Técnicas com múltiplas antenas distribuídas para sistemas sem fios

Mestrado em Engenharia Electrónica e TelecomunicaçõesTransmissão cooperativa, em que uma fonte e um relay cooperam para enviar uma mensagem para o destino, pode proporcionar diversidade espacial contra o desvanecimento nas comunicações sem fios. O objectivo deste projecto é estudar a performance de um sistema de transmissão cooperativo com dois relays equipados com duas antenas, entre o transmissor e o utilizador. Considera-se que a estação base está equipada com duas antenas e o terminal móvel apenas com uma. O sistema cooperativo foi implementado de acordo com as especificações do LTE e avaliado em diversos cenários de propagação, considerando canais com diferentes Relação Sinal Ruído (SNR). Verificou-se que o desempenho do sistema proposto é melhor, quando comparado com o sistema não cooperativo, na maior parte dos cenários estudados.Cooperative transmission, in which a source and relay cooperate to sent a mensage to destination, can provide spatial diversity against fading in wirless telecomunications. The goal of this project is to study the perfomance of a cooperative tranmition systems with two relays equiped with two antennas, between transmitter and user. It is considered that the base station is equipped with two antennas and the mobile terminal with only one. The cooperative system was implemented according to the specifications of the LTE and evaluated at several propagation scenarios, considering channels with diferents Signal to Noise Ratio (SNR). It was found that the perfomance of the proposed system is better when compared with the non-cooperative ones, in most scenarios considered.CODIV/FP7-ICT-200

Application of diversity techniques for solving the problems of the effects impurities in optical fibers on the performance of optical systems

We analyzed the methods for reducing the impact of noise and interference, the performance of digital optical IM-DD system. Performances of digital optical telecommunication systems, as well as their improvement, were analyzed using standard criteria for evaluation: outage probability, average probability, channel capacity, and average fading duration. These performance measures are determined on the basis of statistical characteristics of the first and second rows of signal reception and are part of the technical documentation accompanying each of the realized digital optical communication system. Therefore, the closed form of expressions, derived in this dissertation, which can be used to calculate the statistical characteristics of signal reception, represent a significant contribution, in terms of design of digital optical transmission systems. Our analysis is placed on theoretical consideration on so far untreated cases, and therefore the theoretical basis of physical phenomena that affect the transmission through the digital optical systems, well known from the literature, are not further elaborated. We included a procedure for determining the expression for the multidimensional joint probability density distribution with correlated and uncorrelated random variables. The derived expressions have a wide range of applicability and are an excellent basis for further performance analysis of optical digital transmission systems, in terms of correlated channels, as well as the characteristics of the connection by using multiple-input receiver. Their practical use is demonstrated especially in the section that deals λSK optical systems, as well as the part of that processes - the relay optical systems. Improving the transmission reliability and reducing the impact of noise and interference on the performance of digital optical telecommunication systems, with a reduction in power transmission and increasing the distance between the transmitter and receiver, is analyzed through the applying of techniques using spatial diversity reception. The dissertation discussed the various techniques of spatial combining receiving signals from the receiving branches of optical systems, in terms of reducing impact noise and interference. Ratios were formed and interference signals at the entrance combiner branches and under the terms of the previous chapter are determined by the joint probability density of these relationships for all incoming branches and the corresponding joint cumulative probability. Using this statistical feature of the incoming signal and interference are determined and statistical characteristics of signal-to-interference at the output of given combiner, which represents the next significant contribution to the dissertation. The contribution of these derived expressions can be seen from the aspect of using the results obtained for the case of the proposed statistical modeling of the channel model when considering the reduction of the impact of various types of noise and interference, and examination performance enhancements of digital optical telecommunication systems using diversity reception techniques. Specifically, by assigning appropriate values of parameters in the corresponding expressions, which describe the statistical characteristics of the first order of receipt, an analysis of the value of standard measures of performance of optical telecommunication systems, as well as improve their use of spatial diversity techniques, for cases when the communication channel is exposed to various types of interference and noises. Using the derived expressions can be shown to improve all the standard measure of performance of optical telecommunication systems. Also, when transferred unchanged forces the useful signal and interference, and at the same range of connections, get better system performance (lower values of the probability of cancellation, less the value of average bet error probability, lower average fading duration...). Based on these facts can be concluded that the required the outage probability values (ABEP) for the reception, when we apply the described techniques of receipt, in the same range of connections and the same noise power, can achieve the necessary reduction of the useful signal power in transmission, that is, at the same useful signal power, the same level of interference in the channel, the required the outage probability (ASEP) at the reception, when we apply the described techniques of receipt, can be achieved at larger distances from the transmitting terminal