Open Topics

Vol. 62, n° 9-10, September-October 2007
Content available on Springerlink

Co-channel interference effects as applied to broadband fixed wireless access channel capacity statistical distribution

Athanasios D. PANAGOPOULOS*,**, George E. CHATZARAKIS**

* Wireless & Satellite Communications Group, School of Electrical and Computer Engineering, National Technical University of Athens – 9 Iroon Polytechniou Street, 15780 Zografou-Athens, Greece
** Department of Electrical and Electronics Engineering, School of Pedagogical and Technological, Education (aspete) – Athens, N. Heraklion Attikis, Greece 14121

Abstract Channel Capacity is of primary importance in broadband fixed wireless access (BFWA) networks due to the ever increasing demand for multimedia services and the possibility of providing wireless Internet. One of the major factors limiting capacity in such systems is interference originating from adjacent terrestrial applications belonging to the same BFWA network or to another. Moreover, the performance of broadband fixed wireless access links operating above 10 GHz is predominantly controlled by rain attenuation. The purpose of this paper is the presentation of a physical model for the evaluation of the fraction of the time where the capacity distribution of a broadband fixed wireless access channel under rain fade conditions suffering from co-channel interference, non-exceeds a specified level in (bps/Hz). The proposed analysis examines the capacity distribution properties focusing on the spatial inhomogeneity of rainfall medium. The impact of various operational and geometrical parameters on the performance of interfered broadband wireless access channel capacity distribution is investigated through extended simulations.

Keywords Wireless local loop, Radio Channel, Channel capacity, Signal interference, Fading, Rain, Millimetric wave, Electromagnetic wave propagation, Modeling.

Direct and indirect effects of perceived price on perceived value of mobile phones

Aleksandra PISNIK KORDA, Boris SNOJ

University of Maribor, Faculty of Economics and Business, Marketing Department – Razlagova 14, 2000 Maribor, Slovenia

Abstract Nowadays many leading companies understand that creating outstanding customer value is necessary to achieving sustainable market success. The main problem discussed in this article is the examination of factors affecting perceived value, emphasizing the relationship between perceived price and perceived value. Based on literature and their own findings, the authors designed a model of relationships between researched factors. This model was tested using structural equation modeling. The results reflected that statistically significant relationships exists and that perceived price has direct as well as indirect efects on perceived product value.

Keywords Microeconomics, Portable telephone set, Subjective evaluation, Price, Slovenia, Student, Statistical analysis, Descriptive statitstics, Market survey, Product quality, Risk.

Improvement of xDSL systems performances by a method of cross talk reduction in multiconductor telecommunication cables

Sandrine ROBLOT*, Ahmed ZEDDAM*, Alain REINEIX**

* France Telecom division R&D – 2 avenue P. Marzin 22307 Lannion Cedex, France
** XLIM, Institut de recherche, UMR CNRS 6172, Faculté des sciences et techniques – Université de Limoges, 123, avenue Albert Thomas 87060 Limoges cedex, France.

Abstract DSL (Digital Subscriber Line) technology provides low cost access to the consumers and sources of information for anyone subscribing to classical analogical telephony. Indeed xDSL services enable high-speed digital transmission on conventional telephone lines. For sixteen years that the internet has risen, a great number of offers proposing increasing bit rate have been developed. Considering this increasing demand of high bit rate access, telecommunication operators perpetually work on finding solutions to optimize the copper lines channel. In that way, we present here a new method of crosstalk reduction in a multiconductor telecommunication cable. Interests and limitations of this method are presented and some simulations on a frequency band extending to 30 MHz will picture those theoretical results.

Keywords High rate, High rate, Telecommunication cable, Multiconductor line, Crosstalk, Transmission performance, Access network, Telephone switched network, Impedance watching, Linear parameter.

A new approach for a quality of service management in UMTS networks


* Sup’Com, Route Raoued km 3,5, 2083 Ariana, Tunisie
** Siemens – Rue du Lac Neudiatel 1053, Berges du Lac, Tunis, Tunisie.

Abstract The fast expansion of the applications and services in the 3G mobile networks and the competition between the operators have increased the need to improve the QoS either for the subscribers or for the service providers. The UMTS operators’ principal goal is to guarantee their maximal benefit and offer the best QoS to the subscribers. Our work is funded on the optimisation of the network parameters, especially bit-rate. Our proposal’s goal is to offer the best rate distribution between the subscribers (bit-rate balancing) and to guarantee the load balancing between the network cells. It is based on network and radio engineering concepts. We used the genetic algorithm for the optimisation of the bit-rate allocation and we proposed a new process for the bit-rate and load balancing. The differentiation of the services treatment has been done by the definition of a priority based on each service requirements in QoS. To show the contribution of this approach in the practice, we simulated it on a Tunisian operator’s test platform model. The gotten results showed an increase of the connected users, some very weak blocking and call-drop rates and a better load balancing between the cells.

Keywords UMTS, Quality of Service, Quality management, Optimization, Genetic algorithm, Balancing, Modeling, Simulation.

A Method for Predicting Rain Attenuation in Terrestrial Point-to-Point Line of Sight Links at 97 GHz

Ibrahim DEVELI

Department of Electrical and Electronics Engineering, Faculty of Engineering, Erciyes University 38039, Talas Road, Kayseri, Turkey

Abstract Rain attenuation caused by electromagnetic scattering and absorption is a major design parameter for setting up satellite communication systems operating at frequencies above 10 GHz. In this paper, a method for predicting rain attenuation in terrestrial point-to-point line of sight links at 97 GHz is proposed using previously available experimental data obtained in the south of UK over a period of more than a year. Rainfall rate and percentage of time are used as input data in the proposed prediction method. Results show that our prediction method based on artificial neural networks reveals very good agreement with the experimental data.

Keywords Electromagnetic wave propagation, Rain, Attenuation, Millimetric wave, Live of sight propagation, Radiocommunication, Forecast model, Neural network.

Turbo codes with modified Welch-Costas interleavers


Technical University “Gh. Asachi” Iasi, Faculty of Electronics and Telecommunications – Bd. Carol I no. 11, 700506, Romania.

Abstract An upper bound for the minimum distance of turbo codes with Welch-Costas interleavers is established. This paper also proposes a modified Welch-Costas interleaver for which the obtained minimum distance is larger than the established upper bound. At the cost of a slight increase of memory compared to the classic Welch-Costas interleaver, the minimum distance obtained by the proposed method is comparable to that corresponding to the S-random interleaver.

Keywords Error correcting code, Turbo code, Interleaving, Permutation, Minimal distance.

Novel Analysis and Design Approaches of the Planar Antenna Arrays


Telecommunication Laboratory of ENP, El-Harrach, Algiers, Algeria

Abstract New approaches for the determination of the radiation characteristics of planar arrays are proposed. Conventionally, the best compromise directivity-side lobes level is achieved using Dolf-Chebyshev amplitude distribution. However, classical distribution forms present disadvantages in calculation time, possibility in analyzing larger arrays and the array factor is only optimum in the two principle planes. To overcome these problems, the excitation amplitudes are written under the modal form. The obtained radiated fields compared with measurement results validate the technique. It is also shown that square arrays provide improved performances from point of view of directivity compared to those of rectangular arrays with comparable size. However, above specific array size, the directivity saturates. For this, another modification of the array factor of Chebyshev square array is proposed. The modification preserves the radiation pattern configuration (same number of null radiation directions and sidelobes) and improves both directivity and side lobe levels. Analytical expressions of the array factor, the directivity, maximum half-power beamwidth, and the maximum spacing between elements have been derived. It has been shown that the use of this new technique results in an improved directivity with respect to the classical Chebyshev for a square arrays identical in size, element spacing, direction of the main lobe and side lobes level.

Keywords Antenna array, Plane antenna, Rectangular configuration, Square configuration, Modal analysis, Radiation pattern, Side lobe.

End-to-end service level negotiation protocol for self-management networks

Nader MBAREK, Francine KRIEF

Labri, Université de Bordeaux 1 – 351, cours de la Libération, 33405 Talence cedex, France

Abstract We propose a framework for service level negotiation within self-management systems. The negotiation process occurs between high-level autonomic managers to guarantee an end-to-end service level for specific application traffic flows. In the proposed framework, we provide autonomic systems with a new interaction opportunity thanks to the negotiation with their peers. To be in conformance with the concepts of self-aware management systems, the proposed negotiation protocol called SLNP is used in a Web Services environment.

Keywords Telecommunication service management, Internet,Web service, Bargaining, Autonomous system.

Advanced reconfiguration framework based on game theoretical techniques in autonomic communication systems

Eleni PATOUNI*,***, Sophie GAULT**, Markus MUCK**, Nancy ALONISTIOTI***, Konstantina KOMINAKI***

* Department of Informatics, University of Piraeus, 80 Karaoli & Dimitrion St., 185.35 Piraeus, Parc Les Algorithmes, Greece
** Motorola Labs, Saint-Aubin 91193 Gif sur Yvette cedex, France; {sophie.gault, markus.muck} at
*** Department of Informatics & Telecommunications, University of Athens, 15784 Athens Panepistimiopolis, Ilissia, Greece

Abstract The Autonomic Communications concept forms one promising solution to accommodate the increased complexity of legacy and emerging systems, fostering the automation and minimizing the need for human intervention. This notion implies the introduction of advanced mechanisms for autonomic decision making and self-configuration. The focus of this work is on the introduction of an advanced reconfiguration framework for the support of the following functionalities: i) efficient strategies of terminal attachment to heterogeneous wireless systems are proposed dependent on the evaluation of input stimuli from the surrounding telecom environment. ii) it is shown how to enable optimized selection and attribution of resources, iii) the application of new device configuration is examined, proposing a framework for dynamic protocol stack adaptation. It is indeed necessary to introduce a framework that will enable, policy based reconfiguration decisions supporting dynamic and optimal discovery, download and replacement of necessary protocol functionality. In this context, legacy management and control mechanisms should be enriched with such features operating in either terminal or network equipment. Namely, this contribution discusses cognitive reconfiguration management issues by introducing two basic reconfiguration units encapsulated in a unified management and control architecture: i) the component based protocol stack reconfiguration framework and ii) the resource usage optimization unit. Simulation and performance results presented in the paper prove the technical feasibility of the proposed mechanisms as well as the optimization of reconfiguration actions.

Keywords Telecommunication network, Autonomous systems, Self orgnization, Game theory, Transmission protocol, Mobile radiocommunication, Distributed system, Reserve allocation.

A new identity concerning the weight enumerator of binary linear block codes


France Telecom, division R&D – 38-40 rue du Général Leclerc, 92794 Issy les Moulineaux cedex, France

Abstract Starting from the problem of counting the number of parity check equations of a given code that allow to recover an erasure from a pattern we derive a series of identities involving only the coefficients of the weight enumerator of the code, and thus different from Mac- William’s identities. These relations can also be gathered in a single polynomial equation, which is thought to be new and is the main result of this paper. Some examples with known block codes are given.

Keywords Error correcting code, Linear code, Block code, Enumeration, Weight, Erasure.

Dirty paper coding schemes for MIMO broadcast channels

Samson LASAULCE*, Julien DUMONT**, Gholam Reza MOHAMMAD-KHANI*, Raphaël VISOZ***

* CNRS-Laboratoire des Signaux et Systèmes, Supélec – 3, rue Joliot-Curie, 91192 Gif-sur-Yvette cedex, France
** Laboratoire des Systèmes de Communication, IGM LabInfo, Université de Marne-la-Vallée – 5, bd Descartes, 77454 Marne-la-Vallée cedex 2, France
*** France Télécom, division R&D – 38-40, rue du Général Leclerc, 92794 Issy-les-Moulineaux cedex 9, France

Abstract We propose several dirty paper coding schemes for the broadcast channel when both the transmitter and receivers are equipped with multiple antennas. These schemes are based on channel state information at the transmitter and inspired from information-theoretic concepts. The proposed end-to-end algorithms allows us to evaluate the performance of the broadcast channel in terms of bit error rates and not in terms of coding rates as it is usually the case in the literature. Different inner coding schemes such as the ZF-DPC and MMSE-DPC and different outer coding schemes such as the THS, SCS and TCQ are compared and discussed. We also consider the DPC idea as a way of implementing a multiple access scheme. In this respect it is compared with the well-known TDMA scheme. Sometimes our conclusions show quite surprising results in comparison to what is expected by pure information-theoretic considerations.

Keywords Coding, Information theory, Mobile radiocommunication, Trellis coding, Error rate, Channel capacity, Signal interference.

Decoupled estimation of angular parameters for coherently distributed sources

Ahmed ZOUBIR*, Yide WANG**, Mohamed M. Ould HAIBALLA*,**, Pascal CHARGÉ***

* IREENA École polytechnique – University of Nantes, BP 50609, 44306 Nantes, France.
** SSC, FST – University of Sidi Mohamed Ben Abdellah, Route Immouzer BP 2202 Fez, Morocco.
*** LATTIS, INSA, 135 avenue de Rangueil, 31077 Toulouse Cedex 4, France

Abstract In this paper, we consider the problem of estimating the direction-of-arrivals (DOAs) and angular spreads of uncorrelated coherently distributed sources. The proposed methods enable a decoupled estimation of the DOAs from that of the angular spreads of sources. Compared with existing algorithms, the proposed algorithms improve the robustness to the mismodeling of the spatial distribution of the scatterers. They allow an unambiguous DOAs estimation and don’t need the a priori knowledge of the azimutal power distribution. Furthermore, the proposed techniques work even in the case where the different sources have different angular distribution shape.

Keywords Antenna array, Beamforming, Linear antenna, Arrival angle, Spatial distribution, Multipath propagation, Wave coherence.