Equation-based Approach Research Articles

Complex Signal Processing is Not Complex

Wireless systems often make use of the quadrature relationship between pairs of signals to effectively cancel out-of-band and interfering in-band signal components. The understanding of these systems is often simplified by considering both the signals and system transfer functions as quantities. The complex approach is especially useful in highly integrated multistandard receivers where the use of narrow-band fixed-coefficient filters at the RF and high IF must be minimized. This paper first presents a tutorial review of complex signal processing for wireless applications. The review emphasizes a graphical and pictorial description rather than an equation-based approach. Next, a number of classical modulation architectures are described using this formulation. Finally, more recent developments such as complex filters, image-reject mixers, low-IF receivers, and oversampling analog-digital converters are discussed.

Wave and equation based rate control using multicast round trip time

This paper introduces Wave and Equation Based Rate Control (WEBRC), the first multiple rate multicast congestion control protocol to be equation based. The equation-based approach enforces fairness to TCP with the benefit that fluctuations in the flow rate are small in comparison to TCP.This paper also introduces the multicast round trip time (MRTT), a multicast analogue of the unicast round trip time (RTT). The MRTT is fundamental to the equation-based protocol that each receiver uses to adjust its reception rate. Each receiver independently measures its own MRTT without placing any added messaging burden on the receiver, the sender or the intermediate network elements. Benefits provided by the MRTT include those that the RTT provides to TCP, e.g., reduced reception rates in reaction to buffer filling and fair sharing of bottleneck links. In addition, the use of MRTT is shown to synchronize and equalize the reception rates of proximate receivers and to cause reception rates to increase as the density of receivers increases.Another innovation of WEBRC is the idea of transmitting data with waves: the transmission rate on a channel is periodic, with an exponentially decreasing form during an active period followed by a quiescent period. Benefits of using waves include insensitivity to large IGMP leave latency; a frequency of joins and leaves by each receiver that is small and independent of the receiver reception rate; the use of a small number of multicast channels; fine-grained control over the receiver reception rate; and minimal, at times nonexistent, losses due to buffer overflow.

A semi‐parametric regression analysis of CD4 cell counts

This paper considers the regression analysis of CD4 cell counts, a commonly used indicator and prognostic factor of AIDS progression. For this purpose, a number of methods have been proposed and most of them are based on random effects models. We present an alternative that is based on a mean function regression model. The new method is more natural and particularly appropriate if population parameters such as treatment comparison are mainly of interest. To estimate regression parameters, we present an estimating equation-based approach, which does not require estimation of the baseline mean function. This makes the implementation of the approach and the study of the properties of the estimated regression parameters much easier than those based on random effects models. The method is illustrated with a set of CD4 cell count data arising from an AIDS clinical trial and simulated data. Copyright © 2001 John Wiley & Sons, Ltd.

A semi-parametric regression analysis of CD4 cell counts.

This paper considers the regression analysis of CD4 cell counts, a commonly used indicator and prognostic factor of AIDS progression. For this purpose, a number of methods have been proposed and most of them are based on random effects models. We present an alternative that is based on a mean function regression model. The new method is more natural and particularly appropriate if population parameters such as treatment comparison are mainly of interest. To estimate regression parameters, we present an estimating equation-based approach, which does not require estimation of the baseline mean function. This makes the implementation of the approach and the study of the properties of the estimated regression parameters much easier than those based on random effects models. The method is illustrated with a set of CD4 cell count data arising from an AIDS clinical trial and simulated data.

Video multicast using layered FEC and scalable compression

The use of scalable video with layered multicast has been shown to be an effective method to achieve rate control in heterogeneous networks. We propose the use of layered forward error correction (FEC) as an error-control mechanism in a layered multicast framework. By organizing FEC into multiple layers, receivers can obtain different levels of protection commensurate with their respective channel conditions. Efficient network utilization is achieved as FEC streams are multicast, and only to receivers that need them. Furthermore, FEC is used without overall rate expansion by selectively dropping data layers to make room for FEC layers. Effects of bursty losses are amortized by staggering the FEC streams in time, giving rise to a tradeoff between delay and quality. For rate control at the receivers, we propose an equation-based approach that computes network usage as a function of measured network characteristics. We show that equation-based rate control achieves more fair bandwidth sharing amongst competing sessions as compared to existing multicast rate control schemes such as RLM and RLC. Fairness is achieved since competing sessions sharing a path will measure similar network characteristics. Simulations and actual MBONE experiments are performed using error-resilient, scalable video compression. We find that video quality is significantly improved at the same communication rate when layered FEC is used.

AMGIE-A synthesis environment for CMOS analog integrated circuits

A synthesis environment for analog integrated circuits is presented that is able to drastically increase design and layout productivity for analog blocks. The system covers the complete design flow from specification over topology selection and optimal circuit sizing down to automatic layout generation and performance characterization. It follows a hierarchical refinement strategy for more complex cells and is process independent. The sizing is based on an improved equation-based optimization approach, where the circuit behavior is characterized by declarative models that are then converted in a sequential design plan. Supporting tools have been developed to reduce the total effort to set up a new circuit topology in the system's database. The performance-driven layout generation tool guarantees layouts that satisfy all performance constraints. Redesign support is included in the design flow management to perform backtracking in case of design problems. The experimental results illustrate the productiveness and efficiency of the environment for the synthesis and process tuning of frequently used analog cells.

A 3-D integral equation-based approach to the analysis of real-life MMICs application to microelectromechanical systems

In this paper, we introduce a three-dimensional method-of-moments approach, suitable for the analysis of real-life monolithic circuits for microwave/millimeter waves. It shares the flexibility and the efficiency of the currently available spectral-domain commercial simulators, while allowing all metallizations to have finite thickness and finite conductivity and the ability to handle dielectric discontinuities. The method is successfully applied to several structures, like metal-insulator-metal capacitor, spiral inductors, and microelectromechanical capacitive switches in the 1-50-GHz frequency range.

Innovating adaptive and neural systems instruction with interactive electronic books

This paper describes an integrated strategy to innovate teaching in the undergraduate classroom by appropriately utilizing information technologies. The innovation is an interactive learning environment built around an interactive electronic book (i-book). The i-book is a tight integration of a hypertext document with a simulator. The hypertext specifies the presentation order of the theoretical topics, and the simulator is an essential piece of learning. The lectures exploit the i-book, transforming the classroom into an interactive teaching laboratory. An electronic white board is used in every lecture to teach from the text and run the simulations. Our goal is to teach adaptive systems to undergraduate electrical engineering students. Undergraduates do not have the mathematical background to comprehend the equation-based approach utilized in graduate-level adaptive systems courses. We have used the i-book for undergraduate instruction with very positive results. We are now ready to extend the format for distance learning. This new teaching methodology transcends adaptive systems and can be applied to other engineering and science courses which have access to simulators.

Reliability of iterative linear equation solvers in chemical process simulation

For large-scale problems, it may be attractive to use iterative methods to solve the large, sparse, linear systems that arise in the equation-based approach to process simulation. This is because, as problem sizes grow, direct methods become extremely expensive in terms of both computation time and storage requirements. Iterative methods, however, may not be reliable for the indefinite and highly unsymmetric matrices encountered in a diverse multi-unit flowsheeting problem. An extensive computational study of the reliability of iterative linear solvers on such problems is presented here. Nine different iterative linear solvers are considered, in connection with incomplete factorization preconditioning. These are applied to a set of nine test problems. Results indicate that the ordering of rows and columns in the matrices is a crucial factor in determining the success with which iterative methods can be employed. Results also indicate that in general these multi-unit flowsheeting matrices are difficult to solve by iterative methods, and that, though there is certainly potential in the use of iterative methods, to realize this potential will require improvements in the reordering and/or preconditioning schemes used.

A vertically integrated tool for automated design of ΣΔ modulators

We present a tool that starting from high-level specifications of switched-capacitor (SC) /spl Sigma//spl Delta/ modulators calculates optimum specifications for their building blocks and then optimum sizes for the block schematics. At both design levels, optimization is performed using statistical techniques to enable global design and innovative heuristics for increased computer efficiency as compared with conventional statistical optimization. The tool uses an equation-based approach at the modulator level, a simulation-based approach at the cell level, and incorporates an advanced /spl Sigma//spl Delta/ behavioral simulator for monitoring and design space exploration. We include measurements taken from two silicon prototypes: (1) a 16 b @ 16 kHz output rate second-order /spl Sigma//spl Delta/ modulator; and (2) a 17 b @ 40 kHz output rate fourth-order /spl Sigma//spl Delta/ modulator. Both use SC fully differential circuits and were designed using the proposed tool and manufactured in a 1.2 /spl mu/m CMOS double-metal double-poly technology.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The Calculation of Thermodynamic Properties of Steam for Minimum Computer Access Time

Energy engineers involved in the design of thermal plant often need to compute properties of gases and vapours over a large part of the thermodynamic surface. For such applications an equation-based approach is efficient and accurate. In this paper simple formulations for the thermodynamic properties of steam are provided which enable computations to be made with a significant reduction in computer access time, the comparison being made against the DAMPF reference package.

Computational experiments in equation-based chemical process flowsheeting

The central computational problem in equation-based flowsheeting is the simultaneous solution of a large sparse system of nonlinear algebraic equations. SEQUEL-II, our implementation of the equation-based approach, provides a means for comparing nonlinear equation-solving techniques, in particular the techniques used for computing correction steps, for ge nerating initial guesses, and for evaluating sparse Jacobian matrices. Comparisons are made on the basis of both efficiency and reliability. On a set of fourteen process flowsheeting problems, Powell's dogleg correction step is not only very efficient, but also somewhat more reliable than the Newton step when good initial guesses are not available. Schubert's sparse Jacobian update performs very well, but Bogle and Perkins' new least-relative-change update gives improved performance, when used in connection with either the dogleg or Newton correction step. The use of a hybrid update provides a better approximation of the Jacobian than a sparse update alone, one, and so significantly improves, in terms of number of iterations, the efficiency of the dogleg correction step.

A methodology for equation-based analysis of large chemical processes using the functional matrix

The equation-based approach to process analysis is necessary for efficient optimization of large and complex processes, and involves the problem of solving a large number of equations. To complement this approach, an improved equation-solving system using the functional matrix suggested by Mattione, Meir and Book was developed, and its capacity for the process analysis was demonstrated by case studies.