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     

Low-Voltage Low-Power CMOS RF Four-Quadrant Multiplier

This paper describes a CMOS four-quadrant multiplier intended for use in the front-end receiver by utilizing the square-law characteristic of the MOS transistor in the saturation region. The circuit was simulated in standard 0.5 μm CMOS level 3 MOSIS (BSIM3 SPICE-based). The mixer has a third-order inter modulation (IM3) of 34.7 dBmV, a third-order intercept point (IP3) of -5.7 dBm, 1-dB compression (P-1dB) of -10.4 dBm and the power consumption is 1.18 mW from a single 1.5 V power supply. One of the features of the proposed design is using two MOS transistors limitation to reduce the supply voltage, which leads to reduce the power consumption.     

Positive and Negative Goos-Hauml;nchen Shifts and Negative Phase-Velocity Mediums (alias Left-Handed Materials)

On total reflection from a half-space filled with an isotropic, homogeneous, weakly dissipative, dielectric-magnetic medium with negative phase-velocity (NPV) characteristics, it is shown here that a linearly polarized beam can experience either a negative or a positive Goos-Hauml;nchen shift. The sign of the shift depends on the polarization state of the beam as well as on the signs of the real parts of the permittivity and the permeability of the NPV medium.     

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.     

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].     

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.     

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.     

Time Offsets for Non-orthogonal CDMA Signals

A simple interference reduction method for non-orthogonal downlink CDMA channels is presented in which non-orthogonal CDMA signals are transmitted with different time offsets. An expression of multiple access interference (MAI) is developed and a reduction of MAI power is evaluated by using a numerical method and a computer simulation. The value of the time offset is determined in order to minimize the MAI and the implementation complexity. The performance of the proposed method is evaluated for various channel models.     

Development of LC Optics for Free-space Laser Communications

Free-space laser communications is a very flexible means to connect end users to a high-bandwidth data network via ground-based terminals on top of buildings or to bring a variety of data services to remote locations via satellite terminals in space. External influences on the optical link due to atmospheric turbulence and vibrations in the transmitter's environment require some method of beam control to stabilize the optical link and maintain a high transmission rate. Liquid crystal (LC) optics can provide a compact and low-power solution to beam control in laser communications systems. Besides reviewing recent Japanese activities in the field of free-space laser communications, this paper summarizes four years of research in designing and experimentally evaluating LC beamdeflectors and adaptive lenses that feature simple driving circuitry and have been manufactured specifically with regard to laser communications.     

Spectral Efficiency of Cellular Mobile Radio Systems with Different Traffic Loads

A lower bound on the Shannon capacity of the uplink channel of a narrowband cellular system is evaluated as a function of the reuse distance and the level of shadowing affecting the interfering signals assuming perfect channel state information (CSI) at the receiver. The effect of the first two tiers of interferers is determined, and compared with a simplified evaluation that takes into account only the first tier.Spectral efficiency is evaluated for different traffic loads, to assess the usefulness of traffic control. The performance improvementthat may be obtained by adopting the space diversity, to avoid deep fades in the received signal, is also evaluated. Our results show that traffic control may have a negative effect on the system performance.     

Network Management Information Models

In the first part of this paper, a basic introduction to network management is given and the demand for standards and models of management information is addressed. Existing and new network management standards are then classified, and an overview on the Common Information Model CIM and the Web-Based Enterprise Management WBEM is given. Furthermore, classes for a Network Security Service and finally a Firewall Policy Model are proposed. The proposals are CIM extensions for security management and are being discussed with the Distributed Management Task Force DMTF to become a standard.     

Multifunctional Optical Terminals for Microsatellite Clusters – Design Tradeoffs

We study optical terminals with both communication and ranging capabilities for their potential use in short range free-space applications, typically encountered within a cluster of microsatellites. For our considerations we assume satellites with a unit mass between 10 kg and 100 kg, with mutual distances on the order of a few km, and per link data rates range from a few kbits/s to some 100 Mbit/s. We discuss possible network topologies and multiple access methods, andcompare the performance characteristics of different intensity modulation formats, taking into account not only the task of communication but also that of accurate intra-cluster distance measurement. Our considerations revealbasic tradeoffs to be observed when designing such multifunctional optical terminals.     

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.     

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.     

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.     

Time Delay Estimation by Cross-covariance Maximization of Quadrature Sampled Narrowband Signals

A numerically efficient algorithm for estimating the time delay from observations of a stationary narrowband signal and its delayed version is investigated. Quadrature sampling, a variant of bunched sampling, is applied to estimate samples of the quadrature components of the cross-covariance function of the two signals. The baseband magnitude squared of this function can be maximized for time delay estimation. Because the time delay is unknown, the baseband cross-covariance function cannot be interpolated from the estimated samples. Numerical maximization of the samples' magnitude squared and quadratic interpolation, however, results in a reasonable time delay estimate.     

Configurations Optimizing the Directivity of Planar Arrays

The role of the geometrical configuration of isotropic elements in a planar array is investigated with a view to achieve maximum directivity. Distinctions are made between normal and superdirective regions. It is further shown that the configurations leading to optimum directivities may depend on aperture diameter in a manner somewhat analogous to phase transitions in solid state physics. The effect of losses is estimated and it is shown that, particularly for superconductive materials, they do not affect much the achievable gain.     

Low Voltage Digitally Controlled CMOS Current Conveyor

In this paper, a digitally controlled current conveyo(DCCC) is presented. The proposed DCCC is based on rail-to-rail folded cascode implementation with a current division network (CDN). The CDN is used to provide control on the current gain of the DCCC. The CDN uses a novel current division technique based on differential pairs. The proposed DCCC can operate from ±1.5 V supply voltages. Applications of the proposed DCCC such as variable gain amplifiers (VGA) and digitally tunedfilters have been investigated. PSpice simulations based on the AMI 1.2 µm N-well level 3 parameters are in agreement with the presented work.     

Numerical Simulation of Waveguides of Arbitrary Cross-Section

Finite difference equations are derived for the simulation of dielectric waveguides using an H_z-E_z formulation defined on a nonuniform triangular grid. The resulting equations may be solved as a banded eigenproblem for waveguide structures of arbitrary shape composed of regions of piecewise constant isotropic dielectric, and all transverse fields then computed from the solutions. Benchmark comparisons are presented for problems with analytic solutions, as well as a sample calculation of the propagation loss of a hollow Bragg fiber.     

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.