Showing papers by "Jie Chen published in 2009"

Homography-Based Visual Servo Control With Imperfect Camera Calibration

Abstract: In this technical note, a robust adaptive uncalibrated visual servo controller is proposed to asymptotically regulate a robot end-effector to a desired pose. A homography-based visual servo control approach is used to address the six degrees-of-freedom regulation problem. A high-gain robust controller is developed to asymptotically stabilize the rotation error, and an adaptive controller is developed to stabilize the translation error while compensating for the unknown depth information and intrinsic camera calibration parameters. A Lyapunov-based analysis is used to examine the stability of the developed controller.

Optimal tracking performance of discrete-time systems over an additive white noise channel

Abstract: This paper studies the optimal tracking performance of multiple-input multiple-output (MIMO), finite dimensional, linear time-invariant discrete-time systems with a power-constrained additive white noise (AWN) channel in the feedback path. We adopt the tracking error power as a measure of the performance and examine the best achievable performance by all two-parameter stabilizing controllers. In the due process, a scaling scheme is introduced as a means of integrating controller and channel design, and is optimized to better the tracking performance. In contrast to the standard setting where tracking of a step reference signal is conducted with no communication constraint, in which the tracking error can be made as zero for minimum phase plants, it is shown explicitly herein that the tracking performance will be additionally constrained by the plant unstable poles, as a consequence of noisy, power-constrained channels in the feedback loop.

Limitations on minimum tracking energy for SISO plants

Abstract: This paper discusses the fundamental limitations imposed by the intrinsic characteristic of plants. The plant is stable of unstable. The performance is about minimum tracking energy for tacking error asymptotically approaching zero. Using a time-domain integral of the square of the input as a performance index, we derive relations that represent fundamental limits on the achievable performance for single-input single-output systems. The relations depend on the unstable poles and right half plane zeros of the plant under study, and the stable and minimum part of part is also related. When the plant is unstable, the two-free-of-controller is addressed, too. The limitations are significant references for the controller designs. A numerical example shows the design limitation.

Optimal tracking over an additive white Gaussian noise channel

Abstract: This paper studies the optimal reference tracking problems of finite-dimensional, linear, time-invariant (LTI) systems with an additive white Gaussian noise (AWGN) channel between the controller and the plant. We consider two types of the reference signal: a random variable and a Brownian motion. The power of the tracking error is adopted as the measure of the performance and is to be minimized over all stabilizing two-parameter controllers. We assume the power of the channel input is limited and seek to solve the constrained optimization problem explicitly. It is shown that, besides the power constraint, the lowest power of the tracking error hinges closely on non-minimum phase zeros, the unstable poles and the plant gain.

Concepts, properties, and imaging technologies for GEO SAR

Abstract: Characteristics of Geosynchronous Synthetic Aperture Radar (GEO SAR), including ground velocity, integration time, azimuth resolution and other factors, are investigated. And the relationship between them and orbital elements is analyzed. Then a subaperture mode based on yawing steering which is more suitable for GEO SAR is proposed. By applying this mode reduction of range migration is obvious, and system parameters of L-band GEO SAR are designed, including the antenna size, the pulse width, the peak transmitted power, and pulse repetition frequency. Finally a modified Range Doppler (RD) algorithm based on quintic polynomial and a Chirp Scaling (CS) algorithm based on spectrum mosaic are advanced. Point target simulation is implemented and the azimuth resolution is assessed according to the rule of being able to distinguish adjacent targets. It is demonstrated that the proposed image formation algorithms can provide a spatial resolution better than 15m.

Optimal tracking design and performance analysis for LTI systems with quantization effects

Abstract: This paper studies the tracking problem for linear time-invariant multi-input single-output (MISO) discrete-time systems with quantization effects. Logarithmic quantization laws are adopted in the systems. The tracking performance is measured by the energy of the error response between the output of the plant and the reference signal. Our goals are to design an optimal controller for the tracking problem and to find an explicit formula of the minimum tracking cost. It turns out that the optimal state feedback law can be obtained by solving a modified discrete-time Riccati equation associated with the state space model of the plant and the features of the quantization law. Furthermore, from the unique positive solution of the modified Riccati equation, we obtain an analytic expression for the minimum tracking cost in terms of the nonminimum phase zeros and the bound of quantization error. When the quantization error approaches zero, the minimum tracking cost degrades to the minimum tracking cost of the system without quantization effects, which is presented some existing works. The results obtained in this work explicitly show how is the optimal tracking performance limited by the quantization error.

Optimal tracking over an additive white noise feedback channel

Abstract: This paper studies the best achievable tracking performance of multiple-input multiple-output (MIMO), finite dimensional, linear and time-invariant (FDLTI) system over a additive white noise (AWN) channel in the feedback path. The plant under consideration is assumed to be minimum phase but unstable. The reference input is a vector valued wide-sense stationary (WSS) random process. The power of the tracking error is adopted as the measure of the performance and is to be minimized subject to the channel power constraint. We investigate a joint design of the controller and the scaling factor, which can be interpreted as a simple compensation for the channel. It is shown explicitly that the tracking performance, which in a noise-free setting can be made as zero, depends on plant unstable poles and the power constraint of the AWN channel. It is also shown in the sequel that when the constant scaling is not available, the channel is not exploited to the maximum extent allowable under the power constraint, and the tracking performance deteriorates.

An Average Performance Limit of MIMO Systems in Tracking Multi-Sinusoids With Partial Signal Information

Abstract: This paper studies the best achievable reference tracking performance of MIMO linear time-invariant (LTI) feedback systems with partial reference information. The reference signal to be tracked is a multi-tone sinusoidal signal. It is assumed that, other than the instantaneous values of the reference signal, only the frequencies of the sinusoidal components are known. The tracking performance is measured by the energy of the tracking error. With this partial information of the reference signal, we consider an averaged performance measure and obtain an explicit expression of the best achievable performance. The expression shows how the harmonic frequencies and the zero directions may affect the performance, and further, how a performance degradation may result under the available partial information.

Optimal tracking and power allocation over an additive white noise channel

Abstract: In this paper, we study the optimal tracking performance of multiple-input multiple-output (MIMO), linear and time-invariant system over a parallel additive white noise (AWN) channel. We adopt the power of the tracking error as a measure of the performance and examine the best achievable performance by all two-parameter stabilizing controllers. In addition, we investigate a scaling scheme of the channel to counter the noise and achieve better performance. We show explicitly that the tracking performance is constrained by the plant unstable poles, as well the power constraint and the channel noise level. Furthermore, we examine the power allocation strategy across the sub-channels under this optimal control scheme. It is also found that for decentralized plant with independently designed scaling factors, the tracking system distributes more power to the more demanding sub-channels.

Tracking under additive white Gaussian noise effect

Abstract: This paper investigates the tracking performance of continuous-time, multi-input multi-output, linear timeinvariant systems in which the output feedback is subject to an additive white Gaussian noise corruption. The problem under consideration amounts to determining the minimal error in tracking a Brownian motion random process, which emulates a step reference signal in the deterministic setting. We consider both the unity feedback and two-parameter controllers. In the former case we derive an explicit bound, and in the latter an exact expression of the minimal tracking error attainable under the noise effect. Both results demonstrate how the white Gaussian noise may impede the tracking performance, and how the noise effect may intertwine with such intrinsic characteristics of the plant as unstable poles and nonminimum phase zeros.

Effect of (-)-gossypol (AT-101) on transcriptional regulation of Noxa and Puma and on Mcl-1-mediated cancer cell resistance to apoptosis

Abstract: e14611 Background: AT-101 is being evaluated in Phase II clinical trials for the treatment of human cancers and demonstrates anticancer activity as a single agent and in combination with docetaxel....

Modeling and Simulation of Single-Look Complex Images for Distributed Satelliteborne Interferometric Synthetic Aperture Radar

Abstract: The significance of modeling and simulating the single- look complex (SLC) images for the Distributed Satelliteborne Interferometric Synthetic Aperture Radar (DS-InSAR) system is addressed. Moreover, the simulation modeling for the DS-InSAR SLC images is presented in details, including the geometric model and the radar signal model. Furthermore, an implementation method for DS-InSAR SLC images simulation is proposed, which has the advantage of lower computation loads and higher efficiency compared with the traditional simulation methods. The intensity images and phase interferograms can consequently be generated from the simulated SLC SAR images. Computer simulation results are numerously presented, with the simple conic scenario and the digital elevation model (DEM) of natural terrain. It is straight forward that the simulation results demonstrate the effectiveness of the modeling and simulation method presented in this paper.

Modeling of Complex Radar Target for High-Resolution Synthetic Aperture Radar Image Simulation Based on GRECO

Abstract: The electromagnetic scattering models of complex radar targets, e.g. aircrafts, vehicles etc, are of great significance to Automatic Target Recognition (ATR) of Synthetic Aperture Radar (SAR) imagery. Based on the Graphical Electromagnetic Computing (GRECO) technique, a novel implementation method of complex radar target modeling for the simulation of high- resolution SAR image is proposed. The three-dimensional (3-D) scattering modeling of the complex radar targets is founded on the basis of GRECO. Furthermore, high-resolution SAR image simulation is implemented through echo simulation and image formation procedure with the 3D scatting data generated by using GRECO. Computer simulation results of an aircraft target are provided, with high-resolution millimeter wave SAR system parameters, which illustrate the radar image characteristics such as foreshortening, layover as well as shadowing. The datasets of simulated SAR images with different elevation and azimuth angles are presented, verifying the effectiveness of the method of the paper. The simulated high-resolution SAR images could be applied in ATR research as the input source data.