Inter-Communicative Decentralized Multi-Scale Control (ICD-MSC) Scheme: A new approach to overcome MIMO process interactions

Decentralized PID control has been extensively used in process industry due to its functional simplicity. But designing an effective decentralized PID control system is very challenging because of process interactions and dead times, which often impose limitations on control performance. In practice, to alleviate the detrimental effect of process interactions on control performance, decoupling controllers are often incorporated into a decentralized control scheme. In many cases, these conventional decoupling controllers are not physically realizable or too complex for practical implementation. In this paper, we propose an alternative scheme to overcome the performance limitation imposed by process interactions. This new control scheme is extended from the SISO multi-scale control scheme previously developed for nonminimum-phase processes. The salient feature of the new control scheme lies in its communicative structure enabling collaborative communication among all the sub-controllers in the system. This communicative structure serves the purpose of reducing the detrimental effect of process interactions leading to improved control performance and performance robustness. Extensive numerical study shows that the new control scheme is able to outperform some existing decentralized control schemes augmented with traditional decoupling controllers

Multi-Scale Control: Improved Technique to Overcome Time-Delay Limitation

This paper presents a general multi-scale control scheme which can be used to control processes with significant time-delays. The salient feature of the multi-scale control scheme is to decompose a given plant into a sum of basic factors or modes. An individual sub-controller is specifically designed to control each of the plant modes and subsequently, an overall multi-scale controller is synthesized via combining all of the sub-controllers in a manner to enhance cooperation among these different plant modes. Numerical examples show that the multi-scale control scheme can provide improved performance and robustness over the conventional single-loop PID and Smith predictor schemes

Generalized multi-scale control scheme for cascade processes with time-delays

The cascade control is a well-known technique in process industry to improve regulatory control performance. The use of the conventional PI/PID controllers has often been found to be ineffective for cascade processes with long time-delays. Recent literature report has shown that the multi-scale control (MSC) scheme is capable of providing improved performance over the conventional PID controllers for processes characterized by long time-delays as well as slow RHP zeros. This paper presents an extension of this basic MSC scheme to cascade processes with long time-delays. This new cascade MSC scheme is applicable to self-regulating, integrating and unstable processes. Extensive numerical studies demonstrate the effectiveness of the cascade MSC scheme compared with some well-established cascade control strategies

UWB Waveform Set Design using Löwdin’s Orthogonalization with Hermite Rodriguez Functions

In this paper we design a set of spectrally efficient orthogonal waveforms based on Hermite Rodriguez functions. The design is formulated as a semi-infinite quadratic programming problem and subsequently Löwdin method is used to generate a set of orthogonal waveforms. This approach is able to produce many overlapping orthogonal waveforms with high spectral efficiency

Advanced PID Controller Synthesis using Multiscale Control Scheme

For many decades, PID controller has been widely applied in industries despite the advancement in many advanced control techniques. Process models such as the First-Order plus Deadtime (FOPDT) has often been used to design or tune PID controller. Numerous PID tuning formulas have been established since the well-known Ziegler-Nichols formula introduced in the 1940s. In this paper, we present the multi-scale control approach to constructing a PID tuning formula based on the FOPDT model. The effectiveness of the proposed PID tuning formula is compared with some of the existing formulas reported in the literature

MMSE based transceiver design for MIMO relay systems with mean and covariance feedback

In this paper, the problem of transceiver design in a non-regenerative MIMO relay system is addressed, where linear signal processing is applied at the source, relay and destination to minimize the mean-squared error (MSE) of the signal waveform estimation at the destination. In the proposed design scheme, optimal structure of the source and relay precoding matrices are obtained with the assumption that the relay knows the mean and channel covariance information (CCI) of the relay-destination link and the full channel state information (CSI) of the source relay link. Based on this assumption, an iterative joint source and relay precoder design is proposed to achieve the minimum MSE of the signal estimation at the destination. In order to reduce computational complexity of the proposed iterative design, a suboptimal relay-only precoder design is proposed. A numerical example shows that the performance of the proposed iterative joint source and relay precoder design is very close to that of the algorithm using full CSI

Channel Covariance Information Based Transceiver Design for AF MIMO Relay Systems with Direct Link

In this paper, we propose a design scheme for amplify-and-forward multiple-input multiple-output (AF MIMO) relay system with direct link to minimize the mean-squared error (MSE) of the signal estimation at the destination. In the proposed design scheme, an optimal precoding matrix is derived with the assumption that the full channel state information (CSI) of the source-relay link and partial channel state information such as channel covariance information (CCI) of the relay-destination link are available at the relay. In practical cases, if the destination is closer to the source, the source-destination link cannot be ignored. Hence, in this paper, we assume that the relay knows the partial channel state information of the source-destination link. Based on this assumption, an iterative optimal covariance algorithm is developed to achieve the minimum MSE of the signal estimation at the destination. In order to reduce computational complexity of the proposed optimal covariance algorithm, a suboptimal covariance algorithm is proposed. A numerical example shows that the developed optimal covariance algorithm outperforms the conventional CCI based MSE algorithms

Simplified Robust Design for Nonregenerative Multicasting MIMO Relay Systems

In this paper, we propose a robust transceiver design for nonregenerative multicasting multiple-input multiple-output (MIMO) relay systems where a transmitter broadcasts common message to multiple receivers with aid of a relay node and the transmitter, relay and receivers are all equipped with multiple antennas. In the proposed design, the actual channel state information (CSI) is assumed as a Gaussian random matrix with the estimated CSI as the mean value, and the channel estimation errors are derived from the well-known Kronecker model. In the proposed design scheme, the transmitter and relay precoding matrices are jointly optimized to minimize the maximal mean squared-error (MSE) of the estimated signal at all receivers. The optimization problem is highly nonconvex in nature. Hence, we propose a low complexity solution by exploiting the optimal structure of the relay precoding matrix. Numerical simulations demonstrate the improved robustness of the proposed transceiver design algorithm against the CSI mismatch

Tomlinson-Harashima Precoding Based Transceiver Design for MIMO Relay Systems With Channel Covariance Information

In this paper, we investigate the performance of the Tomlinson-Harashima (TH) precoder based nonlinear transceiver design for a nonregenerative multiple-input multiple-output (MIMO) relay system assuming that the full channel state information (CSI) of the source-relay link is known, while only the channel covariance information (CCI) of the relay-destination link is available at the relay node. We first derive the structure of the optimal TH precoding matrix and the source precoding matrix that minimize the mean-squared error (MSE) of the signal waveform estimation at the destination. Then we develop an iterative algorithm to optimize the relay precoding matrix. To reduce the computational complexity of the iterative algorithm, we propose a simplified precoding matrices design scheme. Numerical results show that the proposed precoding matrices design schemes have a better bit-error-rate performance than existing algorithms