Tesi sul tema "Forward gain"

As the demand for more efficient alternative energies increases, the demand to make the power electronics that go along with those energies increases as well. One of the major power components for photovoltaics is the DC-DC converter required to increase the voltage produced. A hybrid DC-DC boost-forward topology was explored. A switch on the secondary side can be turned off and the converter will take the characteristics of a boost converter. These predictions were confirmed by simulating this cirucit in MatLab Simulink, and finally by building a prototype circuit. A desired output of 170V - 100W was produced and the efficiency was measured. The boost-forward converter peaked at about 85% efficient which was below the 94% efficient boost converter. The boost-forward converter, however, was found to have a higher efficiency than the boost converter when the input voltage was below 34V . The circuit is designed to work as a boost converter when the input voltage is above 34V . When the input drops below that voltage the converter can be put into the boost-forward converter configuration by closing the switch on the secondary side.

Dans les systèmes radio mobiles, la diversité représente une technique efficace pour lutter contre l’évanouissement dû aux multi-trajets. La pleine diversité spatiale est atteinte dans les systèmes multiple-input multiple-output (MIMO). Mais, souvent l’intégration d’antennes multiples au niveau de l’émetteur ou du récepteur est coûteuse. Comme alternative, dans les réseaux sans fil multi-hop, la diversité coopérative garantit des gains de diversité spatiale en exploitant les techniques MIMO traditionnelles sans avoir besoin d’antennes multiples. En outre, la diversité coopérative fournit au réseau : un débit important, une énergie réduite et une couverture d’accès améliorée.Dans ce contexte, l’objectif de cette thèse est de concevoir des schémas de codage pour le canal à relais afin de réaliser une meilleure performance en termes de gain de diversité et de gain de codage. D’abord, nous étudions un système de turbo-codage distribué à L-relais en mode soft-decode-and-forward. Ensuite, nous proposons un système de turbocodage coopératif distribué à L-relais en utilisant la concaténation en parallèle des codes convolutifs. Enfin, afin d’améliorer la fiabilité de détection au niveau du noeud relais, nous proposons la technique de sélection d’antenne/relayage-soft. Pour une modulation BPSK, nous dérivons des expressions de la borne supérieure de la probabilité d’erreurbinaire où les différents sous-canaux sont supposés à évanouissement de Rayleigh, indépendants et pleinement entrelacés avec une information instantanée d’état de canal idéal. Une validation des résultats théoriques est également menée par la simulation
Diversity provides an efficient method for combating multipath fading in mobile radio systems. One of the most common forms of spatial diversity is multiple-input multipleoutput (MIMO), where full diversity is obtained. However, embedding multiple antennas at the transmitter or the receiver can sometimes be expensive. As an alternative to collocated antennas, cooperative diversity in wireless multi-hop networks confirms their ability to achieve spatial diversity gains by exploiting the spatial diversity of the traditional MIMO techniques, without each node necessarily having multiple antennas. In addition, cooperative diversity has been shown to provide the network with importantthroughput, reduced energy requirements and improved access coverage.In light of this, the objective of this thesis is to devise coding schemes suitable for relay channels that aim at showing the best compromise between performance of diversity and coding gains. Firstly, we investigate a distributed turbo coding scheme dedicated to L-relay channels operating in the soft-decode-and-forward mode. Then, we present a proposed distributed turbo coded cooperative (DTCC) scheme, called parallel concatenated convolutional-based distributed coded cooperation. Finally, we investigate antenna/soft-relaying selection for DTCC networks in order to improve their end-to-end performance. Assuming BPSK transmission for fully interleaved channels with ideal channel state information, we define the explicit upper bounds for error probability inRayleigh fading channels with independent fading. Both theoretical limits and simulation results are presented to demonstrate the performances

The superior characteristics of silicon carbide, compared with silicon, have suggested considering this material for the next generation of power semiconductor devices. Among the different power switches, the bipolar junction transistor (BJT) can provide a very low forward voltage drop, a high current capability and a fast switching speed. However, in order to compete on the market, it is crucial to a have high current gain and a breakdown voltage close to ideal. Moreover, the absence of conductivity modulation and long-term stability has to be solved. In this thesis, these topics are investigated comparing simulations and measurements. Initially, an efficient etched JTE has been simulated and fabricated. In agreement with the simulations, the fabricated diodes exhibit the highest BV of around 4.3 kV when a two-zone JTE is implemented. Furthermore, the simulations and measurements demonstrate a good agreement between the electric field distribution inside the device and the optical luminescence measured at breakdown. Additionally, an accurate model to simulate the forward characteristics of 4H-SiC BJTs is presented. In order to validate the model, the simulated current gains are compared with measurements at different temperatures and different base-emitter geometries. Moreover, the simulations and measurements of the on-resistance are compared at different base currents and different temperatures. This comparison, coupled with a detailed analysis of the carrier concentration inside the BJT, indicates that internal forward biasing of the base-collector junction limits the BJT to operate at high current density and low forward voltage drop simultaneously. In agreement with the measurements, a design with a highly-doped extrinsic base is proposed to alleviate this problem. In addition to the static characteristics, the comparison of measured and simulated switching waveforms demonstrates that the SiC BJT can provide fast switching speed when it acts as a unipolar device. This is crucial to have low power losses during transient. Finally, the long-term stability is investigated. It is observed that the electrical stress of the base-emitter diode produces current gain degradation; however, the degradation mechanisms are still unclear. In fact, the analysis of the measured Gummel plot suggests that the reduction of the carrier lifetime in the base-emitter region might be only one of the causes of this degradation. In addition, the current gain degradation due to ionizing radiation is investigated comparing the simulations and measurements. The simulations suggest that the creation of positive charge in the passivation layer can increase the base current; this increase is also observed in the electrical measurements.
QC 20120522

Dans les systèmes radio mobiles, la diversité représente une technique efficace pour lutter contre l'évanouissement dû aux multi-trajets. La pleine diversité spatiale est atteinte dans les systèmes multiple-input multiple-output (MIMO). Mais, souvent l'intégration d'antennes multiples au niveau de l'émetteur ou du récepteur est coûteuse. Comme alternative, dans les réseaux sans fil multi-hop, la diversité coopérative garantit des gains de diversité spatiale en exploitant les techniques MIMO traditionnelles sans avoir besoin d'antennes multiples. En outre, la diversité coopérative fournit au réseau : un débit important, une énergie réduite et une couverture d'accès améliorée.Dans ce contexte, l'objectif de cette thèse est de concevoir des schémas de codage pour le canal à relais afin de réaliser une meilleure performance en termes de gain de diversité et de gain de codage. D'abord, nous étudions un système de turbo-codage distribué à L-relais en mode soft-decode-and-forward. Ensuite, nous proposons un système de turbocodage coopératif distribué à L-relais en utilisant la concaténation en parallèle des codes convolutifs. Enfin, afin d'améliorer la fiabilité de détection au niveau du noeud relais, nous proposons la technique de sélection d'antenne/relayage-soft. Pour une modulation BPSK, nous dérivons des expressions de la borne supérieure de la probabilité d'erreurbinaire où les différents sous-canaux sont supposés à évanouissement de Rayleigh, indépendants et pleinement entrelacés avec une information instantanée d'état de canal idéal. Une validation des résultats théoriques est également menée par la simulation.

Nous étudions un protocole de coopération dans les réseaux MIMO à deux sauts : le rotate-and-forward (RF). Dans ces réseaux, la source et la destination ne communiquent qu'à travers une couche de relais. Nous étudions la performance du protocole RF à partir d'une nouvelle métrique appelée gain de coupure. Ce gain nous permet de décrire le comportement de la probabilité de coupure à des valeurs du rapport signal à bruit moyennes et élevées. En utilisant le gain de coupure, nous comparons la performance du RF aux performances d'autres protocoles ayant le même ordre de diversité que le RF. Nous supposons aussi qu'une voie de retour existe entre la destination et les relais et nous donnons un algorithme qui permet d'améliorer les performances du RF en termes de probabilité de coupure en se basant sur la connaissance des gains du canal. Nous considérons un protocole de codage de réseaux au niveau physique : le compute-and-forward (CF). Nous nous intéressons à la maximisation du débit de calcul et nous montrons que c'est équivalent à la recherche du vecteur le plus court dans un réseau de points donné. Tout d'abord, nous implémentons le protocole utilisant des réseaux de points uni-dimensionnels et des gains de canal réels. Nous nous basons sur la fonction de maximum de vraisemblance (ML) pour proposer une technique de décodage quasi-ML et nous montrons que le décodage s'effectue par une approximation Diophantienne inhomogène. Ensuite, nous généralisons certains de ces résultats au cas des réseaux de points multi-dimensionnels et des gains de canal complexes, et nous proposons un critère de construction des codes en réseaux de points qu'on appelle le facteur de platitude.

Dans un réseau coopératif, différents noeuds coopèrent afin de créer un réseau d’antennes virtuel et exploiter la diversité spatio-temporelle. On s’intéresse d'abord au canal à relai. Afin d'améliorer les performances à bas SNR, on propose une stratégie adaptative pour les protocoles ”amplify-and-forward” (AF) et ”decode-and-forward (DF) qui détermine la meilleure technique de transmission en fonction du canal. Afin de définir un protocole DF à la fois performant et facile à implémenter, on propose ensuite d'utiliser un décodage incomplet aux relais. Cette technique permet d’atteindre les gains de multiplexage et de diversité maximaux, son DMT est le même que celui du protocol AF non-orthogonal (NAF). Pour réduire la complexité aux relais, deux nouvelles méthodes de décodage sont proposées, basées pour l’une sur la structure des codes TAST, et pour l’autre sur une approximation diophantienne. Dans le cas où plusieurs sources transmettent simultanément, on parle de canal coopératif à accès multiple (CMA). Une implémentation pratique et deux améliorations du protocole CMA-NAF sont proposées, ainsi qu’une variante utilisant une stratégie DF. Ces protocoles permettent d’atteindre de meilleures performances asymptotiques et leur DMT est plus proche de la borne MISO. Enfin, si le lien direct entre source et destination est inutilisable, on utilise une stratégie multi-saut. Dans cette thèse, on propose un protocole pour le canal ”K-parallel-path” (KPP), basé sur la sélection de chemin combinée avec un code spatio-temporel de faible dimension. Ce protocole permet d’atteindre les limites théoriques du canal tout en ayant une complexité limitée
In cooperative networks, multiple nodes cooperate to form a virtual antenna array and exploit space-time diversity. The relay channel is first investigated. In order to improve performance at low SNRs, an adaptive strategy is proposed for both amplify-and-forward (AF) and decode-and-forward (DF) protocols. This strategy chooses the best transmission scheme in term of mutual information for each channel realization. To define an easily implementable and efficient DF protocol, we propose to use an incomplete decoding at relays. This technique provides both full rate and full diversity. Its DMT is similar to the one of the well-known non-orthogonal AF (NAF). In order to reduce the decoding complexity at relays, we also propose two decoding methods based on the space-time block code (STBC) structure and diophantine approximation, respectively. When several sources need to transmit simultaneously, a cooperative multiple access (CMA) channel has to be considered. A practical implementation and two modifications of the CMA-NAF protocol defined by Azarian et al. Are proposed, as well as a DF variant, the CMA-IDF. These protocols provide better asymptotic performance and their DMT is closer to the MISO bound. Finally, if the direct link between source and destination is nonexistent or experiences too much fading, a multihop strategy has to be used. In this thesis, a protocol is proposed for the K-parallel-path (KPP) network, based on path selection combined with a small STBC. This protocol achieves the optimal DMT of the KPP channel with a limited complexity

This master’s thesis deals with the design of the switching power supply on the principle of high frequency converter. The goal of this thesis is construction of converter which is using GaN MOSFET transistors and SiC diodes for switching. The converter uses two switch forward power supply topology. Unusually high switching frequency was chosen for the design with power transformer with open magnetic core. The outcome of this work is functional converter which is primarily intended for educational and demonstrational purposes. Multiple parts of this converter are divided into individual blocks, which can be further used for construction of other types of switching converters.

碩士
國立虎尾科技大學
電機工程研究所
98
High voltage gain and high-efficiency converter is an increasing demand at present. These voltages are low for photovoltaic (PV) systems, fuel cells, wind generators and uninterruptible power systems (UPS). Therefore, design of converter becomes a challenge to step-up voltage with high efficiency and high power output. This thesis is a design of Boost-Forward-Flyback (BFF) converter with high voltage gain. The circuit structure is integrated by Boost, Forward and Flyback. Design is simple that circuit needs a pulse width modulation (PWM) signal output only. In addition, at cut-off time, the MOSFET generates spike by way of circuit sent to the output. This way achieve energy recovery, active clamp, and can reduce the voltage stress of power devices to improve circuit efficiency. The experimental results have confirmed that the BFF converter possesses high voltage gain, high efficiency and low voltage stress. This converter can be used in low voltage input and high voltage out-put products. Finally, a suitable high-voltage gain converter is designed for fuel cell with micro-controller unit (MCU), besides to apply in hybrid electric vehicle with li-ion battery.

碩士
國立虎尾科技大學
電機工程研究所
102
This paper proposed a novel dc-dc converter to achieve high step-up voltage gain without an extremely high duty ratio. This thesis is a design of　Boost-Forward-Flyback (BFF) converter　with high voltage gain. The circuit structure is integrated by Boost,　Forward and　Flyback. The proposed converter controlled by only a single pulse width modulation (PWM) for the power switch. The figuration of the proposed converter is a quadratic boost converter with the coupled inductor in the second boost converter. The leakage inductance energy of the coupled inductor can be recycled to reduce the voltage stress and power losses. To deserve, the coupled-inductor can be adjusted by increasing the turn ratios of the secondary-side winding to achieve higher voltage gain feature. The operating principles, theoretical analysis, experimental waveforms and efficiency curves are presented. Finally, a prototype to verify the performance of the proposed converter with input voltage 44~54 V, output voltage 380 V and output power 1.5k W is implemented.

碩士
國立中山大學
通訊工程研究所
100
Dual-hop transmission system can increase the transmission diversity via the cooperation of transmission nodes and can also overcome the channel fading effectively. This thesis proposes an outage probability analysis method for the AF relaying system where multiple antennas are equipped at source node and both the relay node and destination node just carry single antenna. Compare with previous work, the average signal to noise ratio of source to relay and relay to destination links are assumed to be two different variables, therefore we can get a more general performance analysis. We also extend our theoretical analysis to the system where multiple antennas are utilized at destination node. Simulation results are shown to verify the analysis of the proposed schemes in some representative scenarios.

碩士
國立交通大學
電信工程系所
96
In this thesis, a 24GHz forward-looking collision warning antenna operating at 24.025GHz~24.225GHz has been developed. In order to separate transmitted and received signal at reality application, we generally use two kinds of structures. First one is double antenna structure but the drawback is using double area. Another type is single antenna structure, which uses the quadrature hybrid to separate transmitting and receiving signals. The cost is extra 6dB loss. When feed antenna is located lens focal point radiating energy through lens, the main lobe is located at axis. We introduce a new antenna structure putting transmitting and receiving feed antenna at focal point two sides. The main lobes of the transmitting and receiving signal diverge from axis, but the intersectional region of the transmitting and receiving signals is still locate at axis. In practical application, RF active and passive components are surrounded by metal shield. We treat the effect when antenna surrounded by metal wall. We can enhance the isolation between transmitting and receiving port when we properly design the metal wall. We discuss about different space among transmitting and receiving antenna impact on radiation pattern and the isolation between transmitting and receiving port. In the end, we measure the radar cross section of vehicle at different angles. Then we calculate the radar detection region by the radar equation.

Cooperative relay communication is a promising means of wireless communication in which cooperation is used to create a virtual transmit array between the source and the destination, thereby providing spatial diversity for combating the fading channel. In this thesis we develop cooperative communication protocols namely the orthogonal amplify-and-forward (OAF), non-orthogonal and orthogonal selection decode-and-forward (NSDF and OSDF) protocols. The diversity-multiplexing gain tradeoff (DMT) of the three protocols is determined and DMT-optimal distributed space-time code constructions are provided. The code construction is based on Cyclic Division Algebras. The codes constructed are sphere decodable and in some instances incur minimum possible delay. Included in our results is the perhaps surprising finding that the OAF and NAF protocols have identical DMT when the time durations of the broadcast and cooperative phases are optimally chosen to suit the respective protocol. Two variants of the NSDF protocol are considered: fixed-NSDF and variable-NSDF protocol. In the variable-NSDF protocol, the fraction of time occupied by the broadcast phase is allowed to vary with multiplexing gain. In the two-relay case, the variable-NSDF protocol is shown to improve on the DMT of the best previously-known static protocol for higher values of multiplexing gain. Our results also establish that the fixed-NSDF protocol has a better DMT than the NAF protocol for any number of relays.

abstract: Full-duplex communication has attracted significant attention as it promises to increase the spectral efficiency compared to half-duplex. Multi-hop full-duplex networks add new dimensions and capabilities to cooperative networks by facilitating simultaneous transmission and reception and improving data rates. When a relay in a multi-hop full-duplex system amplifies and forwards its received signals, due to the presence of self-interference, the input-output relationship is determined by recursive equations. This thesis introduces a signal flow graph approach to solve the problem of finding the input-output relationship of a multi-hop amplify-and-forward full-duplex relaying system using Mason's gain formula. Even when all links have flat fading channels, the residual self-interference component due to imperfect self-interference cancellation at the relays results in an end-to-end effective channel that is an all-pole frequency-selective channel. Also, by assuming the relay channels undergo frequency-selective fading, the outage probability analysis is performed and the performance is compared with the case when the relay channels undergo frequency-flat fading. The outage performance of this system is performed assuming that the destination employs an equalizer or a matched filter. For the case of a two-hop (single relay) full-duplex amplify-and-forward relaying system, the bounds on the outage probability are derived by assuming that the destination employs a matched filter or a minimum mean squared error decision feedback equalizer. For the case of a three-hop (two-relay) system with frequency-flat relay channels, the outage probability analysis is performed by considering the output SNR of different types of equalizers and matched filter at the destination. Also, the closed-form upper bounds on the output SNR are derived when the destination employs a minimum mean squared error decision feedback equalizer which is used in outage probability analysis. It is seen that for sufficiently high target rates, full-duplex relaying with equalizers is always better than half-duplex relaying in terms of achieving lower outage probability, despite the higher RSI. In contrast, since full-duplex relaying with MF is sensitive to RSI, it is outperformed by half-duplex relaying under strong RSI.
Dissertation/Thesis
Masters Thesis Electrical Engineering 2016

This research thesis seeks to investigate a new method to sense the classical Hall effect in Hall devices under the influence of a magnetic field primarily manufactured in complementary metal oxide semiconductor (CMOS) technologies. The thesis poses a research question enabling the investigation into whether or not the geometrical factor in a classical Hall device can be improved by proposing a new method to sense the Hall effect indirectly in standard CMOS technology. State of the art Hall effect devices rely on low ohmic contacts to sense the Hall voltage effect. These contacts along with the geometry can have an adverse effect on the Hall device sensitivity. Furthermore, the Hall voltage in Silicon can be very limited in comparison to high mobility semiconductor materials. It was found that by replacing the highly doped n-type sensing contacts of the Hall device with highly doped p-type contacts, a vertical bipolar junction transistor could be formed. This transistor, normally considered a parasitic element, ultimately leads to a very useful sensing technique in which the Hall current is sensed and amplified by the transistor forward gain, β + 1. The Hall effect appears as a current through the emitter of the transistor. The major contribution of this research resides in a novel method to measure as well as amplify the Hall effect in a square n-well plate manufactured on a standard CMOS technology. The research also bridges the gap found in literature on the subject of direct versus indirect Hall sensing techniques. The outcome of the research also addresses practical implementations of such alternate methods as well as the effect the methods have on fundamental noise limits and differences in noise between the proposed method and traditional methods. The device although not improving the fundamental geometrical factor of the plate which was found to be dominated by the geometry itself, was proven to be functional as well as behaving according to Hall effect theory. Furthermore, the gain that even low forward gain bipolar transistors contribute to the signal, more than compensates for the loss of Hall effect contributed by the geometrical correction factor. The method also contributes less noise in comparison to typical traditional methods of Hall voltage amplification using operational amplifiers. The proposed method thus allows for a very simple measuring technique that is compatible with standard CMOS technology processes. ## Hierdie navorsings tesis is gemik daarop om 'n nuwe meetmetode te ondersoek om die klassieke Hall effek te meet in Hall toestelle onder die invloed van 'n magneetveld wat primér in komplementêre metaaloksied-halfgeleiertegnologie (CMOS) vervaardig word. Die tesis stel 'n navorsingsvraag wat lei tot die ondersoek van die vraag of die geometriese faktor in 'n klassieke Hall toestel verbeter kan word deur om 'n nuwe metode voor te stel om die Hall effek indirek te meet in standaard CMOS tegnologie. Nuutste navorsing oor meetmetodes in Hall effek toestelle, maak nog steeds staat op lae ohmiese kontakte om die Hall spanning effek te meet. Hierdie kontakte saam met die meetkunde van die toestel, het 'n nadelige uitwerking op die Hall toestel se sensitiwiteit. Verder is die Hall spanning in Silikon baie beperk met vergelyking tot hoë mobiliteit halfgeleier materiale. Daar is gevind dat deur die vervanging van die hoogs gedoteerde n-tipe meetkontakte van die Hall toestel met hoogs gedoteerde p-tipe kontakte, kan vertikale bipolêre transistors gevorm word. Hierdie transistor, gewoonlik beskou as 'n parasitiese element, lei tot 'n baie nuttige meet tegniek waarin die Hall stroom gemeet en versterk word deur die transistor se voorwaartse wins, β + 1. Die Hall effek verskyn as 'n stroom deur die emittor van die transistor. Die grootste bydrae van hierdie navorsing lê in 'n nuwe metode om die Hall effek in 'n vierkantige n-dam plaat wat in standaard CMOS tegnologie vervaardig is te meet sowel as om die sein te versterk. Die navorsing oorbrug ook die gaping gevind in literatuur oor die onderwerp van direkte teenoor indirekte Hall meet tegnieke. Die uitkoms van die navorsing spreek ook die praktiese implementering van die meetmetode aan sowel as die effek wat die meetmetode op fundamentele ruisgrense en verskille in ruis tussen die voorgestelde meetmetode en tradisionele meetmetodes het. Die toestel, hoewel nie gelei het tot ‘n verbetering van die fundamentele geometriese faktor van die plaat wat oorheers is deur die meetkunde van die plaat self, is wel funksioneel bewys, asook dat dit optree volgens Hall effek teorie. Verder is daar gevind dat die wins wat selfs lae voorwaartse wins bipolêre transistors bydra tot die sein, meer as die verlies wat die meetkundige faktor veroorsaak op die Hall effek kan herwin. Dié meetmetode dra ook minder ruis by met vergelyking tot tipiese tradisionele meetmetodes soos operasionele versterkers, wat vir Hall spanning versterking gebruik word. Die voorgestelde meetmetode skep dus ‘n baie eenvoudige meettegniek wat versoenbaar is met standaard CMOS tegnologie prosesse.
Thesis (PhD)--University of Pretoria, 2014.
lk2014
Electrical, Electronic and Computer Engineering
PhD
unrestricted

This dissertation studies the diversity multiplexing tradeoff and the capacity of wireless multiple-relay network. In part 1, we study the setup of the parallel Multi-Input Multi-Output (MIMO) relay network. An amplify-and-forward relaying scheme, Incremental Cooperative Beamforming, is introduced and shown to achieve the capacity of the network in the asymptotic case of either the number of relays or the power of each relay goes to infinity. In part 2, we study the general setup of multi-antenna multi-hop multiple- relay network. We propose a new scheme, which we call random sequential (RS), based on the amplify-and-forward relaying. Furthermore, we derive diversity- multiplexing tradeoff (DMT) of the proposed RS scheme for general single-antenna multiple-relay networks. It is shown that for single-antenna two-hop multiple- access multiple-relay (K > 1) networks (without direct link between the source(s) and the destination), the proposed RS scheme achieves the optimum DMT. In part 3, we characterize the maximum achievable diversity gain of the multi- antenna multi-hop relay network and we show that the proposed RS scheme achieves the maximum diversity gain. In part 4, RS scheme is utilized to investigate DMT of the general multi-antenna multiple-relay networks. First, we study the case of a multi-antenna full-duplex single-relay two-hop network, for which we show that the RS achieves the optimum DMT. Applying this result, we derive a new achievable DMT for the case of multi-antenna half-duplex parallel relay network. Interestingly, it turns out that the DMT of the RS scheme is optimum for the case of multi-antenna two parallel non-interfering half-duplex relays. Furthermore, we show that random unitary matrix multiplication also improves the DMT of the Non-Orthogonal AF relaying scheme in the case of a multi-antenna single relay channel. Finally, we study the general case of multi-antenna full-duplex relay networks and derive a new lower-bound on its DMT using the RS scheme. Finally, in part 5, we study the multiplexing gain of the general multi-antenna multiple-relay networks. We prove that the traditional amplify-forward relaying achieves the maximum multiplexing gain of the network. Furthermore, we show that the maximum multiplexing gain of the network is equal to the minimum vertex cut-set of the underlying graph of the network, which can be computed in polynomial time in terms of the number of network nodes. Finally, the argument is extended to the multicast and multi-access scenarios.

碩士
國立中央大學
資訊工程研究所
99
Human identification is an important issue in identity authentication which can be applied in many applications, such as security monitoring system, ATM authentication, and personal authentication in businesses transactions. There are many mature image-based human identification techniques that have been developed, such as fingerprints, face, and iris biometric modalities. However, these methods impose severe constraints, such as requiring of a cooperative subject, views from certain aspects, and physical contact or close proximity. To relieve these constraints, human gait identification is a new choice to remedy the problems. The existing human gait identification methods, including GEI、GHI、GMI…etc, are formed by combining the whole human gait cycle into one image. In this thesis, an effective human gait identification method is presented by separating one cycle into 4 cycles via different combination methods. Experimental results reveal the feasibility and effectiveness of the proposed method in gait identification. We also compare the performance of GEI and FDHI and through experimenting to explain the effects of the four different cycles. The results confirm that our proposed FDHI identification is better than GEI identification.

Unilateral, below-knee amputees have altered gait mechanics, which can significantly affect mobility. For example, amputees often have asymmetric leg loading as well as higher metabolic cost and an increased risk of falling compared to non-amputees. Below-knee amputees lose the functional use of the ankle muscles, which are critical in non-amputee walking for providing body support, forward propulsion and leg-swing initiation. The ankle muscles also regulate angular momentum in non-amputees, which is important for providing body stability and preventing falls. Thus, compensatory mechanisms in amputee walking are developed to accomplish the functional tasks normally provided by the ankle muscles. In Chapters 2 and 3, three-dimensional forward dynamics simulations of amputee and non-amputee walking were generated to identify compensatory mechanisms and their effects on joint loading and metabolic cost. Results showed that the prosthesis provided body support, but did not provide sufficient body propulsion or leg-swing initiation. As a result, compensations by the residual leg gluteus maximus, gluteus medius, and hamstrings were needed. The simulations also showed the intact leg tibio-femoral joint contact impulse was greater than the residual leg and that the vasti and hamstrings were the primary contributors to the joint impulse on both the intact and residual legs. The amputee simulation had higher metabolic cost than the non-amputee simulation, which was primarily due to prolonged muscle activity from the residual leg gluteus maximus, gluteus medius, hamstrings, vasti and intact leg vasti and ankle muscles. In Chapter 4, whole-body angular momentum in amputees and non-amputees was analyzed. Reduced residual leg propulsion resulted in a smaller range of sagittal plane angular momentum in the second half of the gait cycle. Thus, to conserve angular momentum, reduced braking was needed in the first half of the gait cycle. Decreased residual leg braking appears to be an important mechanism to regulate sagittal plane angular momentum in amputee walking, but was also associated with a greater range of angular momentum that may contribute to reduced stability in amputees. These studies have provided important insight into compensatory mechanisms in below-knee amputee walking and have the potential to guide rehabilitation methods to improve amputee mobility.
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Abnormal electromagnetic wave propagation characterized by negative group velocity and consequently negative group delay (NGD) has been observed in certain materials as well as in artificially built structures. Within finite frequency intervals where an NGD phenomenon is observed, higher frequency components of the applied waveform are propagated with phase advancement, not delay, relative to the lower frequency components. These media have found use in many applications that require positive delay compensation and an engineered phase characteristic, such as eliminating phase variation with frequency in phase shifters, beam-squint minimization in phased array antenna systems, size reduction of feed-forward amplifiers and others. The three principal questions this thesis addresses are: can a generic formulation for artificial NGD structures based on electric circuit resonators be developed; is it possible to derive a quantitative functional relationship (asymptotic limit) between the maximum achievable NGD and the identified trade-off quantity (out-of-band gain); and, can a microwave circuit exhibiting a fully loss-compensated NGD propagation in both directions be designed and implemented? A generic frequency-domain formulation of artificial NGD structures based on electric circuit resonators is developed and characterized by three parameters, namely center frequency, bandwidth and the out-of-band gain. The developed formulation is validated through several topologies reported in the literature. The trade-off relationship between the achievable NGD on one hand, and the out-of-band gain on the other, is identified. The out-of-band gain is shown to be proportional to transient amplitudes when waveforms with defined “turn on/off” times are propagated through an NGD medium. An asymptotic limit for achievable NGD as a function of the out-of-band gain is derived for multi-stage resonator-based NGD circuits as well as for an optimally engineered linear causal NGD medium. Passive NGD media exhibit loss which can be compensated for via active elements. However, active elements are unilateral in nature and therefore do not allow propagation in both directions. A bilateral gain-compensated circuit is designed and implemented, which overcomes this problem by employing a dual-amplifier configuration while preserving the overall circuit stability.

Over one million amputees are living in the United States with major lower limb loss (Ziegler-Graham et al. 2008). Lower limb amputation leads to the functional loss of the ankle plantar flexor muscles, which are important contributors to body support, forward propulsion, and leg swing initiation during walking (Neptune et al. 2001; Liu et al. 2006). Effective prosthetic component design is essential for successful rehabilitation of amputees to return to an active lifestyle by partially replacing the functional role of the ankle muscles. The series of experimental and computer simulation studies presented in this research showed that design characteristics of energy storage and return prosthetic ankles, specifically the elastic stiffness, significantly influence residual and intact leg ground reaction forces, knee joint moments, and muscle activity, thus affecting muscle output. These findings highlight the importance of proper prosthetic foot stiffness prescription for amputees to assure effective rehabilitation outcomes. The research also showed that the ankle muscles serve to stabilize the body during turning the center of mass. When amputees turn while supported by their prosthetic components, they rely more on gravity to redirect the center of mass than active muscle generation. This mechanism increases the risks of falling and identifies a need for prosthetic components and rehabilitation focused on increasing amputee stability during turning. A proper understanding of the effects of prosthetic components on amputee walking mechanics is critical to decreasing complications and risks that are prevalent among lower-limb amputees. The presented research is an important step towards reaching this goal.
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Dissertação de mestrado integrado em Biomedical Engineering (área de especialização em Biomaterials, Biomechanics and Rehabilitation)
Ankle-foot orthoses are orthotic devices that support the ankle joint and are appropriate for several pathologies, mostly the ones that cause dropfoot, which is caused by an ankle joint deficiency. In the present work, a planar multibody model of the human body in the sagittal plane was developed. For this purpose, the MOBILE computational program was utilized. The model simulates the lower limbs and is made of 9 rigid bodies. It has 12 DOFs and is prepared for reproducing kinematic data acquired in a gait lab. Kinematic measurements were obtained in a gait lab from a healthy subject, with and without plastic ankle foot orthoses worn on both feet. The results obtained showed that with the orthoses, the ankle joint behavior is similar to a linear torsional spring, with almost no hysteresis. Ankle kinematics, measured in the gait lab with and without orthoses, were successfully reproduced by forward dynamics using the multibody model developed, which allows for the validation of the presented approach. Furthermore, it was concluded that ankle foot orthoses can be modeled as a spring element acting at the ankle joint, and the use of an ankle foot orthosis reduces the muscle activation at the ankle in about 15%.
Knöchel-Fuß-Orthesen sind orthopädische Geräte, die das Sprunggelenk zu unterstützen und sind für verschiedene Erkrankungen, vor allem diejenigen, die dropfoot, die von einer Sprunggelenks-Mangel verursacht wird dazu führen, angemessen. In der vorliegenden Arbeit wurde ein planarer Multibody Modell des menschlichen Körpers in der Sagittalebene entwickelt. Zu diesem Zweck wurde das MOBILE Rechenprogramm verwendet. Das Modell simuliert die unteren Extremitäten und wird von 9 starren Körpern. Es verfügt über 12 Freiheitsgrade und ist für die Wiedergabe kinematische Daten in einer Ganglabors erworbenen vorbereitet. Kinematische Messungen wurden in einem Ganglabors von einer gesunden Person erhalten, mit und ohne Kunststoff Sprunggelenk Orthesen an beiden Füßen getragen. Die erhaltenen Ergebnisse zeigten, dass mit den Orthesen, das Sprunggelenk Verhalten ähnlich einer linearen Torsionsfeder ist, fast ohne Hysterese. Knöchel Kinematik, in der Ganglabors mit und ohne Orthesen gemessen wurden erfolgreich von Vorwärtsdynamikanalyse Verwendung der Multibody Modell entwickelt, das für die Validierung der dargebotenen Ansatz ermöglicht reproduziert. Darüber hinaus wurde festgestellt, dass Sprunggelenk Orthesen als Feder wirkende Element am Sprunggelenk modelliert werden können, und die Verwendung eines Fußheberorthese verringert die Muskelaktivität am Knöchel in etwa 15%.
As ortóteses do tornozelo são dispositivos ortopédicos que apoiam a articulação do tornozelo e são indicados para uma variedade de patologias, nomeadamente as que causam pé pendente, que é uma deficiência na mobilidade do tornozelo. No presente trabalho, um modelo multibody planar do corpo humano no plano sagital foi criado. Para tal, o software MOBILE foi usado. O modelo simula os membros inferiores e é composto por nove corpos rígidos. Possui 12 graus de liberdade e está preparado para usar dados cinemáticos adquiridos num laboratório de análise da marcha humana como restrições de guiamento. Dados cinemáticos foram obtidos num laboratório de análise da marcha humana, a partir de um indivíduo saudável, com e sem ortóteses plásticas em ambos os pés. Os resultados mostraram que, com a ortótese, o comportamento da articulação do tornozelo é semelhante a uma mola de torção linear, praticamente sem histerese. Os dados cinemáticos do tornozelo, medidos no laboratório de marcha, com e sem ortótese, foram reproduzidos com sucesso por uma dinâmica direta, utilizando o modelo multibody desenvolvido, o que validou a abordagem utilizada. Todas as metodologias encontram-se descritas e explicadas nesta tese e concluiuse que a ortóteses do tornozelo podem ser modeladas como uma mola de torsão que actua na articulação do tornozelo. Concluiu-se também que a utilização de uma ortótese do tornozelo por uma pessoa saudável reduz a activação muscular do mesmo em cerca de 15%.

The importance of cooperative relaying communication in substituting for, or complementing, multiantenna systems is described, and a brief literature review is presented. Amplify-and-forward (AF) and decode-and-forward (DF) relaying are investigated and compared for a dual-hop relay channel. The optimal strategy, source and relay optimal power allocation, and maximum cooperative gain are determined for the relay channel. It is shown that while DF relaying is preferable to AF relaying for strong source-relay links, AF relaying leads to more gain for strong source-destination or relay-destination links. Superimposed and selection AF relaying are investigated for multirelay, dual-hop relaying. Selection AF relaying is shown to be globally strictly outage suboptimal. A necessary condition for the selection AF outage optimality, and an upper bound on the probability of this optimality are obtained. A near-optimal power allocation scheme is derived for superimposed AF relaying. The maximum instantaneous rates, outage probabilities, and average capacities of multirelay, dual-hop relaying schemes are obtained for superimposed, selection, and orthogonal DF relaying, each with parallel channel cooperation (PCC) or repetition-based cooperation (RC). It is observed that the PCC over RC gain can be as much as 4 dB for the outage probabilities and 8.5 dB for the average capacities. Increasing the number of relays deteriorates the capacity performance of orthogonal relaying, but improves the performances of the other schemes. The application of rateless codes to DF relaying networks is studied by investigating three single-relay protocols, one of which is new, and three novel, low complexity multirelay protocols for dual-hop networks. The maximum rate and minimum energy per bit and per symbol are derived for the single-relay protocols under a peak power and an average power constraint. The long-term average rate and energy per bit, and relay-to-source usage ratio (RSUR), a new performance measure, are evaluated for the single-relay and multirelay protocols. The new single-relay protocol is the most energy efficient single-relay scheme in most cases. All the multirelay protocols exhibit near-optimal rate performances, but are vastly different in the RSUR. Several future research directions for fixed-rate and rateless coded cooperative systems, and frameworks for comparing these systems, are suggested.
Communications