SERBIAN JOURNAL OF ELECTRICAL ENGINEERING
Vol. 18, No. 2, June 2021

CONTENTS


Milan Milivojević, Dragi Dujković, Ana Gavrovska
Video Coding and Constant Quality Evaluation using 4k aomenc-AV1 and rav1e-AV1 Formats
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DOI: https://doi.org/10.2298/SJEE2102139M
Abstract: It is much expected from the relatively novel, open, royalty-free AV1 (Alliance for Open Media (AOMedia) Video 1) standard. At this moment, there are many new variants of AV1 format. It is designed for efficient video internet delivery and high-quality video transmission. AV1 is recognized as Google’s VP9 format successor. One of the reference tools used so far for testing AV1 is libaom-AV1. Nevertheless, due to its time-consuming performance, there are now different available standalone solutions for experimental analysis. Here, one such solution AOMedia’s standalone aomenc (aomenc-AV1) is tested in order to analyze quality assessment based on constant quality constraint factor. Three different metrics are calculated for various 4k video content of the same frame rate. Moreover, rav1e implementation was tested for the same visual data, where rav1e-AV1 also represents an AV1 video encoder, which is considered reliable and suitable in most cases, where libaom is not applicable. In this paper, the comparison results between aomenc-AV1 and rav1e-AV1 are shown.
Keywords: Video codecs, 4k/UHD, Constant Quality, aomenc-AV1, libaom-AV1, rav1e-AV1, Bitstream.

Lazar Đokić, Aleksandar Jokić1, Milica Petrović, Nikola Slavković, Zoran Miljković
Application of Metaheuristic Optimization Algorithms for Image Registration in Mobile Robot Visual Control
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DOI: https://doi.org/10.2298/SJEE2102155D
Abstract: Visual Servoing (VS) of a mobile robot requires advanced digital image processing, and one of the techniques especially fitting for this complex task is Image Registration (IR). In general, IR involves the geometrical alignment of images, and it can be viewed as an optimization problem. Therefore, we propose Metaheuristic Optimization Algorithms (MOA) for IR in VS of a mobile robot. The comprehensive comparison study of three state-of-the-art MOA, namely the Slime Mould Algorithm (SMA), Harris Hawks Optimizer (HHO), and Whale Optimization Algorithm (WOA) is presented. The previously mentioned MOA used for IR are evaluated on 12 pairs of stereo images obtained by a mobile robot stereo vision system in a laboratory model of a manufacturing environment. The MATLAB software package is used for the implementation of the considered optimization algorithms. Acquired experimental results show that SMA outperforms HHO and WOA, while all three algorithms perform satisfactory alignment of images captured from various mobile robot poses.
Keywords: Visual Servoing, Mobile robot, Image registration, Whale optimization algorithm, Slime mould algorithm, Harris hawks optimizer.

Konstantin D. Krestovnikov, Ekaterina O. Cherskikh
Development of the Structure and Circuit Solution of a Bidirectional Wireless Energy Transmission System for Swarm Robots
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DOI: https://doi.org/10.2298/SJEE2102171K
Abstract: This paper presents development of a circuit solution design for a bidirectional wireless energy transfer system, based on a resonant self-oscillator. The operation principle of the developed circuit solution in receiving and transmitting mode is described and the elementary circuit diagram is presented together with design ratios. Coil parameters for the resonant circuit are calculated, optimal number of turns in coils is presented, based upon the specified limit value of permissible current. The dependencies of system efficiency from transmitted power, maximum transmitted power, and energy transmission distance are obtained. The developed design, which includes the step-up DC-DC converter, allows to obtain the voltage on the output of the receiving system, equal to or higher than the voltage of the power source of the transmitting system. The specific feature of the proposed system is that it does not require a dedicated control system for operation in resonant mode and changing direction of power transfer. Resonance in transmitting and receiving coils can be maintained, even when their mutual layout is changed, due to utilization of identical resonant circuits and a self-oscillator. Application of the proposed solution is relevant for energy transfer among autonomous robots with limited positioning accuracy, as well as for energy transfer from power supply to robot or in reverse direction.
Keywords: Bidirectional wireless power transmission system, Current fed push-pull inverter, Swarm robotics, Synchronous rectifier.

Noor Kareem Jumaa, Abbas Mohammed Allawy, Mustafa Safaa Hussein Shubbar
Modelling and Optimising a New Hybrid Ad-Hoc Network Cooperation Strategy Performance Using Genetic Algorithm
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DOI: https://doi.org/10.2298/SJEE2102193J
Abstract: The lifetime of an ad-hoc network depends on a mobile device’s limited battery capacity. In ad-hoc multi-hop communication, source nodes use intermediate nodes as a relay to communicate with remote destinations. As cooperation between nodes is restrained by their battery resources, it might not be in their best interests to always accept relay requests. Therefore, if all nodes decide how much energy to spend for relaying, selfish or non-cooperative nodes reduce cooperation by rejecting to forward packets to others, thereby leading to a dramatic drop in the network’s throughput. Three strategies have been founded to solve this problem: tit-for-tat, live-and-let-live, and selective drop. This research explored a new strategy in ad-hoc cooperation which resulted from the combination of the live-and-let-live and selective drop strategies. This new strategy is based on the suggestion to select fewer hops with a low drop percentage and sufficient power to stay alive after forwarding the data packets towards the destination or other relays at the route path. We used a genetic algorithm (GA) to optimise the cooperative problem. Moreover, the fitness equation of the GA population was designed according to the mixing of the two strategies, which resulted in a new optimized hybrid dynamic-static cooperation.
Keywords: Ad-Hoc, Power Consumption, GA, Cooperation Strategy, Optimisation.

Mekaladevi Velusamy, Nirmala Devi Manickam, Jayakumar Madasamy
Design and Analysis of Dual Dumbbell and Rectangular Slots SIW Cavity-Backed Antenna at 2.45 GHz
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DOI: https://doi.org/10.2298/SJEE2102211V
Abstract: The design and realization of a wideband substrate-integrated waveguide (SIW) cavity-backed slot antenna operating at 2.45 GHz for WLAN applications are presented. Dual dumbbell-shaped slots with rectangular slots are u!sed to achieve increased bandwidth. The bandwidth observed is 160 MHz with the dumbbell-shaped slots. Further, it has been improved up to 9.2% by adding a rectangular slot. The wideband antenna is analyzed using ANSYS HFSS and fabricated on FR-4 substrate. The measured results of the proposed design are in good agreement with the simulation results and comparable with the reported results.
Keywords: Cavity-backed antenna, Dual dumbbell slot antenna, Substrate- integrated waveguide (SIW), Bandwidth enhancement.

Mohammadbagher Asadpourahmadchali, Mohsen Niasati1 and Yousef Alinejad-Beromi
Modeling of Different Tower Grounding Systems Using Hybrid Continuous Circuit-Trapezoidal Integration Method
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DOI: https://doi.org/10.2298/SJEE2102225A
Abstract: In order to protect the transmission lines against lightning strikes, it is important to investigate the tower grounding system. In this paper, a recent method called hybrid continuous circuit-trapezoidal integration method is used to calculate the impulse impedance of the grounding system. Moreover, conventional structures of the grounding systems have been simulated and the results show that, with the same wire length, the square with additional wire system has the least impulse impedance as compared to counterpoise, square and crow’s foot. Moreover, the effects of soil resistivity and lightning current rise-time on the impulse impedance of these grounding systems are investigated. It is concluded that the design of the grounding system depends on the geographic location of the site in terms of soil resistivity and isotropic characteristics of the area in terms of lightning current rise-time.
Keywords: Lightning, Grounding system modeling, Hybrid continuous circuit-trapezoidal integration method, Soil resistivity

Gjorgji Ilievski, Pero Latkoski
Classification of Network Traffic Using Supervised Machine Learning Algorithms within NFV environment
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DOI: https://doi.org/10.2298/SJEE2102237I
Abstract: Deep Packet Inspection (DPI) of the network traffic is used on a regular basis within the traditional and virtualized environments. But changes in the network architecture with the introduction of containers, microservices, application functions, network functions, and the penetration of 5G access technology are adding more traffic complexity, especially in the so-called east-west flow direction. Network Functions Virtualization (NFV) has become an unavoidable step for further IP network development. In this context, DPI is becoming a challenge. Furthermore, the penetration of 5G allows access of various kinds of devices to the network with cloudification logic which drives them. This paper provides a performance analysis of a selected set of supervised machine learning (ML) algorithms for classification of network traffic within an NFV environment. The goal is to find a suitable algorithm that will classify the traffic from a point of both precision and speed, especially because in the 5G networks any packet delay may compromise the quality of service requirements. The research shows that out of the 6 algorithms tested, Decision Tree algorithm has the best overall performance, from both classification precision and time consumption point of view. It has proved as a reliable classifier that is performing evenly across different classes. Due to the specifics of the virtualized environments and encryption methods, payload data, source, destination, and port information of the network traffic packets are excluded from any statistical operation used for classification by the ML algorithms.
Keywords: Classification, Machine Learning, Network Functions Virtualization, Network traffic.

Debashish Pal, Soumee Das
C-V and I-V Characterisation of CdS/CdTe Thin Film Solar Cell using Defect Density Model
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DOI: https://doi.org/10.2298/SJEE2102255P
Abstract: This paper presents a detailed study of the current-voltage (I-V) and capacitance-voltage (C-V) measurements made on a CdS/CdTe based solar cell by numerical modeling. Implementation of the simulated cell having a superstrate configuration was done with the help of SCAPS program using defect density model. The I-V characterisation includes window and absorber layer optimisation based on various factors including the impurity doping concentration, thickness and defect density. The energy band diagram, spectral response and current-voltage plot of the optimised cell configuration are shown. C-V characterisation (Mott-Schottky analysis) of the solar cell is conducted at different low frequencies to determine the flatband potential, carrier concentration and to validate the reliability of the results. The optimum device performance was obtained when the active layer was 2 µm thick with a doping level of 1×1015/cm3.
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