SISO Case Research Articles

IRS-Assisted High Mobility Communications Using OTFS Modulation

Intelligent reflecting surface (IRS) has emerged as a promising technology for fifth generation (5G) and beyond wireless networks that are expected to support high mobility applications. Supporting IRS-assisted high mobility communications is nonetheless challenging due to the cascade of doubly-dispersive transmitter-IRS and IRS-receiver channels. To address this issue, we propose a multiple-input multiple-output orthogonal time frequency space (MIMO-OTFS) IRS-assisted communications system with MMSE detection. We present a general time-domain input-output relation, which is also applicable to single-input single-output OTFS (SISO-OTFS). We then design the IRS phase shifts to maximize the received signal-to-noise (SNR) for both SISO and MIMO cases. Numerical results show significantly lower error rates than orthogonal frequency division multiplexing (OFDM) IRS-assisted systems for terrestrial and non-terrestrial high-Doppler communications.

Retrospective cost adaptive harmonic disturbance rejection using dereverberated target models

This paper focuses on adaptive feedback disturbance rejection for lightly damped structures using retrospective cost adaptive control (RCAC). RCAC uses a target model of the closed-loop dynamics in order to enable controller adaptation. The target model captures specific features of the dynamics of the structure; in the SISO case, this information consists of the sign of the leading numerator coefficient, relative degree, and nonminimum-phase zeros of the discretized dynamics. The present paper investigates the feasibility of using a dereverberated transfer function (DTF) as the target model for harmonic disturbance rejection with unknown disturbances. In particular, the dereverberated target model (DTM) obtained by magnitude and phase averaging captures the magnitude and phase trend of the structure but ignores resonances and anti-resonances, thus providing a low-order target model for controller adaptation. The robustness of RCAC is investigated with the target model given by a DTF based on a nominal model with erroneous damping ratio. The technique is implemented experimentally on an acoustic noise control setup.

Distributed cooperative neural control of a class of nonlinear multi‐agent systems with unknown time‐varying control coefficient

SummaryThis article studies the leader–follower cooperative tracking problem of a class of multi‐agent systems with unknown nonlinear dynamics. As the load of the following agent may be changing throughout the whole work process, we consider the control coefficient of the following agent to be time‐varying and nonlinear instead of constant, which is more practical. All agents are connected by the directed communication graph with weighted topology. The followers can have unknown nonidentical nonlinear dynamics and external disturbances. The nonautonomous leader generates the reference trajectory for only part of the followers and others can only receive the information from their neighbors. To achieve the ultimate synchronization of all following agents to the leader, the novel cooperative adaptive control protocols are designed based on the neural approximation and adaptive updating mechanism. A novel singularity‐avoided adaptive updating law is proposed to estimate the control coefficient and compensate for the unknown dynamics online. Lyapunov theory is used to prove the ultimate boundedness of the synchronization tracking error. The correctness and effectiveness of the presented control scheme are demonstrated by two simulations in SISO and MIMO cases, respectively.

LPV modeling of nonlinear systems: A multi-path feedback linearization approach.

This article introduces a systematic approach to synthesize linear parameter‐varying (LPV) representations of nonlinear (NL) systems which are described by input affine state‐space (SS) representations. The conversion approach results in LPV‐SS representations in the observable canonical form. Based on the relative degree concept, first the SS description of a given NL representation is transformed to a normal form. In the SISO case, all nonlinearities of the original system are embedded into one NL function, which is factorized, based on a proposed algorithm, to construct an LPV representation of the original NL system. The overall procedure yields an LPV model in which the scheduling variable depends on the inputs and outputs of the system and their derivatives, achieving a practically applicable transformation of the model in case of low order derivatives. In addition, if the states of the NL model can be measured or estimated, then a modified procedure is proposed to provide LPV models scheduled by these states. Examples are included to demonstrate both approaches.

Reconfigurable Intelligent Surfaces Supported Wireless Communications

Reconfigurable Intelligent Surfaces (RISs) have been recently considered in communication environments for focusing signal reflections to create smart radio environments. As it can create favorable propagation conditions by controlling the phase shifts of the reflected signals at the surface to enhance the communication quality. However, the current proofs of concept require complex operations for the RIS configuration, which are mainly realized via wired control connections. When used in wireless networks, RISs may contribute enhance wireless communications. The present paper, compares the RIS technology with the SISO case and evaluates the performance of RIS assisted communication system by giving an approximation of the achievable data rate and the energy efficiency, and investigates the effect of the achievable data rate and distances on the energy efficiency. In this work, based on a work by Emil Björnson [18], we have studied the impact of RIS on the wireless sensor networks by modifying some parameters and giving more interpretations. In particular, we illustrate numerical results that highlight the spectral efficiency gains of RISs when their size is sufficiently large as compared with the wavelength of the radio waves. In addition, we discuss key open issues that need to be addressed for unlocking the potential benefits of RISs for application to wireless communications and networks.

Robust output regulation for Timoshenko beam equation with two inputs and two outputs

AbstractIn this article, we consider two‐dimensional robust output tracking for a Timoshenko beam equation where the disturbances and references are produced by a finite‐dimensional exosystem. This requires at least two controls from basic output regulation theory of linear systems. The observer‐based error feedback control approach is adopted in investigation through the following steps: (a) for the plant with no systematic uncertainties, choose a set of disturbances and references to obtain a nominal system; (b) for the nominal system, design an observer to realize 2‐copy of the exosystem; (c) find a feedforward control for nominal system; and (d) allocate proportionally the states in feedforward control by those of the observer to obtain an observer based error feedback control also for nominal system. Since the control contains a 2‐copy of the exo‐system and the states of the observer are proportionally allocated in control, the problem is significantly different from SISO cases. The error feedback control is then proved to be bounded and also robust to systematic uncertainties and all disturbances and references produced from the exo‐system. The numerical simulations validate the theoretical results.

Experimental Studies on Energy and Eigenvalue Based Spectrum Sensing Algorithms Using USRP Devices in OFDM Systems

AbstractIn this paper, first, energy detection (ED) based spectrum sensing inorthogonal frequency division multiplexing (OFDM) system using National Instrument (NI) Universal Software Radio Peripheral (USRP) 2942R software defined radio platform has been implemented. It is observed that in practical scenario ED scheme gives poor performance at low gain (G) values. To overcome the shortcomings of energy detection, we propose eigenvalue based detection of the primary user (PU) signal, where the ratio of the maximum eigenvalue to the average eigenvalue is used to detect the PU signal in both the single and multiple antenna systems/SISO and multiple‐input and multiple‐output (MIMO) based CR user. The analytical expression of the performance metric (probability of detection [Pd]) has been derived. Further, the experimental studies show that proposed technique gives optimum (Pd) in both SISO and MIMO case. It has been observed that the proposed technique outperforms the ED based detection even if the Tx‐Rx separation increases.

Tube-Based Internal Model Control of Minimum-Phase Input-Affine MIMO Systems under Input Constraints

In this paper an optimal control approach based on a combination of inversion-based control and internal model control (IMC) is designed to keep the controlled states of a minimum-phase input-affine MIMO system within predefined tubes while respecting input constraints. This contribution extends recently presented results for the SISO case to nonlinear input-affine MIMO systems. The developed approach uses ideas developed in the design of inversion-based IMC controllers for setpoint tracking and extends them to ‘tube tracking’. It shows the interesting result that for input-affine systems the control task of maintaining each controlled state within a tube while minimizing energy consumption and respecting input constraints can be expressed as a convex quadratic optimization problem. This concept allows to handle dynamic systems where the number of control inputs differs from the number of controlled outputs are not equal. The control approach is illustrated by three simulation examples.

On Lyapunov-Lur’e functional based stability criterion for discrete-time Lur’e systems

In this manuscript, we consider the stability problem of Lur’e systems with slope-restricted nonlinearities. We focus on a specific parametrisation of the Lyapunov-Lur’e functional in the literature, and extend it to a higher order. Meanwhile, we show this Lyapunov-Lur’e functional based stability criterion is equivalent to the search for noncausal FIR multipliers with a restricted form for the SISO case. Finally, we discuss the restrictions of this Lyapunov-Lur’e functional approach with some numerical examples.

Globally Optimal Joint Uplink Base Station Association and Beamforming

The joint base station (BS) association and beamforming problem has been studied extensively in recent years, yet the computational complexity for even the simplest SISO case has not been fully characterized. In this paper, we consider the problems for an uplink SISO/SIMO cellular network under the max-min fairness criterion. We first prove that the problems for both the SISO and SIMO scenarios are polynomial time solvable. Secondly, we present a fixed point based binary search (BS-FP) algorithm for both SISO and SIMO scenarios whereby a QoS (Quality of Service) constrained subproblem is solved at each step by a fixed point method. Thirdly, we propose a normalized fixed point (NFP) iterative algorithm to directly solve the original problem and prove its geometric convergence to global optima. Although it is not known whether the NFP algorithm is a polynomial time algorithm, empirically it converges to the global optima orders of magnitude faster than the polynomial time algorithms, making it suitable for applications in huge-scale networks.

Robust Adaptive Control of MIMO Pure-Feedback Nonlinear Systems via Improved Dynamic Surface Control Technique

This paper presents a global dynamic surface control (DSC) method for a class of uncertain multi-input/multi-output (MIMO) pure-feedback nonlinear systems with non-affine functions possibly being in-differentiable. It is well known that the traditional DSC method is commonly used for reducing the design complexity of the backstepping control method; however, the regulation results of the DSC method are semi-global uniformly ultimately bounded (SGUUB). An improved DSC (IDSC) method is first designed in this paper so that the results are global uniformly ultimately bounded (GUUB). Comparing with the traditional DSC method, the parameters of first-order filters in IDSC are time varying rather than constants. The control design for MIMO pure-feedback nonlinear systems researched is much more complex than the SISO cases, and the presence of in-differentiable non-affine functions considered in this paper makes the control design even more difficult. Therefore, we proposed the IDSC method, which can significantly reduce the complexity of the control design for the MIMO pure-feedback nonlinear systems in cooperation with the backstepping method, and it is proved that IDSC can guarantee the GUUB of all the signals of the system. Finally, the simulation results are provided to demonstrate the effectiveness of the designed method.

On the sliding mode control of MIMO nonlinear systems: An input‐output approach

SummaryWe address the sliding mode control design problem for output reference trajectory tracking problems in the special class of MIMO flat systems known as static feedback linearizable systems. We assume unavailable system state components but rely on available inputs and measurable flat outputs. Each controller will largely ignore state and control input couplings by adopting a standard sliding mode controller scheme derived from the SISO case and used this as decoupled input‐to‐flat‐output model. The standard controller arises from a vastly simplified pure integration, additively perturbed, system. The simplified pure integration system controlled trajectories are shown to be time‐scale homotopically equivalent to those of the nonlinear flat system. The basic sliding surface coordinate function design is approached from the perspective of structural integral reconstructors requiring only the inputs and the flat outputs of the system. Integral structural reconstructors were introduced by Fliess et al for the control of linear SISO and MIMO systems, giving rise to the generalized proportional integral control method. Simulations are presented for SISO and MIMO systems and experimental results are reported for a two‐degree‐of‐freedom fully actuated robotic manipulator.

Exploiting Trust Degree for Multiple-Antenna User Cooperation

For a user cooperation system with multiple antennas, we consider a trust degree based cooperation techniques to explore the influence of the trustworthiness between users on the communication systems. For the system with two communication pairs, when one communication pair achieves its quality of service (QoS) requirement, they can help the transmission of the other communication pair according to the trust degree, which quantifies the trustworthiness between users in the cooperation. For given trust degree, we investigate the user cooperation strategies, which include the power allocation and precoder design for various antenna configurations. For SISO and MISO cases, we provide the optimal power allocation and beamformer design that maximize the expected achievable rates while guaranteeing the QoS requirement. For a SIMO case, we resort to semidefinite relaxation (SDR) technique and block coordinate update (BCU) method to solve the corresponding problem, and guarantee the rank-one solutions at each step. For a MIMO case, as MIMO is the generalization of MISO and SIMO, the similarities among their problem structures inspire us to combine the methods from MISO and SIMO together to efficiently tackle MIMO case. Simulation results show that the trust degree information has a great effect on the performance of the user cooperation in terms of the expected achievable rate, and the proposed user cooperation strategies achieve high achievable rates for given trust degree.

The Frisch scheme in multivariable errors-in-variables identification

This paper concerns the identification of multivariable errors-in-variables (EIV) models, i.e. models where all inputs and outputs are assumed as affected by additive errors. The identification of MIMO EIV models introduces challenges not present in SISO and MISO cases. The approach proposed in the paper is based on the extension of the dynamic Frisch scheme to the MIMO case. In particular, the described identification procedure relies on the association of EIV models with directions in the noise space and on the properties of a set of high order Yule–Walker equations. A method for estimating the system structure is also described.

Output Feedback Stabilization for Discrete-Time Systems Under Limited Communication

This paper addresses the output feedback stabilization problem for discrete-time networked control systems with imperfect input channels, i.e., the controller-actuator channels, where both quantization error and packet dropout are involved. A stabilizability condition is first derived for the single-input-single-output (SISO) case. It is shown that stabilization over quantized lossy channel actually involves a trade-off between robust stability control and robust performance control. Furthermore, the results are expanded to triangularly decoupled multiple-input-multiple-output (MIMO) systems and a necessary and sufficient condition is deduced, which also exhibits a compromise between robust stability control and robust performance control in the individual channel as echoing the SISO case.

A note on adaptive observer for the Lur’e differential inclusion system

This paper considers the adaptive observer design problem for the Lur’e differential inclusion system with unknown parameters. Different from the current work, the proposed observer does not hold any set-valued mapping and the uncertain parameters can also be identified. Firstly, the adaptive observer is designed for the Lur’e differential inclusion system, and it is proved to be valid by Lyapunov stability theory. Then, based on the canonical form of the system matrix, the sufficient and necessary condition for one assumption is presented in both SISO and MIMO cases. Finally, numerical examples are simulated to show the effectiveness of the proposed method.

Positive output/state maps and quasi-positive realization of MIMO discrete systems

The positive realization of externally positive systems described by their transfer matrix G(z) is a complex problem whose analysis has been completed only recently, for the SISO case, on the basis of algebraic and geometric approaches that underline the many constraints that condition its solution. These constraints concern the minimal order of the obtained models, the minimality of their parameterizations and even their existence. This paper considers the new category of quasi-positive state-space models introduced in Guidorzi (2014) that limit the assumptions on the nonnegativeness of the state-space trajectories to the only trajectories that can be actually generated by the system under nonnegative controls. It is shown that all externally positive systems admit a quasi-positive minimally parameterized state-space realization whose existence is not conditioned by restrictions on the signs of the parameters of the polynomials in G(z).

Control algorithm for SISO case using F O S with modeling in Simulink

Control algorithm for SISO case using F O S with modeling in Simulink

Stability of a Class of Nonlinear Repetitive Processes with Application to Iterative Learning Control

The paper considers a discrete repetitive process described by the state-space model with static nonlinearity satisfying quadratic constraints (in particular, the SISO case with the sector bounded nonlinearity). Based on the vector Lyapunov function approach developed by the authors, sufficient conditions of pass profile exponential stability are obtained in the form of linear matrix inequalities. These conditions are then applied to the design of an iterative learning control law for a simple nonlinear mechanical system.

OSTBC–MISO–OFDM/OQAM Systems with Time Reversal Technique

Orthogonal frequency division multiplexing with offset quadrature amplitude modulation (OFDM/OQAM) is a multicarrier modulation scheme that can be considered as an alternative to the conventional OFDM with cyclic prefix (CP) for transmission over multipath fading channels. In this paper, we investigate the combination of the OFDM/OQAM with orthogonal space time blok coding (OSTBC) in multiple input single output (MISO) system with time reversal (TR) technique. TR can be viewed as a precoding scheme which can be combined with OFDM/OQAM and easily carried out in a MISO context. We present the simulation results of the performance of OFDM/OQAM system in SISO case compared with the conventional CP-OFDM system and the performance of the combination OSTBC---MISO---OFDM/OQAM with TR compared to Alamouti CP-OFDM. The performance is derived by computing the bit error rate as a function of the transmit signal-to-noise ratio.