ETF Journal of Electrical Engineering

9

Authors: Vlatko Cingoski, Roman Golubovski, Saso Gelev, Goce Stefanov, Goran Klepov

The modern way of living increases the need for attractive sites for tourists to visit. Usually artistic fountains are attractive performing visual and spraying effects synchronized to musical pieces, and thus getting tourists’ attention. This paper proposes one novel method and approach to the problem of controlling and operation of an electric drive of the pumps. The proposed method is a techno-economic compromise achieving coordinated performance of the individual pump without usage of additional expensive servo valves, for the purpose of their synchronization with the choreography based on the desired music theme.

10

Authors: Slavica Tomović, Milutin Radonjić, Milica Pejanović-Djurišić, Igor Radusinović

Resource limitations of sensor nodes are the main weakness of wireless sensor networks (WSNs). This problem is difficult to alleviate in traditional ad-hoc networks, where each node participates in decentralized routing process and independently determines the next-hop to send data towards the destination. In that regard, this paper presents WSN architecture based on principles of software defined networking (SDN), which enables automatic network reconfiguration and optimal management of energy constrained sensor nodes with limited communications abilities. We discuss implementation challenges and the key benefits of software defined WSN design, with a special emphasis on advantages offered by centralized routing algorithms.

10

Authors: Žarko Zečević, Zdravko Uskoković, Božo Krstajić

A new iterative method for phasor estimation of power system is proposed. The proposed technique uses three adaptive algorithms. First two algorithms are used for frequency estimation. Third adaptive algorithm estimates amplitudes and phase angles between phasors. Simulation results confirm that the proposed algorithm exhibits better performances compared to the considered ones.

11

Authors: Miloš Brajović, Ljubiša Stanković, Miloš Daković

This paper addresses the reconstruction problem of non-stationary signals with missing samples. The reconstruction is achieved by using concentration measures of time-frequency representations in combination with a gradient-based iterative algorithm. As an example of time-frequency representation, the S-method is used in the proposed approach. The sparsity of the transform domain, needed for a successful reconstruction, is interpreted through the concept of concentration measures, and limits for successful reconstruction are discussed. Several examples with nonstationary signals which exhibit different concentrations in the time-frequency domain illustrate the presented theoretical concepts.

15

Authors: Aleksandar Sokolovski, Saso Gelev

The scope of this research paper is one very important aspects nowadays, the security and management of one of the most important services the email and all of the alike online services today. This paper attempts to investigate the possible benefits of using standard signature-driven spam detection logic in combination with algorithm for network intrusion detection system (NIDS). The primary objective is to verify that proposed solution (standard signature-driven spam detection logic and NIDS) will be an effective strategy for dealing with email spam detection. The main aim is to determine best possible integration of standard signature-driven spam detection logic in combination with algorithm for NIDS, for creating more effective solution for dealing with email spam and priority mail compared to the previous solutions available. This will be achieved by testing the effectiveness of the solution compared to other solutions until today, by using network simulators NS-3 and other programming tools.

15

Authors: Zoran Veličković, Zoran Milivojević, Milojko Jevtović

One way to protect the copyright of the video content is inserting invisible information - the watermark in the video content. The extraction of the embedded watermark is especially difficult in wireless networks, which are a subject to packet drops. Although multimedia applications are tolerant to packet losses, it cannot be said for their extraction algorithms. In this paper, it is shown that the improved iterative algorithm for watermark extraction from the encoded video can be successfully applied in the wireless environment. The efficiency of the improved algorithm is evaluated in the simulated wireless environment. In the wireless environment with 1% of dropped packets SSIM index was corrected by 24%, while in the environment with 2% of dropped packets SSIM index was corrected by 27.7%.

23

Authors: Ljubiša Stanković, Isidora Stanković

Signals sparse in a transformation domain can be recovered from a reduced set of randomly positioned samples by using compressive sensing algorithms. Simple reconstruction algorithms are presented in the first part of the paper. The missing samples manifest themselves as a noise in this reconstruction. Once the reconstruction conditions for a sparse signal are met and the reconstruction is achieved, the noise due to missing samples does not influence the results in a direct way. It influences the possibility to recover a signal only. Additive input noise will remain in the resulting reconstructed signal. The accuracy of the recovery results is related to the additive input noise. Simple derivation of this relation is presented. If a reconstruction algorithm for a sparse signal is used in the reconstruction of a nonsparse signal then the noise due to missing samples will remain and behave as an additive input noise. An exact relation for the mean square error of this error is derived for the partial DFT matrix case in this paper and presented in form of a theorem. It takes into account very important fact that if all samples are available then the error will be zero, for both sparse and nonsparse recovered signals. Theory is illustrated and checked on statistical examples.