Asymptotic Analysis of Optimal Uniform Polar Quantization

In this paper the simple and complete asymptotically analysis is given for a uniform polar quantizer with respect to mean-square error (MSE) i.e.granular distortion (D_g). We also give the conditions for optimality of the polar quantizer and all main equations for phase partitions and optimal number oflevels are presented. We derive the D_g^opt in a closed form. Thegain ofoptimal uniform polar quantization over product polar quantizations [1–3], is afforded by allowing a variable number of phasesat each magnitude level. We also obtain gain (G) in a closed form.     

Hidden Markov Modeling of Error Patterns and Soft Outputs for Simulation of Wideband CDMA Transmission Systems

In this paper, a Hidden Markov Modeling (HMM) technique for a fast and accurate simulation of bit errors and soft outputs in wireless communication systems is presented. HMMs with continuous probability distributions are considered. Soft outputs and bit errors are combined to error patterns. We focus on binary phase–shift keying (BPSK) modulation for direct–sequence spread spectrum (code–division multiple access, CDMA) transmission as proposed e.g. for the third generation wireless communication system UMTS (uplink for the frequency division duplex mode (FDD)). Comparisons of simulated bit error rates for HMM models and Rake receivers are shown for AWGN, flat fading, and vehicular channel conditions. In order to assess the ability of the HMM to describe the dynamical behaviour of the channel a comparison for transmission with interleaving and convolutional coding is presented. Furthermore calculated autocorrelation functions of the error patterns and error gap distributions corresponding to the Rake receiver and to the HMM, respectively, are presented. Our investigations show a strong dependence of the required HMM order on E_b/N₀ and the channel conditions. The degree of accordance of the HMM outputs and the training data is examined based on calculated statistical scoring indicators.     

Model Order Estimation for Joint Demodulation in DS-CDMA Systems

An iterative algorithm for estimating the number of relevant transmission paths characterized by the model order vector L in the uplink of a direct sequence code division multiple access (DS-CDMA) system is presented. Estimates of simplelower bounds on the probability of correct one-shot symbol estimates are formulated as a function of bit-error rate estimates of all users and maximized w.r.t. L. The joint demodulation for a given value Lis accomplished using a combination of a space-alternating generalized expectation-maximization (SAGE) algorithm for channel parameter estimation and a°multistage detector. Simulation results indicate that the modelorder is estimated correctly even in situations with considerably differentsignal power levels.     

Some Results on Convolutional Coupled Codes: Distance Properties, Performance, and Design

The class of Convolutional Coupled Codes is a promising alternative to classical Turbo-Codes. A Convolutional Coupled Code consists of a cascade of ν identical recursive systematic convolutional (RSC) outer codes and k inner block codes with parameters (2ν, ν, d_i). The codes are linked together such that only the systematic part of the outer codes is encoded with the inner block encoders. Only the redundancy from the inner and outer codes are transmitted. An estimation of the minimum distance is derived. The influence of number, code memory and code polynomials of the outer RSC codes on the distance properties and the convergence behavior of the iterative decoding scheme is studied. With respect to this results, we present a guideline for the optimal design of the RSC outer codes.     

Variance and Covariance Computations for 2-D ARMA Processes

An algorithm is presented to compute the variance of the output of a two-dimensional (2-D) stable auto-regressive moving-average (ARMA) process driven by a white noise bi-sequence with unity variance. Actually, the algorithm is dedicated to the evaluation of a complex integral of the form , where and G(z₁,z₂) = B(z₁, z₂) / A(z₁, z₂) is stable (z₁,z₂)-transferfunction. Like other existing methods, the proposed algorithmis based on the partial-fraction decomposition G(z₁,z₂)G(z ₁ ^-1 , z ₂ ^-1 ) = X(z₁, z₁) / A(z₁,z₂)+ X(z ₁ ^-1 , z ₂ ^-1 ) / A(z ₁ ^-1 , z ₂ ^-1 ). However,the general and systematic partial-fraction decomposition schemeof Gorecki and Popek [1] is extended to determine X(z₁,z₂).The key to the extension is that of bilinearly transforming thediscrete (z₁, z₂)-transfer function G(z₁,z₂)into a mixed continuous-discrete (s₁, z₂)-transferfunction . As a result, the partial-fraction decomposition involves only efficient DFT computations for the inversion of a matrix polynomial, and the value of I is finally determined by the residue method with finding the roots of a 1-D polynomial. The algorithm is very easy to implement and it can be extended to the covariance computation for two 2-D ARMA processes.     

An Improvement of Mobile Users Authentication in the Integration Environments

This paper shows that Tzeng and Tzeng's protocol has a drawback that the protocol can be easily crashed by an evil VLR attack. Therefore, we propose a slight modification to their protocol toimprove their shortcoming. As a result, our protocol does not only enhance the security of Tzeng and Tzeng's protocol but also improves the efficiency.     

Electromagnetic Prospection via Homogeneous and Inhomogeneous Plane Waves: The Case of an Embedded Slab

This paper deals with the linear approximation of the inverse scattering problem for a dielectric slab embedded into a homogeneous half-space. After a proper normalization of the scattered field, the problem at hand is recognized to be related to a Fourier transform inversion with limited data. This permits to resort to the well-known results available in signal processing in order to discuss about the class ofthe retrievable unknowns and the resolution limits achievable by inversion. In particular, the role of both homogeneous and inhomogeneous incident plane waves in carrying out information about the profile under test is investigated and the role played by the dielectric permittivity of the host medium in determining the information content of the scattered field is pointed out.     

Plasmatron with Microwave Excitation of Nonequilibrium Plasma

Testing results of a microwave plasma generator (plasmatron) intended for excitation of a strongly nonequilibrium plasma arepresented. Nonequilibrium properties of the plasma are described in detail.The plasma flame is formed at an open end of a coaxial line under atmospheric pressure. Argon is used as plasma forming gas, and a 10 GHz CW magnetron with 10 W output power is used for plasma excitation.The efficiency of absorption of microwave power in the plasma is higher than90% with specific absorbing capacity of 0,4.4 kW/cm³     

A New State-space-based Algorithm to Assess the Stability of the Finite-difference Time-domain Method for 3D Finite Inhomogeneous Problems

The finite-difference time-domain (FDTD) method is an explicit time discretization scheme for Maxwell's equations. In this context it is well-known that explicit time discretization schemes have a stability induced time step restriction. In this paper, we recast the spatial discretization of Maxwell's equations, initially without time discretization, into a more convenient format, called the FDTD state-space system. This in turn allows us to derive a new algorithm in order to determine the stability limit of FDTD for lossy, inhomogeneous finite problems. It is shown that a crucial parameter is the spectral norm of the matrix resulting from the spatial discretization of the curl operator. In a rectangular simulation domain the time step upper bound can be calculated in closed form and results in a time step limit less stringent than the Courant condition. Finally, the validity of the technique is illustrated by means of some pertinent numerical examples.     

Diffraction of Obliquely Incident Plane Waves by Resistive and Conductive Planar Surfaces

The multiple diffraction of obliquely incident plane waves by the three-part resistive and conductive plane is evaluated via uniform asymptotic high frequency analysis. This analysis is based on a spectral iteration technique consisting of employing the Fourier Integral representation of the diffracted field through the solution of a pair of uncoupled Wiener-Hopf equations. By studying these equations iteratively, the double and triple diffracted fields are obtained through the saddle-point technique. Some numerical examples are also presented.     

Electromagnetic Scattering by an Inhomogeneous Impedance Cylinder

In this paper, the electromagnetic scattering problem related to a circular cylinder with inhomogeneous impedance boundary is solved. This kind of problem may have practical applications such as antenna design since one can obtain a certain radiation pattern by choosing thesurface impedance in an appropriate way. The approach presented in this paper is based on the series representations of the scattering and incident fields. The impedance function is also expanded into a Fourier series. By using orthogonality properties of some special functions the problem is reduced to the solution of a system of linear equations. The problem isalso solved through the extended boundary condition method (T-matrix method). Since an extensive treatment of the T-matrix method is available in the open literature the paper is weighted towards the Fourier series method. The results of both methods are compared. Some illustrative examples showing the effects of different parameters on the scattered field are given.     

On Convolutional Coupled Codes

The error correcting performance of the parallel concatenation of two convolutional codes is very promising. Inspired from this construction which is near the Shannon limit error correction performance, we consider a further development of concatenated codes. In this construction systematic convolutional codes and rate 1/2 systematic block codes are linked together such that only the systematic part of the convolutional codes is encoded with the block encoders. The bits of each information vector of the convolutional codes are scrambled by a given interleaving before entering to the block encoders. Then, differently from the Turbo codes, in which information symbols and the redundancy from the constituent codes are transmitted [1], we transmit only the redundancy from the convolutional and block codes. We call this construction convolutional coupled codes and code coupling is the new scheme of code concatenation. The structural properties of the generator matrix of the convolutional coupled code is investigated. It's minimum distance is lower and upper bounded and we introduce the term of the effective free distance. Simulation results will show, that convolutional coupled codes have the potential of being a realistic alternative to Turbo codes.     

Efficient Scattering Calculations in Complex Backgrounds

The utilization of the Green's tensor associated with a complex optical background (surface, cavity or stratified medium) leads to a dramatic reduction of the computation effort associated with scattering calculations in that background. This approach is illustrated with examples where a mere change of the background Green's tensor makes possible the investigation of completely different physical situations. Two different discretization approaches are compared and similarities between the Green's tensor technique and the Method of Lines are emphasized; in the latter, the utilization of analytic solutions in one specific direction also reduces the discretization of the system.     

Statistical Evaluation of Adaptive Threshold Alignment for a Multi-Carrier CDMA Code Synchronization

This letter presents a statistical analysis of the decision threshold for a multi-carrier (MC) DS/CDMA acquisition system with a reference filter. The probabilities of detection and false alarm are derived, and the mean acquisition time is evaluated as a measure of the system performance. From the results, it is shown that in the performance analysis of the hybrid acquisition system with reference filtering, the statistical evaluation of the decision threshold seems more appropriate than the approximation of the decision threshold adopted in other schemes [7,8].     

Nonlinear Kirchhoff Circuits and Relativity Theory

Kirchhoff circuits consist of interconnections of elements. They are of importance not only for studying electrical phenomena but are ideally suited to model a broad range of physical systems for purposes where conservation of power and energy and related concepts such as passivity and losslessness are of paramount importance. In order to properly characterize such properties in the nonlinear case, the defining relations for nonlinear inductances etc. must have a specific form, but the classical relation for a relativistic mass is not of this type. It is shown that, preserving the classical relativistic kinematics and imposing a very reasonable requirement concerning work done, thus energy rather than momentum, one is naturally led to an expression for force in terms of mass and velocity whose form is in full agreement with that referred to for a nonlinear inductance. This alternative way of modifying Newton's second law requires Newton's third law to be also modified. These two modifications combined produce the same conservation of momentum and the same dynamics of particles in fields as classical relativity. The expression for kinetic energy, however, is different. Logically consistent derivations are presented, and a theoretical and an experimental result are pointed out that tend to offer some support to the alternative theory, or at least do not outrightly contradict it, as implausible as that theory may a priori appear to be. The paper updates earlier results on the subject.     

A Wave Approach to Signal and Noise Modeling of Dual-Gate MESFET

A new procedure for signal and noise modeling of dual-gate MESFET is described in this paper. The small-signal model is based on two cascoded single-gate MESFET intrinsic equivalent circuits embedded in a network representing device parasitics. The wave interpretation of noise is used for defining the noise parameters of each single gate MESFET. Applying this approach, a CAD oriented procedure for extracting the dual-gate MESFETmodel parameters as well as the noise wave temperatures is developed. Modeled scattering and noise parameter characteristics are comparedto the measured ones and quite a good agreement is observed.     

Near Field Analysis of the Modal Scattering at Radiating Apertures

A rigorous method for the determination of the modal scattering at radiating apertures is presented. Near-field boundary conditions to be satisfied on the outer surface of the conducting structure containing the aperture (e.g. a horn antenna) are completely taken into account. The resulting scattering matrix of the radiating aperture can be integrated into any mode-matching technique as a termination for the cascaded structure commonly used to match the aperture to the exciting waveguide. The method is based on a multiple-multipole expansion of the electromagnetic field outside the radiating object in conjunction with a point-matching technique. Horn antennas with elliptical and circular apertures have been analyzed using the suggested method. Excellent agreement with measurement results has been achieved for both the radiation pattern and the aperture scattering parameters.     

Solid solution InxGa1−x AsySbzP1−y−z : A new material for infrared optoelectronics. I. Thermodynamic analysis of the conditions for obtaining solid solutions, isoperiodic to InAs and GaSb substrates, by liquid-phase epitaxy

The diagrams of melt-solid solution (fusibility curves) and solid solution (I)-solid solution (II) (surfaces of spinodal decomposition of solid solutions) phase equilibria in the five-component system In-Ga-As-Sb-P (the solid solutions are isoperiodic to the GaSb and InAs substrates) are calculated. The concentration ranges of the isovalent substitution solid solutions In_xGa_1−x As_ySb_zP_1−y−z , which are accessible for synthesis by liquid-phase epitaxy, are calculated. Fiz. Tekh. Poluprovodn. 31, 410–415 (April 1997)     

Target Multiplicity Performance Analysis of Radar CFAR Detection Techniques for Partially Correlated Chi-Square Targets

Most radar targets are complex objects and produce a wide variety of reflections. An important class of targets is represented by the so-called moderately fluctuating Rayleigh targets, which, when illuminated by a coherent pulse train, return a train of correlated pulses with a correlation coefficient in the range 0<ρ<1 (intermediate between SWII and SWI models). The detection of this type of fluctuating targets is therefore of great interest. On the other hand, the CFAR detection is one of the desirable features for radar receivers. Because of the simplicity of cell-averaging (CA detectors in their implementation, they are commonly used in modern radar systems to automatically adapt the detection threshold to the local background noise or clutter power in an attempt to maintain an approximately constant rate of false alarm. In this paper, we analyze the performance of these detectors for the case where the radar receiver postdetection integrates M square-law detected pulses and the signal fluctuation obeys chi-square statistics with two degrees of freedom. These detectors include the mean-level ML), the greatest-of (GO) and the smallest-of (SO) schemes. In these processors, the estimation of the noise power levels from the leading and the trailing reference windows is based on the CA technique. Exact formulas for the detection probabilities are derived, in the absence as well as in the presence of spurious targets. The primary and the secondary interfering targets are assumed to be fluctuating in accordance with the chi-square fluctuation model with two degrees of freedom. Swerling's well known fluctuation models I and II represent the cases where the signal is completely correlated and completely decorrelated, respectively, from pulse to pulse. Probability of detection curves are presented for the chi-square family of fluctuations, including the Swerling cases I and II. The ML detector has the best homogeneous performance, the SO processor has the best multiple-target performance, while the GO scheme does not offer any merits neither in the absence nor in the presence of outlying targets.     

A New Algorithm for Optimum Multiuser Detection in Synchronous CDMA Systems

Optimum multiuser detection for Code Division Multiple Access (CDMA) systems requires the solution of an NP-hard combinatorial optimization problem. It is well known that the computational complexity of the optimum multiuser detector is exponential with the number of active users in the system. In order to reduce the complexity of the optimum multiuser detection, we propose a Reduced Complexity Maximum Likelihood (RCML) algorithm that includes a set of novel certain boundary rules and characteristics. We investigate the performance and complexity tradeoffs for the RCML algorithm by conducting a set of simulations; Maximum Likelihood (ML) detection as a reference for performance comparisons, and relaxation based Semidefinite Programming (SDPB) algorithm as a reference for complexity comparisons. We show that the RCML algorithm is a promising algorithm for its computational savings over relaxation based algorithms in lightly-to-moderately loaded CDMA systems, and for its optimality in highly loaded CDMA systems.