Prof. Dr. Joachim Holtz
Editor-in-Chief
|
Prof. Dr. Joachim Holtz |
IEEE Transactions on Industrial
Electronics
Volume 45, Number 1, February 1998
Special Section on Multimedia and Communication
Abstract - This paper presents, in a tutorial fashion, the important
features of the multimedia technology. The specific areas addressed are
multimedia and compression standards, computer networks, multimedia
transport and some specific applications employed by industry to date.
Multimedia, and its effective and efficient communication using
compression and networks, are fused together in this tutorial in an
attempt to demonstrate the tight coupling which exists between these two
interrelated technologies.
First, the techniques and properties inherent in both multimedia
and compression standards are presented. Then, the important
characteristics of the major local and wide area networks are summarized.
Next, the communication techniques for the transport of video and video
conferencing are discussed. The new strategies employed to connect homes
through Cable TV and the telephone companies, as well as the new Ethernet
technologies, are also described. Finally, some modern applications of
multimedia communication derived from the auto industry are used to
describe the use of this technology in design, manufacturing and sales.
Abstract - Although humans rely primarily on hearing to process speech, they can also extract a great deal of information with their eyes through lipreading. This skill becomes extremely important when the acoustic signal is degraded by noise. It would therefore be beneficial to find methods to reinforce acoustic speech with a synthesized visual signal for high noise environments. This paper addresses the interaction between acoustic speech and visible speech. Algorithms for converting audible speech into visible speech will be examined, and applications which can utilize this conversion process are presented. Our results demonstrate that it is possible to animate a natural looking talking head using acoustic speech as an input.
Abstract - Image/video compression is widely used in various applications with the advent of the JPEG, MPEG and H.261 standards. Hence most visual data are stored in the compressed format. Spatial scalable encoding of visual data has several applications including browsing visual databases, querying multimedia databases, interactive multimedia communications, etc. In this paper, we propose two novel techniques namely format compatible (FC) DCT and format modified (FM) DCT to implement image/video spatial scalability directly in the DCT compressed domain. The FC-DCT technique can be used to manipulate the standard bit streams, such as JPEG, MPEG, etc., while the FM-DCT technique can be employed in a variety of applications which require fast processing. In contrast to the traditional spatial domain techniques, the compressed domain techniques remove the unnecessary decompression and re-compression procedures, thus having the advantages of reduced computational complexity and storage requirements. Simulation results demonstrate that the proposed DCT domain techniques can achieve a comparable performance at a much lower computational complexity compared to the spatial domain techniques.
Abstract - This paper presents a method for intelligent selection of the quantization scale factor used for varying bit rate and quality in the MPEG2 video encoding standard. The goal is to select the quantization scale factor, above which, noticeable quality degradation occurs. This method uses a bilayer fuzzy logic system to aggregate measurements taken on the block level. The rulebases are designed around the characteristics of the human visual system (HVS). A qualitatively sensitive quantization scale factor can be chosen by taking advantage of the HVS characteristics.
Abstract - One form of multimedia finding increasing utility in factory automation is stereo imaging. Its uses include remote-operation, tele-presence, and object positioning. Stereo imaging, with doubled frames, requires high data rate collection and transmission. Image compression techniques can be utilized to reduce the transmission bandwidth and/or storage space requirements of the stereo pair. This paper develops image compression techniques specific to stereo imaging and compares performance with non-stereo methods. Disparity compensated residual image coding exploits the redundancy between the two images in a stereo pair. Stereo residuals possess special features that can be exploited within a DCT image coding framework. Use of these features results in several dB of performance enhancement across a range of scene types. This approach provides its best performance below 0.75 bits/pixel bitrate for 8-bit grayscale imagery and below 2 bits/pixel for 24-bit color imagery.
Abstract - Video On Demand is one of the key application in the information era. An hinge factor to its wide booming is the huge bandwidth required to transmit digitized video to a large group of clients with widely varying requirements. This paper addresses issues due to heterogeneous clients by proposing a program caching scheme called Partial Video Sequence (PVS) Caching Scheme. PVS Caching Scheme decomposes video sequences into a number of video parts by using a scalable video compression algorithm. Video parts are selected to be cached in local video servers based on the amount of bandwidth it would be demanded from the distribution network and from the central video server. In this paper, we also show that PVS Caching Scheme is suitable for handling vastly varying client requirements.
Abstract - This paper proposes a power-spectrum-based connection admission controller design in ATM switches for multimedia communications. The controller contains a power-spectrum indexed table for managing multimedia call requests, where traffic characteristics of call requests are described by the power spectrum. The power spectrum can be obtained from their claimed traffic parameters of peak rate, mean rate, and peak rate duration; the power spectrum has been shown to have a dominant on system performanc. The results show that the proposed power-spectrum-based connection admission control method achieves higher system utilization and lower call-blocking probability than the equivalent-capacity method.
Abstract - Existing feedback-based rate control schemes supporting the Available Bit Rate (ABR) service in ATM networks mostly employ a single static buffer threshold at each switching node as the forewarning of congestion. In this paper, we first propose a continuous-based adaptive rate control mechanism which employs, logically, an infinite number of thresholds. Each node periodically determines the precise permitted rate of immediate upstream nodes based on a simple fluid model aiming at satisfying both loss-free and starvation-free criteria. The scheme, as will be shown, achieves high utilization and low (zero) cell loss probability under highly bursty (deterministic) traffic, though at the expense of drastic increase in signaling overhead due to frequent adjustment of permitted rates. To reduce overhead, we further propose a so-called the stepwise-based rate control mechanism adopting a limited number of movable thresholds, referred to as the threshold set. The threshold set shifts up (down) reflecting the increase (decrease) in departure rates. Compared to continuous-based control via simulation, stepwise-based control is shown to be efficient and accurate using only a reasonably low number of thresholds. Moreover, we also display simulation results which demonstrate that the stepwise-based mechanism outperforms existing single-static-threshold-based schemes in terms of cell loss probability and link utilization.
Abstract - In this paper, we propose a Quality-Of-Service (QOS) guaranteed Transport System (QTS), which offers various QOSs at the transport layer for broadband multimedia communications. QTS, composed of a bandwidth allocator and a transport protocol module, supports three classes of applications requiring different bit rates, delay sensitivity, and loss sensitivity. The bandwidth allocator intelligently manages the allocation of transport-layer bandwidth at the expense of imposing inevitable blocking of delay-sensitive application connections. The transport protocol module of QTS performs rate-based flow control for delay-sensitive applications based on transfer rates predetermined by the bandwidth allocator. In addition, the module accomplishes errors control only for loss-sensitive applications. As a result, as will be shown, by providing guaranteed rates and reducing the error control overhead, QTS offers satisfactory bounded delays and jitters for delay-sensitive applications while incurring minimal throughput degradation for loss-sensitive applications. Finally, we demonstrate the superiority of QTS over TCP via simulation results in terms of maximum and mean system delays, and delay jitter.
Power Electronics
Abstract - Pulse-width modulated (PWM) current-source rectifiers (CSR), among other alternatives, offer marked improvements over thyristor line commutated rectifiers as a source of variable dc power. Advantages include reduced line current harmonic distortion and complete displacement power factor control, including unity displacement power factor operation. However, due to non-linearities of the PWM-CSR model, their control has usually been carried out using direct line current control in a three-phase stationary frame (abc). This paper proposes the application of a non-linear control technique that introduces more flexibility in the control of the rectifier and results in a more straightforward approach to controller design. The proposed technique is based on a non-linear state variable feedback approach in the rotating frame (dq). The approach allows the independent control of the two components of the line current (active and reactive) with the same dynamic performance regardless of the operating point. The control strategy also eliminates the need for input damping resistors and rejects the effect of supply voltage variations. Furthermore, a space vector modulation (SVM) technique is used to maximize the supply voltage utilization. The paper includes a complete formulation of the system equations and a controller design procedure. Experimental results on a 2 kVA digital signal processor-controlled prototype confirm the validity of theoretical considerations.
Abstract - A systematic and unified approach to modeling PWM dc/dc converters based on the graft scheme is presented in this paper. With the graft scheme, the typical PWM switch mode converters, such as buck-boost, boost-buck (Cuk), sepic and dual sepic, can be generated from the two basic converters, buck and boost. The small signal models of these converters can be, therefore, derived by properly combining those of the buck and boost. Using the proposed approach can help to yield highly related dynamic models of the converters in a family, and, in addition, physical insights into the converters can be readily identified. This has made the proposed modeling method be valuable and viable.
Abstract - Photovolatic systems normally use a maximum power point tracking (MPPT) technique to continuously deliver the highest possible power to the load when variations in the insolation and temperature occur. It overcomes the problem of mismatch between the solar arrays and the given load. A simple method of tracking the maximum power points (MPP*s) and forcing the system to operate close to these points is presented. The principle of energy conservation is used to derive the large- and small- signal model and transfer function. By using the proposed model, the drawbacks of state- space- averaging method can be overcome. The TI320C25 digital signal processor (DSP) was used to implement the proposed MPPT controller, which controls the dc/dc converter in the photovoltaic system, simulations and experimental results show excellent performance.
Drive Control
Abstract - The paper deals with the problem of mechanical resonance in modern servo drive systems having the speed control loop bandwidth and resonance frequency above 100 Hz. To enable the extension of the range of stable gains in the presence of flexible coupling, a simple and straightforward modification of the speed loop controller is proposed in order to augment the performance of present speed controllers, and to make them accordant with mechanical structure suffering from the compliance problem. The paper comprises the analytical considerations, straightforward design guidelines, and results of experimental verification obtained by an experimental setup with the elastically coupled 7 Nm synchronous servo motor and mechanical resonance frequency of 160 Hz.
Abstract - This paper proposes a new initial rotor position estimation method of a sensorless PM (Permanent Magnet) synchronous motor at starting condition, which has no sensitivity to the armature resistance. The method is based on saliency of the rotor, and employs the alternating magnetic field which is excited by a current controller. The phase differences between the magnetizing current references and the voltage references make it possible to estimate the rotor direction accurately without motor parameters except the ratio of direct axis and quadrature axis inductance. Also, the magnetic pole is evidently identified by detecting the voltage reference oscillation phenomena caused by magnetic saturation, which can be performed without motor parameters. The experimental result has proven that the estimation error was within -4.5 to +2.5 mechanical degree even though the armature resistance varied to 125% of the nominal value.
Abstract - In this paper we propose a simple controller for set-point control of robot manipulators. The structure of this controller is composed by a Saturated Proportional- Saturated Derivative feedback plus gravity compensation. Such a control scheme has two practical features. First, for all desired joint position this controller delivers torques inside prescribed limits according with the actuator capability; and second, the steady state position errors owing to static friction can be arbitrarily reduced. In case of absence of friction, we show global asymptotic stability of the closed loop system. The performance of the proposed controller is illustrated via experiments on a two degrees- of- freedom direct drive robot system.
Abstract - The control problem for a Series DC motor is considered. The control approach is model based using a nonlinear mathematical model of a series connected DC motor. Specifically, it is shown that by combination of a nonlinear transformation and state feedback (feedback linearization) the nonlinear control design is reduced to designing a linear control law. To demonstrate its effectiveness, an experimental study of this controller is presented. These experimental results are also compared with a simulation of the closed-loop system. Finally, it is shown that a nonlinear observer (with linear error dynamics) for speed and load-torque can be constructed based only on measurements of the motor current. Experimental results of this speed and load-torque estimator are also presented.
Signal Processing
Abstract - Texture classification is an important first step in image segmentation and image recognition. The classification algorithm must be able to overcome distortions such as scale, aspect and rotation changes in the input texture. In this paper, a new fractal model for texture classification is presented. The model is based on Fractional Brownian Motion. It is also shown that this model is invariant to changes in incident light; empirical results are also given. The isotropic nature of Brownian Motion is particularly useful for outdoor applications where the viewing direction may change. Classification results of this model are presented; comparisons with other texture measurement models indicate that the IFBM model has better performance for the samples tested.
Emerging Technologies
Abstract - In this paper, we present a real-time learning control scheme for unknown nonlinear dynamical systems using recurrent neural networks (RNNs). Two RNNs, base on the same network architecture, are utilized in the learning control system. One is used to approximate the nonlinear system and the other is used to mimic the desired system response output. The learning rule is achieved by combining the two RNNs to form the neural network control system. A generalized real-time iterative learning algorithm is developed and used to train RNNs. The algorithm, is derived by means of two-dimensional (2-D) system theory that is different from the conventional algorithms that employ the steepest optimization to minimize a cost function. This paper shows that an RNN using the real-time iterative learning algorithm can approximate any trajectory tracdegree of accuracy. The proposed learning control scheme is applied to numerical problems and simulation results are included. The results are very promising and this paper suggests that 2-D system theory based RNN learning algorithm provides a new dimension on real-time neural control systems.
Abstract - A new scheme to obtain an optimal fuzzy subsets and rules is proposed. The method is derived from the use of Genetic Algorithms where the genes of the chromosome are classified into two different types. These genes can be arranged in a hierarchical form and one type of genes controls the other type of genes. The effectiveness of this genetic formulation enables the fuzzy subsets and rules to be optimally reduced and yet, the system performance is well maintained. In this paper, the details of formulation of the genetic structure are given. The required procedures for coding the fuzzy membership function and rules into the chromosome are also described. To justify this approach of fuzzy logic design, the proposed scheme is applied to control a constant water pressure pumping system. The obtained results as well as the associated final fuzzy subsets are included in this paper. Because of its simplicity, the method could lead to a potentially low cost fuzzy logic implementation.
Abstract - Recent efforts to incorporate aspects of artificial intelligence into the design and operation of automatic control systems have focused attention on techniques such as fuzzy logic, artificial neural networks and expert systems. The use of computers for direct digital control highlights the recent trend toward more effective and efficient HVAC control methodologies. Researchers in the HVAC field have stressed the importance of self-learning in building control systems and have encouraged further studies in the integration of optimal control and other advanced techniques into the formulation of such systems. Artificial neural networks can also be used to emulate the plant dynamics in order to estimate future plant outputs and obtain plant input/output sensitivity information for on-line neural control adaptation. This paper describes a functional link neural network approach to performing the HVAC thermal dynamic system identification. Methodologies to reduce inputs of the functional link net to reduce the complexity and speed up the training speed will be presented. Analysis and comparison between the functional link network approach and the conventional network approach for the HVAC thermal modeling will also be presented.
Letters to the Editor
Abstract - The present paper investigates the optimal excitation of a switched reluctance motor such that overall drive efficiency is maximized under a variable supply voltage. The result presented in the paper exhibits the improved drive efficiency and the expanded range of operating torque and speed. Furthermore the variable supply voltage may be utilized in reducing torque ripple.
Abstract - A model reference adaptive speed control using neural networks is presented. The robust observer based model reference tracking control technique is used to establish the training patterns. Then, the trained neural networks is used as the adaptive speed controller to robustly track a reference model for an induction motor drive.
Abstract - A discrete-time PID controller whose manipulated variable takes two values, i.e. on and off, is proposed and analyzed. Oversampling technology is employed in the controller design. As to the structure of the controller, a cascade type and a built-in type are proposed. An experimental example is presented.
Abstract - A new multi input-multi output nonlinear control system, based on a simple and straightforward modification of the internal model control, is proposed. The nonlinear modified internal model control structure is completely defined by the inverse process model and guarantees the offset free control. A feedforward neural network inverse model with one hidden layer and a small number of hidden neurons is successfully applied in real-time control of the nonlinear process considered.