Telfor Journal Vol.9 No.2 (2017)

Content

Editorial HyperLink
Editor-in-Chief: Prof. Dr Đorđe Paunović

Performance Evaluation of Software Routers with VPN Features

H. Redžović, A. Smiljanić, and B. Savić
Topic:
Telecommunications Networks
Abstract
This paper presents implementation and analysis of the VPN software router which is based on Quagga and strongSwan open-source software tools. We validated the functionalities of strongSwan and Quagga in realistic environment which include scenarios with link failures. Also, we measured and analyzed the performance of encryption and hash algorithms supported by strongSwan software, in order to advise an optimal VPN configuration that provides the best performance.
Keywords
IPsec protocol, Quagga, Software Routers, Software VPN Solutions, strongSwan.
Full Text
HyperLink Performance Evaluation of Software Routers with VPN Features
Page(s)
74-79
Doi
10.5937/telfor1702074R

Performance of a TV white space database with different terrain resolutions and propagation models

A. M. Fanan, N. G. Riley, M. Mehdawi, and O. Alfahad
Topic:
Radio Communications
Abstract
Cognitive Radio has now become a realistic option for the solution of the spectrum scarcity problem in wireless communication. TV channels (the primary user) can be protected from secondary-user interference by accurate prediction of TV White Spaces (TVWS) by using appropriate propagation modelling. In this paper we address two related aspects of channel occupancy prediction for cognitive radio. Firstly we investigate the best combination of empirical propagation model and spatial resolution of terrain data for predicting TVWS by examining the performance of three propagation models (Extended-Hata, Davidson-Hata and Egli) in the TV band 470 to 790 MHz along with terrain data resolutions of 1000, 100 and 30 m, when compared with a comprehensive set of propagation measurements taken in randomly-selected locations around Hull, UK. Secondly we describe how such models can be integrated into a database-driven tool for cognitive radio channel selection within the TVWS environment.
Keywords
Path loss, Diffraction, Propagation Model, Spectrum Measurement, TVWS, Cognitive Radio.
Full Text
HyperLink Performance of a TV white space database with different terrain resolutions and propagation models
Page(s)
80-85
Doi
10.5937/telfor1702080F

DSP implementation of surround speaker virtualizer for sound bar systems

N. Kaprocki, J. Kovačević, R. Pečkai Kovač, and M. Malko
Topic:
Signal Processing
Abstract
This paper describes one solution for an implementation of the surround speaker virtualization module for a digital signal processor in a sound bar system. The main problem in this system, which consists of a decoder, a renderer and a post-processing module, is complex processing of sound in real-time. In order to achieve real-time execution of these operations and offer customers an affordable product, sound bar system is implemented on an embedded platform. A detailed overview of the system architecture and available resources is given, as the development of modules in an embedded system requires optimal resource usage. Furthermore, numerous challenges and constraints of real-time system programming are presented through the implementation of surround virtualization module, an integral part of the post-processing block. The merits of the proposed architecture are fortified with the measured usage of limited processor resources, and evaluation results confirm that real-time execution of the proposed solution is achieved.
Keywords
audio processing, DSP, real-time, sound bar, surround sound, virtualization.
Full Text
HyperLink DSP implementation of surround speaker virtualizer for sound bar systems
Page(s)
86-91
Doi
10.5937/telfor1702086K

Sparse Representation of FHSS Signals in the Hermite Transform Domain

M. Brajović, A. Draganić, I. Orović, and S. Stanković
Topic:
Signal Processing
Abstract
Signal sparsity is exploited in various signal processing approaches. Signal compression, classification, coding, as well as the recently introduced compressed sensing are some examples where the possibility to represent a signal sparsely determines the efficiency of the applied processing technique. However, the possibility of a sparse signal representation in a transform basis is highly dependent on the signal nature. Therefore, finding a suitable basis where the signal exhibits a compact support is a challenging task. In this paper, the Hermite Transform (HT) is considered as a sparsity domain for the FHSS wireless communication signals. The transform coefficients sparsification is done by optimizing the scaling factor and time-shift of basis functions. The optimization is done by minimizing the concentration measure of HT coefficients. The theory is verified by numerical examples with synthetic FHSS signals.
Keywords
FHSS signals, signal sparsity, sparsification, Hermite transform domain.
Full Text
HyperLink Sparse Representation of FHSS Signals in the Hermite Transform Domain
Page(s)
92-97
Doi
10.5937/telfor1702092B

An Automated Environment for Hardware Testing Using PXI Instrumentation and LabVIEW Software

V. D. Ćatić, N. M. Lukić, I. M. Salom, V. P. Ristić, M. M. Kabović, B. Ž. Planić, and N. M. Nenadić
Topic:
Applied Electronics
Abstract
Reliable and fast testing was a requirement in the serial production of the advanced wireless microphone MIKME. Hence, a system for automatic testing, fully adapted for the product, was developed. The system comprises: 1) a specially designed test fixture – bed-of-nails, on which the device under test is placed, 2) the PXI platform and 3) an application developed in LabVIEW environment. Throughout the design of this system the goal was to achieve maximal automation of the entire test procedure in order to minimize the influence of human factor, and therefore save time and significantly reduce the possibility of error.
Keywords
automated hardware testing, LabVIEW, PXI, test procedures, virtual instrumentation.
Full Text
HyperLink An Automated Environment for Hardware Testing Using PXI Instrumentation and LabVIEW Software
Page(s)
98-103
Doi
10.5937/telfor1702098C

Sentiment Classification of Documents in Serbian: The Effects of Morphological Normalization and Word Embeddings

V. Batanović and B. Nikolić
Topic:
Software Tools and Applications
Abstract
An open issue in the sentiment classification of texts written in Serbian is the effect of different forms of morphological normalization and the usefulness of leveraging large amounts of unlabeled texts. In this paper, we assess the impact of lemmatizers and stemmers for Serbian on classifiers trained and evaluated on the Serbian Movie Review Dataset. We also consider the effectiveness of using word embeddings, generated from a large unlabeled corpus, as classification features.
Keywords
comparative evaluation, lemmatization, morphology, sentiment analysis, stemming, word embeddings.
Full Text
HyperLink Sentiment Classification of Documents in Serbian: The Effects of Morphological Normalization and Word Embeddings
Page(s)
104-109
Doi
10.5937/telfor1702104B

Distributed Resource Allocation in Cloud Computing Using Multi-Agent Systems

A. Mazrekaj, D. Minarolli, and B. Freisleben
Topic:
ddSoftware Tools and Applications
Abstract
The Infrastructure-as-a-Service model of cloud computing allocates resources in the form of virtual machines that can be resized and live migrated at runtime. This paper presents a novel distributed resource allocation approach for VM consolidation relying on multi-agent systems. Our approach uses a utility function based on host CPU utilization to drive live migration actions. Experimental results show reduced service level agreement violations and a better overall performance compared to a centralized approach and a threshold-based distributed approach.
Keywords
Cloud computing, live migration, multi-agent systems, utility function, virtual machines.
Full Text
HyperLink Distributed Resource Allocation in Cloud Computing Using Multi-Agent Systems
Page(s)
110-115
Doi
10.5937/telfor1702104M

ERRATA

Topic:
ERRATA
Abstract
Errata to the July 2017 issue of the Telfor Journal.
Keywords
Full Text
HyperLink ERRATA
Page(s)
116-116