Спосіб отримання завадостійких сигналів для управління автоматизованою системою

Робота викладена на 32 сторінках, у тому числі включає 17 рисунків, список цитованої літератури із 30 джерел.Об’єктом дослідження кваліфікаційної роботи є способи отримання завадостійких сигналів для управління автоматизованими системами. Мета роботи полягає в аналізі видів і джерел завад в автоматизованих системах, а також пошуків шляхів їх усунення. При виконанні роботи проведено аналіз джерел і видів завад, визначено основні методи підвищення завадостійкості автоматизованих систем. У результаті проведеного аналізу, встановлено, що існує декілька методів екранування і заземлення елементів та ліній зв’язку в системах автоматики, але найчастіше для зменшення впливу завад на роботу автоматичної системи використовують гальванічну розв’язк

Performance Analysis of Direct-Sequence Code-Division Multiple-Access Communications with Asymmetric Quadrature Phase-Shift-Keying Modulation

This article considers a quaternary direct-sequence code-division multiple-access (DS-CDMA) communication system with asymmetric quadrature phase-shift-keying (AQPSK) modulation for unequal error protection (UEP) capability. Both time synchronous and asynchronous cases are investigated. An expression for the probability distribution of the multiple-access interference is derived. The exact bit-error performance and the approximate performance using a Gaussian approximation and random signature sequences are evaluated by extending the techniques used for uniform quadrature phase-shift-keying (QPSK) and binary phase-shift-keying (BPSK) DS-CDMA systems. Finally, a general system model with unequal user power and the near-far problem is considered and analyzed. The results show that, for a system with UEP capability, the less protected data bits are more sensitive to the near-far effect that occurs in a multiple-access environment than are the more protected bits

Fast Generation of Receiver-Based Statistics in Frequency Hop Radios without Decoder Simulation

Receiver-based statistics can contain useful information about the quality a wireless channel. We examine methods of generating receiver statistics without real-time simulation of the receiver and the decoder, particularly during a network-level simulation. Attention is restricted to a receiver employing binary orthogonal signaling, noncoherent demodulation, and a soft-decision decoder in a frequency-hop network. Data is gathered from off-line simulations of channel, demodulation, and decoding processes, using a family of turbo product codes. Study and analysis of the data are used to characterize the behavior of the receiver statistics and determine on-line methods of generating the statistics in network-level simulations. To measure the performance of our generation techniques, we compare the results with simulation data. The goal of the generation methods is to provide receiver-based statistics for simulations of higher layer protocols without the need for simulation of the decoding process, which is time consuming. With this goal in mind, we design our generation methods to be simple and fast, favoring approximations over exact replications whenever the resulting simplification is significant. Both demodulator and decoder statistics are considered. Results are given which demonstrate the fidelity of our generation methods

Analytical evaluation of adaptive transmission protocols for Markov models of channels with fading and moderate shadowing

Adaptive transmission protocols are often employed to communicate over wireless channels with fading and other time-varying propagation losses. The protocols compensate for the propagation losses and maintain high throughput by adjusting transmission parameters in response to the channel variations. Performance evaluations for practical adaptive transmission protocols typically require simulation of both the time-varying processes and the procedure by which the protocol derives information about the channel quality. In this thesis, we develop an analytical method to evaluate the performance of two practical protocols, an adaptive coding protocol and an adaptive modulation and coding protocol, which rely on statistics derived from the demodulation process. Our method for performance analysis avoids the need for simulations of the adaptive protocols and the derivation of statistics that are used for adaptation; furthermore, our approach avoids the simulation of the time-varying channel

Layered Adaptive Modulation and Coding For 4G Wireless Networks

Emerging 4G standards, such as WiMAX and LTE have adopted the proven technique of Adaptive Modulation and Coding (AMC) to dynamically react to channel fluctuations while maintaining bit-error rate targets of the transmission. This scheme makes use of the estimated channel state indication (CSI) to efficiently utilize channel capacity for next transmission, but it brings with it the stale CSI problem due to the frequently channel fluctuations. As its objective, this thesis focuses on mitigating the vicious effect of stale CSI by proposing a novel framework that incorporate AMC with layered transmission through Superposition Coding (SPC) is introduced. A layered multi-step finite-state Markov chain model (FSMC) is developed under this framework, to effectively assist the system in selecting the optimal modulation and coding scheme as well as the power allocated for each layer in every multi-resolution unicast transmission. Extensive simulations are conducted to verify the proposed framework and compare its performance with other counterparts. The effects of changing key parameters, such as the complexity factor and step size, are also investigated to get close to real world performance. Results demonstrate that the proposed framework can achieve better spectrum efficiency than similar counterparts, due to its improved robustness to the stale CSI problem for each multi-resolution modulated transmission, also these show that the performance of two-layer scheme is good enough for layer allocation, without need of more layers

New Coding/Decoding Techniques for Wireless Communication Systems

Wireless communication encompasses cellular telephony systems (mobile communication), wireless sensor networks, satellite communication systems and many other applications. Studies relevant to wireless communication deal with maintaining reliable and efficient exchange of information between the transmitter and receiver over a wireless channel. The most practical approach to facilitate reliable communication is using channel coding. In this dissertation we propose novel coding and decoding approaches for practical wireless systems. These approaches include variable-rate convolutional encoder, modified turbo decoder for local content in Single-Frequency Networks, and blind encoder parameter estimation for turbo codes. On the other hand, energy efficiency is major performance issue in wireless sensor networks. In this dissertation, we propose a novel hexagonal-tessellation based clustering and cluster-head selection scheme to maximize the lifetime of a wireless sensor network. For each proposed approach, the system performance evaluation is also provided. In this dissertation the reliability performance is expressed in terms of bit-error-rate (BER), and the energy efficiency is expressed in terms of network lifetime

Modulation adaptative pour les systèmes MIMO dans un environnement minier souterrain

La technique de modulation adaptative augmente considérablement le débit des systèmes de communications sans fil en ajustant l'indice de modulation en fonction des conditions de changement du canal. Par exemple, lorsque le canal est en mauvais état (c'est à dire, à faible SNR), nous pouvons réduire la taille des constellations du signal afin d'améliorer et optimiser les performances du système. Inversement, lorsque le canal est en bon état (SNR élevé), nous pouvons augmenter la taille de la constellation du signal afin d'augmenter le débit de données. Les systèmes à antennes multiples, ou systèmes MIMO (Multi Input Multi Output) exploitent la dimension spatiale et les réseaux d'antennes pour transmettre plusieurs flux parallèles dans le même canal de fréquence. En effet, ils ont le potentiel d'augmenter la capacité du canal proportionnellement aux nombres d'antennes émettrices et réceptrices considérées, en particulier dans les environnements riches en multi-trajets tels que les mines souterraines. Dans ce projet, nous proposons d' associer la modulation adaptative au système MIMO dans le canal de propagation minier souterrain qui est un milieu confiné et interne. La première adapte les modulations en émission en fonction des conditions radio afin de maximiser l'efficacité spectrale tout en respectant une contrainte sur la probabilité d'erreur. Alors que la deuxième présente des avantages importants pour améliorer la fiabilité et le débit de transmission

Desenvolvimento de Técnicas Inteligentes Visando Melhorar a Eficiência Energética em Redes Ópticas Elásticas

Reduzir os gastos energéticos em redes de comunicação tem sido um dos grandes desafios enfrentados nos últimos anos. Este trabalho de tese apresenta novas estratégias para a redução de consumo de energia e melhoramento da eficiência energética em redes ópticas. Estas estratégias baseiam-se na alocação e alteração dos parâmetros da rede óptica de forma mais eficiente (ex: modulação, codificação) em função das condições do canal óptico. Neste trabalho, primeiro, foi investigada a técnica de modulação adaptativa (Adaptative Modulation - AM), onde o nível de símbolos no esquema de constelação de uma modulação é alterado de acordo à distância óptica e o número de slots considerada. Assim, foi possível garantir a qualidade de transmissão (Quality of Transmission - QoT) durante o processo de roteamento e alocação do espectro da rede. A segunda técnica proposta utiliza um código adaptativo. O código corretor de erro (Forward Error Correction - FEC) a ser implementado na rede varia como função da relação sinal ruído óptico (Optical Signal to Noise Ratio - OSNR) e do número de slots também. Finalmente, é proposta uma técnica híbrida, a qual é uma combinação das duas estratégias mencionadas anteriormente (modulação adaptativa e código adaptativo). Neste caso, os parâmetros de modulação e o tipo de código são alterados simultaneamente. Os resultados analíticos demonstraram que o consumo energético é reduzido, a eficiência da rede é melhorada e a probabilidade de bloqueio é diminuída