No. 2 (2001)
Published:
2001-06-30
ARTICLES FROM THIS ISSUE
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Challenges before National Institute of Telecommunications after fifty years of its activity
Abstract
In the year 2001 we celebrate the fifty anniversary of the activity of National Institute of Telecommunications under its present name (in Polish: Instytut Łączności). Although we can date earlier the beginnings of the Institute, we will not present here its detailed history that is discussed in other papers. This paper presents rather the transformation of the Institute in last years, resulting from the systemic transformation of Poland. We describe: new mission of the Institute, the results of structural changes of the Institute in last five years, an outline of long-term research programme. Finally, the paper addresses the challenges before the Institute on the verge of the new milenium.
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Intra- and inter-cell interference investigations for broadband radio access systems above 10 GHz
Abstract
Local multipoint distribution systems (LMDS) operating above 10 GHz have a large bandwidth (2--3 GHz) but a very limited range. These systems can provide coverage to a few kilometers only. The size of the macro cells illuminated by the base stations, where line of sight (LOS) exists, is 1 to 6 km. To provide coverage to customers where LOS is not possible, repeaters or passive reflectors may be used. In this paper we present first results of reflection measurements at 42 GHz, and based on that, simple multipath studies, taking into account the beamwidth of the antennas of both, transmitter and receiver. Secondly, LOS cochannel and adjacent channel interference are assessed for cellular LMDS networks. As suggested in the CRABS report, the maximal spectral efficiency can be obtained with a dual frequency and polarization reuse plan. This frequency and polarization reuse leads to interference. In this paper we have first calculated the cochannel interference (CCI) and the adjacent channel interference (ACI) due to the frequency/polarization reuse schemes suggested in the CRABS report. The effects of the variation of the half power beam width (HPBW) of the receiver, the time percentage parameter p, and the cell radius on C are also reported. In the latter part of the paper we propose a simple interference reduction technique based on re-orientation of the receiver antennas. We have also explored the possibility of using trellis coded modulation (TCM) for reducing interference levels. Initial results have been found to be quite encouraging.
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Radio wave propagation and single-cell coverage prediction of broadband radio access systems including passive reflectors
Abstract
This paper presents the scheme of a software planing tool for single microcells of broadband radio access systems operating at millimeter waves, providing local multipoint distribution services (LMDS), particularly in urban or suburban areas. The aim of this planing tool is to provide operators with information, which supports the assessment of the profitability by calculating link budgets and the area coverage and by roughly estimating the maximum number of potential customers, i.e. the total number of households in a~certain area, as well as the number of customers (households) which will actually be covered from a site. A household is here considered as a single apartment or flat, thus a building usually consists of several households. This novel household-estimation model is able to estimate the number of households based only on the 3D-data of buildings, without using residential data. Besides the optimization of line-of-sight (LOS) coverage, also the possibility is considered to enhance the coverage into shadowed areas by using optimized reflectors as passive repeaters up to distances of 1 km from the base station, depending on the system margin and the rain climate zone. All calculations are based on 3D-databases of both, buildings and vegetation.
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Fuzzy logic classifier for radio signals recognition
Abstract
This paper presents a new digital modulation recognition algorithm for classifying baseband signals in the presence of additive white Gaussian noise. Elaborated classification technique uses various statistical moments of the signal amplitude, phase and frequency applied to the fuzzy classifier. Classification results are given and it is found that the technique performs well at low SNR. The benefits of this technique are that it is simple to implement, has generalization property and requires no apriori knowledge of the SNR, carrier phase or baud rate of the signal for classification.
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Modelling of CDMA systems
Abstract
This paper describes a model of a system with wideband CDMA that is a proposal of user access for future UMTS. This model has been implemented using OPNET tool. The model enables network architecture, radio interface, mobile station motion, call generation, signalling, etc. The examples of simulation results of call and handover blocking probability are also presented in this paper.
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Performance of CDMA systems with Walsh and PN coding
Abstract
Wideband CDMA method has been recently investigated for its using in the future communication systems. Such systems capacity depends on many factors, the main is multi-access interference (MAI). MAI~is an inherent CDMA property connected to correlation characteristics of codes used to access and to spreading. The influence on CDMA performance of these codes families and parameters is presented in this paper. The standard Gaussian approximation has been used for interference analysis. Bit error rate (BER) on detector output is a~measure of interference influence on transmission quality. It can be used for SNRi evaluation on receiver input for channel assignment and handover procedures. The results of interference analysis for the pseudo-noise sequences (M-sequences, Gold, de`Bruin and Jennings) as well as for the Walsh orthogonal mapping are presented in this paper.
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Model of e-book for distance-learning courses
Abstract
Structure of electronic book, prepared as auxiliary materials of courses for specialists in the field of telecommunications and informatics, will be described. Assumptions undertaken and their grounds will be presented. Model of a~single lecture, way of a control of student progress and technique of movement through the course content will be described.
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IP over optical network: strategy of deployment
Abstract
In this paper, we present main issues of application IP technology directly over optical transport network. The capabilities of WDM transmission systems and techniques which allow the integration of IP with the physical layer are discussed. A detailed description of most solutions is reported. In particular the MPLS/MP$mathbf{lambda}$S techniques are discussed in detail. Also problems for further development are outlined.
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Analysis of optical-microwave mixing process in electro-optical modulators
Abstract
The principle of operation and the general parameters of the electro-optical Mach-Zehnder modulators are reminded in the paper. With the use of the mathematical relationships describing the transmission of the optical signal through the modulator, the theoretical model of the optical signal transmission with two modulating signals at two frequencies will be presented. The theoretical relationships describing the efficiency of the optical-microwave mixing and frequency multiplying in the two-tone operation will be derived. The analysis and the simulations will be performed for different operating points, where the nonlinearity of the transmission characteristic is specially strong.
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Methods for description of the total field propagation in the irregular dielectric waveguides
Abstract
Numerical and semi-analytical methods useful for analysis of the total field propagation in dielectric waveguides with sharp and smooth discontinuities are reviewed. The efficiency of these methods to model the field propagation in such structures is discussed comparatively. As an example, spatial transient regime of the radiation field propagation in planar step-index waveguide excited by a Gaussian beam is simulated numerically by two different beam propagation methods.
