نشریه مهندسی مخابرات جنوب
پیاپی 32 (تابستان 1398)

The network-based computer systems play critical role in our modern society; so there is highly chance these systems might be target of intrusion and attacks. In order to implement full-scale security in a computer network, firewalls and other intrusion prevention mechanisms aren’t always enough and needs other systems called intrusion detection systems. An Intrusion detection system can be set of tools, algorithms and evidence that help to identify, locate and report illegal or not approved activities by the network. Intrusion detection systems can be established by software or hardware systems and each have their own advantages and disadvantages. Because of various characteristics of intrusion detection data, in this research we select effective characteristics using improved genetic algorithm. Then by means of standard data mining techniques, we present a model for data classification.For performance evaluation of this suggested method, we used NSL-KDD database that has more realistic records than other intrusion detection data.

In this paper, we identify "variable time systems with slow changes" using Legendre basic functions. Physical phenomena behave with time-varying behavior for a variety of reasons. To model these systems, we need models with time-dependent parameters. In this paper, in order to identify, we consider a system that has time-varying parameters with slow changes. Select the input of this time-varying system of PRBS type, which is a frequency-rich signal. The results for noise cases are also largely acceptable. In this article, the system in question is called STV system for short.

This paper allocates subcarriers and power to each OFDMA user to minimize total user data rates due to overall power constraints, bit error rates, and proportionality between user data rates. Here we propose a non-duplicate method that makes our user rate possible by releasing severe fit constraints. This method is less complex than existing methods and gives us more user data simulation. In this article, by developing a subcarrier allocation scheme that makes the power allocation problem linear and expresses the approximate proportionality of the data, it extends the power allocation problem to a solution for simultaneous linear equations and simulates the results of the allocation algorithm. The proposed achieves an overall capacity that is less inconsistent than the previous method and significantly reduces computations while achieving acceptable data fit.

Phase shifting transformers are used to control the power transmitted through the lines by changing the amplitude and phase angle of the voltage. In the first group, mechanical switches and moving parts are used in PST types, and in the second group, semiconductor switches and electronic power converters have replaced mechanical switches. In this article, the analysis of internal structure and performance of Class A, D and E phase shift transformers is expressed and using a program, power distribution in the power grid in two modes of use of phase shift transformers and without these transformers in soft The MATLAB software is simulated and the numerical results of the effect of phase shift transformers on current and power distribution between two 110KV parallel lines are investigated. It turns out that phase shifting transformers are used to control the distribution of active power between lines, and in Class A phase shifting transformers, the upper and lower limits of the thyristor fire angle are a function of the operating conditions of the power system and the limiting determinant. The performance of these transformers is the high harmonic content of the output voltage. In Class D, GTO switches are used and their switching on and off is forced by switching method, and one of their outstanding features is that the converters do not depend on the operating conditions of the system, whose output can be controlled continuously and in all conditions.

Here, to improve the quality of the reconstructed image, a kind of fractal compression method is proposed, which is based on block classification and quadratic tree segmentation. First, the image is divided by an adaptive quadruple tree method. Sub-blocks are then classified at each level. Experimental results show that the image reconstructed and amplified by this method has a higher peak-to-peak signal-to-noise ratio (PSNR) and a better visual effect than the adaptive quadratic splitting method, while the compression ratio Has also increased.

In this paper, we have designed and implemented low voltage drop regulators and very small output changes using new solutions. In the regulator circuit structure, for the first time, two solutions of body power supply and variable voltage reference have been used. The power supply of the body, with the aim of increasing the gain of the regulation loop and using the variable voltage reference, has been done with the aim of further stabilizing the output voltage and increasing the power supply removal ratio (PSRR). Another important point in this paper is the implementation of the error amplifier with the help of three single-headed operational amplifiers with PMOS input, which significantly increases the accuracy of the regulation loop. The obtained PSRR value is equal to 46dB at a frequency of 1KHz. The input voltage can vary between 1.8V to 2.5V and the stabilized output voltage is 1.6V. The maximum output voltage ripple is equal to 1mV, which is equivalent to 0.03%. The output ohmic load is equal to 20  and the average capacitive load is equal to 100pF. The maximum output current for the desired output impedance and voltage drop of 0.2V is equal to 80mA.