Zhixin Liu

Active Disturbance Rejection Position Control for a Magnetic Rodless Pneumatic Cylinder

This paper presents an active disturbance rejection position control scheme for a magnetic rodless cylinder in servo systems without pressure states. It is very hard to achieve precise position control of magnetic rodless cylinders due to nonlinearity from large friction force and hysteresis. In this paper, the overshoot, which has a negative influence on position control, is effectively reduced by using a tracking differentiator. Furthermore, the nonlinearity is estimated by a designed extended-state observer. In addition, the self-stable region theory is used to prove the convergence of the extended-state observer. Finally, both control precision and response speed are guaranteed via a nonlinear error feedback controller in the pneumatic system. Experimental results show that the steady-state error within 0.05 mm is achieved for a step signal.

Robust fuzzy-scheduling control for nonlinear systems subject to actuator saturation via delta operator approach

This paper focuses on robust fuzzy-scheduling control for nonlinear systems with actuation saturation via delta operator approach. A class of T-S fuzzy delta operator systems is extended to describe nonlinear systems subject to actuator saturation and linear fractional uncertainty. Moreover, a set invariance condition is established for T-S fuzzy delta operator systems. Based on the set invariance condition, an optimization approach is proposed to estimate the domain of attraction for the T-S fuzzy delta operator systems. The domain of attraction is arbitrarily close to a null controllable region by the designed PDC control law or non-PDC control law. Furthermore, the non-PDC control law is proposed by using fuzzy weighting-dependent Lyapunov function. The effectiveness of the developed techniques is shown through a numerical example.

Pricing-based spectrum leasing in cognitive radio networks

According to the property rights model of cognitive radio, primary users who own the spectrum resource have the right to lease part of the spectrum to secondary users (SUs) in exchange for appropriate profit. In this study, the authors propose a pricing-based spectrum leasing framework between one primary user and multiple SUs. In this scenario, the primary user attempts to maximise its utility by setting the price of spectrum, the selected SUs have the right to decide their power levels to help the primary users transmission, aiming to obtain corresponding spectrum access time. Then, the spectrum leasing problem can be cast into a Stackelberg game, which jointly maximises the utilities of primary user and SUs. Moreover, the authors design a joint relay selection and admission control algorithm, which can select the proper SUs and protect all the active SUs’ performance. Numerical results show that the proposed pricing-based spectrum leasing framework is effective, and the performance of the primary user and the SUs is both improved, compared with the traditional mechanism without cooperation.

Extended-state-observer-based adaptive control for synchronisation of multi-agent systems with unknown nonlinearities

This paper studies the problem of synchronisation to a desired trajectory for non-linear multi-agent systems. By introducing extended state observer approach, decentralised adaptive controllers are designed for distributed systems which have non-identical unknown non-linear dynamics. The non-identical unknown non-linear dynamics allows for a tracked command dynamics which is also non-linear and unknown. State variables of agents can be obtained only in the case where leader agent and the network communication topology for multi-agent systems is strongly connected digraph network structures. A Lyapunov-function-based approach is given to show that the tracking error is ultimately bounded. Some simulation results are given to demonstrate the effectiveness of the developed techniques in this paper.

Price bargaining based on the Stackelberg game in two-tier orthogonal frequency division multiple access femtocell networks

This study presents a solution to the interference management scheme and resource allocation strategy for the two-tier femtocell networks, where the femtocell users (FUEs) share the same frequency band with the existing macrocell users. It is assumed that the FUEs compete for the available spectrum to fulfil their own communication. And the macrocell base station protects itself by pricing the interference from the FUEs, which formulates the Stackelberg game. In this study, two effective pricing schemes, uniform pricing scheme and non-uniform pricing scheme, combining with admission control are proposed to maximise the revenues and protect the quality of service requirements. The Stackelberg equilibriums for the proposed games are investigated. Besides, a novel distributed interference pricing algorithm is provided for the uniform pricing case. Numerical results show that, in two-tier femtocell networks with shared spectrum, the proposed pricing schemes are effective in resource allocation and performance protection.

Robust Power Control for Amplify-and-Forward Relaying Scheme

Power control problem is investigated for amplify-and-forward cellular relay network in this letter. Since the wireless channels vary with time, we aim at a power allocation scheme that is robust to the fluctuations. An optimization problem is formulated which targets at utility maximization subject to a pre-defined outage probability threshold and limited power at relay station. With that, a distributed iterative algorithm is proposed to obtain the optimal power. Numerical results show the effectiveness of the algorithm, and also present the robustness of this system.

Fault Detection for Uncertain Fuzzy Systems Based on the Delta Operator Approach

This paper investigates the problem of designing a robust fault-detection for uncertain T-S fuzzy models based on the delta operator approach. By means of the T-S fuzzy delta operator systems, a fuzzy fault detection filter system is constructed via the delta operator approach. The worst case fault sensitivity has been formulated in terms of linear matrix inequalities. The proposed fault-detection filter not only ensures the H−-gain from a fault signal to a residual signal greater than a prescribed value, but also guarantees the H∞-gain from an exogenous input to a residual signal less than a prescribed value in terms of the solvability of linear matrix inequalities. The linear matrix inequalities can be solved by an effective algorithm. A numerical example is provided to illustrate the effectiveness of the proposed design techniques.

Balance energy-efficient and real-time with reliable communication protocol for wireless sensor network

Abstract In many wireless sensor network applications, it should be considered that how to trade off the inherent conflict between energy efficient communication and desired quality of service such as real-time and reliability of transportation. In this paper, a novel routing protocols named balance energy-efficient and real-time with reliable communication (BERR) for wireless sensor networks (WSNs) are proposed, which considers the joint performances of real-time, energy efficiency and reliability. In BERR, a node, which is preparing to transmit data packets to sink node, estimates the energy cost, hop count value to sink node and reliability using local information gained from neighbor nodes. BERR considers not only each sender energy level but also that of its neighbor nodes, so that the better energy conditions a node has, the more probability it will be to be chosen as the next relay node. To enhance real-time delivery, it will choose the node with smaller hop count value to sink node as the possible relay candidate. To improve reliability, it adopts retransmission mechanism. Simulation results show that BERR has better performances in term of energy consumption, network lifetime, reliability and small transmitting delay.

Robust power control for femtocell networks under outage-based QoS constraints

This paper studies a robust uplink power control scheme with imperfect channel state information (CSI) in two-tier femtocell network systems. Aiming at enhancing the systems robustness, we formulate an outage-based robust optimization problem. Specifically, we focus on two scenarios including partial CSI feedback and no CSI feedback. In the former scenario, channel gain error vectors obey multivariate Gaussian distributions. We propose a novel transformation method, which is based on Q-radial distribution, to obtain the closed-form expressions. In the latter scenario, channel gain includes path loss attenuation and Rayleigh fading. For the complex channel models, a novel method is given to extract closed-form approximations. Then, two iterative algorithms are provided. Also, admission control algorithm is applied. Finally, simulation results are given to show the validity of our proposed algorithms.

Stability Analysis of Delta Operator Systems with Actuator Saturation by a Saturation-Dependent Lyapunov Function

This paper proposes the stability of delta operator systems subjected to actuator saturation by a saturation-dependent Lyapunov function. This saturation-dependent Lyapunov function captures the real-time information on the severity of actuator saturation in delta domain. Linear matrix inequalities-based methods are developed for analyzing the stability of the delta operator system. Numerical example is given to illustrate the effectiveness of the developed techniques.