Characterization of Forced Vibration for Difference Inclusions: A Lyapunov Approach

A Lyapunov approach to the characterization of forced vibration for continuous-time systems was recently proposed in. The objective of this paper is to derive counterpart results for discrete-time systems. The class of oscillatory input signals to be considered include sinusoidal signals, multitone signals, and periodic signals which can be described as the output of an autonomous system. The Lyapunov approach is developed for linear systems, homogeneous systems (difference inclusions), and nonlinear systems (difference inclusions), respectively. It is established that the steady-state gain can be arbitrarily closely characterized with Lyapunov functions if the output response converges exponentially to the steady state. We also evaluate other output measures such as the peak of the transient response and the convergence rate. Applying the results to linear difference inclusions, optimization problems with linear matrix inequality constraints can be formulated for the purpose of estimating the output measures. This paper's results can be readily applied to the evaluation of frequency responses of general nonlinear and uncertain systems by restricting the inputs to sinusoidal signals. Similar to continuous-time systems, it is observed that the peak of the frequency response can be strictly larger than the gain for a linear difference inclusion.     

大气信道下窄线宽激光器对相干通信系统性能影响研究

在空间下行相干激光通信系统中,激光器的线宽大小会影响通信系统的性能,而窄线宽激光器能有效降低激光器线宽引起的激光器相位噪声,目前已经成为相干激光通信系统的首选。光信号在大气信道传输时,大气湍流会引起光信号强度和相位的波动,从而进一步影响系统的通信性能。针对上述问题,基于四相移键控(Quadri Phase Shift Keying, QPSK)通信系统的工作原理,进一步考虑窄线宽激光器线宽和大气湍流引起的光信号强度和相位的波动,给出了空间下行QPSK通信系统误码率模型。并基于该模型,数值仿真分析了窄线宽激光器对空间下行相干激光通信系统性能的影响。结果表明：大气湍流不仅严重影响系统性能,也会弱化激光器线宽对系统性能的影响。而对于大气湍流影响而言,其引起的相位波动要大于光强波动的影响。此外,随着通信速率增大,激光器线宽对于系统性能影响也会随之降低。文中对于空间下行相干激光通信系统的优化设计和调试具有一定的实际参考意义。     

CMA自适应阵列在CDMA通信系统的应用

由于CDMA(Code Division Multiple Access)通信系统实施了功率控制，在基带不能直接用CMA进行自适应阵列的波束形成．通过分析CDMA系统的特点，我们提出在接收信号解扩后再应用CMA进行波束形成．这种新的波束形成方法不仅为CMA自适应阵列在CDMA系统中的应用提供了一种途径，而且还能防止CMA收敛到错误信号上，从而提高系统的可靠性．仿真结果表明，与全向天线系统相比，采用CMA自适应阵列的系统性能有了很大的改善，系统的容量得到成倍的增加．在强干扰情况下，虽然CMA的干扰方向信号抑制效应变弱，但其性能改善仍然十分明显．     

基于目标照明回光的瞄准误差修正方法精度分析及实验验证

激光发射系统通常受到瞄准误差的影响,使得发射光束的中心偏离靶目标,造成能量传输损失和系统性能下降。激光对目标照明后的散射回光信号可以反映瞄准误差的信息,通过对散射回光信号的测量可以对瞄准误差进行修正来提高激光发射系统的瞄准性能。研究了一种基于目标照明回光的瞄准误差修正方法。利用目标回光信息与瞄准误差的关系,通过随机并行梯度下降(SPGD)算法对瞄准误差进行校正,分析了影响瞄准误差校正精度的因素。实验数据验证了理论分析结果。     

Disturbance Response Techniques for Digital Control Systems

An adequate disturbance response is important to obtain good regulation in automatic control systems. This paper considers the form of the disturbance response for variable digital control systems with proportional-plus-integral feedback, and derives the relationship between the system responses to both reference and disturbance signals. The choice of optimum parameters is considered, and it is shown that good system response for both reference and disturbance signals can readily be obtained for the case of closed-loop control with complete feedback.     

Toeplitz properties of the block matrices encountered in theprocessing of spatiotemporal signals

Various signal processing applications, such as system identification, FIR (finite impulse response) Wiener filtering, linear prediction, and spectral estimation, are known to lead to the solution of Toeplitz systems for the case of one-dimensional signals and to Toeplitz-block Toeplitz systems for the case of two-dimensional signals. The authors investigate such systems for the case of L-dimensional signals with L>2 and emphasize their block and persymmetrical nature. Such important characteristics allow the use of fast algorithms for signals of any dimension. The case of three-dimensional signals is treated in detail not only because it is of special interest for video applications, but also because the reasoning used for this case can be straightforwardly applied to higher-dimension signals     

基于内存反射光纤网络的分布式测控系统

针对某型红外导引头综合测试性能测试的需求,以分布式控制系统为模型,构建一种基于内存反射光纤网络的红外导引头测控系统.利用内存反射网的高速和实时性,结合目标模拟器和三轴转台控制单元,能够实时测量导引头的数字、模拟、LVDS等信号,分析评估导引头的综合性能指标.     

Design and analysis of an optimal controller for parallel multi-inverter systems

Optimal control methodology is applied to the design of the feedback loops of a multi-inverter uninterruptible power supplies system. The control signals thus obtained will minimize a performance index, which is a function of the output voltage error, the inductor currents of all inverters and the reference signals. This enables the controller to achieve the desired objectives like minimization of the circulating current and reduction of error of the output voltage. The robustness of the controller has also been investigated. Through frequency-domain analysis, it is shown that variations in the number of paralleled inverters in the system have only small influence on the performance of the system. Therefore, the optimal controller designed for a fixed number of inverters can also work well in systems with variable number of paralleled inverters. Three experimental 110 Vac/1.1 KVA inverters are built and paralleled to verify the analysis and theoretical predictions.     

MIMO-assisted space-code-division multiple-access: linear detectors and performance over multipath fading channels

In this contribution, we propose and investigate a multiple-input-multiple-output space-division, code-division multiple-access (MIMO SCDMA) scheme. The main objective is to improve the capacity of the existing direct-sequence (DS)-CDMA systems, for example, for supporting an increased number of users, by deploying multiple transmit and receive antennas in the corresponding systems and by using some advanced transmission and detection algorithms. In the proposed MIMO SCDMA system, each user can be distinguished jointly by its spreading code signature and its unique channel impulse response (CIR) transfer function referred to as spatial signature. Hence, the number of users might be supported by the MIMO SCDMA system and the corresponding achievable performance are determined by the degrees of freedom provided by both the code signatures and the spatial signatures, as well as by how efficiently the degrees of freedom are exploited. Specifically, the number of users supported by the proposed MIMO SCDMA can be significantly higher than the number of chips per bit, owing to the employment of space-division. In this contribution, space-time spreading is employed for configuring the transmitted signals. Three types of low-complexity linear detectors, namely, correlation, decorrelating, and minimum mean-square error (MMSE) are considered for detecting the MIMO SCDMA signals. The bit-error rate performance of the MIMO SCDMA system associated with these linear detectors are evaluated by simulations, when assuming that the MIMO SCDMA signals are transmitted over multipath Rayleigh-fading channels. Our study and simulation results show that MIMO SCDMA assisted by multiuser detection is capable of facilitating joint space-time despreading, multipath combining, and receiver diversity combining, while simultaneously suppressing the multiuser interfering signals.     

合作式MIMO雷达通信一体化系统的检测与互信息增益

本文研究合作式多输入多输出（Multiple-input multiple-output, MIMO）雷达通信一体化系统的性能,雷达系统和通信系统在共存的基础上相互合作。一方面,通信端将信息与雷达端共享,则源自雷达发射机和通信发射机的目标回波都被利用起来以完成雷达任务,一体化系统可等效为主被动混合式的MIMO雷达系统,有利于提高雷达方面的性能。另一方面,雷达端将信息与通信端共享,则在传统通信基础上,经雷达目标反射的通信信号也可被加以利用,完成通信任务,有利于提高通信方面的性能。本文以雷达目标检测概率和通信互信息为例,推导雷达系统和通信系统的性能,分析表明合作给MIMO雷达通信一体化系统中雷达端和通信端都带来了性能提升。进一步,针对功率有限的系统,讨论合作式MIMO一体化系统的功率分配问题,并仿真得到了最优的功率分配方式。      

Optimal control at energy performance index of the mobile robots following dynamically created trajectories

In practice, the problem of motion control of the wheeled mobile robots is often neglected. Wheeled mobile robots are strongly nonlinear systems and restricted by non-holonomic constraints. Motion control of such systems is not trivial task and usage of non-optimal control signals can lead to deterioration of the overall robot system's performance. In case of autonomous application of the mobile robots all parts of its control system should work perfectly. The paper presents the theory and application of the optimal control method at the energy performance index towards motion control of the two-wheeled mobile robot during the realisation of complex, dynamically created trajectories. With the use of the proposed control method the two-wheeled mobile robot can realise effectively the desired trajectory, which is generated ad-hoc by the navigation system of the robot. Thus the proposed method can be used for motion control of autonomous or semi-autonomous wheeled mobile robots. The presented results of both computer simulations and experiments indicate that the proposed method works effectively from the point of view of the motion control of two-wheeled mobile robot. Movement of the mobile robot appeared reliable and predictable during all the tests.     

Precise onset detection of human motor responses using a whiteningfilter and the log-likelihood-ratio test

Investigation of the human motor system frequently requires precise determination of the motor response onset indicating the time of movement initiation (e.g., in reaction time experiments). This paper presents a new model-based algorithm for computerized response onset detection in kinematic signals (e.g., joint angle). The response onset is identified as an abrupt change in the (time-varying) parameters of a statistical process model adapted to the measured signal. The accuracy of the algorithm is assessed by statistical simulations, and the performance of the method is compared to the performance of conventional onset detection methods using simulated as well as real kinematic signals. Results show that onset detection can substantially be improved by including a priori knowledge on the physiological background of the measured signals to the decision process.     

Design of optimal-control systems with prescribed closed-loop poles

A new design procedure for linear systems is proposed to find the feedback vector and the weighting matrix of a quadratic performance index, which can be directly determined by the characteristic equations of the open- and closed-loop system, in order that the performance index is minimised and that the closed-loop system can achieve a set of prescribed poles.     

雷达编码信号相位抖动抗主动欺骗干扰

抗干扰雷达长期以来是雷达领域的研究热点,数字射频存储器（Digital Radio Frequency Memory, DRFM）技术通过转发最大程度模拟真实目标信号的欺骗干扰信号,对传统抗干扰雷达带来挑战。本文针对脉冲多普勒（Pulse Doppler, PD）雷达提出一种抗DRFM转发式干扰方法,该方法通过对发射波形相位抖动调制,在保留雷达发射的脉冲相干性的同时,使雷达接收机在DRFM干扰设备没有对雷达发射信号完全接收转发的情况下,具有一定的抗欺骗干扰能力。仿真结果表明,通过提高相位调制幅度与调制单元数,可以有效提高真假目标辨别概率,同时,相位抖动使信号的峰值旁瓣电平（peak sidelobe level,PSL）提升和雷达的杂波抑制能力降低可控。     

Symbol timing estimation with CPM modulation

Symbol timing in continuous phase modulated signals is investigated making use of maximum likelihood estimation methods. Nondata-aided algorithms are proposed with a feedforward structure. They are suitable for digital implementation and can be employed with either full or partial response signaling. Multilevel symbol alphabets are allowed and the modulation index may be arbitrary. The performance is assessed by analysis and simulation. It turns out that full response schemes are comparatively easier to synchronize. Difficulties arise with partial response signaling especially with long frequency pulses     

Detection of clipped code-division multiplexed signals

Code-division multiplexing (CDM) is a robust transmission scheme recently adopted for satellite multimedia broadcasting systems. A drawback of CDM is its high peak-to-average power ratio, which can be reduced by clipping the baseband CDM signal. However, clipping introduces in-band noise that may considerably degrade system performance. Proposed is an iterative decision-directed technique for detecting clipped CDM signals. The performance of the algorithm is studied by means of computer simulation. Simulation results show that the proposed technique can provide significant performance improvement compared to a conventional (linear) detection of clipped CDM signals.     

Probability of error analysis of digital partial responsecontinuous phase modulation with two-bit differential detection andoffset receiver diversity in fast Rayleigh fading channels

The performance of constant envelope digital partial response continuous phase modulation (PRCPM) with two-bit differential detection and offset receiver diversity is theoretically analyzed in fast Rayleigh fading channels. A simple closed-form expression for the probability of error is derived and evaluated for cases of practical interest to researchers and designers of land mobile radio systems. It is shown that the dynamic bit error rate (BER) performance is considerably improved using the offset diversity scheme. Thus, many PRCPM signals having a compact power spectrum can be used in future digital mobile radio systems     

Joint Estimation of Time Delay and Clock Error in the Incoherent Reception Systems

The assumption that observed signals are ideally received is commonly used in the literature on time-delay estimation. However, for practical digital receivers, the received radio-frequency signals are usually downconverted to the baseband and digitized by analog-to-digital converters. Because inaccurate and unstable system clocks are used, frequency and phase offsets are usually induced by the frequency-mixing procedure, whereas a time stretch may ensue from the sampling procedure. The aforementioned problems are almost inevitable for incoherent reception systems. Therefore, the neglect of imperfect reception for incoherent systems may reduce the performance of conventional time-delay estimation methods. In this paper, employing refined signal models developed specifically for incoherent time-delay estimation in active and passive systems, the corresponding joint maximum likelihood estimates of time delay and system-clock frequency error are proposed. The Cramér–Rao lower bounds (CRLBs) on time-delay and clock frequency error estimations are also derived. The performance of the proposed time-delay estimators can be improved for frequency/phase offsets and time stretches, approaching the performance of the CRLBs in scenarios of moderate and high signal-to-noise ratios. Furthermore, both CRLBs analysis and simulation results verify that the accuracy of the proposed time-delay estimator is unaffected by the performance of the system clock in moderate scenarios.     

Simulation of communication systems

When both a complex system and a complex channel model are encountered, the result is typically a design or analysis problem that cannot be solved using traditional (pencil and paper) mathematical analysis. Computer-aided techniques, which usually involve some level of numerical simulation, can be a very valuable tool in these situations. The purpose of this article is to provide a tutorial review of some of the basic techniques of communication system simulation. The authors consider the basic techniques used to represent signals, generate signals, and model linear systems, nonlinear systems, and time-varying systems within a simulation. They consider the important problem of using a simulation to estimate the performance of a communication system