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
The basic characteristics of Orthogonal Frequency Division Multiplex (OFDM) systems with DQPSK modulation and channel estimation with an adaptive transversal filter and LMS algorithm are analyzed and presented in this paper. In the simulation environment designed for this purpose, we analyzed the effects of frequency offset on the performance of OFDM digital communications and presented the method for improving system performance in the presence of frequency offset. We analyzed the influence of OFDM system parameters on system’s performance for various values of frequency offsets, filter lengths and the number of subcarriers. Finally, we compared the result with the one for a perfectly synchronized OFDM/DQPSK system with differential and coherent demodulation.
Keywords: orthogonal frequency-division multiplexing, differential quadrature phase-shift keying, frequency offset, frequency synchronization, LMS algorithm, adaptive transversal filter.
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Subject Category: Communication Theory
Page(s): 64-67
Turbo codes are employed in every robust wireless digital communications system. Those codes have been adopted for the satellite return channel in DVB-RCS (Return Channel via Satellite) standard. In Software Defined Radios (SDRs), Field Programmable Gate Array technology (FPGA) is considered a highly configurable option for implementing many sophisticated signal processing tasks. The implementation for such codes is complex and dissipates a large amount of power. This paper studies the efficient implementation of quantized DVB-RCS turbo coding. Also, a low-power, turbo encoder for DVB-RCS is described using a VHDL code. The proposed encoder design is implemented on Xilinx Virtex-II Pro, XC2vpx30 FPGA chip. FPGA Advantage Pro package provided by Mentor Graphics is used for VHDL description and ISE 10.1 by Xilinx is used for synthetization.
Keywords: DVB, FPGA, Quantization, Software Defined Radios, Turbo codes, VHDL.
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Subject Category: Communication Theory
Page(s): 68-73
The three-dimensional presentation of phonocardiac signal, simultaneously considering time, amplitude and frequency, allows the determination of morphological characteristic segments in phonocardiogram (PCG), both in short and long sequences. For this purpose, the STFT (Short-Time Fourier Transform) spectrogram images were used. By applying some methods known from image processing it is possible to recognize and extract basic heart sounds and murmurs from such time-frequency images. The method is tested over several characteristic test phonocardiac signals.
Keywords: Morphological processing, murmur, phonocardiogram, spectrogram, STFT.
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Subject Category: Signal Processing
Page(s): 74-77
In this paper we present a novel approach in Multiple-Input Multiple Output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) channel estimation technique based on a Decision Directed Recursive Least Squares (RLS) algorithm in which no pilot symbols need to be integrated in the data after a short initial preamble. The novelty and key concept of the proposed technique is the block-wise causal and anti-causal RLS processing that yields two independent processings of RLS along with the associated decisions. Due to the usage of low density parity check (LDPC) channel code, the receiver operates with soft information, which enables us to introduce a new modification of the Turbo principle as well as a simple information combining approach based on approximated aposteriori log-likelihood ratios (LLRs). Although the computational complexity is increased by both of our approaches, the latter is relatively less complex than the former. Simulation results show that these implementations outperform the simple RLS-DDCE algorithm and yield lower bit error rates (BER) and more accurate channel estimates.
Keywords: MIMO, OFDM, Channel Estimation, Turbo Receiver Processing, LDPC Codes.
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Subject Category: Signal Processing
Page(s): 78-81
Bells are specific sound sources. They have distinct, but, unlike musical instruments, inharmonious partials. These partials arise from modes of vibration of the bell and depend on dimensions and potential irregularities of the bell. Therefore, the question of a just noticeable difference in the church bell sound is of great importance. Analysis of subjective tests with synthetic sounds of two bells, different in size, is described in this paper. We report results for a just noticeable difference of partial frequency in the range 10-15 cents. Frequency dependence, is also, noticed.
Keywords: church bell, just noticeable difference, subjective test
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Subject Category: Multimedia
Page(s): 82-85
A reverberation radius, also called a critical distance, is an important parameter in sound reproduction. Statistical approach gives a simple formula for its calculation, and some simple methods for its measurement were described in literature. To measure the critical distance in real rooms, a more accurate method is proposed. This paper is concerned with that method. Accuracy of the method was analysed and the results of critical distance measurement in several rooms of different sizes and acoustical characteristics are presented.
Keywords: critical distance, reverberation radius, room acoustics, sound reproduction.
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Subject Category: Multimedia
Page(s): 86-91
Diffusivity is a geometrical feature of the room which is proportional to the dimension of relief on its interior surfaces. This paper presents the results of analysis which investigates the correlation between diffusivity in a room and parameters calculated from a recorded impulse response. The analysis was performed using a specially prepared physical model of a parallelepipedic room with different combinations of flat and diffusive interior surfaces.
Keywords: absorption, acoustic measurement, diffusion, impulse response, physical model.
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Subject Category: Multimedia
Page(s): 92-97
A new algorithm for spatial segmentation using hexahedral finite elements, combined with the algorithm for spatial segmentation using quadrilateral elements, is presented. Problems with combining the algorithms for segmentation by hexahedral and quadrilateral elements in the hybrid FEM-MOM technique are pointed out. An example of analysis of a scatterer at resonant frequency is given.
Keywords: Electromagnetic analysis, finite element methods, geometrical modeling, hybrid techniques, meshing, method of moments.
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Subject Category: Applied Electromagnetics
Page(s): 98-101
Due to the quick evolution of manufacturing processes, the demand for more flexible automation systems is on the rise. To answer these requirements, distributed motion control architecture based on intelligent drives tends more and more to replace the traditional solutions. This paper presents the control of an articulated arm robot with two local intelligent servo drives connected on a CAN network to a motion controller which receives the trajectory of the robot from a computer. The control structure is based on a single CAN network where local intelligent servo drives, a motion controller and a computer are connected.
Keywords: articulated arm robot, CAN network, intelligent servo drives, distributed control system, motion coordinator.
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Subject Category: Applied Electronics
Page(s): 102-106
In this paper we present a novel softwarebased home control platform suitable as an extension to digital home appliances that are equipped with a CPU (settop boxes, home theatre systems, TV sets, gaming consoles, etc). By using an appliance they are already accustomed to, users become able to control lights, appliances and media playback in their homes. Intelligence and awareness are achieved with a support for execution of recipes – preprepared scripts that define timely actions and respond to triggers obtained from sensors. Software abstraction layer facilitates integration of any desired communication protocol. In our prototype, we supported Zigbee and DMX for light control, X10 for light/appliances control over power line, as well as Ethernet-based optical cameras as motion / presence sensors and UPnP / DLNA based equipment for distributed media playback.
Keywords: domotics, smart home, set-top box, Zigbee, DMX, home automation
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Subject Category: Applied Electronics
Page: 107-112