基于MIMO-DFE的BLAST接收机的差错传递控制的研究

近期对于BLAST(Bell Laboratories Layered space-time)的研究从平坦衰落信道转向频率选择性衰落信道,基于MIMO-DFE(Multiple-Input-Multiple-Output Decision Feedback Equalizer)的接收机结构因此受到了广泛的关注.然而由于这类接收机本身的反馈结构,性能可能会由于差错传递而大大下降.本文将传统判决反馈均衡器的差错传递控制方法推广到多入多出(MIMO)系统中,仿真结果表明,本文提出的带差错传递控制的接收机能够有效控制差错传递.     

基于连续干扰消除的超奈奎斯特信号迭代接收技术

为了消除超奈奎斯特(FTN)调制技术引入的干扰,设计了基于连续干扰消除(SIC)的Tur-bo迭代均衡接收机.对于单载波FTN系统,首先建立了FTN信号等效模型,然后接收机根据等效模型和译码器输出的软信息重建干扰,并通过多次连续干扰消除和译码逐步消除,具有较低的复杂度.同样地,在多载波FTN系统中,根据译码器输出的软信息和成型脉冲的时频特性重建引入的干扰并通过多次迭代给予消除.仿真表明,在加速因子不是太小时,基于SIC-Turbo均衡的接收机能够有效消除干扰,可获得近似正交传输时的误码性能.     

基于贝叶斯网络的测试性分层建模方法

针对目前考虑不确定因素的测试性模型存在建模难度高、结构复杂、层次化建模困难、学习能力弱、不确定信息表达形式差的问题,面向电子设备提出了一种基于贝叶斯网络的测试性分层建模方法.以原有的贝叶斯网络模型与多信号流图模型为研究对象,对二者的参数、结构特点及优势短板进行分析,根据二者的互补性与测试性建模需求对贝叶斯网络模型进行改进.模型以故障、信号关系替代故障、测试关系,以信号节点间的连接表征故障传递,利用电路结构与层次划分确定模型结构,采用贝叶斯方法确立模型参数,运用贝叶斯网络推理能力对测试性指标进行计算.以放大滤波电路为例建立模型,通过模型计算测试性指标,并进行了证据处理测试,通过对比多信号模型可知,模型测试性指标计算准确、证据处理能力强,验证了建模方法的有效性与实用性.     

基于肖特基二极管的275 GHz三倍频器研制

为达到接收机中550 GHz混频器前端本振源的输出功率,对核心器件倍频器进行了研究.采用固态电子器件的方式设计并实现了275 GHz非平衡式三倍频器.通过建立理想倍频器电路模型,分析了肖特基二极管管芯参数对整体倍频器性能的影响,并对电路中等效电容、电感值及输入输出匹配端阻抗和相位进行了优化设计,以提升带外抑制特性和倍频...     

典型目标的BRDF实验室测量与模型验证

通过研究典型目标双向反射分布函数实验室测量与建模的方法分析目标的散射特性.给出F4(聚四氟乙烯)粉压制板及所测样品的反射光强度,通过经标定过的反射标准板传递,在半球空间内计算出样品在红外(1.06μm)波段的双向反射分布函数.根据五参数半经验统计模型和遗传算法,对各样片的BRDF进行了优化建模.按照模拟实验数据的标准均方误差最小的标准选择了模型参数.并将实验测量结果与模型输出进行了比对.结果表明该方法是分析目标散射特性的可行性方法.     

密码学原语中信任传递语义研究

以可信计算和信任管理为背景,考察密码学原语中所包含的信任传递语义,进而借助于目前较为成熟的密码学理论为信任传递机理进行建模,提出了信任传递语义模型的雏形,分析了多种典型数字签名原语中的信任传递语义.分析结果表明所提模型具有很强的概括能力.最后,展望了该模型在IP 网络信任管理系统设计及分析中的潜在应用.     

基于多面无相位近场数据的电磁干扰源等效建模

针对现有无相位近场数据的偶极子建模很难精确对干扰源进行等效的问题,对现有无相位近场数据的干扰源等效建模中所采用的双面迭代方法进行了改进,改进方法主要是采用2个以上不同高度的磁场幅度数据;对双面迭代方法中平面的选择以及改进方法中平面数量和起始面的选择进行了讨论;以干扰源辐射磁场重构的均方根误差(Root Mean Square Error, RMSE)作为偶极子建模准确度评价依据,与现有双面迭代方法及其他优化方法等效建模出的偶极子模型进行了对比验证,对比结果显示该改进方法具有更高的准确度。     

线性预编码OFDM系统的迭代接收机

线性预编码是OFDM系统在频率选择性衰落信道中利用频率分集的有效方法.为了进一步提高性能,本文提出了一种线性预编码OFDM系统的迭代接收机,该迭代接收机采用基于线性最小均方误差准则(LMMSE)的turbo均衡算法及其简化方法,具有很低的计算复杂度.本文同时还提出通过使用长度不小于等效离散时间信道的时延扩展长度的线性预编码器和迭代接收机,可获得完全的频率分集增益.仿真表明本文提出的方法在多径干扰严重的信道条件下的误码率性能接近AWGN下界.     

基于扩展路径识别算法的水声OFDM系统低复杂度迭代稀疏信道估计

移动OFDM水声通信系统中,基于压缩感知的稀疏信道估计方法计算量较大,不适用于实时通信.针对这一问题,该文基于一致多普勒信道模型提出一种扩展路径识别(GPI)算法.该方法首先使用信道多普勒扩展矩阵构造等效发射序列,将多普勒信道转化为等效线性时不变信道.然后使用GPI算法估计信道多普勒及各路径的时延及幅度参数,实现低复杂度稀疏信道估计.此外,该文将GPI算法扩展到Turbo接收机中,通过利用信道译码器反馈的数据符号先验信息迭代提高信道估计精度.仿真结果表明,所提方法的性能优于传统的路径识别算法,且与OMP算法接近,而其计算量远低于后者.     

双基SAR压制式干扰功率特性分析

从双基SAR干扰方程出发,将发射功率等与发射机有关的参数之积等效为干扰机在目标处探测到的回波功率强度,简化了干信比方程.推导了一定干信比下的干扰机等干信比覆盖区域,详细分析了此区域的特性及其与干扰机参数的关系.最后,从接收机已知角度讨论了有效干扰时,干扰机的等效辐射功率、干信比及干扰机到接收机距离三者之间的关系.仿真验证了理论分析的正确性.     

一个高效的有向传递签名方案

传递签名是由Micali和Rivest在2002年首先提出的,主要用于对二元传递关系进行签名.已有的传递签名方案都是无向的,只适用于对等价关系签名,提出有向传递签名方案是个留待解决的公开问题.该文提出一个高效的全序有向传递签名方案,并证明该方案在选择明文攻击下是安全的.在方案中,签名的β_uv部分被限定在0和q/2之间,以防止敌手由(u,v)的签名伪造(v,u)的签名,从而保证签名的有向性.将该方案与无向传递签名方案结合,提出一个可对任何有向二元传递关系进行签名的方案.     

Optimized signaling for MIMO interference systems with feedback

The system mutual information of a multiple-input multiple-output (MIMO) system with multiple users which mutually interfere is considered. Perfect channel state information is assumed to be known to both transmitters and receivers. Asymptotic performance analysis shows that the system mutual information changes behavior as the interference becomes sufficiently strong. In particular, beamforming is the optimum signaling for all users when the interference is large. We propose several numerical approaches to decide the covariance matrices of the transmitted signals and compare their performance in terms of the system mutual information. We model the system as a noncooperative game and perform iterative water-filling to find the Nash equilibrium distributively. A centralized global approach and a distributed iterative approach based on the gradient projection method are also proposed. Numerical results show that all proposed approaches give better performance than the standard signaling, which is optimum for the case without interference. Both the global and the iterative gradient projection methods are shown to outperform the Nash equilibrium significantly.     

Improved receivers for coherent FSK systems

There has been considerable interest over the last decade in the detection of digital coherent lightwave signals corrupted by phase noise. However, the majority of the work has been in the performance analysis of various modulation schemes. In addition, the receivers studied have, in general, been zero-phase noise optimal or ad hoc modifications of these. In this paper, we consider the design problem of constructing optimal receivers for systems using frequency shift keying (FSK). Using the innovations approach, we show the format of the optimal receiver and use a small phase noise approximation to derive suboptimal receivers. Also, receivers based on optimum linear filters are also derived. Both receivers are analyzed by simulation and performance improvements over the standard receivers are shown. Furthermore, the receivers developed can equally well be used to further improve the performance of other detection schemes such as postdetection filtering and time diversity. The methodology is also used to derive equivalent receivers for systems using on-off keying (OOK)     

模糊聚类分析和排序在研究生招生中的应用

模糊聚类分析按一定要求和规律对模糊性问题加以处理,通常先建立模糊相似关系而后按实际要求进行分类。文中针对研究生招生工作,组建模糊数学模型,在用传递闭包法求得聚类顺序的基础上,根据"物以类聚"的思想,提出了基于模糊聚类的两种多指标综合排序方法,为以后解决同类问题提供了新思路。     

一种基于超节点理论的本体关系消冗算法

本体作为指导知识图谱数据构建的上层结构,在知识图谱技术中具有重要意义。本体在发展的过程中会形成结构上的冗余。现有的本体消冗方法无法处理含有等价关系的本体结构,只能针对单一类属关系进行冗余的检测与消除。该文针对含有等价关系的本体提出一种基于超节点理论的消冗算法,首先将相互等价的节点看作超节点,消除单一类属关系之间的的冗余;然后还原等价节点,消除等价关系与类属关系之间的冗余。在计算机生成网络和真实网络上的实验和分析表明,该算法能够准确识别关系冗余,具有较高的稳定性和综合性能。     

对色散信道的预编码-判决反馈均衡联合最优设计

本文提出了利用滤波器组预编码及判决反馈均衡对色散信道实现收/发联合最优设计的方法.该方法以最大互信息量为设计准则,在固定发送功率约束条件下得到了新的设计结果.证明了预编码器使频率选择性信道等价为一组独立的平坦衰落子信道,且后向反馈滤波器等价为一条直通子信道,结论表明系统各子信道的信噪比与采用线性均衡结构的结果相比有所增加,从而使系统具有更低的误码率性能.文章通过仿真验证了该结论     

All-digital impulse radio with multiuser detection for wireless cellular systems

Impulse radio is an ultrawideband system with attractive features for baseband asynchronous multiple-access, multimedia services, and tactical wireless communications. Implemented with analog components, the continuous-time impulse radio multiple-access model utilizes pulse-position modulation and random time-hopping codes to alleviate multipath effects and suppress multiuser interference. We introduce a novel continuous-time impulse radio transmitter model and deduce from it an approximate one with lower complexity. We also develop a time-division duplex access protocol along with orthogonal user codes to enable impulse radio as a radio link for wireless cellular systems. Relying on this protocol, we then derive a multiple-input/multiple-output equivalent model for full continuous-time model and a single-input/single-output model, for the approximate one. Based on these models, we finally develop design composite linear/nonlinear receivers for the downlink. The linear step eliminates multiuser interference deterministically and accounts for frequency-selective multipath while a maximum-likelihood receiver performs symbol detection. Simulations are provided to compare performance of the different receivers.     

标准模型下基于身份的传递签名

基于waters的签名方案,提出了第一个基于身份的传递签名方案,方案被证明在标准模型下是安全的.与现有的传递签名方案相比,该方案将签名传递的不可伪造性归约到基于双线性配对的CDH问题上,并给出了方案的复杂度分析.     

Equivalent refractive index of MQW waveguides

In this paper, we have proposed some new numerical and semi-analytical methods for developing an equivalent three-layer model of an MQW waveguide. The waveguiding properties like effective index, field distribution, and fractional power within the core of the waveguide of these equivalent structures are compared with those of previously reported equivalent methods. These results are also compared with the results obtained from the exact multilayer analysis of the MQW waveguide. The waveguiding properties are accurately predicted by the semi-analytical method using variational analysis, and the computational effort is significantly reduced. The use of the three-layer equivalent is illustrated in obtaining an estimation of the waveguide losses and is used to study the effect of nonlinearity     

Robust Transceiver Optimization in Downlink Multiuser MIMO Systems

We study robust transceiver optimization in a downlink, multiuser, wireless system, where the transmitter and the receivers are equipped with antenna arrays. The robustness is defined with respect to imperfect knowledge of the channel at the transmitter. The errors in the channel state information are assumed to be bounded, and certain quality-of-service targets in terms of mean-square errors (MSEs) are guaranteed for all channels from the uncertainty regions. Iterative algorithms are proposed for the transceiver design. The iterations perform alternating optimization of the transmitter and the receivers and have equivalent semidefinite programming representations with efficient numerical solutions. The framework supports robust counterparts of several MSE-optimization problems, including transmit power minimization with per-user or per-stream MSE constraints, sum MSE minimization, min-max fairness, etc. Although the convergence to the global optimum cannot be claimed due to the intricacy of the problems, numerical examples show good practical performance of the presented methods. We also provide various possibilities for extensions in order to accommodate a broader set of scenarios regarding the precoder structure, the uncertainty modeling, and a multicellular setup.