By placing millions of space sunshades, of the order of 104 m2 at the sub-Lagrangian point L1',between the sun and Earth, solar radiation can be reduced enough to achieve the necessary temper-ature reduction to enable a slow down of the global warming. The vast amount of space sunshadesposes significant challenges on the communication system, as the probability of interference, whichcan distort information, increases with the number of simultaneously communicating units.This thesis aims to design a potential structure for the communication system that minimizesinterference as much as possible. To reduce the number of simultaneously communicating units, thesunshades are arranged in cell formation, where a mother is placed in the center with daughtersaround that only communicate with their specific cell mother. Direct communication betweenthe Earth and space sunshades is not possible as the interference from solar radiation can causesignificant distortion on the signals. Therefore, relay satellites are placed in orbit around thesub-Lagrangian point L1' at a sufficient distance to avoid the effects of solar radiation. Thus, thecommunication between the mothers and Earth is instead routed via the relay satellites. Sincecommunication between such a large number of entities in space has not been investigated before,this approach could provide a possible basic design framework for designing such infrastructure inthe future.

The interconnection of molecular machines with different functionalities to form molecular communication systems can increase the number of design possibilities and overcome the limited reliability of the individual molecular machines. Artificial information exchange using molecular signals would also expand the capabilities of single engineered cell populations by providing them a way to cooperate across heterogeneous cell populations for the applications of synthetic biology and lab-on-a-chip systems. The realization of molecular communication systems necessitates analysis and design of the communication channel, where the information carrying molecular signal is transported from the transmitter to the receiver. In this thesis, significant progress towards the use of microfluidic channels to interconnect molecular transmitter and receiver pairs is presented. System-theoretic analysis of the microfluidic channels are performed, and a finite-impulse response filter is designed using microfluidic channels. The spectral density of the propagation noise is studied and the additive white Gaussian noise channel model is developed. Memory due to inter-diffusion of the transmitted molecular signals is also modeled. Furthermore, the interference modeling is performed for multiple transmitters and its impact on the communication capacity is shown. Finally, the efficient sampling of the signal transduction by engineered bacterial receivers connected to a microfluidic channel is investigated for the detection of the pulse-amplitude modulated molecular signals. This work lays the foundation for molecular communication over microfluidic channels that will enable interconnection of engineered molecular machines.

Este trabalho faz uma extensa e detalhada análise de sistemas ópticos coerentes baseados na tecnologia de acesso múltiplo por divisão de código, com ênfase naqueles em que o processo de codificação do sinal óptico é realizado por meio de deslocamentos de fase no domínio espectral (SPECTS-OCDMA). Apesar de ser um estudo numérico, esforços são concentrados na tentativa de aproximar estes cenários simulados aos cenários mais realistas, implementados em laboratórios. Nesse contexto, levando em consideração o impacto dos efeitos dispersivos e nãolineares da fibra óptica em sistemas SPECTS-OCDMA, são modelados diversos dispositivos que constituem o sistema de recepção do sinal óptico (nonlinear optical loop mirror e nonlinear thresholder), e mostradas suas influências no desempenho do sistema. Isso permite identificar o exato grau de interferência que cada código de uma determinada família de códigos causa nos outros códigos da mesma família. Esta análise é diferente de tudo previamente reportado para os sistemas OCDMA, porque até então sempre se supôs que todos os códigos de uma mesma família têm o mesmo desempenho. Também é demonstrado que uma escolha ótima do conjunto de códigos reduz consideravelmente a taxa de erro de bit (BER). Os conjuntos ótimos de códigos são obtidos em termos do padrão de interferência causado por todos os códigos no usuário de interesse. Isso permite mostrar que o uso de conjuntos ótimos de códigos não só melhora o desempenho geral do sistema em termos de BER, mas também elimina a quebra de ortogonalidade (nunca levada em consideração em análises anteriores de sistemas OCDMA) devido à diafonia (crosstalk). Este aspecto também é resolvido com detalhes neste trabalho uma vez que ele compromete seriamente a segurança do sistema contra espiões (intencionais e não intencionais). Ainda visando a modelagem de dispositivos voltados para sistemas ópticos coerentes, também foi investigado neste trabalho a evolução de pulsos ultracurtos e de alta potência (com fase modulada no domínio espectral) em fibras altamente não-lineares. Esse fenômeno conhecido por geração de luz supercontínua é caracterizado por um forte alargamento espectral induzido por efeitos não-lineares no meio óptico, e que encontra uma grande variedade de aplicações, como tomografia por coerência óptica, espectroscopia e metrologia de frequência. Entretanto, o ajuste do espectro obtido após a propagação para uma dessas aplicações requer uma escolha correta da fibra óptica e da fonte de pulsos ultracurtos utilizados. Uma vez que esses parâmetros estão definidos, fica muito difícil conseguir um ajuste fino do espectro obtido. Dessa forma, a vantagem da utilização de pulsos modulados é a possibilidade de se realizar uma sintonia fina do espectro obtido para uma aplicação desejada. Além disso, essa técnica permite a geração de pentes de frequências ópticos (optical frequency combs) sintonizáveis. / In this work we perform a comprehensive analysis of a spectral phase-encoded time spreading optical code division multiple access (SPECTS-OCDMA) system. Despite being a numerical study, efforts were concentrated on the investigation of more realistic scenarios using as much information as possible from implemented test-beds in laboratories. In this context, after take into account the impact of dispersive and nonlinear effects of optical fiber in SPECTS-OCDMA systems, some devices of the optical signal reception subsystem are modeled (nonlinear optical loop mirror and nonlinear thresholder), and their influences on system performance are shown. This allowed for the first time in the OCDMA literature the identification of the exact degree of interference that each code of a particular family of codes causes on other codes of the same family. This analysis considerably advances the common sense adopted in the literature in which all codes of the same family perform equally. It is demonstrated that an adequate (optimal) choice of codes can reduce considerably the bit error rate (BER). The optimal code-sets are obtained in terms of the interference pattern caused by every code on the code of interest. Furthermore, it is shown that the use of optimal code-sets not only improves the overall system performance in terms of BER, but also eliminates the orthogonality failure (never accounted for in previous OCDMA analysis) due to crosstalk. This issue is also addressed in details in this work since it seriously compromises the security of the system against (intentional or unintentional) eavesdroppers. Still aiming at modeling devices for coherent optical systems, it is investigated the evolution of ultrashort high-power pulses (spectrally phase modulated) in high nonlinear fibers. This phenomenon known as supercontinuum generation is characterized by strong spectral broadening induced by nonlinear effects in optical medium, and finds a wide range of applications such as optical coherence tomography, spectroscopy and frequency metrology. However, tailoring the supercontinuum (SC) spectra to a specific application requires the correct choice of the optical fiber and the ultrashort pulse source. Once these parameters are defined, it becomes very difficult to achieve a fine tune of the generated spectra. Therefore, an alternative is to phase modulate the input pulse to adjust the generated spectra to a specific application. Also, we show that this technique allow us to generate tunable optical frequency combs simply by adjusting the modulation parameters.

Neste trabalho propomos e analisamos algoritmos de alocação dinâmica de banda para rede óptica passiva (PON) de acesso padrão GPON (Gigabit PON). Estes algoritmos utilizam dados oriundos de SLA (service level agreement) para gerenciar a alocação de banda e classificar em 4 contêineres de tráfego (T-CONT) o tráfego gerado em 16 ONUs (optical network unit). Na transmissão upstream é utilizada a técnica de multiplexação por divisão de tempo (TDM) para gerenciar o acesso ao meio, evitando colisões. O primeiro algoritmo proposto aloca banda garantida para as ONUs e distribui a banda não utilizada de acordo com critério baseado em três SLAs. A taxa de bit upstream é 1,25 Gbps e o desempenho do algoritmo é analisado com base na variação do atraso de pacotes em função do tráfego gerado nas ONUs. O segundo algoritmo proposto utiliza ponderação de tráfego. Neste, analisamos o comportamento dos atrasos e a quantidade de banda solicitada e atendida por ONU quando as bandas garantida e extra são alteradas. Por fim, acrescentamos em nossa implementação um intervalo para o processamento do algoritmo de alocação dinâmica de banda (DBA) e resposta do hardware relacionado ao ciclo de interrogação. Então, analisamos o atraso de pacotes quando variamos o intervalo de processamento do DBA. Ao final, propomos uma solução preliminar para minimizar estes atrasos. Os resultados obtidos por meio de simulação computacional mostram a versatilidade dos algoritmos. / In this work we propose and analyze the performance of dynamic bandwidth allocation algorithms for optical passive networks (PON) in GPON standard (Gigabit PON). These algorithms use data from SLA (service level agreement) to manage bandwidth allocation and classify in 4 traffic containers (T-CONT) the traffic generated by 16 ONUs (optical network unit). In the upstream transmission the time division multiplexing (TDM) technique is used to manage the medium access, avoiding collisions. The first proposed algorithm allocates guaranteed bandwidth for the ONUs and distributes the bandwidth not used according to the criteria based on three SLAs. The upstream bit rate is 1.25 Gbps and the algorithm performance is analyzed based on the packets delay variation versus the traffic generated by ONUs. The second proposed algorithm uses weighted traffic. In this, we analyze the delay performance and the required bandwidth for each ONU and how much it is served when the guaranteed and extra bandwidth are changed. Finally, we added in our implementation an interval for the processing of the dynamic bandwidth allocation algorithm (DBA) and response of the hardware related to the interrogation cycle. In the end, we propose a preliminary solution to minimize these delays. The results obtained by means of computational simulation show the versatility of the algorithms.

Il est attendu que les radios flexibles constituent un tournant technologique majeur dans le domaine des communications sans fil. Le point de vue adopté en radios flexibles est de considérer les canaux de communication comme un ensemble de ressources qui peuvent être accédées sur demande par un réseau primaire sous licence ou de manière opportuniste par un réseau secondaire à plus faible priorité. Du point de vue de la couche physique, le réseau primaire n’a aucune information sur l’existence de réseaux secondaires, de sorte que ces derniers doivent explorer l’environnement aérien de manière autonome à la recherche d’opportunités spectrales et exploiter ces ressources de manière optimale. Les phases d’exploration et d’exploitation, qui impliquent la gestion de nombreux agents, doivent être très fiables, rapides et efficaces. L’objectif de cette thèse est de modéliser, d’analyser et de proposer des solutions efficaces et quasi optimales pour ces dernières opérations.En ce qui concerne la phase d’exploration, nous calculons le test optimal de Neyman-Pearson de détection de plusieurs sources primaires via un réseau de capteurs. Cette procédure permet à un réseau secondaire d’établir la présence de ressources spectrales disponibles. La complexité calculatoire de l’approche optimale appelle cependant la mise en place de méthodes moins onéreuses, que nous rappelons et discutons. Nous étendons alors le test de détection en l’estimation aveugle de la position de sources multiples, qui permet l’acquisition d’informations détaillées sur les ressources spectrales disponibles.Le second volet de cette thèse est consacré à la phase d’exploitation optimale des ressources au niveau du réseau secondaire. Pour ce faire, nous obtenons une approximation fine du débit ergodique d’un canal multi-antennes à accès multiples et proposons des solutions peu coûteuses en termes de feedback afin que les réseaux secondaires s’adaptent rapidement aux évolutions rapides du réseau primaire. / Future cognitive radio networks are expected to come as a disruptive technological advance in the currently saturated field of wireless communications. The idea behind cognitive radios is to think of the wireless channels as a pool of communication resources, which can be accessed on-demand by a primary licensed network or opportunistically preempted (or overlaid) by a secondary network with lower access priority. From a physical layer point of view, the primary network is ideally oblivious of the existence of a co-localized secondary networks. The latter are therefore required to autonomously explore the air in search for resource left-overs, and then to optimally exploit the available resource. The exploration and exploitation procedures, which involve multiple interacting agents, are requested to be highly reliable, fast and efficient. The objective of the thesis is to model, analyse and propose computationally efficient and close-to-optimal solutions to the above operations.Regarding the exploration phase, we first resort to the maximum entropy principle to derive communication models with many unknowns, from which we derive the optimal multi-source multi-sensor Neyman-Pearson signal sensing procedure. The latter allows for a secondary network to detect the presence of spectral left-overs. The computational complexity of the optimal approach however calls for simpler techniques, which are recollected and discussed. We then proceed to the extension of the signal sensing approach to the more advanced blind user localization, which provides further valuable information to overlay occupied spectral resources.The second part of the thesis is dedicaded to the exploitation phase, that is, the optimal sharing of available resources. To this end, we derive an (asymptotically accurate) approximated expression for the uplink ergodic sum rate of a multi-antenna multiple-access channel and propose solutions for cognitive radios to adapt rapidly to the evolution of the primary network at a minimum feedback cost for the secondary networks.

Orientador: Celso de Almeida / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-09-11T21:24:05Z (GMT). No. of bitstreams: 1 CarvajalMora_HenryRamiro_M.pdf: 10096746 bytes, checksum: 558790b8f1575c8f3b46fe6c7418920d (MD5) Previous issue date: 2014 / Resumo: Neste trabalho, é avaliado o desempenho do enlace reverso de redes celulares que utilizam a técnica de múltiplo acesso por divisão de código com multiportadoras (MC-CDMA) em termos da probabilidade de erro de bit média (BER) e da eficiência espectral média. O sistema de comunicações analisado utiliza a técnica MC-CDMA, um arranjo linear de antenas na estação rádio base, entrelaçamento em frequência, combinação de máxima razão (MRC), modulação adaptativa, controle de potência e um prefixo cíclico grande o suficiente para eliminar os efeitos da interferência intersimbólica (ISI) e da interferência entre portadoras (ICI). O cenário estudado considera a presença de interferência de múltiplo acesso (MAI) e interferência de co-canal (CCI). A caracterização do canal considera a presença de ruído aditivo gaussiano branco (AWGN), perda de propagação exponencial e desvanecimento lento e seletivo em frequência que segue a distribuição de Rayleigh. Neste contexto, expressões analíticas exatas e fechadas para a BER média tanto para a modulação BPSK, quanto para a modulação M-QAM são obtidas. A exatidão das expressões é validada através de simulações de Monte Carlo. Ademais, uma expressão para a eficiência espectral celular média é determinada, a qual é uma função do fator de reuso de canais, do incremento da largura de banda devido ao prefixo cíclico, do carregamento do sistema, do fator de espalhamento, dos raios da célula e da modulação utilizada. Os resultados indicam que utilizar um fator de reuso de canais de 1 é a maneira mais eficiente de usar o espectro. No entanto, esse fator de reuso é crítico em relação às taxas de transmissão. Ademais, evidenciando que a técnica de múltiplo acesso por divisão de frequências ortogonais (OFDMA) é um caso particular da técnica MC-CDMA, os resultados mostram que a máxima eficiência espectral média obtida com a técnica OFDMA é menor do que aquela obtida com a técnica MC-CDMA / Abstract: In this work the performance of cellular networks uplink is evaluated using the multicarrier-code division multiple access (MC-CDMA) technique in terms of the mean bit error rate (BER) and the mean spectral efficiency. The analyzed communications system is supposed to employ the MC-CDMA technique, a linear antenna array in the base station, frequency interleaving, maximal ratio combining (MRC), adaptive modulation, control power and a cyclic prefix large enough to eliminate the effects of intersymbol interference (ISI) and intercarrier interference (ICI). The studied scenario assumes the presence of multiple access interference (MAI) and co-channel interference (CCI). The channel characterizations considers the presence of additive white gaussian noise (AWGN), exponential path-loss and slow and frequency selective Rayleigh fading. In this context, exact and closed analytical expressions for the mean BER for both BPSK modulation, as for M-QAM modulation are obtained. The accuracy of the expressions is validated through Monte Carlo simulations. Also, an expression for the mean cellular spectral efficiency is determined, which is a function of the channel reuse factor, the bandwidth increases due to the cyclic prefix, the system load, the spreading factor, the cell radius and the modulation employed. The results show that using an unitary channel reuse factor of 1 is the most efficient way to use the spectrum. However, this reuse factor is critical in relation to transmission rates. Moreover, considering that the orthogonal frequency division multiple access (OFDMA) technique is a particular case of MC-CDMA, the results show that the maximum mean spectral efficiency achieved with the OFDMA technique is lower than that obtained with the MC-CDMA technique / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica

In general, PN code synchronization consists of two steps: PN code acquisition (coarse alignment) and PN code tracking (fine alignment), to estimate the delay offset between received and locally generated codes. Recently, the schemes with a joint adaptive process of PN code acquisition and the weight coefficients of smart antenna have been proposed for improving the received signal-to-interference-plus-noise ratio (SINR) and simultaneously achieving better mean-acquisition-time (MAT) performance in direct-sequence code-division multiple access (DS-CDMA) systems. In which, the setting of the threshold plays an important role on the MAT performance. Often, the received SINR is varying, using the fixed threshold acquisition algorithms may result in undesirable performance. To improve the above problem, in this thesis, a new adaptive threshold scheme is devised in a joint adaptive code acquisition and beam-forming DS-CDMA receiver for code acquisition under a fading multipath and additive white Gaussian-noise (AWGN) channels. The basic idea of this new adaptive threshold scheme is to estimate the averaged output power of smart antenna to scale a reference threshold for each observation interval, such that it can approximately achieve a constant false alarm rate (CFAR) criteria. The system probabilities of the proposed scheme are derived for evaluating MAT under a slowly fading two-paths channels. Numerical analyses and simulation results demonstrate that the proposed adaptive threshold scheme does achieve better performance, in terms of the output SINR, the detection probability and the MAT, compared to a fixed threshold method.

Next generation mobile communication systems require the use of linear RF power amplifier for higher data transmission rates. However, linear RF power amplifiers are inherently inefficient and usually require additional circuits or further system adjustments for better efficiency. This dissertation focuses on the development of new efficiency enhancement schemes for linear RF power amplifiers. The multistage Doherty amplifier technique is proposed to improve the performance of linear RF power amplifiers operated in a low power level. This technique advances the original Doherty amplifier scheme by improving the efficiency at much lower power level. The proposed technique is supported by a new approach in device periphery calculation to reduce AM/AM distortion and a further improvement of linearity by the bias adaptation concept. The device periphery adjustment technique for efficiency enhancement of power amplifier integrated circuits is also proposed in this work. The concept is clearly explained together with its implementation on CMOS and SiGe RF power amplifier designs. Furthermore, linearity improvement technique using the cancellation of nonlinear terms is proposed for the CMOS power amplifier in combination with the efficiency enhancement technique. In addition to the efficiency enhancement of power amplifiers, a scalable large-signal MOSFET model using the modified BSIM3v3 approach is proposed. A new scalable substrate network model is developed to enhance the accuracy of the BSIM3v3 model in RF and microwave applications. The proposed model simplifies the modeling of substrate coupling effects in MOS transistor and provides great accuracy in both small-signal and large-signal performances.

Many communications signal formats are not power efficient because of their large peak-to-average power ratios (PARs). Moreover, in the presence of nonlinear devices such as power amplifiers (PAs) or mixers, the non-constant-modulus signals may generate both in-band distortion and out-of-band interference. Backing off the signal to the linear region of the device further reduces the system power efficiency. To improve the power efficiency of the communication system, one can pursue two approaches: i) linearize the PA; ii) reduce the high PAR of the input signal. In this dissertation, we first explore the optimal nonlinearity under the peak power constraint. We show that the optimal nonlinearity is a soft limiter with a specific gain calculated based on the peak power limit, noise variance, and the probability density function of the input amplitude. The result is also extended to the fading channel case. Next, we focus on digital baseband predistortion linearization for power amplifiers with memory effects. We build a high-speed wireless test-bed and carry out digital baseband predistortion linearization experiments. To implement adaptive PA linearization in wireless handsets, we propose an adaptive digital predistortion linearization architecture that utilizes existing components of the wireless transceiver to fulfill the adaptive predistorter training functionality. We then investigate the topic of PAR reduction for OFDM signals and forward link CDMA signals. To reduce the PAR of the OFDM signal, we propose a dynamic selected mapping (DSLM) algorithm with a two-buffer structure to reduce the computational requirement of the SLM method without sacrificing the PAR reduction capability. To reduce the PAR of the forward link CDMA signal, we propose a new PAR reduction algorithm by introducing a relative offset between the in-phase branch and the quadrature branch of the transmission system.

Selected mapping (SLM) schemes are commonly employed to reduce the peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems. It has been shown that the computational complexity of the traditional SLM scheme can be substantially reduced by adopting conversion vectors obtained by using the inverse fast Fourier transform (IFFT) of the phase rotation vectors in place of the conventional IFFT operations. To ensure that the elements of these phase rotation vectors have an equal magnitude, conversion vectors should have the form of a perfect sequence. This study firstly presents three novel classes of perfect sequence, each of which comprises certain base vectors and their cyclically shifted versions. Three novel low-complexity SLM schemes are then proposed based upon the unique structures of these perfect sequences. It is shown that while the PAPR reduction performances of the proposed schemes are marginally poorer than that of the traditional SLM scheme, the three schemes achieve a substantially lower computational complexity. Since the three proposed PAPR reduction schemes cannot be utilized in the orthogonal frequency division multiple access (OFDMA) system. A low-complexity scheme for PAPR reduction in OFDMA uplink systems using either an interleaved or a sub-band sub-carrier assignment strategy is also proposed in the second part of this study. The proposed scheme requires just one IFFT operation. The PAPR reduction performance of the proposed scheme is only marginally poorer than that of the traditional SLM scheme. However, the proposed schemes have significantly lower computational complexities. Besides, multiple-input multiple-output (MIMO) OFDM systems with space-frequency block coding (SFBC) are well-known for their robust performance in time selective fading channels. However, SFBC MIMO-OFDM systems have a high computational complexity since the number of IFFTs required scales in direct proportion to the number of antennas at the transmitter. Furthermore, SFBC MIMO-OFDM systems have a high PAPR. Accordingly, a low-complexity PAPR reduction scheme for SFBC MIMO OFDM systems with the Alamouti encoding scheme is proposed in this study. Extending this scheme obtains two low-complexity transmitter architectures for SFBC MIMO-OFDM systems with a general encoding matrix and an arbitrary number of transmitter antennas. The proposed schemes achieve a significant reduction in computational complexity by fully exploiting the time-domain signal properties of the transmitted signal. In addition, a PAPR reduction scheme is presented based on the proposed transmitter schemes. It is shown that the PAPR reduction performance of the proposed scheme is almost as good as that of the traditional SLM scheme, but is achieved with a substantially lower computational complexity.