7 research outputs found
Maximum likelihood estimation of statistical properties of composite gamma-lognormal fading channels
We propose maximum likelihood (ML) methods for estimating the parameters of composite gamma-lognormal fading channels. Newton-Raphson and expectation-maximization (EM) algorithms are developed to compute the ML estimates of the mean and variance of the shadowing component, and the Nakagami-m parameter of the fading component. We also derive Crame/spl acute/r-Rao bounds (CRBs) for the unknown parameters. Numerical simulations demonstrate the performance of the proposed method
Maximum Likelihood Estimation of Statistical Properties of Composite Gamma-Lognormal Fading Channels
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