Fan-Ren Chang

H/sub /spl infin// control for nonlinear descriptor systems

In this paper, we study the H/sub /spl infin// control problem for nonlinear descriptor systems governed by a set of differential-algebraic equations (DAEs) of the form Ex/spl dot/ = F(x, w, u), z = Z(x, w, u), y = Y(x, w, u), where E is, in general, a singular matrix. Necessary and sufficient conditions are derived for the existence of a controller solving the problem. We first give various sufficient conditions for the solvability of H/sub /spl infin// control problem for DAEs. Both state-feedback and output-feedback cases are considered. Then, necessary conditions for the output feedback control problem to be solvable are obtained in terms of two Hamilton-Jacobi inequalities plus a weak coupling condition. Moreover, a parameterization of a family of output feedback controllers solving the problem is also provided.

A Solution to the Ill-Conditioned GPS Positioning Problem in an Urban Environment

For GPS positioning, it is normally required that there be at least four GPS satellites in view. However, due to the frequent blockage of signals in an urban environment, it is difficult to meet that requirement; therefore, the operation of the GPS receiver may be interrupted. How to deal with this problem so that the service can be continuous is the main theme of this paper. The pseudorange predictor and the receiver clock bias predictor may be used to estimate the pseudorange and clock bias, respectively. The altitude-hold algorithm is developed to provide additional information under the assumption that the altitude of the vehicle is approximately a constant, which is deemed appropriate for urban applications. Furthermore, for land vehicles, it may be assumed that the speed of the vehicle is not significantly varying so that the constraint-filtering method with soft constraint may be applied. The integration of these methods yields a successful algorithm to manage the ill-conditioned positioning problem if the number of visible satellites drops to below 4. From both static and dynamic experimental results, it is shown that the proposed methodology indeed gives rise to an effective scheme that can sustain the service for a few minutes, even if there is no satellite in view at all.

A High-Range-Accuracy and High-Sensitivity Harmonic Radar Using Pulse Pseudorandom Code for Bee Searching

This paper presents a 9.4/18.8-GHz harmonic radar to investigate the behavior of bees with colony collapse disorder. The challenges of using harmonic radar for bee searching include the requirements of high range accuracy and high sensitivity. A new harmonic radar using the pseudorandom code positioning technique to simultaneously achieve high range accuracy and high sensitivity is proposed. This study also proposes a new method to cancel the local leakage to further improve sensitivity. To realize the transponder, a compact antenna is designed using the topology characteristics of the composite right/left-handed transmission-line concept. The measured sensitivity of the transceiver is -120 dBm, which is 27 dB lower than the noise level. Field testing results demonstrate a 60-m detection range within 1-m distance error with 1.75-W transmitting power. The significant improvement of the sensitivity and the range accuracy reveal the advantages of applying the code-positioning technique to the harmonic radar.

Robust Control Analysis and Design for Discrete-time Singular Systems

Abstract In this paper, we propose a simple approach to analyze stability robustness of discrete-time singular systems under structured perturbations, The developed robustness criteria are then applied to solve robust regional pole-assignment problems of singular systems. A robust control design algorithm, via state feedback, is also given. The robust stability problem of singular systems is more complicated than that of regular systems, Not only stabiliti robustness but system regularity and impulse elimination should be considered simultaneously. This is the first paper, as far as we are aware, to deal with the problems about robust stability analysis and robust control design for singular systems with structured uncertainties. Although only discretetime case is discussed, several results can be directly applied to continuous-time systems as well.

Highly accurate real-time GPS carrier phase-disciplined oscillator

A low-cost highly accurate real-time GPS carrier phase disciplined oscillator system based on a single-frequency receiver is presented. In order to estimate the average frequency offsets of an oven-controlled crystal oscillator (OCXO) with respect to the GPS, the OCXO was connected to a modified GPS receiver to replace its original oscillator. Hence, the behavior of the OCXO was determined from the GPS carrier phase observations. The average frequency offsets of the OCXO with respect to the GPS could be estimated by performing difference operations on carrier phase observations of all satellites in view between two measurement epochs. To overcome the interference coming from the atmospheric delay, a real-time dynamic neural-wavelet forecasting filter was proposed. The parameters of the filter were obtained according to the results of a three-day experiment, in which the GPS carrier phase observations of a stand-alone configuration and a common-view configuration were compared. The compressed average frequency offsets were then used by the neural model predictive controller (MPC) for steering the OCXO via D/A converters. From our experiments, the normalized frequency offset of the disciplined OCXO could be improved from about two parts in 10/sup 9/ to about three parts in 10/sup 14/, and the frequency stability (MDEV) could be improved from about eight parts in 10/sup 10/ to about four parts in 10/sup 14/ over 24 h.

Modeling and hierarchical tracking control of tri-wheeled mobile robots

After exploring the structure of the dynamics derived by using the Appell equation, we propose a hierarchical tracking controller for a tri-wheeled mobile robot in this paper. With appropriately chosen privileged variables, the reduced equations are decoupled from the kinematic equations associated with the underlying nonholonomic constraints. This special character of the system makes it possible to separate the design into three levels: motion planning, kinematic, and dynamic. In the proposed scheme, a fuzzy inference engine in the kinematic level is used to update the desired trajectory computed in the motion-planning level. An adaptive sliding-mode controller is then adopted to track the new reference values of privileged variables in the dynamic level, which subsequently drives the nonprivileged variables. Simulation results show the effectiveness of such a tracking-control scheme, which concurrently takes kinematics and dynamics into consideration. All system variables can be tracked asymptotically to their desired values, which are assured by the skew-symmetric property of the Appell equation

The generalized state-space description of positive realness and bounded realness

Positive realness and bounded realness are two important issues in system theory. Some related applications about these notions include analysis and synthesis of passive networks, optimal designs in control and estimation, stability investigations in linear/nonlinear closed-loops; etc.. In this paper, we propose the equations of constant matrices, which are stabilizable and detectable realizations of impulse-free generalized state-space systems, to describe the positive real and bounded real properties. The established generalized positive real lemma and generalized bounded real lemma are necessary and sufficient. They are the extensions of results by B.D.O.Anderson nd S.Vongpanitlerd (1973), in which the state-space realizations are considered. The impulse-free generalized state-space systems contain both finite and nondynamic infinite modes. The state-space systems contain finite modes only. To express those algebraic restrictions among state variables is easier in the generalized state-space.

Frequency syntonization using GPS carrier phase measurements

A new methodology of frequency syntonization using GPS carrier phase double differences is presented. The proposed scheme can achieve the traceability of frequency dissemination and obtain the very high frequency stability in the short term, as well as in the long term. The GPS receivers used in our system were elaborately modified in order to estimate the frequency offset of the remote low-cost oven-controlled crystal oscillator clock with respect to the primary cesium atomic clock in real time by performing the double differences on the GPS carrier phase observables. The fuzzy controller and the proportional-derivative controller were employed to implement the controllers of our system, respectively. Through the D/A converter, the remote clock was then steered to synchronize with the primary clock. For averaging times of one day under the configuration of about a 30-m baseline, our experimental results show that the accuracy of the remote clock can be improved from about 3/spl times/10/sup -9/ to about 3/spl times/10/sup -14/, and the stability of the remote clock can be improved from about 3/spl times/10/sup -10/ to about 2/spl times/10/sup -14/. Moreover, the 30-m baseline tests with the common high-performance cesium clock revealed that our system has a frequency stability of about 2/spl times/10/sup -16/ for averaging times of one day.

Using multi-frequency for GPS positioning and receiver autonomous integrity monitoring

Algorithms using multi-frequency for GPS positioning and receiver autonomous integrity monitoring (RAIM) are proposed by the authors. In the conventional algorithms, only single frequency L1 is applied. After the L2 and L5 signals are applied, the ionospheric delay can be removed. Therefore, the variance of the measurement error is reduced, the positioning accuracy is improved, and the detection time of satellite failure is decreased. In addition, a cleaner parity vector is obtained, so the incorrect exclusion rate (IER) is significantly reduced. This paper provides a systematic way to derive the algorithms of the positioning and RAIM for multi-frequency GPS receiver. Simulation results show that, in comparison with the conventional single frequency method, the proposed multi-frequency algorithms not only possess more accurate positioning results, but also demonstrate higher performance in detecting small failures and, in detecting large failures, demonstrate a similar level of performance. Moreover, simulation results also verify that the proposed method has lower IER than the conventional single frequency method.

Systematic backstepping design for B-spline trajectory tracking control of the mobile robot in hierarchical model

The purpose of this paper is to investigate the trajectory tracking problem of the mobile robot. The method integrates a kinematic controller and a torque controller into the dynamic model using backstepping techniques. First, the analytic B-spline function is used to generate a smoothly feasible trajectory between the initial and desired configuration so that the motion path can pass through desired intermediate points and satisfy the kinematic constraints and curvature restrictions. Second, a set of sufficient conditions and a systematic transform procedure are presented for determining if a nonlinear kinematic model can be converted to the integrator chained form which significantly reduced the complexity of designing the privileged velocity. Finally, an adaptive tracking control is developed for the hierarchical model based on backstepping methodology and computed-torque techniques to achieve global asymptotically stable. Simulation results are utilized to illustrate the effectiveness of the proposed control architecture.