不同战场环境下超低空导弹目标抗多径方法

多径干扰是影响超低空探测的主要因素,针对防空导弹对超低空导弹目标探测问题,研究了不同战场环境下的抗多径方法。采用物理光学法与等效电磁流混合方法(PO+MEC)快速获取导弹目标的电磁散射特性,结合传统的四路径模型,并引入导引头天线方向图对其进行修正,提取出不同战场环境下超低空导弹目标的多径干扰。仿真结果表明,不同的战场环境对应着不同的布儒斯特角,混凝土、半干地、干地和湿地环境下所对应的布儒斯特角分别为30°、26.5°、21.5°和10.5°;当导引头采用VV极化方式以布儒斯特角下视探测超低空导弹目标时,多径干扰达到极小水平,所接收信号的信干比达到极大水平,此时导引头对于超低空导弹目标的探测能力最强,目标回波最为明显。仿真结果对于防空导弹弹道优化具有借鉴意义,为超低空对抗打下基础。     

A pulse radiolysis and pulsed laser study of the pyrromethene 567 triplet state

The triplet state of pyrromethene 567, a molecule with potential as a solid state laser dye, has been characterized in benzene by pulse radiolysis in terms of its absorption spectrum, lifetime, self-quenching, electronic excitation energy, triplet–triplet extinction coefficient and oxygen quenching rate constant. The use of laser flash photolysis has then allowed determination of the triplet quantum yield, efficiency of formation of singlet oxygen (¹Δ_g), and the rate constant for reaction of the latter species with the ground state. The affects of oxygen on the fluorescence and triplet yields demonstrate that oxygen-induced intersystem crossing is important, the sum of these parameters being unity within experimental error. The mechanism of reaction of P-567 with ¹Δ_g in benzene is predominantly physical in character with only a small (6%) contribution from chemical reaction.     

Decision-directed Kalman particle filter with application to the MIMO phase noise channel

Demodulation of data transmitted over time-varying channels with a free running hidden Markov state, like the phase noise channel or the fading channel, requires that the receiver tracks the hidden channel state. The tracking technique adopted in the paper is based on non-data-aided sequential importance sampling, also known as particle filtering.The paper proposes a new particle filtering framework for data communication receivers based on an importance distribution such that each individual particle becomes a decision-directed Kalman filter relying upon its local symbol-by-symbol hard decisions. In this framework, different particles are left free to take different sequences of decisions. This leaves to the receiver the possibility of exploring different sequences of transmitted modulation symbols. The weight of the particle will be high for those particles that took in the past the correct sequence of decisions, while will be low for those particles that took wrong decisions. In the resampling procedure, particles with high weight will survive, while particles with low weight will be terminated, leaving space to the birth of new particles resampled from the surviving ones.The crucial point in importance sampling is the choice of the importance distribution and the main novelty of the paper is the proposal of an importance distribution such that the particles of the particle filter become decision-directed Kalman filters. One important benefit brought by our proposed method is that, being non-data-aided, it does not need pilot symbols, thus allowing to preserve the transmission rate. A significant application example, presented and developed in the paper, is constituted by MIMO systems affected by phase noise, where the channel state vector consists of many parameters.     

DS-UWB系统中一种稳定快速同步算法

本文分析了超宽带通信系统中同步算法的特点及其重要性,提出了一种快速捕获最大能量值路径信号的同步算法,利用室内多径信道的传输特性和多假设快速同步算法的特点,通过快速捕获具有最大能量值路径信号来实现稳定的定时同步。文中推导了平均捕获时间的表达式,并进行了仿真实验。结果表明,与已有的各种快速算法相比,本文推荐的算法具有更快速、更稳定的同步性能。     

基于编码的OFDM系统性能仿真

OFDM在多径衰落信道中,一些子载波由于深衰落会完全被丢失,从而影响整个系统的误码性能.因此,必须将OFDM系统与信道编码结合起来以提高整系统的误码性能.构建了基于编码的OFDM仿真系统,通过仿真比较了基于LDPC码、乘积积累码(PA)和卷积码的OFDM系统在多径衰落信道下的BER性能.研究了信道块衰落长度与编码性能之间的关系,仿真结果分析表明,LDPC码和PA码在不引入交织的情况下,均可获得比引入交织的卷积码更大的性能增益,表明LDPC码和PA码在无线信道环境下具有很好的适应性.     

一种消除多径对Galileo系统跟踪影响的新方法

为了消除多径对Galileo系统的影响,提高定位精度,介绍了一种抑制多径影响的新方法——高分辨率跟踪技术,并将其应用在多径跟踪抑制方面。主要通过介绍Galileo系统的BOC(binary offset carrier)信号、多径对BOC信号相关特性的影响以及多径对Galileo跟踪性能的影响,给出用高分辨率技术来进行多径抑制的方法。仿真结果显示,高分辨率跟踪技术对多径有很好的抑制能力。     

基于丢包率预测的多路径网络负载均衡策略

为了弥补传统多路径网络负载均衡策略在网络状态改变前无法预先提供相应预测信息的不足,提出了一种基于预测多路径丢包率的负载均衡策略.该策略以主动测量获取的每条路径的丢包率为观察值,采用确定型时间序列预测为预测手段,利用预测的丢包率作为负载分配的依据.此外,在负载均衡的调节中,提出了利用丢包率作为每条路径流量分配比例的惩罚函数,将流量引入丢包率低的路径.分析及仿真结果证明,该策略能有效地均衡负载,减少网络的丢包率.     

恶劣电力线信道中一种新的高速通信方式

为了在恶劣复杂的电力线多径信道上传输高速的数字信号,该文提出了一种新的电力线通信(PLC)方式--基于THP预编码的单载波正交振幅调制(QAM)方案.该方案使用THP预编码来均衡信道从而达到去除码间干扰的目的,实现最大可能的利用电力线信道资源.计算机仿真实验和实际测试表明:单载波QAM能够在短距离内实现在电力线上传输高速数据,并且具有很好的比特误码率性能.     

无线Mesh网络多路径路由协议设计的思路

在分析目前无线Mesh网络（WMN）多路径路由协议研究现状的基础上,根据WMN多路径路由协议的关键问题和设计要求,提出设计多路径路由协议的思路,以从整体上解决WMN环境下负载均衡问题,提高网络应用的安全性和可靠性。     

Spatial and Temporal CM Equalization for Broadband Wireless Indoor Networks at Millimeter Waves

Based on a new multipath channel model, a spatial-temporal combined CM equalization approach is derived at millimeter waves. Computer simulations are presented to testify the theoretical analysis. It is shown that this method can compensate the signal degradation caused by indoor multipath propagation. The convergence behavior of the spatial-temporal CMA is also analyzed.