基于DMF捕获系统频率选择性信道下捕获性能的分析

对基于数字匹配滤波器(DMF)捕获系统在频率选择性信道下的捕获性能进行了深入讨论，利用状态转移图推导出单次驻留判决方式时平均捕获时间的表达式，对平均捕获时间与多径分量的关系进行了数字分析。得出的主要结论是：对于多径分量为非衰落信号时，多径分量之间的能量差别越大，系统捕获性能越好，多径分量的能量相等时，系统捕获性能最差，且随着可以分离的多径路数的增加下降；对于多径分量为慢衰落信号时，多径信道的捕获性能好于单径信道(非频率选择性衰落信道)，且多径分量之间的能量差别越大，系统捕获性能越差，当多径分量的能量相等时，捕获性能最好，这与非衰落信道的情形相反。因此在频率选择性衰落信道中，采用分集接收可以改善系统的捕获性能。     

OFDM系统抗多径衰落性能计算机仿真分析

本文分析了多径衰落信道接收信号的特点,建立了多径传播的仿真模型,并对正交频分复用OFDM系统,分别通过AWGN高斯信道、两径瑞利衰落信道、六径瑞利衰落信道进行计算机模拟仿真,得出OFDM系统具有抗多径衰落性能的结论.     

UWB信号多径性能分析

分析了超宽带(UWB)信号抗多径衰落的原理,比较了UWB信号在只有加性高斯白噪声(AWGN)信道和AWGN室内密集多径信道两种环境下的误码率性能,得出UWB信号比窄带信号具有更低的多径衰落储备。     

通信系统中多径衰落信道传输性能的改进

通信系统中多径衰落信道传输性能的改进是当前比较热门的研究课题.我国的通信系统中多径衰落信道传输性能还存在严重的劣势,还存在着诸多有待解决的问题.在实用瑞利衰落信道下,存在加性高斯白噪声,对直接序列扩频通信系统抑制码片内、外多径干扰的能力进行理论分析与计算机仿真.在多径衰落信道较强的条件下,与提高扩频增益相比,增加扩频码的码长对于提高移动通信系统的抗多径衰落性能更加有效,但是扩频增益并非越高越好,需合理选取;证实扩频通信系统在多径瑞利衰落信道中传输时能有效地克服多径衰落.本文简要分析了瑞利衰落信道模型,并深入的研究和探讨了扩频通信系统抗多径干扰性能.     

移动通信信道的建模与仿真

针对移动通信的特点,本文以中继卫星通信链路为主要研究对象,分析了该链路通信信道中存在的传播损耗,并以此为基础建立了链路通信的信道模型;最后仿真分析了不同的通信传输速率在加性高斯白噪声(AWGN)衰落信道、多径Rayleigh衰落信道、Rician衰落信道以及复杂衰落信道中的误码率特性曲线,仿真结果表明,满足Rayleigh衰落信道模型的信号分量对系统的性能影响较大,且传输速率越高,信号分量中的反射分量与多径分量影响越大。     

多径衰落信道下基于循环累积量的调制分类算法

针对多径衰落信道,通过利用各阶循环累积量来对常见单载波信号进行调制分类。首先分析推导了在多径衰落信道下模拟和数字单载波信号一阶、二阶和四阶的循环累积量特征,寻找出不同信号在特定循环累积量下的谱峰特征的区别,最后利用CAFR检测算法通过树形判决完成信号的调制分类。通过理论推导和仿真分析,验证了算法在多径衰落信道下调制分类的可行性和抗噪声性能。算法不需要信号的先验知识,在多径衰落信道下性能鲁棒,适用场合较广。      

多径衰落信道的典型特征分析及仿真研究

分析了多径衰落信道的时间选择性和频率选择性,并讨论比较了多径效应和多普勒效应对信道产生的影响,从时域和频域的角度进行了仿真分析,仿真数据表明时不变多径衰落信道和时变多径衰落信道分别随着时域扩展和频域扩展的增加而使信号衰落加剧。     

自适应滤波在扩频信号分集接收中的应用研究

使用自适应滤波器完成对扩频信号的扩频码捕获后,传输信道中由于信号衰落造成的多径信号的幅度就可以从自适应滤波器收敛后的系数权值向量上体现出来.根据分集接收的理论分析,依据多径信号的信号幅度值进行分集接收在理论上是可行的,因此利用自适应滤波器对接收到的多径信号进行隐分集接收是完全可行的.使用自适应滤波器在完成扩频码捕获的同时,在不增加额外硬件支路的情况下就可以实现对多径信号的分集接收功能,从而改善在多径衰落环境下的信道传输性能.     

频率选择性慢衰落信道下的一种Rake接收技术

通过对无线通信信道传输特性的讨论,以瑞利信道和莱斯信道为模型,研究在QPSK扩频调制下接收端信号的同步、多径分离与按增益合并.仿真实现了频率选择性慢衰落信道下的一种Rake接收技术,结果表明用他来减小多径衰落是有效的.     

OFDM-ROF下行链路的性能研究

OFDM技术与ROF技术结合为实现低成本、高速数据传输的移动网络提供了可能,但光纤链路的非线性以及无线信道的多径衰落降低了系统性能。在建立ROF下行链路的传输函数模型基础上,分析ROF下行链路对OFDM信号性能的影响。传输模型包括激光器,光纤链路以及无线信道。分析在不同光调制指数、光纤长度及无线多径信道下接收信号的误差矢量、三阶非线性失真和互调失真。仿真结果显示：随着调制指数、光纤长度的增加,以及无线信道的多径衰落使得接收信号性能下降。此分析为OFDM-ROF下行链路的线性化以及无线信道均衡方案选择提供了理论基础。     

低空多径环境下雷达目标检测性能研究

针对低空多径环境下不同体制雷达目标检测性能展开研究,通过优化配置雷达阵元达到多径环境下的最优检测性能。建立低空多径环境下雷达接收信号模型,引入多径功率传播因子,将经典的Swerling目标起伏模型推广应用于低空多径环境,采用特征函数法推导低空多径环境下不同体制雷达的检测概率。仿真研究了多径功率传播因子对检测性能的影响,比较不同体制雷达的检测性能,结果表明多输入单输出雷达兼具相控阵雷达和多输入多输出雷达的优点,在多径环境下具有稳定的检测性能。     

多径衰落的数学模型及分析

多径效应是影响低仰角测控系统正常工作的重要因素。介绍了多径效应产生的机理,建立了多径衰落的数学模型。无线电信号在收发天线间传播时,存在直射路径和多条反射路径,当直射信号和反射信号相互抵消时就会产生多径效应。依据建立的数学模型,分析了多径衰落产生的条件和对系统影响的程度。多径衰落产生的位置由地面站天线高度、飞行器飞行高度和二者之间的距离决定,多径衰落深度主要由地面对电波的反射系数决定。在上述分析的基础上,提出了避免和减小多径衰落对系统影响的几种措施。     

URLM: Utilising reinforcement learning to schedule subflows in MPTCP

Parallel transmission in multiple access networks using MultiPath TCP (MPTCP) greatly enhances the throughput. However, critical packet disorder is commonly observed due to traffic fluctuation and path diversity. Although several predictive scheduling algorithms have been proposed to solve this problem, they cannot accommodate prediction accuracy and real-time adaptation simultaneously in a dynamic network environment. The time overhead in modifying scheduling parameters to adapt to network changes leads to performance degradation in throughput and packet disorder. In this study, we propose a scheduling algorithm called U tilising R einforcement L earning to Schedule Subflows in M PTCP (URLM). We apply reinforcement learning to select an optimal scheduling parameter in real time, which brings significant time benefits for modifying the parameters. The simulation comparison experiments show that URLM reduces the average number of out-of-order packets and the time overhead in adapting to network changes while improving global throughput.     

一种改进的GNSS多径抑制性能评估方法

多径误差包络曲线是评估多径抑制性能的一种重要方法.一般在研究时,该方法采用简单化多径模型.基于简单化多径模型,分析了与环境相关的多径信号模型.在环境相关的多径模型基础上提出了环境相关的多径误差包络曲线,通过软件仿真了该多径误差包络曲线,并分析比较了2种多径抑制性能评估方法.     

GNSS接收机抗多径技术

分析了多径信号特性及其对全球导航卫星系统(GNSS)接收机伪距测量和载波相位测量的影响,从抗多径天线和基带信号处理两方面对GNSS接收机的各种多径抑制方法进行了比较与分析,指出高精度GNSS接收机会同时采用抗多径天线和基带信号处理以达到较好的多径误差抑制效果.     

水声信道的计算机仿真研究

简要分析水声信道的传播特性,建立水声时变多径信道的数学模型,给出一种水声信道的多径传播的计算机仿真方法。通过仿真结果,分析水声信道多径传播的特点,有助于对水声信道的了解及相关问题的设计。     

一种改进的基于串行干扰抵消的Rake接收机

在基于串行干扰抵消的Rake接收机的基础上作了改进,提出了一种新的Rake接收机结构,对其进行了原理和性能分析,给出了Matlab仿真结果,并与基于串行干扰抵消的Rake接收机性能进行了比较。仿真结果表明,改进的基于串行干扰抵消的Rake接收机性能明显得到提高,同时减小了误码率。     

SCTP多路径传输在移动网络中的应用研究

移动网络中信令网已具备IP承载的能力,本文主要对SIGTRAN协议簇中SCTP协议的多路径传输进行研究,测试并解决移动网络中多厂家设备间多路径的配合问题。     

Effectiveness of Reliable Routing Protocols in Mobile Ad Hoc Networks

Due to unpredictable topology change and frequent link failure, it becomes evident major challenge to provide the stable route between source and destination in mobile ad hoc networks. Unlike previous multipath routing schemes for redundancy and unicast routing protocol utilizing the longest route expiration time measured by geographical information supported by Global Positioning System (GPS), we develop a framework to establish the most stable route based on measured frequency of link failure, available battery as well as the number of actual connections. To evaluate performance of proposed scheme, we provide practical simulation results for multipath and unicast routing protocol in terms of packet delivery ratio, control overhead, average hop length as well as end-to-end delay. Through analysis of simulation results, we demonstrate that our scheme shows better performance than general unicast routing protocol as well as similar packet delivery ratio to multipath routing protocol with less maintenance overhead. Ki-Il Kim received the M.S. and Ph.D. degrees in computer science from the Chungnam National University, Daejeon, Korea, in 2002 and 2005, respectively. He is currently with Department of Information Science, Gyeongsang National University as a faculty member. His research interests include routing for MANET, QoS in wireless network, multicast, and sensor networks. Sang-Ha Kim received the B.S. degree in chemistry from Seoul National University, Seoul, Korea, in 1980. He received the M.S. and Ph.D. degrees in quantum scattering and computer science from the University of Houston, Houston, TX, in 1984 and 1989, respectively. From 1990 to 1991, he was with the Supercomputing Center, SERI, Korean Institute of Science and Technology (KIST) as Senior Researcher. He joined Chungnam National University, Daejeon, Korea, in 1992, where he is a Professor. His current research interests include wireless networks, ad hoc networks, QoS, optical networks, and network analysis.     

Performance analysis and test for passive RFID system at UHF band

Performance analysis and test for passive radio frequency identification (RFID) system at ultra high frequency (UHF) band in free space and line-of-sight (LOS) indoor environments are conducted in this article. Performance degradation of different materials is presented, in terms of power received by tag and reader, communication range and link information rates, etc. Particularly, the multipath fading and root mean square (RMS) delay spread in LOS indoor environments are analyzed by a 5-ray model with different polarization, such as horizontal polarization, vertical polarization and circular polarization. A practical test is carried out on an indoor balcony of an office building. In addition, the electric field environment is simulated to analyze multipath degradation using the tool of Ansoft HFSS. According to the test, the recognition rate is almost consistent with the results of theoretical analysis and simulation. The small scale fading and the field nulls are observed. The multipath degradation significantly affects the passive RFID system on communication range and recognition rate, and it is also one of the key limitations on system performance. The variations of power in multipath environments can also influence the information rates, while the rates are still enough for available standard and applications at short range.