Dan Alexandru Stoichescu

Model Fitting and Model Evidence for Multiscale Image Texture Analysis

This paper gives an overview of the two levels of Bayesian inference: model fitting and model selection and shows how they can be used for the image texture analysis. The applied models are the Gauss‐Markov and Gibbs auto‐binomial Random Fields. In the second part the article introduces a linear model for the image wavelet coefficients able to explain the full description of the spatial, inter‐scale and inter‐band behavior of a multi‐resolution decomposed image. The model parameters, model variance and evidence are used to characterize the image texture.

A Petri net approach to multicellular chopper control

In this paper, a new control algorithm for multicellular converters is introduced. The multicellular converters are a class of switched hybrid systems which consist in the association of a number of commutation cells linked with floating voltage sources. The proposed control takes advantage of the hybrid characteristics of the system in order to develop a Petri net model for the converter and design a control method based on this model which ensures a minimum number of commutations. This last aspect of the control is important in order to have a longer life for the components and reduce the harmonic content of the output by reducing the value of dV/dt.

Discrete event control for multicell choppers driving DC machines

In this paper an idea of control for a multicell chopper driving a DC machine is introduced by taking into account the capacitors voltage constraints. The multicell choppers fall into the category of dynamical switched systems and have gained a lot of popularity due to their high performances, compared to the classic chopper structures. They reduce the stress on the components by reducing the value of dV/dt and by distributing the voltage over the n cells (on each capacitor). This last property is very important in high power applications, reducing the costs of the components as well as being able to control each cell individually. The idea of the control algorithm introduced in this paper will be tested on a 2 cells — 2 branches structure driving a DC machine, under ideal and real conditions.

Performance Improvement of a Multi-head Optical Wireless Communication System.

Free space optics represents a fast and economical method to transmit digital data at the speed of the order of the Gbps at a distance of a few kilometers. The major limitation is the atmospheric attenuation, especially fog, which can affect the quality of transmission, transfer rate and transmission distance. A useful metric to monitorize the processes is the BER factor. This paper proposes a combination of adaptive optics that use multiple heads of transmission which are focused simultaneously on a single photodetector at the receiver end, in order to provide redundancy and to sustain a minimum data-rate transfer and/or assuring a transmission distance at an acceptable BER. It is assessed, through the simulation, the optimal (technically and economically) number of optical transmitters for which we get a real quality improvement of the transmission for a given bitrate-distance factors.

The approach of wavelength dense multiplexing using free space optical systems

This paper aims to explore the ways of implementation for WDM technology that is specific for high capacity fiber optic systems, using FSO terrestrial links. It will study the peculiarities of the CWDM-SO versus DWDM-SO transmission, stating their limits (transmission distance versus BER for constant bitrate and atmospheric attenuation). It will calculate the BER value for each CWDM/DWDM channel, idealized and real conditions (with attenuation). The simulations will be made under Optiwave environment for a system with 8 CWDM/DWDM channels, performance evaluation being made using the eye diagram, WDM and optical spectrum analyzers.

A hybrid mobile biometric-based e-voting system

Information technology changes and gives shape to networked society all over the world today and its solutions are becoming main drivers in almost all fields of human life activity. One of those solutions is the empowerment of e-government technologies through mobile solutions. Although the acceptance rate of e-government applications is increasing, e-voting is hardly accepted as main tool in its field because it lacks in offering reliable solutions to common problems like fraud, bribery, anonymous character of the vote and absence of reliable independent observation. This paper proposes a mobile biometric-based design that solves such challenges and preserves transparency, privacy, and anonymity along with other essential services, using techniques such as Secure Sockets Layer encryption, certificate keys and 30 to 60 available seconds for security tokens. The paper also presents requirements analysis for the proposed design system of the hybrid mobile biometric-based e-voting system.

A new stopping criterion for turbo decoders based on the minimization of error probability

This paper proposes a new criterion to stop the iterations in turbo decoders, based on the minimization of the probability of erroneous decisions, hence the name MinPe. The criterion analyses the evolution of Log-Likelihood Ratio (LLR) and compares the distance between the distributions of the LLRs negative and positive values with a threshold depending on the average of positive LLRs values. The iterative decoding process is stopped if the distance is greater than the threshold. The performances are analyzed in terms of Average Number of Iterations (ANI) and Bit Error Rate (BER) and compared with those of other classical criterions.

Influence of control type on chaotic behavior of the Alpazur oscillator

This paper studies the influence of different implementation methods of a simple control algorithm over the chaotic behavior of a specified circuit. Two new methods are presented: one is using a microcontroller and the other is using logical gates. The article also presents a unique approach to modelling a negative resistance as simple as possible, closely resembling a proposed mathematical dependency.

Multi-head wavelength division multiplexing free space optical system

Optical transport represent a fast method to transport data at a speed of Gbps order. A subcategory is represented by free space optics that can transport (digital) data over free space (usually atmosphere). Wavelength division multiplexing is a technology used for fiber optics, but with some adaptations can be useful, on a short range, for free space optical communication. This paper propose a method to use multi-head at the transmitter side, for redundancy, every head transporting a number of CWDM wavelengths in order to provide a minimum bitrate and/or assuring a transmission range at a designed BER. It is calculated, by simulation, the optimal number of optical heads for wich we obtain a real improvement in quality of transmission for a given bitrate/distance ratio.

Streamlining the functioning of the FSO systems by choosing the optimal transmission/reception components

FSO systems are becoming more and more used taking under consideration the ease of installation and exploitation under the conditions of the supply of a major fraction of optical fiber bandwidth at reasonable cost. Choosing elements for manufacturing FSO transceivers must keep into account their destination. FSO transceivers can be made using LED or LASER devices at the transmission side, the reception side could be equipped with PIN or APD diodes. This paper makes an analysis of the behavior of semiconductor LASER and LED sources, as well as semiconductor devices PIN and APD for reception side, in various attenuation scenarios, with the aim of achieving an optimization of FSO transceiver, corresponding to different geographical areas, taking into account the specific area and attenuation induced by atmospheric factors, in order to obtain an optimal functioning/price ratio. In this paper it is calculated the bit error rate versus transmission distance for various combinations of sources/receivers, using the Matlab and Optiwave modeling environment, for point to point optical system communication.