Showing papers in "Aeu-international Journal of Electronics and Communications in 2001"
TL;DR: An overview and classification of optical burst switching schemes and present burst reservation concepts is given and a new analysis is introduced that allows to calculate the loss probabilities of a two-class system based on the reservation mechanism just-enough-time for arbitrary offsets.
Abstract: Summary In this paper, we give an overview and classification of optical burst switching schemes and present burst reservation concepts. The performance of various basic reservation mechanisms proposed in literature is compared. Furthermore, a new analysis is introduced that allows to calculate the loss probabilities of a two-class system based on the reservation mechanism just-enough-time (JET) for arbitrary offsets. Finally, a variety of new results is presented including the dependence of burst loss probabilities on offset, burst length distribution, and interarrival distribution.
274 citations
TL;DR: A practical model of mobile HTTP users, based on an extrapolation of WWW users in current wire-line networks, is presented; this model is expected to be accurate enough to be used in simulation studies for network planning purposes.
Abstract: Summary Data applications are expected to play an increasingly important role in the next generation mobile communication services. To plan these networks, detailed models of data users with diverse applications are required. The purpose of this study is to provide practically usable traffic models for data users in wireless networks, e.g. GPRS. We start with a discussion of well-known models in the literature, where the focus is on their applicability in mobile networks. A practical model of mobile HTTP users, based on an extrapolation of WWW users in current wire-line networks, is presented; this model is expected to be accurate enough to be used in simulation studies for network planning purposes. Finally, models for other emerging data applications are also taken into account.
108 citations
TL;DR: A modification of SCTP is proposed and evaluated which significantly enhances the performance in long delay environments and highlights some advantages over TCP.
Abstract: Summary IP-based networks grow rapidly and coexist with other universal basic telecommunication infrastructures, namely with the ISDN, mobile networks and ATM networks. Since all infrastructures are capable of carrying all applications and services, there is a growing need for interworking. To be able to transfer signaling traffic originating in the other networks via IP networks, a family of protocols is being defined based on SCTP, a new end-to-end transport protocol. This paper describes some features of SCTP in detail and highlights some advantages over TCP. In addition, a modification of SCTP is proposed and evaluated which significantly enhances the performance in long delay environments.
45 citations
TL;DR: In this paper, the authors present a new approach to the design of simulation models for spatio-temporal mobile radio channels, which are important for the design, optimization, and test of antenna array based mobile communication systems.
Abstract: Summary This paper presents a new approach to the design of simulation models for spatio-temporal mobile radio channels, which are important for the design, optimization, and test of antenna array based mobile communication systems. The proposed spatio-temporally correlated simulation model is completely deterministic and enables the emulation of the desired fading behaviour with comparably little effort. Moreover, it can be configured flexibly to simulate not only different kinds of theoretical channels with given spatial, temporal, and frequency correlation properties, but also real-world fading channels for mobile communication systems with adaptive antennas.
39 citations
TL;DR: In this paper, the authors describe the properties of those sequences (matrix) that meet equality in the Welch's lower bound on total squared correlation, called also Welch Bound Equality (WBE) sequences.
Abstract: Summary In this paper we describe the properties of those sequences(matrix) that meet equality in the Welch's lower bound on total squared correlation. These sequences are called also Welch Bound Equality (WBE) sequences. The generalized WBE sequences (matrix) are defined. Same definitions on majorization are introduced in order to characterize the eigenvalues of a hermitian matrix. A new algorithm for generating WBE spreading sequence multisets is proposed. We apply the proposed algorithm when all users have different average-channel-input energy constraint in the case of synchronous CDMA channels. We obtain real optimum signature sequences that maximize the sum capacity of S-CDMA channels.
32 citations
TL;DR: More universal integration methods are considered in this paper: the so-called general linear methods which cover in particular linear multistep methods and Runge-Kutta methods and a network theoretical approach is used.
Abstract: Summary Methods based on the wave digital concept are suited for the modelling of passive physical systems. The generated wave digital models inhere both a high physical transparency as well as a variety of good numerical properties. However, the wave digital concept is known for linear multistep methods only. In this context, passivity imposes a limited accuracy. To this end, more universal integration methods are considered in this paper: The so-called general linear methods which cover in particular linear multistep methods and Runge-Kutta methods. In order to establish a new theory for these integration methods, a network theoretical approach is used. A new class of Runge-Kutta methods will be derived. The generated algorithmic models inhere the same good properties as wave digital models but their numerical accuracy is increased. A simulation example for a nonlinear physical system will be given.
32 citations
TL;DR: In this paper, the suitability of titanium and chromium doped aluminum oxide material as laser material is examined and their fluorescence and lifetime measurements are presented, and the modifications due to the annealing condition are subject to investigations.
Abstract: Summary Amorphous thin films with very low attenuation are grown by MO-PECVD. The modifications due to the annealing condition are subject of investigations. Aluminum oxide waveguides are doped with erbium for applications in telecommunication to develop an integrated optical amplifier. AlsoAl 2 O 3 doped with transition elements to develop tunable solid state lasers for spectroscopic measurements is of interest. Lasers with broadest fluorescence bands are Ti:Sapphire lasers or chromium doped specific crystals or glasses. In this paper the suitability of titanium and chromium doped aluminum oxide material as laser material is examined. Titanium and chromium doped waveguides have been annealed. Their fluorescence and lifetime measurements are presented.
32 citations
TL;DR: In this article, the radiation quality factor of a lossless linearly polarised structure which fits a spheroidal volume is evaluated by numerical integration of the evanescent energy outside the sphenroid for the axially polarised field.
Abstract: Summary Limitations for the radiation quality factor, Q , of a lossless linearly polarised structure which fits a spheroidal volume are searched for. The Q is evaluated by numerical integration of the evanescent energy outside the spheroid for the axially polarised field. The minimum Q for a prolate spheroid is found for a narrower radiation pattern than the sin θ-figure characteristic for an elementary dipole, while for the oblate, the minimum turns out for a broader pattern than that of an elementary dipole. The results agree with the previous theory, stating that the Q of a linearly polarised antenna can not be smaller than ( ka )- 3 + ka - 1 , k being the wave number and a the radius of the smallest circumscribed sphere. The graphs showing the influence of the axial ratio on the radiation Q should be of practical interest in the design of wide band antennae of small electrical size as not only the maximum dimension of the antenna, but also its shape and polarisation is taken into account.
30 citations
TL;DR: In this article, a numerical analysis of reflecting and transmitting properties of multi-layered structures composed of doubly pe- riodic arrays of metallic strips is presented, where array elements have been selected having the shape of the capital letters C, S and Ω.
Abstract: A numerical analysis of reflecting and transmitting properties of multi-layered structures composed of doubly pe- riodic arrays of metallic strips is presented in this paper. Array elements have been selected having the shape of the capital letters C, S and Ω. The metallic strips of arrays are placed on a thin dielectric substrate. These strips may include a con- centrated impedance loading. The interferences in the multi- layered array systems, due to multiple reflections of waves between the layers, combined with the resonance properties of single layers lead the structure to acquire typical properties of the photonic band gap (PBG) crystals.
30 citations
TL;DR: In this paper, the authors describe the properties and the design of recursive halfband-filters with approximately linear phase by coupling an appropriately designed allpass of even degree n A with a delay of order m = n A ±1, and obtain the desired solution by solving a corresponding approximation problem for the phase of the allpass.
Abstract: Summary The paper describes the properties and the design of recursive halfband-filtersThe two possibilities of being complementary are introduced The lowpass with the transfer function H Lp ( z )and the corresponding highpass, described by H Hp ( z ) = H Lp (- z )can either be strictly complementary or power complementary According to the respective symmetry, the impulse responses, transfer functions and frequency responses possess certain characteristic properties, which are described in section 2 It turns out that these resulting symmetries of the frequency response reduce the number of the choosable design parameters We can only prescribe the cutoff frequency and the tolerated deviation either for the passband or the stopband In the third section we treat the design of halfband-filters with approximately linear phase By coupling an appropriately designed allpass of even degree n A with a delay of order m = n A ±1 we obtain the desired solution by solving a corresponding approximation problem for the phase of the allpass The resulting lowpass and highpass are strictly as well as power complementary!The kind of approximation will be done in the sense of maximal flatness, where a closed form solution exists [8], or in the sense of Chebychev, where the solution is obtained iteratively [13] The design of systems with minimum phase is presented in section 4 The resulting lowpass and highpass are power complementary Closed form solutions yield Butterworthand Cauer filters, if a maximal flat or a Chebychev approximation is desired In all cases a fixed relation exists between the passband frequency Ω P and the tolerated deviation δ P in the passband when the degree n has been chosen
23 citations
TL;DR: An attempt has been made to design broadband networks constructed with a cascade connection of low pass LC ladders connected with commensurate transmission lines based on the two-variable description of the Simplified Real Frequency Technique.
Abstract: Summary The design of microwave filters, matching networks, amplifiers, that is the “Broadband Networks” with mixed lossless lumped and distributed elements, has been a significant concern of the circuit theoreticians of the field. Yet, there has been no complete practical solution introduced in the literature so far. In this paper, an attempt has been made to design broadband networks constructed with a cascade connection of low pass LC ladders connected with commensurate transmission lines. The new design procedure is based on the two-variable description of the Simplified Real Frequency Technique. Up to five mixed-elements explicit equations are given to describe some selected network topologies. In general, synthesis is carried out employing a decomposition technique first introduced by Alfred Fettweis. A “Double Matching Design” exampleis presented to exhibit the merits and the application of the new approach.
TL;DR: In this paper, the Bartky's adaptive quadrature was used to enhance the computation of the matrix elements of the moment (MEoP) method for electromagnetic scattering by bodies of revolution.
Abstract: Summary The problem of electromagnetic scattering by bodies of revolution is considered. The generation of the matrix elements of the moment method consumes a major portion of the computational time. This time is primarily spent in evaluating the modal Green’s functions which is usually evaluated using an adaptive numerical integration method. The aim of this work is to use the Bartky's adaptive quadrature to enhance the computation of these functions. The method is very efficient and can be easily embedded in existing codes.
TL;DR: In this article, the bilocal-approximated strong-propertyfluctuation theory (SPFT) was implemented in the long-wavelength regime for biaxial bianisotropic and chiroferrite composite mediums endowed with ellipsoidal microstructural topology and orientation diversity.
Abstract: Summary The bilocal-approximated strong-property-fluctuation theory(SPFT) was implemented in the long-wavelength regime for biaxial bianisotropic and chiroferrite composite mediums endowed with ellipsoidal microstructural topology and orientation diversity. Small differences exist between the estimates afforded currently by the SPFT on the one hand and the Bruggeman as well as the incremental Maxwell Garnett homogenisation formalisms on the other hand – as functions of volume fraction, inclusion shape, andorientation diversity. In contrast, the effect of the correlation length issignificant, and is likely to yield to experimental clarification.
TL;DR: In this paper, an immitance-based method is presented to model measured orcomputed data, obtained from a passive one-port physical device by means of its Darlington equivalent, where the given data is modeled as a lossless two port terminated in a unit resistor.
Abstract: Summary An immitance-based method is presented to model measured orcomputed data, obtained from a “passive one-port physical device” by means of its Darlington equivalent. In other words, the given data ismodelled as a lossless two port terminated in a unit resistor. The basis of the new modelling tool rests on the numerical decomposition of the given immitance data into its Foster and minimum parts. Therefore, the proposed technique does not require any choice for the circuit topology to build the model. Rather, the optimum circuit topology that characterises thegiven data is the natural consequence of the modelling process proposed in this paper. A main algorithm is presented to construct the model from the given data. It is expected that the proposed modelling tool will findpractical applications in the behaviour characterisation, simulation, and design of high speed/high frequency analog/digital mobile communication sub-systems manufactured on VLSI chips. An antenna-modelling example is included to systematically exhibit the implementation of the modelling technique.
TL;DR: In this paper, the half-wave resonance of the inclusions is identified as the mechanism responsible for enhanced microwave absorption in synthetic composites which employ thin metal wires in a lossy dielectric host.
Abstract: Summary Microwave absorption by a lossy dielectric material containing thin metal wires is considered. The wires are bent to create either chiral, non-chiral or racemic unit cells. No physical mechanism is found to support patents which were granted between 1990 and 1993, and related claims in the engineering literature, that chirality is the key to improved microwave absorbers. Instead, in synthetic composites which employ thin metal wires in a lossy dielectric host, half-wave resonance of the inclusions – not their geometric shape – is identified as the mechanism responsible for enhanced absorption. It is also found that – even in an essentially lossless host – resonant steel wires, whether chiral or not, can strongly absorb electromagnetic waves.
TL;DR: The goal of this paper is to cover some of the aspects relevant for an actual implementation of the methods derived, and procedures for the synthesis of corresponding wave flow diagrams are developed.
Abstract: Summary Recently, the concept of passive Runge-Kutta methods for numerical integration has been presented. With the fundamental theory thus provided, the goal of this paper is to cover some of the aspects relevant for an actual implementation of the methods derived. For this, procedures for the synthesis of corresponding wave flow diagrams are developed. Some design examples for PDIRK methods are given. Finally, a simulation example is presented in order to verify the functionality of the methods derived.
TL;DR: In this article, an efficient design methodology for high-capacity dense wavelength-division multiplexed systems is presented, in contrast to complex and time-consuming numerical simulations, analytical equations and heuristic approximations are used to model the system performance.
Abstract: Summary An efficient design methodology for high-capacity dense wavelength-division multiplexed systems is presented. In contrast to complex and time-consuming numerical simulations, analytical equations and heuristicapproximations are used to model the system performance. They facilitate first-order performance estimates and the identification of limiting effects even for multi-Tb/s systems within a few seconds. Taking into account local and accumulated group velocity dispersion, impairments due to fibre nonlinearities are described as a function of the average optical input power per channel. In combination with thedegradation of the optical signal-to-noise ratio caused by optical amplifier noise the maximum transmission distance versus optical input power can bedetermined. The validity of the models is verified by means of numerical simulations and system experiments. The dependence on data rate, modulation format, fibre type and dispersion compensation scheme is determined. Practical examples illustrate the usefulness of our design approach.
TL;DR: In this paper, the central limit theorem applied to the random parameters that characterize the microscopic constituents, the probability density function, mean, uncertainty and confidence intervals of various macroscopic effective constitutive material and wave parameters are derived.
Abstract: Summary The statistical macroscopic characterization of composite materials in simple and complex electromagnetic environments is addressed. Based on the central limit theorem applied to the random parameters that characterize the microscopic constituents, the probability density function, mean, uncertainty and confidence intervals of various macroscopic effective constitutive material and wave parameters are derived. The implications ofthe randomness of the external field on these parameters are also investigated.
TL;DR: In this article, a very simple expression for the narrow aperture dimension of the horn is obtained and used in the optimum gain pyramidal horn design, which does not need the application of the iterative methods, and are not restricted to the longhorn designs.
Abstract: Summary A new, very simple expression for the narrow aperture dimension of the horn is obtained and used in the optimum gain pyramidal horn design. The design parameters are computed from the simple and explicit formulas. These formulas do not need the application of the iterative methods, and are not restricted to the long-horn designs. The gain of a designed pyramidal horn is determined without approximating the path length error. Design examples are given to illustrate the performance of the design technique proposed in this paper.
TL;DR: In this article, an isolated, semi-infinite, open-ended, single-shell, zigzag carbon nanotube (CN) is considered in the optical regime.
Abstract: Summary Scattering of electromagnetic cylindrical waves by an isolated, semi-infinite, open-ended, single-shell, zigzag carbon nanotube (CN) is considered in the optical regime. The CN is modeled as a smooth homogeneous cylindrical surface with impedance boundary conditions known from quantum-mechanical transport theory. An exact solution of the diffraction problem is obtained by the Wiener-Hopf technique. The differences between the scattering responses of metallic and semiconducting CNs are discussed.
TL;DR: In this paper, different designs of digital optical switches (DOS) in polymers utilizing the thermo optical effect are compared with respect to their applicability in switching matrices and their crosstalk performance.
Abstract: Summary We discuss and compare different designs of digital optical switches (DOS) in polymers utilizing the thermo optical effect (y-branched DOS, three branched DOS, DOS cascade with partially merged switching stages, DOS with integrated attenuators) with respect to their applicability in switching matrices and their crosstalk (CT) performance. The underlying oversized rib waveguide concept is also briefly discussed with emphasis on the integration of absorbers. Finally we present results for an optimized matrix switch design.
TL;DR: In this paper, a continuous-time active mode (CM) active filter for low frequency operation using dual-output current conveyors (DO-CCII) is proposed. But the proposed circuit simultaneously produces three basic filter responses at its high impedance outputs and it has good passive and active sensitivity performance.
Abstract: Summary The realisation criteria of continuous-time current-mode (CM) active filters for low frequency operation are investigated. New lossless and lossy integrators for low frequency operation using dual-output current conveyors (DO-CCII) are proposed. Basing on these building blocks, a CM universal filter with low natural frequencies suitable for integrated circuit implementation is presented. Using the proposed filter, natural frequencies as low as a few ten hertz can be achieved on an integrated circuit chip without using any external passive components. The proposed circuit simultaneously produces three basic filter responses at its high impedance outputs and it has good passive and active sensitivity performance.
TL;DR: In this article, statistical evidence based on two long-term IP traffic traces is given for the amount of waiting time which is due to different phases of a Web connection -domain name lookup, connection establishment, requesting and finally transferring an item.
Abstract: Summary Web browsing is the application producing most of the traffic observed on the Internet backbones today. While this is obviously an enormous success for a single application that was created only a decade ago, many users experience Web access as a “world wide waiting” process. In this paper, statistical evidence based on two long-term IP traffic traces is given for the amount of waiting time which is due to different phases of a Web connection – domain name lookup, connection establishment, requesting and finally transferring an item. Nearly half the delay in an average HTTP/TCP connection is due to the first three components and only the rest can be influenced significantly by higher speed access systems for large downloads.
TL;DR: In this paper, a 2×2 matrix algebra for electromagnetic wave propagation in stratified biaxial media is presented, which is based on the continuity of the tangential components of the electric and magnetic field vectors.
Abstract: Summary We present a new 2×2 matrix algebra for electromagnetic wave propagation in stratified biaxial media. Our method is based on Maxwell's equations and the continuity of the tangential components of the electric and magnetic field vectors and gives an exact complete solution. No restrictions are necessary for the orientations of the axes of the dielectric tensors of the stratified medium and the properties of the incident plane wave. A complete and systematic methodology is provided for calculating all wave parameters and all properties of the reflected and transmitted waves in terms of 2×2 Fresnel reflection and transmission matrices.
TL;DR: In this paper, the problem of determining an unknown rectilinear source from the knowledge of its radiated field over a bounded observation domain located in the near zone, orthogonal and centered with respect to the source is dealt with.
Abstract: Summary The problem of determining an unknown rectilinear source from the knowledge of its radiated field over a rectilinear bounded observation domain located in the near zone, orthogonal and centered with respect to the source is dealt with. In particular, we firstly analyze the information content of data by means of the Singular Value Decomposition of the radiation operator. Secondly, the resolution limits achievable in the reconstruction are discussed by examining the effect of the key geometrical parameters of the measurement configuration.
TL;DR: In this article, the error probability in a Rayleigh fading channel with corre- lated fading amplitudes is derived for a multicarrier CDMA transmission and a closed form expression for the probability can be expressed by an in-tegral over a finite interval which can be easily evaluated numerically.
Abstract: We present an new method for the analytical calculation of the error probability in a Rayleigh fading channel with corre- lated fading amplitudes. Even though the method can be applied for more general problems, we restrict ourselves on the investiga- tion of a multicarrier CDMA transmission. The frequency cor- relation between the fading amplitudes of the carriers is given by the delay power spectrum of the channel. We generalize the well- known analytical expressions for the pairwise error probability of the uncorrelated Rayleigh channel to this case of correlated fad- ing. This probability can be expressed in a closed form by an in- tegral over a finite interval which can be easily evaluated numer- ically. We present some examples to show how much of the diver- sity of a code remains useful if the transmission channel does not provide an arbitrary degree of diversity.
TL;DR: In this article, a novel method for the analysis of a wide range of coplanar and microwave T-junctions is presented based on the Method of Lines (MOL) method.
Abstract: Summary A novel method for the analysis of a wide range of coplanar and microwave T-junctions is presented The concept is based on the Method of Lines Two crossed two-dimensional discretization schemes are combined with the impedance transformation for modelling the central region of the structure This approach is validated by comparison with results obtained by FDTD method and Sonnet software
TL;DR: This paper proposes two bandwidth efficient resource allocation policies that are applicable for data services in the downlink of a Wideband Code Division Multiple Access (W-CDMA) network to optimize the total downlink system capacity.
Abstract: Summary The Universal Mobile Telecommunications System (UMTS) has to support various services and applications with diverse bit rate and quality of service (QoS) requirements. This paper proposes two bandwidth efficient resource allocation policies that are applicable for data services in the downlink of a Wideband Code Division Multiple Access (W-CDMA) network. These resource allocation strategies take the interference and radio channel conditions of the different users into account to optimize the total downlink system capacity. It is shown that this provides a significant improvement compared to the conventional approach where each user receives the same bit rate irrespectively of its radio channel conditions. This is particularly important, because the downlink is the bottleneck of a W-CDMA system due to the asymmetric traffic characteristics of data services.
TL;DR: In this paper, the classical Engset traffic model is generalized to fractional values of sources and servers, which can be expressed in terms of continued fraction expansions, resulting in an effective numerical procedure.
Abstract: Summary We consider the classical Engset traffic model. Time congestion, call congestion, and traffic congestion formulae for a system with S sources and n servers are generalised to fractional values of sourcesand servers. The generalised Engset time congestion formula can be written in terms of incomplete beta functions, which can be conveniently expressed in terms of a continued fraction expansions, resulting in an effective numerical procedure. Associated recursion formulae for the generalised Engset time congestion are similar to the well-known recursions for integral values of both S and n. In the particular case that n is integral and S is fractional (S≫n) we present a simple Markovian traffic model, an Engset–Poisson mixture, from which it becomes clear how to physically interpret an Engset traffic source with fractional S. Numerical examples are given.
TL;DR: In this article, the authors present several different methods for generating the division factor sequences controlling the programmable frequency divider in the phase-locked-loops (PLL) system.
Abstract: Summary In the field of fractional divider phase-locked-loops (PLL) there exist several different methods for generating the division factor sequences controlling the programmable frequency divider in the PLL. The overall behaviour of the fractional PLL strongly depends on the proper choice of the division factor sequence. Therefore some concepts for generating these fractional sequences are discussed and the behaviour of the division factor sequences will be analysed with respect to the overall PLL behaviour. In addition some sources of disturbances are mentioned.