Telfor Journal Vol.13 No.1 (2021)

Content

Dynamic Spectrum Access with Deep Q-learning in Densely Occupied and Partially Observable Environments

S. Tomovic and I. Radusinovic
Topic:
Mobile and Wireless Networks
Abstract
In this paper, we propose a new Dynamic Spectrum Access (DSA) method for multi-channel wireless networks. We assume that DSA nodes do not have prior knowledge of the system dynamics, and have only partial observability of the channels. Thus, the problem is formulated as a Partially Observable Markov Decision Process (POMDP) with exponential time complexity. We have developed a novel Deep Reinforcement Learning (DRL) based DSA method which combines a double deep Q-learning architecture with a recurrent neural network and takes advantage of a prioritized experience buffer. The simulation analysis shows that the proposed method accurately predicts a channel state based on the fixed-length history of partial observations. Compared with other DRL methods for DSA, the proposed solution can find a near-optimal policy in a smaller number of iterations and suits a wider range of communication environments, including dynamic ones, where channel occupancy pattern changes over time. The performance improvement increases with the number of channels and with a channel state transition uncertainty. To boost the performance of the algorithm in densely occupied environments, multiple DRL exploration strategies are examined and evaluation results are presented in the paper.
Keywords
Cognitive radio, Reinforcement learning, Q-learning.
Full Text
HyperLink Dynamic Spectrum Access with Deep Q-learning in Densely Occupied and Partially Observable Environments
Page(s)
1-6
Doi
10.5937/telfor2101001T

Reduced-Complexity Offset Min-Sum Check Node Unit for Layered 5G LDPC Decoder

V. L. Petrović and D. M. El Mezeni
Topic:
Communication Theory
Abstract
This paper presents a novel approach for the reduced-complexity Min-Sum (MS) decoding of low density parity check (LDPC) codes in the partially parallel layered decoder architecture, which contains a large number of serial check node processors. Reduced complexity is obtained by using the variant of the single-minimum Offset Min-Sum (smOMS) algorithm that approximates a second minimum with the addition of the variable weight parameter to the minimum value. Although the reduced-complexity MS algorithms primarily reduce hardware resources in fully parallel implementations, the results showed that a considerable reduction can be obtained if serial check node processors are used. The paper also proposes a better subminimum estimation for irregular codes from 5G new radio (5G NR). The method uses smaller subminimum estimation weights in check nodes with a higher degree and higher weights in check nodes with a smaller degree, which leads to the significant improvement in the SNR performance. Additionally, it is shown that SNR performance can be further improved by applying offset before minimum calculation, which differs from conventional Min-Sum approaches.
Keywords
5G new radio, layered decoding, low density parity check (LDPC) codes, min-sum (MS) algorithm.
Full Text
HyperLink Reduced-Complexity Offset Min-Sum Check Node Unit for Layered 5G LDPC Decoder
Page(s)
7-12
Doi
10.5937/telfor2101007P

Testing RFoF Link for Transmitting HF-OTHR Signal Between Transmitter and Receiver Shelters

P. Petrović, B. Džolić, N. Lekić, N. Grbić, A. Ćupurdija, V. Orlić, and M. Erić
Topic:
Transmission Systems
Abstract
HF-OTHR site contains two equipment shelters, up to 1 km away from each other, that need to be connected for transmitting a FMCW signal. This connection, if realized using a coaxial cable, has shown itself to be vulnerable to external electromagnetic discharges, which can damage the sensitive radar equipment. This paper explores and tests the possibility of using Radio-Frequency-over-Fiber (RFoF) link as an alternative to a coaxial cable for transmission of signal, in order to ensure the immunity from external sources of electromagnetic interference (EMI).
Keywords
Radio-Frequency-over-Fiber – RFoF, High-Frequency Over-the-Horizon Radar – HF-OTHR, Electromagnetic Interference.
Full Text
HyperLink Testing RFoF Link for Transmitting HF-OTHR Signal Between Transmitter and Receiver Shelters
Page(s)
13-18
Doi
10.5937/telfor2101013P

Genetic Algorithm Applied to Discrete Optimization of Band-Pass Microwave Filter

D. Ninković and D. Olćan
Topic:
Applied Electromagnetics
Abstract
We propose a design approach for band-pass microwave filters based on optimization of discrete-valued parameters of filters using an implementation of (1 + (λ, λ)) genetic algorithm. If the filter is made of SMD components then only discrete values are allowed. The proposed design approach yields a solution with feasible components values in the end, without further need for tuning and adjustments of component values that is needed in the case when real numbers are used during optimization. The optimization setup is run for 20 times and obtained (suboptimal) solutions are presented. One of the best optimized solutions of a band-pass filter is chosen for further analysis. The found filter design is verified using a circuit solver including the yield analysis, 3D electromagnetic simulations and by measurements of the manufactured prototype. The presented results as well as the optimization run-time show that the proposed approach based on discrete optimization can be used to design microwave filters.
Keywords
Band-pass filter, discrete optimization, genetic algorithm.
Full Text
HyperLink Genetic Algorithm Applied to Discrete Optimization of Band-Pass Microwave Filter
Page(s)
19-24
Doi
10.5937/telfor2101019N

Designing a Downsized Quadrature Directional Coupler

D. A. Letavin
Topic:
Applied Electromagnetics
Abstract
To miniaturize directional couplers, the replacement of their quarter-wave sections with electrodynamic structures with equivalent characteristics at smaller physical dimensions is used. It is shown that the structures used have filtering properties and act as low-pass filters. It is set at what cutoff frequency the low-pass filters must be calculated to obtain a phase shift of 90 degrees.
Keywords
Directional coupler, dielectric constant, microstrip line, substrate.
Full Text
HyperLink Designing a Downsized Quadrature Directional Coupler
Page(s)
25-28
Doi
10.5937/telfor2101025L

Advanced High-Gain Slot Antenna Arrays for 5G and Radar Applications

M. Milijic and B. Jokanovic
Topic:
Applied Electromagnetics
Abstract
This paper presents an advanced design of high-gain slot antenna array at K-band using slots as radiating elements serially fed by coplanar waveguide (CPW). The arrays consist of identical slots of rectangular shape positioned symmetrically relative to the CPW feeding line. Firstly, the linear arrays of 14 slots are examined considering mainly their bandwidth and radiation characteristics. In addition, two identical linear sub – arrays of 14 slots are investigated when they have separate feeding in the form of two generators for each sub – array. Last, a CPW T-junction is employed to feed the antenna consisting of 2 x 14 slots which resulted in a wide operating bandwidth and maximum gain of 21.0 dBi which proved to be 2.25 dB less gain than with independent feeding. In order to enhance the antenna gain, both arrays are terminated with open-circuited stubs, so that the energy remaining after the last array element is reflected from the stub and re-radiated through the slot arrays. The length of the stubs is optimized to provide that the reflected wave is in phase with the forward-traveling waves at all the slot locations. In that way, very little energy is wasted and consequently the antenna gain is increased. The feed simplicity and uniplanar configuration of the slot arrays, designed for the frequency range 24.25-27.5 GHz, makes them attractive for radar sensors and high capacity 5G technology applications.
Keywords
Antenna array, Symmetrical slot antenna, CPW-fed antenna, Series feeding, CPW T-junction.
Full Text
HyperLink Advanced High-Gain Slot Antenna Arrays for 5G and Radar Applications
Page(s)
29-34
Doi
10.5937/telfor2101029M

Quality Assessment Experiment for 4k SVT-AV1 Video Format

A. M. Gavrovska, M. S. Milivojevic, and G. Zajic
Topic:
Multimedia
Abstract
The industrial consortium AOMedia has recently developed the AV1 (AOMedia Video 1) format considered as a successor of VP9. One of the main goals with the video coding and compression format is to enable efficient web based video content delivery, as in the case of OTT (Over-the-top) services. Nowadays, there are different AV1 software implementations available for experimental analysis besides the reference tool libaom. The Scalable Video Technology for AV1, or SVT-AV1 codec, is oriented towards further optimizations for specific Intel hardware. In this paper, we have performed a video quality assessment experiment with some of the SVT-AV1 implementations using 4k like video. The results show the advantages of SVT-AV1 format, as well as its performance for different quantization factors.
Keywords
SVT-AV1, Quality Assessment, Mp4, 4k, internet, VP9, HEVC, Streaming services.
Full Text
HyperLink Quality Assessment Experiment for 4k SVT-AV1 Video Format
Page(s)
35-40
Doi
10.5937/telfor2101035G

Reliability Testing, Noise and Error Correction of Real Quantum Computing Devices

I. P. Galanis, I. K. Savvas, A. V. Chernov, and M. A. Butakova
Topic:
Quantum Computing
Abstract
From Pharmacology to Cryptography and from Geology to Astronomy are some of the scientific fields in which Quantum Computing potentially will take off and fly high. Big Quantum Computing vendors invest a large amount of money in improving the hardware and they claim that soon enough a quantum program will be hundreds of thousands of times faster than a typical one we know nowadays. But still the reliability of such systems is the main obstacle. In this work, the reliability of real quantum devices is tested and techniques of noise and error correction are presented while measurement error mitigation is explored. In addition, a well-known string matching algorithm (Bernstein–Vazirani) was applied to the real quantum computing device in order to measure its accuracy and reliability. Simulated environments were also used in order to evaluate the results. The results obtained, even if these were not 100% accurate, are very promising which proves that even these days a quantum computer working side by side with a typical one is reliable and especially when error mitigation techniques are applied.
Keywords
Qiskit, Quantum programming, quantum noise, quantum error, Error mitigation, string matching.
Full Text
HyperLink Reliability Testing, Noise and Error Correction of Real Quantum Computing Devices
Page(s)
41-46
Doi
10.5937/telfor2101041G

FINKI Scholar, a Publications Database for Faculty of Computer Science and Engineering Scholars

B. Risteska Stojkoska, H. Gjorshevski, and E. Mitreva
Topic:
Software Tools and Applications
Abstract
The aim of this paper is to develop a web application where scholars of the Faculty of Computer Science and Engineering (FINKI) at the University of Ss. Cyril and Methodius can display and share their projects and publications. Visitors can view, search through, and filter the authors, projects and publications that can be added and edited by the administrators via the administrator panel. In this paper, we first explain the type of system we are building and go through similar existing systems explaining how they work and what they offer. Then, we go through the programming languages and technologies we decided to use to develop this web application. After that, the development phase follows, where we describe each of the features we implemented. In The Final Product section we finally show images where you can see how the web application works and what it looks like. We finish the paper with a conclusion, briefly summarizing what we have achieved.
Keywords
application, FINKI, Laravel, MySQL, publications, PHP, scholars, web.
Full Text
HyperLink FINKI Scholar, a Publications Database for Faculty of Computer Science and Engineering Scholars
Page(s)
47-52
Doi
10.5937/telfor2101047R

Cryptospatial Blockchain Sharia Hotel Based on Practical Byzantine Fault Tolerance

M. A. R. Suryana, A. T. Wibowo, A. Izuddin, F. M. Amin, A. B. Gumelar, and MY T. Sulistyono
Topic:
Software Tools and Applications
Abstract
This research develops an application based on android that uses four interconnected nodes in a network with the Practical Byzantine fault tolerance (PBFT) blockchain method to value object geospatial retrieval. First, this application uses two types of users, general users and surveyors. Second, a surveyor location is validated within a radius of fifty meters from the central point of assets location using midpoint circle validation. Third, PBFT is used to access and validate and guarantee consistency by data using JSON-DIFF algorithm.
Keywords
Blockchain PBFT, Geospatial Retrieval, JSON-DIFF Algorithm. Midpoint Circle Validation.
Full Text
HyperLink Cryptospatial Blockchain Sharia Hotel Based on Practical Byzantine Fault Tolerance
Page(s)
53-57
Doi
10.5937/telfor2101053S