On the outage probability‐constrained solutions for MIMO‐based cognitive radio systems: Achievable and tight Ergodic capacity bound

Two closed‐form solutions for the approximation bound in relation to resource allocation for multiple‐input multiple‐output (MIMO) ‐based cognitive radio systems are provided. The design problem is actualized in the underlay scenario for a single‐user strategy. The concentration is mainly on the Ergodic capacity constrained by an outage probability at the secondary receiver, regarding our imperfect knowledge of the interference channel at the transmitter. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Neutralizing interferences in two‐hop amplify‐and‐forward MIMO relay systems

In this paper, we present the interference neutralization technique for two‐hop multiple‐input multiple‐output (MIMO) relay systems. It enables multiple MIMO transmitters (sources) to simultaneously transmit independent data streams to their MIMO receivers (destinations) without mutual interferences, thereby improving spectral efficiency of the systems. To neutralize the mutual interferences using multiple amplify‐and‐forward (AF) MIMO relays, we establish the sufficient condition for the antenna configuration in the MIMO relay networks, and provide a filter design technique for the AF MIMO relays. The proposed method increases sum rates of the systems linearly with the number of transmitters participating in simultaneous transmission. To improve the sum rates further, this method is combined with transmit power allocation using the water‐filling algorithm. In addition, it is shown that by employing the minimum number of relays required to meet the sufficient condition, the system cost for the proposed method can be reduced without compromising the sum rate performance severely. Finally, simulation results successfully demonstrate that by exploiting radio resources such as frequency and time efficiently, the proposed method achieves a higher sum rate than the existing techniques based on interference avoidance. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

基于频谱感知的认知无线网络容量研究

动态频谱分配是认知无线电网络实现的关键所在,要实现动态频谱分配就必须快速准确的感知主用户的工作状况,感知时间的长短直接影响到认知无线网络的容量和对主用户的干扰程度,在主用户保护模式(PUP)和固定认知用户频谱利用率模式(CUS)下对认知无线网络容量与感知时间的关系进行了研究,仿真结果显示设计感知时间是非常重要的,同时,当感知时间超过单位时帧长度的5%后协同更多的认知用户与不协同对认知网络容量影响区别不大。     

基于隐马尔可夫模型的认知无线频谱切换方法

认知无线网络(cognitive radio network,CRN)中,为降低认知用户对授权用户干扰,需尽可能的减少频谱切换次数。提出了一种基于预测信道空时间(prediction of the channel idle time,PCIT)的认知无线动态频谱切换方法。该方法基于已知状态序列的隐马尔可夫模型(known-state sequence hidden Markov model,KSS-HMM),利用信道状态的历史信息预测信道未来空闲时间期望及传输数据包的数量,并给出了备选信道的选择方法,通过比较每个备选信道的传输数据量来选择最佳信道进行数据传输。仿真结果表明,与随机信道选择和传统选择方法相比,该方法能明显减少信道切换次数,同时提高了认知用户的吞吐量。     

基于车载通信网络的认知无线电信道分配技术的研究

车载通信网络的移动性对无线网络的信道分配提出了高要求,认知无线电技术能适应这一要求。将认知无线电的信道分配技术运用到车载通信网络中,根据实际交通状况对车载通信网络进行建模,主用户和认知用户分别实体化为无线网络用户及车载通信用户;运用协作最大化带宽和（CMSB）算法对认知用户进行信道分配。仿真分析结果表明在给定的车载通信网络模型下,CMSB能极大地优化网络吞吐量,并能保证一定的分配公平性。     

Robust hard decision combination scheme based on Kullback–Leibler divergence for cooperative spectrum sensing in cognitive radio

Cognitive radio (CR) network is a new, emerging research area because it has the ability to improve spectrum utilization by detecting and using vacant channels that are unused by licensed users. Reliable detection of the licensed user signal is a prerequisite for CR network to avoid interference to the licensed user. Cooperative spectrum sensing (CSS) is able to offer better sensing performance in comparison with individual sensing. However, CSS is vulnerable to attack from malicious users who falsify sensing data. In this paper, we propose a robust hard decision combination rule based on the Kullback–Leibler divergence (KL divergence) for CSS. The proposed scheme can achieve sensing performance similar to that of the optimal hard decision combination rule, the Chair–Varshney rule, while not requiring information on the signal‐to‐noise ratio. Furthermore, the proposed scheme can provide secure CSS against some common types of malicious users without any user identification step. Our simulation results prove the effectiveness of the proposed scheme. © 2012 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Observer‐based adaptive neural control of uncertain MIMO nonlinear systems with unknown control direction

This paper investigates adaptive neural network output feedback control for a class of uncertain multi‐input multi‐output (MIMO) nonlinear systems with an unknown sign of control gain matrix. Because the system states are not required to be available for measurement, an observer is designed to estimate the system states. In order to deal with the unknown sign of control gain matrix, the Nussbaum‐type function is utilized. By using neural network, we approximated the unknown nonlinear functions and perfectly avoided the controller singularity problem. The stability of the closed‐loop system is analyzed by using Lyapunov method. Theoretical results are illustrated through a simulation example. Copyright © 2012 John Wiley & Sons, Ltd.     

Transmit power allocation algorithm in cognitive radio MISO system based QPSK constellation

This paper considers a spectrum‐sharing cognitive radio (CR) multiple‐input–single‐output (MISO) system which consists of a secondary user transmitter (SU‐Tx) having multiple transmit antennas, K secondary user receivers (SU‐Rxs) each having a single antenna, and a primary user (PU) having a single antenna. The channel state information (CSI) for the links between SU‐Tx and SU‐Rxs are assumed to be perfectly known at the SU‐Tx. To ensure the quality of service (QoS) of PU and maximize channel capacity of SU, we formulate the channel capacity as a multiconstraint optimization problem and propose a power allocation algorithm based on QPSK constellation to solve the problem. Finally, numerical simulations are conducted to corroborate our theoretical results. It is shown that the proposed algorithm is capable of achieving a large channel capacity with fast convergence. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Complex two‐dimensional TNIPM for l1 norm‐based sparse optimization to collocated MIMO radar

In collocated multiple‐input multiple‐output (MIMO) radar, because of the sparse nature of the received signal in the three dimensions of range, angle, and Doppler, accurate estimates of range/angle/Doppler parameters can be achieved using a sparse signal recovery. In this paper, we develop a complex two‐dimensional truncated Newton interior point method (2D TNIPM) for l₁‐norm‐based sparse optimization. Because of the 2D sparse representation of received signal in collocated MIMO radar systems, the performance of proposed algorithm is investigated in order to estimate the target position and velocity. Simulation results show that the 2D TNIPM requires much lower computations compared to the 1D one. Also, it outperforms some other 2D algorithms in the estimation of range, angle, and Doppler parameters under low signal‐to‐noise ratios. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A new approach for flicker analysis using information‐theory‐based wavelet energy entropy

Flicker is one of the critical power quality disturbances seen in power distribution networks nowadays. Besides its effects on the human life, it causes malfunctioning and misoperation of sensitive electrical equipment. The measurement of the flicker level is defined in IEC 61000‐4‐15 standard by a flicker meter, which deals only with voltage signals and is not sufficient to understand the contribution of the load and background power systems separately. Therefore, in this letter we present a new approach to the evaluation of flicker characteristics in the light of multiresolution wavelet analysis and information‐theory‐based wavelet energy entropy analysis together. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A cluster‐based sequential cooperative spectrum sensing scheme utilizing reporting framework for cognitive radios

The cognitive radio (CR) technology is being considered as a novel approach for improving the spectrum utilization by detecting and using the vacant spectrum bands of licensed users. Cooperative spectrum sensing (CSS) is the most promising method for offering more reliable sensing performance compared to individual sensing. However, in a large CR network, CSS requires a huge number of sensing result transmissions from cognitive radio users (CUs) to the fusion center (FC), which can result in overhead traffic of the control channel and lack of power consumption of the CUs. In this paper, we propose a cluster‐based sequential cooperative spectrum sensing (SCSS) scheme utilizing a reporting framework to reduce the number of direct reports from CUs to FC while keeping similar sensing performance as the conventional CSS. By using the proposed scheme, the power consumption in the sensing process and the overhead of the control channel can be significantly reduced. Simulation proves the efficiency of the proposed scheme. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

An indirect adaptive pole‐placement control for MIMO discrete‐time stochastic systems

In this paper, an indirect adaptive pole‐placement control scheme for multi‐input multi‐output (MIMO) discrete‐time stochastic systems is developed. This control scheme combines a recursive least squares (RLS) estimation algorithm with pole‐placement control design to produce a control law with self‐tuning capability. A parametric model with a priori prediction outputs is adopted for modelling the controlled system. Then, a RLS estimation algorithm which applies the a posteriori prediction errors is employed to identify the parameters of the model. It is shown that the implementation of the estimation algorithm including a time‐varying inverse logarithm step size mechanism has an almost sure convergence. Further, an equivalent stochastic closed‐loop system is used here for constructing near supermartingales, allowing that the proposed control scheme facilitates the establishment of the adaptive pole‐placement control and prevents the closed‐loop control system from occurring unstable pole‐zero cancellation. An analysis is provided that this control scheme guarantees parameter estimation convergence and system stability in the mean squares sense almost surely. Simulation studies are also presented to validate the theoretical findings. Copyright © 2005 John Wiley & Sons, Ltd.     

Rejection of unknown periodic disturbances for continuous‐time MIMO systems with dynamic uncertainties

Rejection of unknown periodic disturbances in multi‐channel systems has several industrial applications that include aerospace, consumer electronics, and many other industries. This paper presents a design and analysis of an output‐feedback robust adaptive controller for multi‐input multi‐output continuous‐time systems in the presence of modeling errors and broadband output noise. The trade‐off between robust stability and performance improvement as well as practical design considerations for performance improvements are presented. It is demonstrated that proper shaping of the open‐loop plant singular values as well as over‐parameterizing the controller parametric model can significantly improve performance. Numerical simulations are performed to demonstrate the effectiveness of the proposed scheme. Copyright © 2016 John Wiley & Sons, Ltd.     

Robust model order reduction technique for MIMO systems via ANN‐LMI‐based state residualization

Even though model order reduction (MOR) techniques for linear dynamical systems are developed rather properly, there are still quite a lot of issues to be considered. This paper addresses a novel MOR technique for multi‐input multi‐output system with dominant eigenvalue preservation, which leads to controller cost minimization. The new technique is formulated based on an artificial neural network (ANN) prediction of an upper triangular form of the system state matrix A. Using the new system state matrix along with the linear matrix inequality (LMI) optimization method, a permutation matrix is obtained which leads to the new formulation of the complete system considered for MOR. Utilizing the non‐projection state residualization technique, a reduced model order is obtained. The proposed ANN‐LMI‐based MOR method is compared with well‐known reduction techniques such as the balanced Schur decomposition, proper orthogonal decomposition (POD), and state elimination through balanced realization. Copyright © 2010 John Wiley & Sons, Ltd.     

Robust learning controller design for MIMO stochastic discrete‐time systems: An H∞‐based approach

This paper is devoted to designing iterative learning control (ILC) for multiple‐input multiple‐output discrete‐time systems that are subject to random disturbances varying from iteration to iteration. Using the super‐vector approach to ILC, statistical expressions are presented for both expectation and variance of the tracking error, and time‐domain conditions are developed to ensure their asymptotic stability and monotonic convergence. It shows that time‐domain conditions can be tied together with an H_∞‐based condition in the frequency domain by considering the properties of block Toeplitz matrices. This makes it possible to apply the linear matrix inequality technique to describe the convergence conditions and to obtain formulas for the control law design. Furthermore, the H_∞‐based approach is shown applicable to ILC design regardless of the system relative degree, which can also be used to address issues of model uncertainty. For a class of systems with a relative degree of one, simulation tests are provided to illustrate the effectiveness of the H_∞‐based approach to robust ILC design. Copyright © 2011 John Wiley & Sons, Ltd.     

Sliding mode disturbance observer‐based adaptive control for uncertain MIMO nonlinear systems with dead‐zone

In this paper, an adaptive integral sliding mode control (ISMC) scheme is developed for a class of uncertain multi‐input and multi‐output nonlinear systems with unknown external disturbance, system uncertainty, and dead‐zone. The research is motivated by the fact that the ISMC scheme against unknown external disturbance and system uncertainty is very important for multi‐input and multi‐output nonlinear systems. The system uncertainty, the unknown external disturbance, and the effect of dead‐zone are integrated as a compounded disturbance, which is well estimated using a sliding mode disturbance observer (SMDO). Then, the adaptive ISMC based on the designed SMDO is presented to guarantee the satisfactory tracking performance in the presence of system uncertainty, external disturbance, and dead‐zone. Finally, the designed adaptive ISMC strategy based on SMDO is applied to the attitude control of the near space vehicle, and simulation results are presented to illustrate the effectiveness of the proposed adaptive ISMC scheme using the SMDO. Copyright © 2016 John Wiley & Sons, Ltd.     

An observer‐based controller for a class of polynomial fuzzy systems with disturbance

In this paper, a new observer‐based controller for a class of polynomial fuzzy systems with disturbance is proposed. First, by some appropriate equivalence transformation of the polynomial fuzzy model, the first output‐sized states can be obtained directly from the output, which eventually enables us to obtain the feedback control gain and observer‐related parameters together without considering the so‐called separation principle. Second, with the disturbance in mind, a PI‐type observer is suggested. Finally, the sum of squares for the stability of the closed‐loop observer‐based control system is provided. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A convex optimization approach to adaptive stabilization of discrete‐time LTI systems with polytopic uncertainties

This paper suggests a simple convex optimization approach to state‐feedback adaptive stabilization problem for a class of discrete‐time LTI systems subject to polytopic uncertainties. The proposed method relies on estimating the uncertain parameters by solving an online optimization at each time step, such as a linear or quadratic programming, and then, on tuning the control law with that information, which can be conceptually viewed as a kind of gain‐scheduling or indirect adaptive control. Specifically, an admissible domain of stabilizing state‐feedback gain matrices is designed offline by means of linear matrix inequality problems, and based on the online estimation of the uncertain parameters, the state‐feedback gain matrix is calculated over the set of stabilizing feedback gains. The proposed stabilization algorithm guarantees the asymptotic stability of the overall closed‐loop control system. An example is given to show the effectiveness of the proposed approach. Copyright © 2014 John Wiley & Sons, Ltd.     

Robust stability analysis and improved design of phase‐locked loops with non‐monotonic nonlinearities: LMI‐based approach

Due to nonlinear nature of several phase detectors, linear approximation method often leads to performance degradation in many phase‐locked loops (PLLs), particularly when the phase errors are sufficiently large. A third or higher order PLL, in spite of the ability to track a wider variety of inputs and having higher operating‐frequency range, requires more design attention in order to ensure stable tracking. In this work, with the nonlinearities inserted into the system's model, suitable criteria that take into account the nonlinearities' non‐monotonicity, sector and slope bounds are employed to establish robust stability conditions. The result is applicable to any PLLs without order and type restrictions. For Type‐1 PLLs, the resulting condition can be used to search for the maximum stable loop gain, which is also linked to the lock‐in range of the system. In the later part of this work, the focus is devoted towards designing PLLs with high lock‐in range, which is performed via mixing the proposed method with H _∞ synthesis. The searches for the parameters in both PLL analysis and design are expressed in terms of convex linear matrix inequalities, which are computationally tractable. To illustrate the improvement introduced via this approach, several numerical examples and simulations are included with comparisons over conventional methods. Copyright © 2017John Wiley & Sons, Ltd.     

Power‐efficient burst‐mode RF transmitter based on reference‐adaptive multilevel pulse‐width modulation

Burst‐mode operation of power amplifier (PA) based on multilevel pulse‐width modulation (MPWM) has been frequently discussed as a potential solution to achieve higher efficiency in radio frequency (RF) transmitters. In this paper, a novel multilevel PWM modulator is proposed that utilizes adaptive triangular reference waveforms. As compared with conventional MPWM modulators, the proposed architecture provides significant wider design space such that the efficiency of system can be effectively optimized. A general transmitter architecture based on the proposed concept is analyzed in terms of power efficiency. Efficiency optimization procedures are presented according to input magnitude statistics. Based on the proposed modulator, an optimized 2.4‐GHz RF transmitter is designed in a 0.18‐μm complementary metal‐oxide‐semiconductor (CMOS) process. The circuit‐level simulations show that it delivers 25.8‐dBm peak output power with 46.1% peak efficiency. For a 20‐MHz worldwide interoperability for microwave access (WiMAX) signal with 8.5‐dB peak‐to‐average‐power ratio (PAPR), this transmitter achieves 28.8% (average) efficiency at 17.3‐dBm (average) output power with an error vector magnitude (EVM) of 2.97% rms.