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Focusing on a time-division duplex (TDD) multiple-input-single-output (MISO) beamforming system, this study investigates the robust uplink pilot time interval (UPTI) design to overcome the impact of delay and channel estimation error. In TDD beamforming systems, the base station estimates the downlink (DL) channel state information (CSI) by exploiting the received uplink (UL) pilots and the channel reciprocity. Then, utilising the estimated DL CSI, the beamforming vector in the DL transmission is generated. Owing to the constraints of the TDD frame structure and the UL pilot overhead, there inevitably exist delay and estimation error between the estimated and the actual DLCSI, which would degrade system performance. In this study, the upper bound is first derived on ergodic rate for TDD MISO beamforming systems with channel estimation error and delay. Then, with any one given setting of the normalised UL pilot overhead, the optimal robust UPTI is designed, which maximises the upper bound on ergodic rate in the worst case of the CSI delay (i.e. in the case of maximum delay). Simulation results validate that the designed optimal robust UPTI can not on I y maximise the upper bound on ergodic rate but also be adaptive to the variation of channel conditions very well. [ABSTRACT FROM AUTHOR]

This study presents a gravitational search algorithm (GSA) for reactive power dispatch (RPD) problem. RPD is an optimisation problem that decreases grid congestion with one or more objective of minimising the active power loss for a fixed economic power schedule. The proposed algorithm is used to find the settings of control variables such as generator terminal voltages, transformer tap settings and reactive power output of the compensating devices, in order to active power losses minimisation in the transmission system. In this study, GSA is examined and tested on the standard IEEE 30-bus, 57-bus and 118-bus test systems with different test cases such as minimisation of active power losses, improvement of voltage profile and enhancement of voltage stability. To show the proposed algorithm of effectiveness and the obtained results are compared with those reported in the literature. Simulation results demonstrate the superiority and accuracy of the proposed algorithm, and considering the quality of the solution obtained, the proposed algorithm seems to be effective and robust to solve the RPD problem. [ABSTRACT FROM AUTHOR]

In this work, a robust and oblivious image watermarking scheme based on discrete wavelet transform (DWT) for copyright protection is presented. The original unmarked image is not required for watermark extraction. Third-level DWT is applied to the original cover image. Third- and second-level horizontal detail sub-band (LH2 and LH3) coefficients are grouped into different blocks. Grouping of the coefficients is done in such a way that each block should contain one coefficient from LH3 sub-band and four coefficients from LH2 sub-band. In each block, the first minimum and the second minimum are identified and modified according to the watermark bit. After watermark insertion, inverse DWT is applied to the sub-bands with modified coefficients to obtain the watermarked image. For watermark extraction, a threshold-based decoder is designed. Embedding and extraction process are characterised with parameters and genetic algorithm is used for parameter optimisation. Optimisation is to maximise the values of peak signal-to-noise ratio of the watermarked image and normalised cross correlation of the extracted watermark. The performance of the proposed scheme is compared with the existing schemes and significant improvement is observed. Experimental results show that, this algorithm is highly robust for many image attacks on the watermarked image. [ABSTRACT FROM AUTHOR]

Model predictive control (MPC) is an optimisation-based algorithm which usually requires a numerical method to calculate the solution of the problem. Inherently, numerical methods for optimisation problems are implemented on a finite-precision hardware platform and are subject to the appearance of numerical instabilities of catastrophic cancellation and ill-conditioned matrices. These anomalies are difficult to detect and overcome, and for safety-critical applications, it is essential to have a mechanism that can at least issue a warning when an arithmetic instability occurs. Towards this direction, Monte Carlo arithmetic (MCA) for the floating-point (FP) number system has been used for both detection and mitigation of catastrophic cancellation and ill-conditioned matrices. An alternative to FP is the Logarithmic Number System (LNS) that recently has been proposed for the real-time hardware implementation of embedded MPC. In this study the authors present the adaptation of MCA to LNS for detecting and mitigating catastrophic cancellation, forming the Monte Carlo Logarithmic Number System (MCLNS). An inherent drawback of MCA is the accuracy deterioration which is a direct consequence of the randomisation in the arithmetic operations. Additionally, multiple simulations of the system result in performance deterioration equal to the number of simulations. Using off-line simulations it is possible to determine the necessary hardware requirements to achieve desired accuracy under performance constraints. These trade-offs are studied and analysed for an MPC algorithm, and the hardware implementation cost of MCLNS is quantified by synthesis on a Xilinx Virtex-IV FPGA. [ABSTRACT FROM AUTHOR]

This study investigates the robust quantised H∞ control problem for active suspension systems. First, based on the half-vehicle suspension model, the dynamical system with polytopic parameter uncertainties, which are caused by vehicle load variation, is established. In the meanwhile, the active suspension system performance, namely ride comfort, road holding and suspension deflection, are taken into account for the control design aim. Secondly, an input delay approach is utilised to transform the resulting active vehicle suspension system with sampling and quantisation measurements into a continuous-time system with a delay in the input sector bound uncertainty. Thirdly, robust quantised H∞ performance analysis and controller synthesis criteria are presented in the form of convex optimisation problem by exploiting the Lyapunov functional approach. The existing robust quantised H∞ controller condition not only guarantees the robust asymptotical stability of the closed-loop system, but also satisfies the output constrained performance. Finally, the effectiveness and application of the proposed method can be demonstrated by providing a design example. [ABSTRACT FROM AUTHOR]

In this study, the authors propose an iterative registration algorithm with point-based representation. The task is to geometrically transform a mobile object to a stationary object. Without a good initial position for two shapes with high-curvature features, traditional point-based algorithms have many challenges, such as suffering from slow convergence or divergence. For these problems, the authors define a new distance function to describe the point-surface distance, where the point-surface shortest distance is considered. Then, a non-linear optimisation model is established to calculate the optimal transformation. Moreover, the convergence of the proposed algorithm is derived and analysed from the viewpoint of geometrical optimisation. The proposed method does not require surface representation, feature extraction, curvature computation and is more applicable when initial position is rough. Its efficiency and robustness are verified by a series of experiments. [ABSTRACT FROM AUTHOR]

A bilevel optimisation framework is proposed to find the proportional-integral-derivative (PID) controller with balanced performance in terms of transient response, actuator preservation and robustness. In the lower level problem, the transient performance is optimised so that the balanced controller can be designed with minimal controller output variation in the upper level problem, where the requirement on transient performance is relaxed to a pre-specified extent. The robustness of the system is guaranteed by constraints on the maximum sensitivity in both problems. The trade-off between transient performance and actuator preservation is controlled uniformly for diverse process dynamics by a single parameter, which characterises the uniformness of relaxation in transient performance. By choosing different values of this parameter, tuning rules are provided for first order plus time delay (FOPTD) processes for set point following and load disturbance rejection, respectively. The efficiency of these tuning rules is demonstrated by examples covering the whole plant family set. [ABSTRACT FROM AUTHOR]

In this study, an optimisation-based approach is proposed for the robustness analysis of an attitude and orbit control system (AOCS) for flexible satellites. Several optimisation methods, including local gradient-based algorithms, global evolutionary algorithms and hybrid local/global algorithms are applied to the problem of analysing the robustness of a full-authority multivariable controller with respect to several frequency and time domain performance criteria, for a 6 degree of freedom simulation model of a satellite with large sun shields. The results of our study reveal the advantages of optimisation-based worst-case analysis over traditional Monte Carlo simulations for systems with flexible dynamics. In particular, it is shown that frequency domain analysis can provide useful guidance for the formulation of subsequent time domain tests, and that hybrid local/global optimisation algorithms can produce more reliable estimates of worst-case performance, while also reducing the associated computational overheads. The proposed approach appears to have significant potential for improving the industrial flight clearance process for next-generation high-performance satellite control systems. [ABSTRACT FROM AUTHOR]

This study presents an optimisation-based audio watermarking scheme using group-amplitude quantisation. To enhance the robustness, the watermark is embedded in the lowest-frequency coefficients in discrete wavelet transform (DWT). The performance of this watermarking scheme is analysed in terms of audio quality (signal-to-noise ratio (SNR)) and robustness (bit error ratio (BER)). As there is a tradeoff relationship between the audio quality and robustness, this study presents an optimisation-based group-amplitude quantisation scheme for audio watermarking. First, SNR is rewritten as a watermarking cost function in matrix form. Then an equation connecting the watermarking cost function and the group-amplitude quantisation equation is proposed. Second, the Lagrange principle is used to derive the optimisation solution. The optimal results are then applied to embed the watermark. Finally, the performance of the proposed scheme is tested. Experimental results show that the hidden data are robust against most common attacks, such as re-sampling, MP3 compression, low-pass filtering and amplitude scaling. [ABSTRACT FROM AUTHOR]

A dynamic model for the stabilisation loop of a two-axis gimbaled sensor system is formulated and system parameters have been identified by practical experiments. The validity of the dynamic model is illustrated by the experimental and simulation result. The Lead-proportional-integral (PI) controller design using a loop-shaping method based on the frequency response for the stabilisation loop of the sensor system is realised. This practical design approach has been proven to be simple and robust in actual application. The robust H∞ controller design approach combining model matching and mixed sensitivity problem to improve the command following and disturbance rejection performance in the presence of external disturbances and model uncertainties is implemented, which is designed within the framework of the standard H∞ optimisation problem by combining a conventional mixed sensitivity and model matching problem with robust stability. The experimental and simulation results show that the both two proposed controllers satisfy all desired requirements for the stabilisation loop associated with the gain crossover frequency, the gain and phase margin and the body-motion decoupling performance. It is shown through performance comparison and analysis that the proposed H∞ controller is preferable to the proposed Lead-PI controller in terms of system stability, the disturbance rejection rate and because of its fast time response characteristics. However, it is clear that the two proposed controller design procedures for the robust control of the stabilisation loop of a two-axis gimbaled sensor system can be very effective in practical applications in terms of both stability and disturbance rejection. [ABSTRACT FROM AUTHOR]

In this paper, a new interaction prediction approach for hierarchical control of non-linear large-scale systems is presented. The proposed approach uses a new gradient-type coordination scheme which is robust with respect to the parameters' variation, and also has a good convergence rate. In classical coordination strategies, which can be divided into the gradient-type and substitution-type approaches, it is not possible to improve the robustness and the convergence rate at the same time, since by increasing one the other decreases. The proposed approach has the main advantages of the gradient-type algorithms in being independent of the parameter's variation and also the initial guess of the coordination vector. In addition, because of the proposed coordination strategy, in which the update of the coordination vector directly causes the reduction of the coordination error, the number of iterations is considerably reduced. The robustness and convergence rate of the proposed approach against the other interaction prediction approaches are shown through simulations of a benchmark problem. The simulation results also show the effectiveness of the proposed approach in solving constrained optimisation problems having non-quadratic cost functions. Comparisons are also made with the solutions obtained using centralised approach. [ABSTRACT FROM AUTHOR]

With reference to the model-based autotuning of industrial regulators, like PIs or PIDs, this study proposes some indices to evaluate the obtained tuning, including its robustness against model errors, in a more informative and straightforward way with respect to traditional ones such as the phase margin. As a by-product, the proposed indices allow one to express the regulator in alternate ways, so as to ease the possible optimisation-based tuning procedures (a matter just sketched herein owing to space limitations). Some example tuning methods are presented to illustrate the idea. Simulation tests and a laboratory application are reported. [ABSTRACT FROM AUTHOR]

The issue of introducing generic design constraints (practical or ‘real-life’ constraints) in robust control design procedures is discussed. A strategy, based on a hierarchy of optimisation methods, is proposed here. An ℋ∞ design algorithm constitutes the bottom level of this hierarchy, and a general-purpose optimisation algorithm (a genetic algorithm) is employed for tuning the parameters of the ℋ∞ controller, searching for the solutions that satisfy the earlier mentioned ‘practical constraints’. Practical results obtained in a pilot-scale plant with fluid-level and flow-rate control as controlled variables are included to show the applicability of the proposed method. [ABSTRACT FROM AUTHOR]

The robust H∞ filtering problem subject to pole-placement constraints for continuous-time systems with the polytopic type uncertainties is considered. Different from those considered in the literature, the regional pole-placement constraints considered here focus on the filter dynamics. To solve the problem, the π-sharing theory is extended to offer a stability criterion that covers the bounded real lemma as a special case, and the linear matrix inequality approach is adopted to develop filter design methods based on the convex optimisation procedure. One numerical example is given to illustrate the proposed methods. [ABSTRACT FROM AUTHOR]

A finite horizon model predictive control (MPC) algorithm that is robust to modelling uncertainties is developed along with the construction of a moving average system matrix to capture modelling uncertainties and facilitate the future output prediction. The authors' main focus is on the step tracking problem. Using linear matrix inequality techniques, the design is converted into a semi-definite optimisation problem. Closed-loop stability, known to be one of the most challenging topics in finite horizon MPC, is treated by adding extra terminal cost constraints in the semi-definite optimisation. A simulation example demonstrates that the approach can be useful for practical applications. [ABSTRACT FROM AUTHOR]

A new method for the design of multivariable internal model control (IMC) is proposed, aimed at obtaining good loop performance and small loop couplings based on linear matrix inequalities (LMIs). The decoupling design with performance constraints is formulated into an optimisation problem with LMI constraints, and thus the problem can be solved effectively. Robust stability is analysed and simulations show that good control performance can be achieved. [ABSTRACT FROM AUTHOR]

A sign subband adaptive filter (SSAF) for acoustic echo cancellation is proposed, which is derived by minimising the L1-norm of the subband a posteriori error vector subject to a constraint on the tap-weight vector of the filter. In addition, a variable regularisation parameter (VRP) is introduced to improve the performance of the SSAF. Simulation results are presented to verify the good robustness of the proposed VRP-SSAF against double-talk. [ABSTRACT FROM AUTHOR]