Novel spreading codes for multicarrier code division multiple access based cognitive radio networks with sidelobe suppression

The deployment of multicarrier code division multiple access as the transmission scheme of the spectrum overlay based cognitive radio (CR) networks faces two challenging issues: (i) the need for spreading codes with arbitrary length and (ii) the interfering effect of the leaked power (due to spectral sidelobes) to the adjacent spectral band used by the primary system. To meet these challenges, we propose two novel complex spreading code sets. For this purpose, a cost function is defined as the ratio of the power leaked to the adjacent primary band to the power transmitted to the band allowed for CR operation. The cost function is shown to be convertible to a trace ratio problem. The two complex spreading code sets are determined by deploying two different standard solutions. The first is the conventional but approximate solution based on generalized eigenvalue decomposition (GEVD) method, and the other is an iterative algorithm that converges to the optimal solution and hence outperforms the GEVD based solution. Simulation results show that by a slight decrease in number of users, the code set yielded by iterative algorithm suppresses the leaked power to almost zero. The applicability of the proposed code sets in different scenarios is discussed. Copyright © 2012 John Wiley & Sons, Ltd.     

柔性机构动态可靠性分析的新方法

为了改善柔性机构动态可靠性分析的效率和精度,基于支持向量机SVM(Support Vector Machine)回归理论,提出了一种柔性机构动态可靠性分析高效率高精度的SVM回归极值法SREM(SVM Regression Extremum Method)。首先,介绍了柔性机构可靠性分析的基本理论;其次,融合蒙特卡洛法MC(Monte Carlo)和SVM回归理论,建立了柔性机构动态响应极值的代理模型,并利用代理模型进行柔性机构可靠性分析。最后,利用SREM法对柔性机构实例进行了可靠性分析,并与MC和人工神经网络ANN(Artificial Neural Networks)的分析结果进行比较。结果显示,在小样本情况下,进行柔性机构动态可靠性分析时,SREM的计算效率和计算精度都比ANN高;SREM的计算效率比MC大大提高,计算精度与MC相当。验证了在柔性机构可靠性分析中SREM的高效率和高精度,并证明了SREM在柔性机构可靠性分析中的可行性和有效行性。     

MC34063 DC/DC转换控制电路测试方法概述

目前,DC/DC转换器广泛应用于远程及数据通信、计算机、办公自动化设备、工业仪器仪表、军事、航天等领域,涉及到国民经济的各行各业。文章以其中有一定代表性的MC34063电路为例,扼要介绍其电特性和用其构成的升压电路的测试方法,并解析其测试原理和升压电路设计中的注意事项,对DC/DC转换器的分析测试和量产测试提供一些借鉴。     

Projected gradient descent based on soft thresholding in matrix completion

Matrix completion is the extension of compressed sensing. In compressed sensing, we solve the underdetermined equations using sparsity prior of the unknown signals. However, in matrix com- pletion, we solve the underdetermined equations based on sparsity prior in singular values set of the unknown matrix, which also calls low-rank prior of the unknown matrix. This paper firstly introduces basic concept of matrix completion, analyses the matrix suitably used in matrix completion, and shows that such matrix should satisfy two conditions： low rank and incoherence property. Then the paper provides three reconstruction algorithms commonly used in matrix completion： singular value thresholding algorithm, singular value projection, and atomic decomposition for minimum rank ap- proximation, puts forward their shortcoming to know the rank of original matrix. The Projected Gradient Descent based on Soft Thresholding （STPGD）, proposed in this paper predicts the rank of unknown matrix using soft thresholding, and iteratives based on projected gradient descent, thus it could estimate the rank of unknown matrix exactly with low computational complexity, this is verified by numerical experiments. We also analyze the convergence and computational complexity of the STPGD algorithm, point out this algorithm is guaranteed to converge, and analyse the number of it- erations needed to reach reconstruction error. Compared the computational complexity of the STPGD algorithm to other algorithms, we draw the conclusion that the STPGD algorithm not only reduces the computational complexity, but also improves the precision of the reconstruction solution.     

基于MC33035的永磁无刷直流电机控制器的设计

介绍了以MC33035为基础的电动车控制电路的设计方案。     

Monte‐Carlo Study of Triblock Copolymer/Homopolymer Blend Films

The morphologies of triblock copolymer/homopolymer blend films confined between two neutral hard walls were studied via MC simulations on a simple cubic lattice. For ABA/A and ABA/B blend films, the effects of φ_h (the volume fraction of the homopolymer) and M_h/M_b (the ratio of the molecular mass of the homopolymer to that of the corresponding blocks) on the morphologies were investigated in detail. For both ABA/A and ABA/B blend films, a higher φ_h or M_h/M_b would result in stronger macrophase separation between the triblock copolymer and homopolymer. For ABA/C blend films, M_h/M_b hardly influences the morphologies of homopolymer domains regardless of whether the homopolymer C is more compatible with block A or with block B. Compared to AB/A and AB/C blend films, the morphologies of ABA/A (or ABA/B) and ABA/C blend films are much more irregular. The simulated results in this work show good consistency with experiments and other simulations.

     

基于GPRS上的现代物流通信解决方案

针对传统的物流调度系统,提出了一种基于GPRS上的现代物流通信解决方案。利用成熟的GPS、GPRS全球定位技术和先进的第三方物流概念和Internet技术,通过计算机对数据的深层次分析,实现对车辆货物的及时掌握跟踪,及时调配,做出最优的路线规划,从而提高生产综合效益,该系统能监控第三方物流的货物购、运、调、存、管、加工和配送全过程。     

一种ZigBee硬件平台的设计与实现

选择MC9S08GB60和MC13192构建了一种实现ZigBee的硬件系统框架,并在此基础上阐述了电源电路、MC13192与MC9S08GB60接口电路和MC13192射频模块的详细设计:文章的最后介绍了硬件测试过程.     

一种联合均衡和多用户检测的SDCMA盲算法

该文提出了用于MC DS-CDMA系统中的两种SDCMA(最陡下降常模算法)盲检测方法,一种是SDCMA盲均衡算法,在此基础上,提出了另一种联合均衡和多用户检测的SDCMA盲算法。同时还将这两种算法与基于子空间的MMSE(最小均方误差)盲检测算法进行比较。仿真结果表明,这两种SDCMA算法的BER(误比特率)性能均优于子空间法,而且联合均衡和多用户检测的SDCMA盲算法利用同时对均衡权值向量和多用户检测器向量进行自适应更新,能较大程度地改善系统性能,是这3种盲算法中性能最佳的一个。     

提高高频雷达带宽的多载波技术研究

天波雷达工作在高频段,其工作带宽受电离层特性和人工信号干扰的限制,工程信号带宽一般只有十几千赫兹。利用多输入多输出(MIMO)原理,研究发射一组正交多载波调制的带宽为十几千赫兹的线性调频(LFM)信号照射目标,在接收端经匹配滤波和等效发射波束成形技术重建这一组回波信号成宽带信号,以增大雷达系统信号带宽。理论分析表明:在不考虑高频雷达多模多径情况下,发射N个频率间隔f_p=B的正交多载波调制LFM信号,在接收端采用匹配滤波和空时信号处理技术,将使接收信号带宽提高大约N倍。采用Watterson短波信道模型的仿真结果验证了理论分析的正确性。这表明在高频雷达多径环境不严重时,采用该方法可以提高雷达的距离分辨力。