, it is possible to develop more and more smaller devices, with diverse geometries to operate satisfactorily in these systems. This paper aims to propose alternatives to microstrip antennas for UWB systems operate in the range between 3.1 and 10.6 GHz, with a patch on circular ring. Some techniques are analyzed and employed to increase the bandwidth of proposed antenna: the insertion of a parasitic elements and a rectangular slit in the displaced ground plane. For this, key issues are presented as the basic principles of UWB systems, the fundamental theory of antennas and microstrip antennas. The simulations and experimental characterization of constructed antennas are presented, as well as analysis of parameters such as bandwidth and radiation pattern
As antenas de microfita s?o amplamente utilizadas nos sistemas de comunica??o sem fio devido ?s suas caracter?sticas de baixo custo, peso, menor complexidade de constru??o e fabrica??o, al?m de sua versatilidade. Os sistemas UWB surgiram como uma alternativa ?s comunica??es sem fio de curtas dist?ncias por oferecerem maior capacidade e menor distor??o por multipercurso que outros sistemas com a mesma finalidade. Aliando as vantagens das antenas de microfita ?s caracter?sticas do UWB ? poss?vel desenvolver dispositivos cada vez menores e com geometrias diversificadas para operar satisfatoriamente nesses sistemas. Este trabalho tem como objetivo propor alternativas de antenas de microfita para operar em sistemas UWB, na faixa entre 3,1 e 10,6 GHz, com patch em anel circular. S?o empregadas e analisadas algumas t?cnicas para aumentar a largura de banda das antenas propostas: a inser??o de elementos parasitas e de uma fenda retangular no plano terra deslocado. Para isto, s?o apresentados temas fundamentais como os princ?pios b?sicos dos sistemas UWB, a teoria fundamental de antenas e antenas de microfita. S?o apresentadas as simula??es e caracteriza??es experimentais das antenas constru?das, bem como uma an?lise de par?metros como a largura de banda e o diagrama de radia??o

Having a device with the capability of measure motions from gait produced by a human being, could be of most importance in medicine and sports. Physicians or researchers could measure and analyse key features of a person's gait for the purpose of rehabilitation or science, regarding neurological disabilities. Also in sports, professionals and hobbyists could use such a device for improving their technique or prevent injuries when performing. In this master thesis, I present the research of what technology is capable of today, regarding gait analysis devices. The research that was done has then help the development of a suggested standalone hardware sensor node for a Body Area Network, that can support research in gait analysis. Furthermore, several algorithms like for instance UWB Real-Time Location and Dead Reckoning IMU/AHRS algorithms, have been implemented and tested for the purpose of measuring motions and be able to run on the sensor node device. The work in this thesis shows that a IMU sensor have great potentials for generating high rate motion data while performing on a small mobile device. The UWB technology on the other hand, indicates a disappointment in performance regarding the intended application but can still be useful for wireless communication between sensor nodes. The report also points out the importance of using a high performance micro controller for achieving high accuracy in measurements.

碩士
國立中山大學
光電工程研究所
96
Ultra Wide Band (UWB) is a short-pulse electrical signal, which is widely used for short distant wireless communication due to its low path loss, good immunity to multipath propagation, and high data rate. The main target transmission area of UWB is within 10 meters. Using optical fiber as carrier can bust up the communication capacitance in long distance range because of high capacitance, low loss propagation, and TDM and WDM compatible properties of fiber. Thereby, the technique of UWB on fiber has become more and more important. In this work, a novel method using waveguide photodetector (WP) with short termination for interface of optical fiber and wireless is proposed and demonstrated. The structure is simple without employing any complicated frequency mixer, intermediate frequency, or complex systems. This work is divided into two parts: (1) generation of UWB electrical signals and (2) wavelength conversion of UWB through WP. In the former, a WP with short termination is used in the device. The photocurrent excited by short optical pulse is distributive generated through the waveguide, forming two opposite directions of electrical waves. By reflection on the short termination, the reversed phase of one electrical wave is added to another electrical wave through a delay line, forming a monocycle of UWB signal. By appropriate design on the length of waveguide, the band of 2-10GH is demonstrated, fitting the requirement of FCC (Federal Communications Commission). In the second part of this paper is the wavelength conversion of UWB. The active region of WG is multiple quantum wells (M.Q.W.), which is not only served as photo-absorption layer, but also can be used the electroabsorption material. By pumping M.Q.W.s with high optical power, the cross absorption properties can be applied for wavelength conversion. By pumping power of 12dBm, the wavelength-converted UWB signal is successfully demonstrated at range of 1545nm-1570nm. Using this method, the application of UWB on router of fiber optical network is expectable.

碩士
國立中央大學
電機工程研究所
99
Ultra-wide band (UWB) has huge amount of bandwidth and thus is highly potential in giga-bit data rate transmission. However, to avoid conflict with other existing standard in the same spectrum, UWB’ emit power is restricted under a very low level (almost noise level compare to 802.11n). So the noise problem would be the key point of UWB transceiver design and thus is the main issue of this thesis. To solve this problem, we apply cooperative communication into UWB to form a multi device communication system. The basic idea of cooperative communication is to share antennas to gain diversity between devices in each with only one antenna. This thesis will discuss the UWB cooperation strategy in literatures mentioned. Not only propose a new cooperation strategy, but also we step forward taking the advanced issue into consideration when designing the UWB cooperation system. The proposed cooperation strategy can achieve almost 100% time-spectrum utilization. Besides, based on game theory, the cooperation cost concept is introduced. This concept will indeed affect how the relay to make a decision to join cooperation network under the game theory framework. Considering the cooperation cost, the partial cooperation scheme is also proposed for a more flexible cooperation system. In addition to single transceiver system, the iterative Wiener filter algorithm is proposed for channel estimation. In the last, cooperative network and channel estimation algorithm is analyzed and simulated. Simulation result shows that the performance gains a significant benefit with our proposal.

碩士
長庚大學
電機工程學研究所
97
The wireless high speed transmission won’t satisfy the customer due to the bottleneck of the high-frequency wireless technology. This study focuses on design of an optical ultra-wideband (UWB) pulse train with on-off keying (OOK) modulation scheme for bidirectional multi-carrier radio-over-fiber (ROF) communication systems. The mathematic modeling of multi-carrier UWB system is setup to evaluate the performance of Gaussian-like subcarriers. The generated optical Gaussian-like pulses can provide the several GHz bandwidths and improve the fiber dispersion and inter-symbol interference (ISI) problems for high-bit-rate transmissions. Finally, we set up a practical experimental system to prove our proposed schemes. Compared with the orthogonal subcarrier and Gaussian subcarrier technology, the Gaussian subcarrier UWB system can provide the excellent transmission performance for small channel spacing. Modeling analysis and experiment results demonstrate that the proposed architecture can provide a large capacity and lower interference noise for the multi-channel UWB wireless communications.

博士
淡江大學
電機工程學系博士班
101
The genetic algorithm （GA）, particle swarm optimization （PSO）, asynchronous particle swarm optimization （APSO） and dynamic differential evolution （DDE） are used to optimizing the objective functions (criterion for measuring the effectiveness of the obtained optimized algorithm solution) and solved in indoor ultra-wide band （UWB） communication system. First, the optimal locations of the transmitter antenna for maximum received power in large area (>10m) UWB wireless communication systems with a mobile transmitter and uniformly distributed receivers are evaluated in the whole indoor environment, algorithm optimizers are used to search the best location of the transmitter antenna to maximize the received powers. The number of the receiver points is chosen as the objective function where the received power from any transmitter is less than –40dB. An optimization procedure for the location of the transmitter is employed to minimize the number of the transmitting antennas and maximize the received power in the coverage area. Based on the shooting and bouncing ray/image （SBR/Image） performance, the channel received power for any given location of the transmitter can be computed. The optimal transmitting antenna location for maximizing the received power is searched by algorithms. Obtained simulation results illustrate the feasibility of using the integrated ray-tracing, and optimization methods to find the optimal transmitter locations in determining the optimized coverage of a wireless network. The investigated results can help communication engineers improve their planning and design of indoor wireless communication. Besides, the algorithm are used to search the multiple objective functions which maximize the received power and minimize the bit error rate （BER） in indoor UWB communication system. The impulse responses of different transceiver antenna locations are computed by SBR/Image techniques, and the channel impulse response is further used to calculate corresponding BER. The BER performance of the binary pulse amplitude modulation （B-PAM） impulse radio UWB system is calculated. The objective function is chosen as the number of the receiver points where the received power from any transmitter is less than –40dB or at 100M bps transmission rate and for a BER > 10-6. Numerical results show that the performance for increasing of received power and decreasing of BER by optimization algorithm is quite good. The second part, a circular array of eight UWB printed dipole transmitting antennas, which the excitation voltage and feed length was regulated by algorithm, is used to minimize the BER. The receiving antenna is one UWB dipole antenna. The UWB impulse responses of the indoor channel for any transmitter-receiver location are computed by SBR/Image techniques, inverse fast Fourier transform and Hermitian processing. By using the impulse response of multipath channel, the performance of the B-PAM impulse radio UWB system with circular antenna array can be calculated. Based on the topography of the circular antenna array and the BER formula, the array pattern synthesis problem can be reformulated into an optimization problem and solved by the algorithm. The algorithm is used to regulate the antenna excitation voltage and feed length of each array element to minimize the BER performance of the communication system. Simulation results show that the synthesized antenna array pattern is effective to focus maximum gain to the LOS path which scales as the number of array elements. In other words, the receiver can increase the received signal energy to noise ratio. The synthesized array pattern also can mitigate severe multipath fading in complex propagation environment. As a result, the BER can be reduced substantially in indoor UWB communication system. Moreover, communication characteristic of indoor multiple-input multiple-output （MIMO）UWB circular antenna array is presented. The transmitting and receiving antennas are both circular array of eight UWB printed dipole antennas. By using the frequency responses of multipath channel, the channel capacity of the MIMO-UWB system with circular antenna array can be calculated. Based on the topography of the antenna and the channel capacity formula, the array pattern synthesis problem can be reformulated into an optimization problem and solved by the algorithm. The algorithm is used to regulate the antenna excitation voltage and feed length of each array element to maximize the channel capacity performance of the communication system. The algorithm optimization is applied to a high order nonlinear optimization problem. The novelties of our approach is not only choosing channel capacity as the objective function instead of side-lobe level of the antenna pattern, but also consider the antenna excitation voltage and feed length effect of each array element. The strong point of the algorithm is that it can find out the solution even if the performance index cannot be formulated by simple equations. Obtained simulation results illustrate MIMO-UWB smart antenna transmission dramatically increases channel capacity not only due to the beamforming gain and diversity gain but also MIMO spatial multiplexing technique makes full use of multipath fading.

碩士
長庚大學
電機工程研究所
95
This study focuses on wireless multi-band ultra-wideband (MB-UWB) with orthogonal frequency division multiplexing (OFDM) technology for radio-over-fiber communication systems. This system can provide a high -peed data rate under wireless transmission. In general UWB wireless systems generate output pulses with electronic structure. But the electronic structure is not easy to generate so narrow pulses. However, the optical signal can provide a greatly wide bandwidth, the UWB pulses are easier to generate by the optical devices than to generate by the electronic devices. In this paper, we propose a new scheme to generate Gaussian pulse signals for UWB wireless systems, which is composed of a gain-switched distributed feedback (DFB) laser diode, a electro-absorb modulator(EAM), a filter, a erbium doped fiber amplifier (EDFA) and a pair of sectorized omnidirectional antennas. The generated impulse signal can provide the bandwidths several MHz to GHz for the transmission of high-bit-rate data and fit in with 500MHz for FCC specification. This system has used VPI Transmission Maker software to simulate already. In this paper we experiment it on hardware and prove it can work. We also measure intersymbol interference (ISI) and eye diagram with different channel of center frequency. Use this result to expand for MB-OFDM systems to reduce bandwidth and increase data transmission rate. The proposed scheme can be used for high-bit-rate wireless MB-UWB systems.

碩士
國立中山大學
通訊工程研究所
97
A circuit design of baseband transceiver for direct sequence ultra-wide band system is presented in this thesis. A low complexity Viterbi decoder is also proposed. This Viterbi decoder circuit is based on compare-select-add unit and trace-forward architecture. The decision bit operator is reduced to one adder and this can lower down the hardware complexity. Further, two trace-forward operators are used in the survivor management unit. Only two single port SRAM’s with a length of T are applied for reducing the area of memory. The chip is implemented by TSMC standard 0.18-μm 1P6M CMOS process with core area 1.061 × 1.069 mm2. The post-layout simulation with 1.8V supply at 25 shows that the proposed direct sequence ultra-wide band system of baseband transceiver chip can work above 141 MHz with 86.41 mW power dissipation.

碩士
長庚大學
電機工程學研究所
97
The requirement of transmission data rates is more increasing for wireless communication system in recent years. The Ultra-wideband (UWB) communication technique and system owned the large bandwidth can utilized, high transmission rates and low power consumption, it being the center of attraction for new age wireless communication technique. In this thesis, we utilize the MB-OFDM UWB modulation technique on fiber communication system. This system architecture composed of the MB-OFDM UWB signal modulation development module, distributed feedback (DFB) laser, electro-absorb modulator (EAM), erbium doped fiber amplifier (EDFA), array waveguide grating (AWG), and UWB antennas. This system can provide the data transmission rates from 53Mbps to 480Mbps. The experimental MB-OFDM UWB-over-Fiber communication system demonstrated the transmission data rate can up to 480 Mbps in wireless distance of 1 m. When the transmission data rate is 53 Mbps, the wireless distance can extended to 3 m. It’s also can utilizing the time-frequency code (TFC) to avoid the frequency selective fading and multipath propagation. Take the MB-OFDM UWB technique compared with other modulation (BPSK, OOK) techniques, we can found the received bit error rate will better than other modulation when testing transmission data rates from 53 Mbps to 200 Mbps for wireless distance 1 m to 3 m in indoor environment. Therefore, combing the MB-OFDM UWB and fiber is a suitable transmission way for high speed radio-over-fiber (RoF) communications systems and according for the requirement of high speed wireless communication in future.

碩士
國立中山大學
通訊工程研究所
96
The direct sequence ultra-wideband (DS-UWB) system has the characteristics of low transmission power constraints and wide transmitted bandwidth. The wide bandwidth will introduce fine timing resolution and severe inter-symbol interference (ISI), which will is cause larger delay spread. Therefore, the traditional acquisition methods are no longer suitable here. A modified acquisition method and a coarse channel estimation algorithm are proposed in this thesis. Three different strategies with composition of acquisition and channel estimation are compared. Based on three strategies, the tasks of coarse acquisition and channel estimation can be achieved with limited length of acquisition sequence. From simulation results, the parallel strategy is robust enough to operate under the UWB channel in severe ISI conditions and the time duration for completing the tasks of coarse acquisition and channel estimation meets the specification of IEEE 802.15.3a.

This thesis is concerned with modeling of both space and time variations of Ultra Wide Band (UWB) indoor channels. The most common empirically determined amplitude distribution in many UWB environments is Nakagami distribution. The latter is generalized to stochastic diffusion processes which capture the dynamics of UWB channels. In contrast with the traditional models, the statistics of the proposed models are shown to be time varying, but converge in steady state to their static counterparts. System identification algorithms are used to extract various channel parameters using received signal measurement data, which are usually available at the receiver. The expectation maximization (EM) algorithm and the Kalman filter (KF) are employed in estimating channel parameters as well as the inphase and quadrature components, respectively. The proposed algorithms are recursive and therefore can be implemented in real time. Further, sufficient conditions for the convergence of the EM algorithm are provided. Comparison with recursive Least-square (LS) algorithms is carried out using experimental measurements. Distributed stochastic power control algorithms based on the fixed point theorem and stochastic approximations are used to solve for the optimal transmit power problem and numerical results are also presented. A framework which can capture the statistics of the overall received signal and a methodology to estimate parameters of the counting process based on the received signal is developed. Furthermore, second moment statistics and characteristic functions are computed explicitly and considered as an extension of Rice’s shot noise analysis. Another two important components, input design and model selection are also considered. Gel’fand n-widths and Time n-widths are used to represent the inherent error introduced by input design. Kolmogorov n-width is used to characterize the representation error introduced by model selection. In particular, it is shown that the optimal model for reducing the representation error is a finite impulse response (FIR) model and the optimal input is an impulse at the start of the observation interval.

博士
淡江大學
電機工程學系博士班
97
This dissertation focuses on the research of channel capacity of multiple-input multiple-output ultra-wide band (UWB) systems. On the one hand UWB systems possess a nature of high channel capacity, and on the other hand multiple-input multiple-out (MIMO) approach can be used to enhance channel capacity effectively. Thus, it is expectable that UWB systems can be combined with multiple-input multiple-output approach to fulfill the necessity of high transmission rate in the future. It is well-known that UWB systems combining multiple-input multiple-out approach can yield high data rates in theory. However, some problems must be overcome further in order for the combined system to work in the realistic environment. As a result, this dissertation analyzes the problems on channel capacity of the combined system in the realistic environment, and proposes a suitable method to tackle them. By measurement is the most direct and useful method to predict channel characteristics of the realistic environment, but the method is often expensive, time-consuming and having a lot of natural restrictions. In contrast to measurement, the same process can be carried out through simulation to overcome these drawbacks as long as the accuracy of the simulation can be proven. Therefore, this dissertation proposes two simulation methods, and they are compared with the measured results given by related works in the literature. Our study results demonstrate that the simulation methods not only can eliminate the drawbacks of measurement but also yield good computation accuracy. This dissertation calculates the channel capacity of the combined system by simulation in the realistic environment. First, the channel capacity affected by symmetric and asymmetric antenna deployment is calculated. Symmetric antenna deployment is used for multiple-input multiple-out in most researches. However, asymmetric antenna deployment is more suitable than symmetric antenna deployment in some scenarios. The study results are used to decide which deployment is suitable for the combined system. Next, the channel capacity of the combined system with single co-channel interference is calculated. Since a lot of co-channel interferences exist for cellular systems, the interferences can be assumed as random variable. However, the assumption may be unsuitable for the combined system because the system belongs to wireless personal area network (WPAN) and just few co-channel interferences exist. The study results are used to decide whether MIMO can effectively reduce co-channel interference (CCI), and quantify the effects of applying different antenna arrays on the combined system.

碩士
中原大學
電子工程研究所
95
This thesis presents a Voltage-Controlled Ring Oscillator (VCO) with third-order harmonic cancellation technique for low-band Ultra-Wideband (UWB) system. The VCO consists of three-stage delay cells and an adder load. Use the adder to add the two output signals that have phase delay 60 degrees from ring-oscillator. Then that can effective to make oscillator output signal third harmonic suppress ratio lower than -40dBc. In order to produce the more pure output signal and make it while inputting to Polyphase Filter it is phase error exported can drop by a wide margin . The simulation result shows the operating frequency range from 3924MHz to 4534MHz, center frequency at 4224MHz, and tuning range is 0V ~ 1.8V. The output power is -10.44dBm, the gain of vco(Kvco) is 339MHz/V. The simulated third harmonic rejection is - 43dBc at 4224MHz, phase noise is - 101 dBc/Hz @ 5MHz offset. The power consumption is 11.93 ~ 13.12 mW at 1.8V supply voltage in a 0.18um standard RF CMOS process.

The advancement in the eld of cold-atoms has generated a lot of interest in the condensed matter community. Cold-atom experiments can simulate clean, disor-der/impurity free systems very easily. In these systems, we have a control over various parameters like tuning the interaction between particles by the Feshbach resonance, tuning the hopping between lattice sites by laser intensity and so on. As a result, these systems can be used to mimic various theoretical models, which was hindered because of various experimental limitations. Thus, we have an ex-perimental tool in which we can start with a simple theoretical model and later tune the model experimentally and theoretically to simulate the real materials. This will be helpful in studying the physics of the real materials as we can control interactions as well as the impurities can also be taken care of. But the advance-ment in the eld of cold atoms has seen a roadblock for the fermions in optical lattices. The super uid and anti-ferromagnetic phases has not been achieved for fermions in optical lattices due to the \cooling problem" (entropy issues). In this thesis, we have addressed the issue of the \cooling problem" for fermions in optical lattice systems and studied the system with determinant quantum Monte Carlo technique. We start by giving a general idea of cold-atoms and optical lat-tice potentials, and a brief review of the experimental work going on in the cold-atomic systems. Experimental limitations like \fermionic cooling problem" have been discussed in some detail. Then we proposed a bilayer band-insulator model to circumvent the \entropy problem" and simultaneously increasing the transi-tion temperature for fermions in optical lattices. We have studied the attractive Hubbard model, which is the minimal model for fermions in optical lattices. The techniques that we have used to study the model are mean- eld theory, Gaussian uctuation theory and determinant quantum Monte Carlo numerical technique. . Chapter-1 : provides a general introduction to the ultra-cold atoms, optical lattice and Feshbach resonance. In this chapter we have discussed about cold-atom experiments in optical lattice systems. Here, we have brie y discussed the control over various parameters in the experiments. The goal of these experiments is to realize or mimic many many-body Hamiltonians in experiments, which until now was just a theoretical tool to describe various many-body physics. In the end we give a brief idea for introducing disorder in the cold-atom experiments discuss the limitations of these experiments in realizing the \interesting" super uid and anti-ferromagnetic phases of fermionic Hubbard model in optical lattices. Chapter-2 : gives a brief idea of \Determinant Quantum Monte-Carlo" (DQM C) technique that has been used to study these systems. In this chapter we will discuss the DQM C algorithm and the observables that can be calculated. We will discuss certain limitation of the DQM C algorithm like numerical instability and sign problem. We will brie y discuss how sign problem doesn't occur in the model we studied. Chapter-3 : discusses the way by which we can bypass the \cooling problem" (high entropy state) to get a fermionic super uid state in the cold atom experi-ments. In this chapter we propose a model whose idea hinges on a low-entropy band-insulator state, which can be tuned to super uid state by tuning the on-site attractive interaction by Feshbach resonance. We show through Gaussian uctua-tion theory that the critical temperature achieved is much higher in our model as compared to the single-band Hubbard model. Through detailed variational Monte Carlo calculations, we have shown that the super uid state is indeed the most stable ground state and there is no other competing order. In the end we give a proposal for its realization in the ultra-cold atom optical lattice systems. Chapter-4 : discusses the DQM C study of the model proposed in chapter- 3. Here we have studied the various single-particle properties like momentum distribution, double occupancies which can be easily measured in cold-atom ex-periments. We also studied the pair-pair and the density-density correlations in detail through DQM C algorithm and mapped out the full T U phase diagram. We show that the proposed model doesn't favor the charge density wave for the interaction strengths we are interested in. Chapter-5 : gives a brief idea of the e ect of adding an on-site random disorder in our proposed bilayer-Hubbard model. We study the e ect of random disorder on various single-particle properties which can be easily veri ed in cold-atom ex-periments. We studied the suppression of the pair-pair correlations as we increase the disorder strength in our proposed model. We nd that the critical value of the interaction doesn't change in the weak-disorder limit. We estimated the critical disorder strength needed to destroy the super uid state and argued that the tran-sition from the super uid to Bose-glass phase in presence of disorder lies in the universality class of (d + 1) XY model. In the end, we give a schematic U V phase diagram for our system. Chapter-6 : We studied the bilayer attractive Hubbard model in different lattice geometry, the bilayer honeycomb lattice, both in presence and in absence of the on-site random disorder. We discussed how the pair-pair and density-density cor-relations behave in the presence and absence of disorder. Through the finite-size scaling analysis we see the co-existence of the super fluid and the charge density wave order at half- lling. An in nitesimal disorder destroys the CDW order com-pletely while the super uid phase found to be robust against weak-disorder. We estimated the critical interaction strength, the critical temperature and the critical disorder strength through nite-size scaling, and provide a putative phase diagram for the system considered.

The advancement in the eld of cold-atoms has generated a lot of interest in the condensed matter community. Cold-atom experiments can simulate clean, disor-der/impurity free systems very easily. In these systems, we have a control over various parameters like tuning the interaction between particles by the Feshbach resonance, tuning the hopping between lattice sites by laser intensity and so on. As a result, these systems can be used to mimic various theoretical models, which was hindered because of various experimental limitations. Thus, we have an ex-perimental tool in which we can start with a simple theoretical model and later tune the model experimentally and theoretically to simulate the real materials. This will be helpful in studying the physics of the real materials as we can control interactions as well as the impurities can also be taken care of. But the advance-ment in the eld of cold atoms has seen a roadblock for the fermions in optical lattices. The super uid and anti-ferromagnetic phases has not been achieved for fermions in optical lattices due to the \cooling problem" (entropy issues). In this thesis, we have addressed the issue of the \cooling problem" for fermions in optical lattice systems and studied the system with determinant quantum Monte Carlo technique. We start by giving a general idea of cold-atoms and optical lat-tice potentials, and a brief review of the experimental work going on in the cold-atomic systems. Experimental limitations like \fermionic cooling problem" have been discussed in some detail. Then we proposed a bilayer band-insulator model to circumvent the \entropy problem" and simultaneously increasing the transi-tion temperature for fermions in optical lattices. We have studied the attractive Hubbard model, which is the minimal model for fermions in optical lattices. The techniques that we have used to study the model are mean- eld theory, Gaussian uctuation theory and determinant quantum Monte Carlo numerical technique. . Chapter-1 : provides a general introduction to the ultra-cold atoms, optical lattice and Feshbach resonance. In this chapter we have discussed about cold-atom experiments in optical lattice systems. Here, we have brie y discussed the control over various parameters in the experiments. The goal of these experiments is to realize or mimic many many-body Hamiltonians in experiments, which until now was just a theoretical tool to describe various many-body physics. In the end we give a brief idea for introducing disorder in the cold-atom experiments discuss the limitations of these experiments in realizing the \interesting" super uid and anti-ferromagnetic phases of fermionic Hubbard model in optical lattices. Chapter-2 : gives a brief idea of \Determinant Quantum Monte-Carlo" (DQM C) technique that has been used to study these systems. In this chapter we will discuss the DQM C algorithm and the observables that can be calculated. We will discuss certain limitation of the DQM C algorithm like numerical instability and sign problem. We will brie y discuss how sign problem doesn't occur in the model we studied. Chapter-3 : discusses the way by which we can bypass the \cooling problem" (high entropy state) to get a fermionic super uid state in the cold atom experi-ments. In this chapter we propose a model whose idea hinges on a low-entropy band-insulator state, which can be tuned to super uid state by tuning the on-site attractive interaction by Feshbach resonance. We show through Gaussian uctua-tion theory that the critical temperature achieved is much higher in our model as compared to the single-band Hubbard model. Through detailed variational Monte Carlo calculations, we have shown that the super uid state is indeed the most stable ground state and there is no other competing order. In the end we give a proposal for its realization in the ultra-cold atom optical lattice systems. Chapter-4 : discusses the DQM C study of the model proposed in chapter- 3. Here we have studied the various single-particle properties like momentum distribution, double occupancies which can be easily measured in cold-atom ex-periments. We also studied the pair-pair and the density-density correlations in detail through DQM C algorithm and mapped out the full T U phase diagram. We show that the proposed model doesn't favor the charge density wave for the interaction strengths we are interested in. Chapter-5 : gives a brief idea of the e ect of adding an on-site random disorder in our proposed bilayer-Hubbard model. We study the e ect of random disorder on various single-particle properties which can be easily veri ed in cold-atom ex-periments. We studied the suppression of the pair-pair correlations as we increase the disorder strength in our proposed model. We nd that the critical value of the interaction doesn't change in the weak-disorder limit. We estimated the critical disorder strength needed to destroy the super uid state and argued that the tran-sition from the super uid to Bose-glass phase in presence of disorder lies in the universality class of (d + 1) XY model. In the end, we give a schematic U V phase diagram for our system. Chapter-6 : We studied the bilayer attractive Hubbard model in different lattice geometry, the bilayer honeycomb lattice, both in presence and in absence of the on-site random disorder. We discussed how the pair-pair and density-density cor-relations behave in the presence and absence of disorder. Through the finite-size scaling analysis we see the co-existence of the super fluid and the charge density wave order at half- lling. An in nitesimal disorder destroys the CDW order com-pletely while the super uid phase found to be robust against weak-disorder. We estimated the critical interaction strength, the critical temperature and the critical disorder strength through nite-size scaling, and provide a putative phase diagram for the system considered.

A large variety of material systems for light emission and detection were studied: from very small band gap semiconductors for infra-red (IR) detectors to wide band gap semiconductors for ultra violet (UV) emission as well as CdSe/ZnSe QDs for single photon emitters and rare earth doped oxides for laser fabrication. The growth and characterization aspects were tackled. This work will focus on the relations between the growth procedures and the optical properties. The information that can be gained from optical studies as well as the limitations of those ones will be explained in each case. Following that, a number of projects will be presented. The main one will be based on how to circumvent the problems linked with p-type doping of wide bandgap semiconductors. This project, based on field effect hole injection in wide band-gap semiconductors addresses the major challenge of fabricating efficient deep UV emitters.