TELFOR is the abbreviation for the Telecommunications Forum, a long lasting scientific, engineering and professional event which started in 1993 in Belgrade, Serbia. Initial idea was to establish a new modest national scientific conference in Telecommunications and related areas. During the years, that idea evolved in such a way that today TELFOR is a huge regional international conference, having also its several other parallel tracks, like special presentations of companies, presentations and papers of invited experts, exhibition of telecommunications hardware, software, systems and services, then seminars, tutorials, round tables, etc. During TELFOR’s existence several thousands of scientific papers were presented and published, quite a number of them being with a considerable quality and important results.
Having such resources at disposal, establishing a new scientific journal, the TELFOR Journal, was a very natural next step for several reasons:
- Authors with favourable TELFOR reviewers’ assessments would have additional chances to improve and expand their initial ideas;
- Editorial board would have a wide set of prospective invited authors;
- After some time of existence, one could expect that TELFOR Journal would attract independent authors to submit their papers to be considered for publishing.
The TELFOR Journal is a new journal. The first volume consisting of two issues was published during the TELFOR 2009 conference in November 2009. That first volume of the Journal was intended to present a selection of the improved and expanded versions of the best scientific papers presented at Telecommunications Forum 2008. Due to the short period of time elapsed, it is not possible to make any final conclusions, but one could surely judge that the first impressions of the scientific and research community were positive, both with respect to the Journal scientific quality and the very nice design.
Within the period of the last year the Editorial board noted the increase of the interest in publishing in the TELFOR Journal, mainly between the TELFOR conference authors.
The second volume of the TELFOR Journal, again with two issues, will be electronically published before or during the TELFOR 2010 conference. Printed copies are due later, depending on the scope of the paid subscriptions.
The TELFOR Journal is published in the English language, with both electronic and printed versions, minimally with the two issues per year. Having in mind that recent studies have shown that freely available papers are cited very often, the Editorial board decided that electronic version will be free of charge.
The TELFOR Journal is an IEEE co-supported publication and it is following all the IEEE rules, procedures, and consequently the scientific quality.
The large spectrum of TELFOR Journal topics accounts for the rapid convergence through telecommunications towards the information and knowledge society. The Journal provides a medium for exchanging research results and technological achievements accomplished by the scientific community from academia and industry.
Editor-in-Chief
Prof. Dr Đorđe Paunović
This paper presents the concept of green telecommunication networks and provides information about the power consumption within fixed line and wireless communication networks. It outlines the significance of energy efficiency in modern and future telecommunication networks and suggests directions for optimizing network performance in terms of energy demands. Numerous examples and reviews are also discussed. The aim is to introduce the reader to current green technologies and outline the necessity for energy efficiency in information and communication technology.
Keywords: Green telecommunication networks, ICT and energy efficiency.
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Subject Category: Telecommunication Policy
Page(s): 2-7
Routing protocol election in MANET (Mobile Ad Hoc Network) is a great challenge, because of its frequent topology changes and routing overhead. This paper compares performances of three routing protocols: Destination Sequenced Distance Vector (DSDV), Ad Hoc Ondemand Distance Vector (AODV) and Dynamic Source Routing (DSR), based on results analysis obtained using simulations with different load and mobility scenarios performed with Network Simulator version 2 (NS-2). In low load and low mobility scenarios routing protocols perform in a similar manner. However, with mobility and load increasing DSR outperforms AODV and DSDV protocols.
Keywords: AODV, DSDV, DSR, MANET.
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Subject Category: Telecommunications Networks
Page(s): 8-10
The paper analyzes implementations of BGP protocol on commercial and open-source routers and presents how some existing BGP extensions and routing table isolation mechanisms may be used to solve issues found in standard BGP implementation.
Keywords: Autonomous system, BGP protocol, BGP polices.
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Subject Category: Telecommunications Networks
Page(s): 11-17
In this paper we provide a performance analysis for real-time services with a limited bandwidth in a single-cell Mobile WiMAX network. We analyze the most critical performance parameters for real-time services, such as voice over IP. Since the throughput is a given constraint for a real-time service, the focus is on delay and jitter introduced by the Mobile WiMAX technology. We have used different user velocities, including nomadic users as well as mobile users. The main contribution of this paper is that we have shown that Mobile WiMAX can be efficiently used for real-time services with applied admission control and priority over non-real-time traffic, because it is adding a very small portion to the delay budget for the real-time service, as well as it keeps the jitter far below the end-to-end jitter threshold for telephony in a Mobile WiMAX network.
Keywords: Analysis, Mobile, Performance, WIMAX.
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Subject Category: Telecommunications Networks
Page(s): 18-21
It is known that transmit channel side information (CSIT) is used to enhance the performance of space-time block codes based multi-antenna communication links. In this paper, we analyze how transmission algorithms can be adapted to the channel condition based on the degree of the available CSIT and the system diversity order. The precoding design criterion considered is minimizing the average pairwise error probability. The analyzed parameters are the bit error rate (BER) and the link throughput.
Keywords: CSIT, precoding, STBC, waterfilling.
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Subject Category: Radio Communications
Page(s): 22-26
In this paper an efficient procedure for determination of small-signal and noise behavior of microwave transistors for various bias conditions is proposed. An empirical transistor noise model based on an equivalent circuit (improvement of Pospieszalski’s noise model) is considered. Since it is necessary to extract values of the model equivalent circuit for each bias point (which requires the measured data acquiring and repeated time consuming extraction procedures), it is proposed to use an artificial neural network to model the bias dependence of the equivalent circuit parameters. In that way, it is necessary to acquire the measured data and extract the equivalent circuit parameters only for several operating biases used for the network training. Once the neural network is trained, the device small-signal scattering and noise parameters are easily obtained for an arbitrary bias point from the device operating range without changes in the model. The proposed modeling approach is exemplified by modeling of a specific MESFET device in a packaged form.
Keywords: artificial neural network, microwave transistor, signal and noise modeling, bias conditions.
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Subject Category: Radio Communications
Page(s): 27-31
In this paper we present the performances evaluation of infrastructure 802.11b/g QoS networks, in both HCF (Hybrid Coordination Function) operating modes: EDCA (Enhanced Distributed Channel Access) and HCCA (HCF Controlled Channel Access). Besides comparing these two modes in terms of total network throughput (between themselves as well as against the theoretical limit), in this paper we introduce further analyses: impact of modulation scheme on the total throughput, determination of throughput for different traffic categories and average packet delivery delay.
Keywords: EDCA, HCCA, HCF, MAC layer, QoS, WLAN.
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Subject Category: Radio Communications
Page(s): 32-37
Today, implementation of wavelength division multiplexing in the Ethernet passive optical network (EPON) is considered as one of the most perspective solutions for the bottleneck problem in the access network. With the development of new applications and services, multimedia applications above all, quality of service (QoS) support becomes a major concern in WDM EPON, as it was the case in EPON. In this paper, WDM EPON architecture is presented along with a novel algorithm for wavelength and bandwidth allocation with full QoS support. Besides theoretical analysis, simulation results are presented and they confirm a good performance of presented solution.
Keywords: DWBA algorithm, quality of service, WDM EPON.
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Subject Category: Optical Communications
Page(s): 38-42
This paper researches the routing and wavelength assignment (RWA) problem in wavelength routed optical WDM networks with the wavelength conversion capability at different network nodes. We studied the static case in which all connection requests are known in advance, thus a routing decision can be made based on the complete knowledge of the traffic to be served by the network. The Bee Colony Optimization (BCO) metaheuristic is applied to solve the RWA problem. We carried out a comprehensive simulation study of the performance of the proposed BCORWA algorithm for different network topologies and traffic scenarios. The obtained simulation results are analyzed and compared.
Keywords: lightpath, optical WDM network, routing and wavelength assignment (RWA), wavelength conversion.
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Subject Category: Optical Communications
Page(s): 43-48
This paper presents practical laboratories for teaching purpose in Supervisory Control and Data Acquisition (SCADA) systems. A SCADA system is described in terms of architecture, process interfaces, functionality, and application development facilities. These concepts are implemented on an integrated automation system, particularly for digital control of electric drives with a distributed peripheral, i.e., Totally Integrated Automation with Democase from Siemens. Using this system, a wide range of applications can be designed, implemented and tested. A practical labs set is presented to introduce gradually the main SCADA elements, and finally to develop an application to control an induction motor in interlocked manual/automatic mode, with touch-screen Human Machine Interface (HMI). The system employs industrial busses like PROFIBus and industrial Ethernet. The SCADA system also shows trends, alarms, motor frequency and automatic sequence of motor speed profile.
Keywords: Automatic control, engineering education, ethernet, hardware configuration, laboratory works, profibus, programmable logic controller (PLC), supervisory control and data acquisition (SCADA), WinCC Flexible.
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Subject Category: Software Tools and Applications
Page: 49-54
This paper presents the work carried out on recovering, manipulating, unificating, labeling and processing of documents developed within the congresses of TAEE (Technologies Applied to the Teaching of Electronics). The process developed consists of the creation of digital objects and documents arising from the extraction of metadata which define each digital object as a learning object. With the joint between a learning object and its metadata some information extrapolation is possible in multiple environments. Thus, these units of information permit the implementation of web environments, the study and analysis of their contents and the creation of file structures for their incorporation in repositories in a massive way.
Keywords: Metadata, repository, LOM, Learning Object.
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Subject Category: Software Tools and Applications
Page: 55-58
The institutional repository created at UNED (Universidad Nacional de Educación a Distancia, Spain) is a project, originating, from the UNED Library computer services, that aims to provide coverage to members and academic staff at the University. The project, currently in full operation, offers a set of services for the management, preservation and access over the Internet of digital materials created by its members. Derived from these services, the purpose of the repository is the spread of the documentary funds as a tool of consultation and divulgation to researchers, scientists and educators in general. This document describes the functional and technical features of the repository, whose implementation keeps Fedora as backend application as well as Fez as Web interface. Both are freeware distributed under GPL license, making it suitable for academic environments, due to reduced costs for computer equipment and constant upgrading resulting in a permanent immunity to obsolescence. Among the features presented in this paper, there are: the visualization of multiple presentations, the dynamic transformation of the contents with subsequent adaptation to environments outside the repository and the definition of relationships between objects.
Keywords: digital object, Fedora, integration of services, repository, reusability.
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Subject Category: Software Tools and Applications
Page: 59-62