Florin Enache

Theoretical and practical implementation of scrambling algorithms for speech signals

The problem of secure information transmission over an unsecured medium is very important in the communication systems and especially in the military systems. Speech scrambling is one of the methods used to prevent unauthorized decryption of the message. In this paper three scrambling techniques are presented and their performances are analyzed. These methods were tested based on some real audio signals that they were recorded in an anechoic chamber.

Sidelobe reduction in pulse-compression radar using the stationary phase technique: An extended comparative study

According to pulse-compression radar theory, the sidelobe reduction using nonlinear frequency modulation (NLFM) signal processing represents a major and present research direction. Although in literature a lot of techniques to design efficient NLFM waveforms are indicated, one of the most important methods as application area is focused on stationary phase technique (SPT) use. Consequently, the main objective of this paper is to make an extended comparative study as sidelobe suppression among some very promising NLFM laws achieved by applying of a proper SPT synthesis algorithm. In addition, some aspects related to the suitable choice of the parameters involved in the synthesis process of NLFM signals are also indicated.

Smart sensor for chemical compounds concentration

A Smart Sensor used for measuring the concentration of chemical compounds in fluids/solutions is designed, implemented and tested. The sensor comprises a potentiostat employed for three-electrode electrochemical cell (biosensor) biasing, a transimpedance amplifier and a digital interfacing system. The stability of the potentiostat and the linearity of the transimpedance amplifier are theoretically and experimentally investigated. Finally, the high performances of the smart sensor are demonstrated by simulations and measurements.

Sparse array antenna design based on dolph-chebyshev and genetic algorithms

In this paper an original method for the synthesis of a planar sparse array antenna is presented. The aim is to obtain a planar sparse array antenna starting from a Dolph Chebyshev radiating elements feeding distribution and cancelling feeding for as large a number of elements as possible while maintaining the performances in terms of directivity characteristics, by applying optimization with genetic algorithms. Planar sparse array antennas with square shapes and variable number of elements are analyzed and synthesized using this new method.

Analysis of direct current nonlinear electrical circuits by means of symbolic computation and genetic algorithms

The paper presents a method for the determination of the bias point of nonlinear electrical circuits, based on the modified nodal method, by utilization of symbolic computation and genetic algorithms. For the solving of the circuit it is written the equations system corresponding to the modified nodal method in a partial symbolic form. On the basis of the partial symbolic form of these equations an error function is generated which gives the circuit solution by minimization. In the paper are presented a few examples of circuits, for which iterative solving is not convergent. These circuits could be solved by means of the elaborated method.

Extended Partially Overlapped Channel Interference Model and Study for 802.11 Wi-Fi Communications

In this paper the authors extend the tests and model verification related to the partially overlapped channel interference in Wi-Fi communications. Recently more and more papers have investigated the side effects of the channel interference on the throughput parameter. The paper proposes a theoretical model and an experimental approach to obtain useful information regarding channel allocation and spatial reuse in conditions of the intense traffic, by exploiting the data related to the site interference. The paper results determined how smart planning of the operating channel versus the observed interference spectrum configuration can reduce the amount of interference impact and eventually improve Wi-Fi network performance and it also confirmed an alternative way to avoid interferences, without changing the channels configuration (desired or jamming), which consists on getting out of the jamming signals interference range, after estimating this range.

Optimization of non-uniform linear antenna array with linear and parabolic parameters variations

The paper presents the design of non-uniform linear antenna arrays with symmetrical elements, considering linear and parabolic variations for distances between elements and a non-uniform distribution of currents through the elements. Starting from an imposed radiation pattern the coefficients, which describe the linear and parabolic variations of the array antenna parameters, are determined using optimization with genetic algorithms. Using this approach, the number of variables of the fitness function is reduced from 2N to 2, which can be helpful in the implementation of real-time algorithms used in complex/dynamic adaptive arrays.

Some considerations about third-order statistics for different types of radar signals

The signal processing techniques based on higher-order statistics are used in many applications due to their interesting properties. These techniques are very useful when the signals are affected by the gaussian noises. In this paper the higher-order moments and the moment spectra for deterministic signals are theoretically described. An analysis of the third-order statistics for some particularly signals used in radar domain is presented.

Experimental characterization of a high accuracy amperometric sense and control circuit for three-electrode biosensors

A Sense and Control Circuit (SCC) developed for amperometric concentration evaluation is redesigned, based on preliminary experimental investigations. This cost-effective circuit comprises a potentiostat for three-electrode electrochemical cell (biosensor) control and a transimpedance amplifier for cell current sensing. Stability, noise robustness and response time are improved, as demonstrated by experiments and simulations. SCC performances are evaluated in comparison with a professional system, by H2O2 concentration measurements.

Optimal design of circular antenna array using genetic algorithms

This paper presents the design of circular antenna array with isotropic radiators by optimization using genetic algorithms. The problem consists in the obtaining of an imposed radiation pattern starting from a uniform circular antenna array. The goal is achieved using non-uniform distances between the circles which the radiators are disposed on and a non-uniform distribution of currents through the radiators on the successive circles. The work results and the paper conclusions reveal advantage of our approach versus the uniform circular antenna array. Also an important result is the reduction of the number of variables in the fitness function, which creates good premises for the implementation of real-time algorithms useful in complex/dynamic adaptive arrays.