A generalized method for analyzing shielded thin microstripdiscontinuities

An integral equation method for the accurate full-wave analysis of shielded thin microstrip discontinuities is described. The integral equation is derived by applying the reciprocity theorem and then solved by the method of moments. In this derivation, a coaxial aperture is modeled with an equivalent magnetic current and is used as the excitation mechanism for generating the microstrip currents. Computational aspects of the method have been explored extensively. A summary of some of the more interesting conclusions is included     

A generalized framework for iterative source-channel decoding

Joint source-channel decoding is considered for a transmission system, in which the quantizer indices of several autocorrelated source signals are bit-interleaved, commonly channel encoded, and transmitted in parallel. Since the optimal decoding algorithm is not feasible in most practical situations, iterative source-channel decoding has been introduced. The latter is generalized in the present paper. Furthermore, it is shown in detail, that iterative source-channel decoding can be derived by insertion of appropriate approximations into the optimal joint decoding algorithm. The approximations allow the decomposition of the optimal decoder into two parts, which can be identified as the constituent decoders for the channel-code and the source-code redundancies. Similar as in other concatenated coding systems, the constituent decoders are applied in an iterative decoding scheme. Its performance is analyzed by simulation results.     

Bragg's law generalized to time-space periodic media

Bragg's law for scattering from space-periodic media is generalized to take into account that the scatterers are moving. Scattering from a Bragg cell with an acoustic disturbance is studied, and the frequency shift of the scattered wave is derived, without approximations, as a Doppler shift.     

A framework for analyzing and designing scale invariant remotesensing algorithms

The land surface exhibits heterogeneity across a range of spatial scales. Remote sensors provide integrated information at the pixel scale, however, there is important spatial variability at scales smaller than the scale of the sensor. On the other hand, large scale models that use remotely sensed data do not require them at the same spatial resolution at which remote sensors are required to operate. In this paper, a framework for testing aggregation-disaggregation properties of remote sensing algorithms is presented. The proposed framework provides a systematic approach for parameterizing the land surface heterogeneity effects. For the estimation of the pixel scale response, the lumped response should be modified by the variance and covariance terms. This representation of land surface heterogeneity could lead to substantial savings in remote sensing data storage and management. Using simulated land and vegetation scenarios, the authors have successfully parameterized subpixel scale heterogeneity effects for the estimation of vegetation index, by modeling the variances and covariance terms with the pixel scale values     

A framework for analyzing the user membership in cellular CDMAnetworks

A theoretical framework is developed to analyze the user membership in cellular networks. The main interest is on code-division multiple-access (CDMA) networks, although the validity of the proposed approach is not restricted to these networks. The membership of a user terminal to a certain base station (BS) is established if the local mean attenuation to this BS is the lowest one among all surrounding BSs. The estimate of local mean attenuation on the radio links from a mobile terminal to each of the surrounding BSs is carried out through proper filtering of the sequences of received signal strength measurements taken on broadcast signals at regular time intervals. In CDMA networks, pilot channels can be considered, while broadcast control channels can be generically considered in narrow-band systems. A decision is made each time on whether the terminal is to be assigned to its “current” BS or if it would be better served by a different BS. Two performance measures are considered: the probability that the best BS is not selected and the average number of membership switchings per time unit. A channel model with log-normal shadowing and fast fading superimposed is considered. Analytical expressions for the above-mentioned performance measures are derived in a general system scenario. From numerical results, it is seen that a proper choice of filter parameters is required to achieve the lowest values for both performance measures. Moreover, these values are not negligible when the mobile terminal is close to a boundary cell region. The obtained results are considered to be of interest in handover and power control algorithms     

Design techniques for subcarrier multiplexed broadcast opticalnetworks

Design techniques which enable the performance of subcarrier multiplexed FM broadcast optical networks to be optimized at the planning stage are described. At the transmitter node, criteria for maximizing the subscriber carrier-to-noise ratio (CNR) are presented. At the subscriber node, it is shown that under the majority of circumstances, the optimum direct detection receiver consists of a low-noise III-V avalanche photodiode and high-impedance front-end preamplifier. Sensitivities approaching -40 dB (1 mW) for 16.5 dB CNR in 36 MHz subscriber bandwidth are predicted for a 60-channel system. Preliminary experimental tests on an optical-feedback subcarrier receiver showed -34 dB (1 mW) sensitivity at 1.55 μm from 16.5 dB CNR in a 36 MHz bandwidth centered on 1.2 GHz with a 12% modulation index single-channel FM test signal     

A framework for analyzing levels of analysis issues in studies of e-collaboration

There has been a proliferation of competing explanations regarding the inconsistent results reported by the e-collaboration literature since its inception. This study advances another possible explanation by investigating the range of multilevel issues that can be encountered in research on the use of synchronous or asynchronous group support systems. We introduce concepts of levels of analysis from the management literature and then examine all empirical studies of e-collaboration from seven information systems journals for the period 1999-2003. We identified a total of 54 studies of e-collaboration in these journals, and after excluding 18 nonconforming studies - those that were primarily conceptual, qualitative, or exploratory only-we analyzed the levels of analysis issues in the remaining 36 empirical studies. Based on our analysis and classification of these studies into six different clusters according to their levels of analysis, we found that a majority of these studies contain one or more problems of levels incongruence that cast doubts on the validity of their results. It is indeed possible that these methodological problems are in part responsible for the inconsistent results reported in this literature, especially since researchers' frequent decisions to analyze data at the individual level - even when the theory was formulated at the group level and when the research setting featured individuals working in groups -may very well have artificially inflated the authors' chances of finding statistically significant results. Based on our discussion of levels of analysis concepts, we hope to provide guidance to empirical researchers who study e-ollaboration.     

A generalized framework for distributed power control in wireless networks

Most power control algorithms that aim at hitting a signal-to-interference ratio (SIR) target fall within Yates' framework. However, for delay-tolerable applications, it is unnecessary to maintain the SIR at a certain level all the time. To maximize throughput, one should increase one's power when the interference level is low, and the information transmission rate is adjusted accordingly by adaptive modulation and coding techniques. This approach is called opportunistic communications. In this paper, we generalize Yates' result and establish a new framework, which is applicable to systems supporting opportunistic communications and with heterogeneous service requirements. Simulation results show that our proposed algorithm yields significant improvement in throughput when compared with the conventional target tracking approach.     

A unified framework for performance evaluation over generalized fading channels

In this paper, we present a unified framework to analyze the performance of the average bit error probability (BEP) and the outage probability over generalized fading channels. Specifically, we assume that the probability density function (PDF) of the instantaneous signal-to-noise ratio \(\zeta \) is given by the product of: power function, exponential function, and the modified Bessel function of the first kind, i.e., \(f_{\zeta }(\zeta )=\zeta ^{\lambda -1}exp\left( -a\zeta ^{\beta }\right) I_{v}\left( b\zeta ^{\beta }\right) \). Based on this PDF, we obtain a novel closed-form expression for the average BEP over such channels perturbed by an additive white generalized Gaussian noise (AWGGN). Note that other well-known noise types can be deduced from the AWGGN as special cases such as Gaussian noise, Laplacian noise, and impulsive noise. Furthermore, we obtain a novel closed-form expression for the outage probability. As an example of such channels, and without loss of generality, we analyze the performance of the average BEP and the outage probability over the \(\eta \)–\(\mu \) fading channels. Analytical results accompanied with Monte-Carlo simulations are provided to validate our analysis.     

A generalized framework for probabilistic design with application to rotors

This paper generalizes an existing method for deriving probability models of manufacturing quality metrics. We specifically consider the problem of deriving probability models for the inertia tensor of a rotor. The inertia tensor is a 3 /spl times/ 3 matrix that determines various dynamical properties of the rotor as it spins, affecting its reliability. The key contribution of this paper is that the quality metric of interest is a matrix or a second-order tensor, and the various manufacturing imperfections that cause deviations in the inertia tensor may be vectors. Existing methods, by contrast, assume that the quality metric, as well as the manufacturing imperfections, are scalar quantities. By using rotational properties of matrices & vectors, we show that the relationship between the inertia tensor, and the manufacturing errors must have a specific form, when the errors are small. This structure significantly restricts the class of allowable distributions for the inertia tensor. For example, we show that the multivariate s-normal distribution is not a physically appropriate distribution for the inertia tensor. The results in this paper, while applied specifically to the inertia tensor, are general, and depend only on transformational properties of vectors & matrices. Thus, the framework is applicable to modeling other engineering systems involving second-order tensors, such as the stress tensor, or strain tensor.     

A brief summary of a generalized framework for power spectral estimation

This correspondence presents a brief summary of a generalized framework for power spectral estimation and shows how three previous estimation methods fit into this framework as special cases. Further, this correspondence clarifies some recent comments made on spectral estimation; in particular specific references are given that strongly support the use of overlapped weighted segment averaging for spectral estimation.     

A new stable hybrid three-dimensional generalized finite difference time domain algorithm for analyzing complex structures

In this paper, we propose a new stable hybrid, three-dimensional (3-D), generalized finite difference time domain algorithm-formulated by using of the cell method (CM) (a finite volumes type method)-designed to analyze objects with fine details without using very small time steps dictated by the Courant condition. The new algorithm is an extension to the 3-D cases of an analogous hybrid two-dimensional algorithm, also formulated by the CM, and presented earlier by the authors in a previous publication. We carry out a detailed analysis of the stability of the proposed algorithm, paying special attention to the phenomenon of late time instabilities. Finally, the results of some numerical tests are provided to show the absence of instabilities and the efficiency of the hybrid algorithm.     

A generalized framework for hybrid simulation of multi-component structures using iterative field refinement

When applying computational simulation techniques to scattering or radiation problems, it is often possible to decompose a complicated geometry into simpler elemental structures (i.e., a helicopter rotor system into its individual blades). By then simulating each component separately, a given problem can be decomposed into smaller and more manageable components, as long as account is taken of the coupling between each component. To implement such coupling, this paper describes a generalized iterative field refinement (IFR) framework, and demonstrates how it can be used as a basis for many hybrid approaches. Within this framework, IFR can also be used to accelerate simulation of geometries made up of rotated, translated, reflected, or replicated versions of a given structure. Several examples are given to show that an approach built around IFR reduces total computation time while allowing the combination of different analysis methods in treating each of the separate components comprising the structure.     

Intermediate-node-initiation (INI): A generalized signaling framework for optical burst-switched networks

In this paper, we discuss different signaling techniques for optical burst-switched networks. We develop a generalized signaling framework for optical burst-switched networks, which provides guidelines about the performance of each signaling technique based on the different parameters in the framework. The two commonly used signaling techniques in optical burst switching are two-way based tell-and-wait (TAW) and one-way based just-enough-time (JET). TAW suffers from high end-to-end packet delay, while JET suffers from high packet loss. There is no signaling technique that offers flexibility in terms of both loss and delay. We propose a hybrid signaling technique called intermediate-node-initiated (INI) signaling for optical burst-switched networks. INI can provide different levels of loss and delay characteristics based on end-user application requirements. The granularity of INI ranges between the one-way based and the two-way based signaling techniques. In INI reservation of channels is initiated at an intermediate node, known as the initiating node, in both forward and backward directions at the same time. We show that by appropriately selecting the initiating node, we can simulate both TAW and JET using the INI signaling technique. Through simulations, we shown that INI performs better than TAW in terms of average end-to-end packet delay and better than JET in terms of burst loss probability. We extend the INI signaling technique to provide QoS differentiation in the OBS core, differentiated INI (DINI), by carefully choosing different initiation nodes depending on delay and loss requirements of end-user applications. Through extensive simulations, we show that the DINI technique outperforms the existing offset-based QoS technique.     

A generalized protection framework using a new link-State availability model for reliable optical networks

This paper investigates a generalized protection framework for availability-guaranteed connection provisioning in an optical wavelength-division-multiplexed (WDM) network. Reliability is a crucial concern in high-speed optical networks. A service level agreement (SLA), which mandates high service availability even in the face of network failures must be met in provisioning a reliable connection. In this study, a new link-state-modeling mechanism is developed to form a dynamic link-state parameter called link and resource availability (LRA), which represents physical-layer availability and resource status for an optical link. Such up-to-date link-state information can be used by a standard link-state routing protocol to efficiently provision reliable connections. Based on the link-state availability model, LRA, a connection-provisioning algorithm is then proposed which can guarantee customers' availability requirements. A new generalized protection model is developed through dynamic LRA-based provisioning. Numerical results demonstrate the performance of the proposed provisioning approach to be promising.     

The generalized forward-backward method for analyzing thescattering from targets on ocean-like rough surfaces

In Holliday et al. (1995, 1996), the iterative forward-backward (FB) method has been proposed to solve the magnetic field integral equation (MFIE) for smooth one-dimensional (1-D) rough surfaces. This method has proved to be very efficient, converging in a very small number of iterations. Nevertheless, this solution becomes unstable when some obstacle, like a ship or a large breaking wave, is included in the original problem. In this paper, we propose a new method: the generalized forward-backward (GFB) method to solve such kinds of complex problems. The approach is formulated for the electric field integral equation (EFIE), which is solved using a hybrid combination of the conventional FB method and the method of moments (MoM), the latter of which is only applied over a small region around the obstacle. The GFB method is shown to provide accurate results while maintaining the efficiency and fast convergence of the conventional FB method. Some numerical results demonstrate the efficiency and accuracy of the new method even for low-grazing angle scattering problems     

A framework for analyzing the information monitoring and decisionsupport system investment tradeoff dilemma: an application to crisismanagement

The simplest form of a system consists of an input, a process which adds value to the input, and an output containing actionable information. The value of the output from a system is a function of not only the quality of the input but also the appropriateness, validity, and reliability of the transforming process. For certain classes of decisions such as those that correspond to crisis management, even the most simplistic version of a system presents problems for system developers and hence decision makers. Unlike in highly structured decision settings where precise models exist and high quality data is readily available, decision making in crisis settings involves ill-structured tasks which pose considerable problems for those responsible for the investment of a limited information resource budget. This paper presents a framework for analyzing the information monitoring decision support system tradeoff dilemma that occurs in crisis management settings, it concludes with several insights and recommendations for future research     

A self-tuning controller for switched reluctance motors

A self-tuning controller for switched reluctance motors is presented, A torque ripple minimizing controller is implemented with online system identification and adaptation technique. The controller uses a nonlinear model of the machine that is updated online using a recursive identification algorithm. The real-time approach improves the overall robustness of the system. Experimental results are presented to validate the self-tuning algorithm     

A switched diversity receiving system for mobile radio

A low cost switched diversity receiving system has been developed for use in UHF-FM mobile radio. The input of a single receiver is switched back and forth between two antennas upon command from a signal level sensing logic circuit. The system has been measured on simulated Rayleigh fading channels and has been found to give a significant improvement to both voice and data signals.     

A novel unipolar converter for switched reluctance motor

A configuration of a unipolar power converter with improved switching performance suitable for switched-reluctance motor supply is presented. The switched-reluctance motor operation principle is presented and its ideal characteristics are considered. The proposed converter is described and its operation is analyzed. The converter characteristics are studied with the aid of computer simulation. Current control of the proposed converter is considered. A prototype converter has been built to verify the analysis results and to validate the simulation. The design procedure is presented and experimental results which confirm the analysis are given and discussed