基于复小波包的多载波CDMA系统在Nakagami-m衰落信道下的性能

在分析多载波码分多址(MC-CDMA)的原理基础上, 提出了一种基于复小波包的MC-CDMA系统. 同时, 研究了该系统分别采用等增益合并和最大比合并时在Nakagami-m衰落信道下的性能; 并推导了相应的误码率表达式. 该系统能克服通常MC-CDMA系统由于插入循环前缀(CP)所带来的频谱效率的下降. 理论分析和仿真结果表明:该系统要优于通常MC-CDMA系统和基于实小波包的MC-CDMA系统, 有着优越的抗多径衰落和多址干扰能力,而且该系统也优于采用CP的通常MC-CDMA系统.     

MIMO-OFDM系统中快衰落信道的估计

A channel estimation approach for orthogonal frequency division multiplexing with multiple-input and multipleoutput （MIMO-OFDM） in rapid fading channels is proposed. This approach combines the advantages of an optimal training sequence based least-square （OLS） algorithm and an expectation-maximization （EM） algorithm. The channels at the training blocks are estimated using an estimator based on the OLS algorithm. To compensate for the fast Rayleigh fading at the data blocks, a time domain based Gaussian interpolation filter is presented. Furthermore, an EM algorithm is introduced to improve the performance of channel estimation by a few iterations. Simulations show that this channel estimation approach can effectively track rapid channel variation.     

Time-domain clustered transmit power adaptation for OFDM system in fading channels

INTRODUCTION The growing demand for wireless multimedia services requires reliable and high data rate commu- nications over a wireless channel. However, the reli- ability is significantly limited by the ability of com- bating the intersymbol interference (ISI) introduced by the time dispersive nature of the wireless channel. Multicarrier transmission systems, especially OFDM systems, have aroused great interest in recent years as a potential solution to overcome ISI (Hanzo et al., 200…     

多输入多输出无线光通信系统中的自适应调制技术

在基于强度调制、直接检测的多输入多输出无线光通信系统中,为了保证发射信号非负特性,提出一种基于直流偏置的自适应调制技术,并且利用奇异值分解将多输入多输出信道转换为并行信道。此外,提出一种基于 QR 分解、逐次干扰消除的自适应调制技术。在目标误比特率性能条件下,利用 QR 分解、逐次干扰消除的特性将多输入多输出信道等效为并行信道。根据最大化可达速率的优化目标,最优地给各个子信道分配功率。仿真结果表明所提出的2种自适应调制方法在保证误比特率性能和平均发射光功率恒定的前提下,有效地提高了系统的传输速率。这2种自适应调制技术在利用多输入多输出技术空分复用增益的同时,进一步提高了无线光通信系统的频谱利用率。     

使用混沌调制方法实现交流电机电磁干扰抑制

Instead of avoiding occurrence of chaos in motor drives,chaos is positively utilized in this paper.A new chaotic pulse width modulation (PWM) scheme is proposed and implemented for AC motors,which functions to significantly suppress harmonic peaks and hence acoustic noise.The key is to employ the Chua's circuit for generating a desired chaotic sequence.By using a practical induction motor,computer simulation and experimental results verify that the chaotic PWM has advantages of harmonic peak suppression and simple hardware implementation over the conventional PWM and random PWM.     

应用于无线传感网频率合成器的0.5V低电压鉴频鉴相器设计

基于0.13μm CMOS技术设计了一个应用于无线传感网频率合成器、电源电压为0.5 V的鉴频鉴相器.它的功能是比较输入信号的频率和相位差,并输出一个与该差值成比例的电压.因电源电压是0.5 V,所以该电路采用低阈值晶体管.为了增大相位误差的检测范围和提高最大工作频率,该电路采用了脉冲锁存的结构.当输入信号频率为2 M...     

Acute phase reactants, challenge in the near future of animal production and veterinary medicine

INTRODUCTION The systemic acute phase reaction known to occur on infection, inflammation, trauma, burns, ma- lignancies and tissue damage in general, has been studied by scientists from various disciplines. In the last decade, emphasis has been laid on application of blood tests for acute phase reactants to monitor ani-mal health in general, as well as for human patients suffering from specified classes of diseases (Gruys et al., 2005). However, basic mechanistic patterns as- sociated wit…     

Taking teachers' continuous professional development (CPD) beyond reflection: adding shared sense-making and collaborative engagement for professional renewal

While reflection continues to be promoted as a central feature of teachers' continuous professional development (CPD) activities in Scotland and elsewhere, a wider debate across professions and national boundaries has opened as to how reflection might be re-conceptualised to restore its social and critical dimensions. This paper seeks to contribute to this debate, arguing that drawing ideas from the literatures on both reflection and communities of practice provides a sounder foundation upon which to build CPD activities that are likely to support professional renewal than that provided by either concept by itself. In particular, the authors draw on their participation in a number of Scottish research and development projects to focus on shared sense-making and collaborative engagement as activities that can enhance reflection. The paper concludes with a set of design principles for CPD activities.     

加性高斯白噪声信道中典型信号的信噪比估计

信噪比是衡量通信质量的重要参数,正确估计出信号的信噪比能为后续信号的研究提供重要信息。现结合多种信噪比估计的方法,在仅需调制方式的先验信息下,对不同种类的调制信号有针对性地进行信噪比估计,能够有效估计6种典型信号。其中包括调幅信号AM和2ASK,调相信号BPSK、QPSK,调频信号MSK、2FSK。仿真实验表明,该法对信噪比在0¹8dB的信号能有效进行估计,估计偏差在0.5dB以内。     

用于三相PWM并网逆变器的改进型幅相控制方法

In this paper, a vector regulating principle of the phase and amplitude control （ PAC ） method for three-phase grid-connected inverters is presented. To solve the problem of heavy inrush current and slow dynamic response when system starts up, the starting voltage prediction control and the current feed-forward control are proposed and used, which improve the dynamic performance of the system in the PAC. The experimental results carried out on a three-phase grid-connected inverter proved the validity of the proposed method.     

新型驱动相位控制技术提高硅微机械陀螺仪稳定性的方法

为了增强硅微机械陀螺仪的零偏稳定性,减少其受温度的影响,从数字信号处理的角度提出了一种提高驱动模态驱动相位精确度的方法.通过零偏信号生成的原理,分析出驱动相位的偏差是影响其性能的主要因素.采用基于FPGA数字信号处理实现方式的锁相环闭环控制原理,实现了对驱动相位的精确控制.给出了一种抑制相位误差的解调方法.对比模拟电路,新型数字电路很好地抑制了零偏的漂移,零偏稳定性由60°/h 提高到19°/h.新的数字控制方法显著提高了对驱动相位的控制精度,达到了增强零偏稳定性的目的.     

在Kerr媒质中J-C模型的测量相位算符的涨落和压缩

By using the theory of measured phase operator proposed by Barnett and Pegg,dynamic properties of phase of a field are studied.The time evolution and squeezing of measured phase opoerators of a coherent field ineracting with a two-level atom in the cavity with or without the Kerr medium are investigated.The influences of virtual cavity field on squeezing of measured phase operator are studied.Our numerical results show that the squeezing effects are clearly influenced Kerr medium parameters,the field intensity,and the detuning.Moreover,the influence of the virtual-photon field makes more quantum noise in the evolution of measured phase opoerators.     

Quantitative feedback theory and zero phase error tracking control combined robust control for radar truck leveling simulator

Radar leveling system is the key equipment for improving the radar mobility and survival capability. A combined quantitative feedback theory(QFT)controller is designed for the radar truck leveling simulator in this paper, which suffers from strong nonlinearities and system parameter uncertainties. QFT can reduce the plant uncertainties and stabilize the system, but it fails to obtain high-precision tracking. This drawback can be solved by a robust QFT control scheme based on zero phase error tracking control(ZPETC)compensation. The combined controller not only possesses high robustness, but greatly improves the system performance. To verify the effectiveness and the potential of the proposed controller, a series of experiments have been carried out. Experimental results have demonstrated its robustness against a large range of parameters variation and high tracking precision performance, as well as its capability of restraining the load coupling among channels. The combined QFT controller can drive the radar truck leveling platform accurately, quickly and stably.     

Voice over distance: a case of podcasting for learning in online teacher education

This paper reports on a case study of an online pre-service teacher education course in a New Zealand university aimed at exploring the potential of student-generated podcasts as a form of interactive formative assessment at a distance. The study was part of a wider two-year funded project with the overall goal of documenting, developing, and disseminating effective and innovative e-learning practice. Findings from lecturer and tutor interviews, student focus group (FG) discussion, and course evaluations indicate that the podcasting task provided opportunities for the course lecturer, tutors, and students to learn and share ideas with one another. The experience empowered students to develop the skills and confidence to initiate more independent inquiry into technologies to support their pedagogical purposes. The study contributes to a better understanding of the skills, dispositions, and knowledge needed to prepare teacher candidates for teaching-learning contexts where information and communication technologies are increasingly pivotal.