卫星移动信道特点和模型的研究

分析了卫星移动信道的特点，并根据传输环境的不同。提出了3种不同的模型，并推导出相应的概率密度函数，使得对信道特性的描述更加直观、合理。     

基于模型的无线信道分组传输特性仿真研究

结合使用Gilbert模型和Jakes改进模型,对无线移动信道模型进行仿真,准确地模拟了实际中的无线多径衰落信道。改进的信道模型中增加了突发错误状态,更加符合实际信道特征。仿真结果证明了丢包率与分组大小之间近似为线性关系,曲线的斜率随误比特率的增长呈线性增长模式。     

矢量多径信道的衰落相关特性

研究了天线阵系统中矢量多径信道的空－时－频衰落相关特性，分析并仿真了角度扩展和阵元间距对接收信号空间相关特性的影响。     

移动衰落信道的计算机仿真模型

讨论了移动衰落信道特点,研究了移动衰落信道的模型,主要分析了模型中复乘性因子的产生方法,之后给出了产生该复乘性因子的计算机仿真模型,最后对于模型中有色高斯信号的产生进行了计算机仿真。     

多径衰落移动无线系统中的同频道干扰预测

同频道干扰是微蜂窝结构移动通信网所要考虑的一个核心问题，要想成功地对任何一种频率再用无线系统进行规划设计，就必须很好地了解并分析研究同频道干扰对系统性能的影响。本文对具有Ｎａｋａｇａｍｉ衰落和对数正态衰落的同频道干扰特性进行了理论分析，并提出了对微蜂窝多径衰落移动无线电系统中的同频道干扰及其影响进行预测的近似方法。     

移动无线信道实时瑞利衰落模拟器

本文介绍了一种模拟移动无线电接收中遇到的瑞利分布衰落的设备。该设备由软件和硬件组成,用两个独立的高斯噪声信号对无线电信号进行同相和正交调制,相加后得到瑞利衰落信号。接收信号理论上的功率谱用FIR数字滤波器对伪噪声的功率谱进行整形来近似。噪声的产生和滤波均由单板机实现。改变单板机CTC定时器的输入时间常数,就可直接调整模拟衰落信号的衰落速率。对设备的测试结果表明:模拟的衰落信号的包络统计与理论统计特性和实验观察基本一致。     

衰落信道基于卡尔曼滤波的信噪比估计

无线通信场景中,由于复杂的电磁环境及移动通信双方之间的相对运动,使无线信道存在着严重的多径衰落及多普勒效应.信噪比是通信信道的重要衡量指标,直接指导通信策略的制定.针对多径衰落信道条件,提出基于卡尔曼滤波辅助的信噪比估计算法,利用卡尔曼滤波的方法对信道进行平滑,之后选取合适的长度进行信噪比估计.最后针对不同信道条件下信...     

无线移动信道的仿真

本文介绍了利用MATLAB来对无线移动信道进行仿真的方法。首先解释移动信号多径传播和因此造成的衰落的基本特性，然后重点对常见的瑞利衰落和莱斯衰落进行仿真；为了对衰落有个直观的表达，在仿真衰落的同时也给出了衰落幅度的分布或概率密度函数。     

一种通用无线衰落信道仿真器的设计与实现

介绍了一种典型瑞利衰落信道的仿真模型,给出了该仿真器的软件以及硬件结构的设计方案,并详细阐述了实现的方法.实验证明:该仿真器可灵活改变信道参数,能够满足多种测试环境的需要.     

卫星衰落信道分析与建模

在研究分析传统Rayleigh信道和Rice信道抽头时延模型的基础上,采用两条多径路线代替传统模型,提出一个具有确定数学表达式的简化卫星信道模型,只需对该模型中的两个参数取适当的取值,就可以得到不同的衰落强度和衰落中心频率的卫星信道.理论和仿真结果表明,当时延τ=.63ns,β=0.75时,可以获得的最大衰落幅度为10...     

一种移动通信信道仿真器的FPGA实现

介绍了一种基于现场可编程逻辑阵列器件（FPGA）的移动通信信道仿真器设计和实现方案,该仿真器可以实时模拟移动通信信道的传播特性。重点分析了信道仿真器硬件实现中的关键技术,包括高斯噪声源的硬件实时产生、窄带多普勒滤波器的设计以及多径衰落信道在FPGA硬件电路中的实时处理。采用8组独立的均匀随机分布数据加权产生的数据可以满足高斯噪声源分布特性和实时性的要求,此半实物移动通信信道仿真器能为实际移动通信设备的优化设计提供了解决方案。     

阴影衰落信道下多波束卫星移动通信系统的动态信道分配策略

针对已有动态信道分配策略在阴影衰落环境中性能损失较大的问题,对卫星移动通信系统的阴影衰落信道模型进行分析,提出了一种动态信道分配策略。该策略结合用户的运动状态,通过在用户的预测运动轨迹上选取抽样点,将这些抽样点的平均干扰作为信道分配的指标,并采用链路质量约束避免了流量较大时的性能恶化。仿真结果表明提出的动态信道策略可在不增大阻塞率的前提下,在中低流量时将用户平均信噪比提高约0.5 dB。该策略可以应用于阴影衰落信道下的地面移动卫星通信系统,以提高用户的平均链路性能。     

关于移动信道分析模型的研究

移动信道特性的研究是移动通信系统研究领域中最重要的部分，也是近年来研究的热点之一。其中多径传播和阴影效应是信道的主要特点，几乎任何统计特性都建立在此基础上。主要是介绍一种移动信道的分析模型，该模型的地理环境为市区，即移动台和基站之间不存在直视波（LOS），并从多普勒功率谱的角度给出了接受信号振幅和相位的概率密度函数（PDF）盈自相关和互相关函数。     

基于支持向量域的快衰落信道混沌预测

以多径无线衰落信道存在奇怪吸引子为前提，从支持向量域SVD出发，研究了无线衰落信道的响应特性。根据相空间延迟重构理论建立了快衰落信道的预测模型，使用训练集合作为支持对象元素，通过机器自学习缩小模型泛化误差上界，采用最小二乘支持向量域，实现了非线性高维相空间映射，预测了衰落信道。实验结果表明：支持向量域含支持向量数少，运算速度快，顽健性强，核函数选择灵活，为自适应实时估计和检测提供了一种方法。该方法在小样本和未知信道概率密度下，信道预测值和真实值取得了一致。     

Effective capacity channel model for frequency-selective fading channels

To efficiently support quality of service (QoS) in future wireless networks, it is important to model a wireless channel in terms of connection-level QoS metrics such as data rate, delay and delay-violation probability. To achieve this, in [7], we proposed and developed a link-layer channel model termed effective capacity (EC) for flat fading channels. In this paper, we apply the effective capacity technique to modeling frequency selective fading channels. Specifically, we utilize the duality between the distribution of a queue with superposition of N i.i.d. sources, and the distribution of a queue with a frequency-selective fading channel that consists of N i.i.d. sub-channels, to model a frequency selective fading channel. In the proposed model, a frequency selective fading channel is modeled by three EC functions; we also propose a simple and efficient algorithm to estimate these EC functions. Simulation results show that the actual QoS metric is closely approximated by the QoS metric predicted by the proposed EC channel model. The accuracy of the prediction using our model can translate into efficiency in admission control and resource reservation. Dapeng Wu received B.E. in Electrical Engineering from Huazhong University of Science and Technology, Wuhan, China, in 1990, M.E. in Electrical Engineering from Beijing University of Posts and Telecommunications, Beijing, China, in 1997, and Ph.D. in Electrical and Computer Engineering from Carnegie Mellon University, Pittsburgh, PA, in 2003. From July 1997 to December 1999, he conducted graduate research at Polytechnic University, Brooklyn, New York. During the summers of 1998, 1999 and 2000, he conducted research at Fujitsu Laboratories of America, Sunnyvale, California, on architectures and traffic management algorithms in the Internet and wireless networks for multimedia applications. Since August 2003, he has been with Electrical and Computer Engineering Department at University of Florida, Gainesville, FL, as an Assistant Professor. His research interests are in the areas of networking, communications, multimedia, signal processing, and information and network security. He received the IEEE Circuits and Systems for Video Technology (CSVT) Transactions Best Paper Award for Year 2001. Currently, he is an Associate Editor for the IEEE Transactions on Vehicular Technology and Associate Editor for International Journal of Ad Hoc and Ubiquitous Computing. He served as Program Chair for IEEE/ACM First International Workshop on Broadband Wireless Services and Applications (BroadWISE 2004); and as TPC member of over 30 conferences. He is Vice Chair of Mobile and wireless multimedia Interest Group (MobIG), Technical Committee on Multimedia Communications, IEEE Communications Society. He is a member of the Best Paper Award Committee, Technical Committee on Multimedia Communications, IEEE Communications Society. He is also Director of Communications, IEEE Gainesville Section. Rohit Negi received the B.Tech. degree in Electrical Engineering from the Indian Institute of Technology, Bombay, India in 1995. He received the M.S. and Ph.D. degrees from Stanford University, CA, USA, in 1996 and 2000 respectively, both in Electrical Engineering. He has received the President of India Gold medal in 1995. Since 2000, he has been with the Electrical and Computer Engineering department at Carnegie Mellon University, Pittsburgh, PA, USA, where he is an Associate Professor. His research interests include signal processing, coding for communications systems, information theory, networking, cross-layer optimization and sensor networks.     

Joint data and channel estimation for TDMA mobile channels

One of the main problems in time-division multiple-access (TDMA) digital mobile communications is the poor performance of the receiver for fast-fading channels. We propose to use a novel joint data and channel estimation (JDCE) technique to improve performance. The basic idea of this method originates from the so-called generalized likelihood ratio (GLR) test of classical detection theory. The technique was combined with the well-known Viterbi algorithm and applied to blind equalization by Seshadri [1]. In this paper, we introduce this technique to TDMA mobile communications. We find that the problems of delayed channel updating and divergence caused by error decision feedback in conventional maximum likelihood sequence estimation with decision delay (MLSE/DD) can be completely solved. An improvement of 4.5 dB can be obtained compared with the MLSE/DD method when it is applied to the Northern American Digital Cellular (NADC) system. The specified IS-54 requirement of 19 dB signal-to-noise ratio (SNR) at a bit error rate (BER) of 3% and a vehicle speed of 100 km/h can be met with a remarkable margin of 8 dB. When the intersymbol interference (ISI) of a channel is not severe, the required computation is moderate. For example, in the NADC system, the computational burden of the JDCE method is twice that of the MLSE/DD method if the least-mean-squares (LMS) algorithm is used for channel tracking.This work was presented in part in the Third International Symposium on Personal, Indoor and Mobile Radio Communications, Boston, MA, October 1992.     

基于分层几何单反射原理的连续时间时变矢量信道模型

提出了一种适用于智能天线技术的新的基于分层几何单反射原理的连续时间时变矢量信道传播模型。在此基础上,直接从矢量信道冲击响应出发,得到了宽带连续时间无线信道数学模型,通过改变几何参数,可以仿真具有任意衰落特性的无线信道。*     

快衰落信道中交织器设计方法

本文提出一种衰落信道中交织器设计的新方法,根据衰落信道的电平交叉率和平均衰落时间估计突发差错长度,结合LDPC编码的误码曲线确定门限电平,设计相应的交织器。仿真结果验证该方法降低交织器延时,并在快衰落信道下得到较理想的系统性能。     

多径条件下阵列天线相位关系分析

针对多径条件下阵列天线阵元间的相位差,研究了散射体在发射台附近的有直达路径、无直达路径以及远端强反射等传播方式下的相位关系计算模型,通过仿真计算,分析了相位关系的统计特征.该计算模型可模拟多径环境下的矢量信道参数,可用于通过相位信息进行到达方位测量的测向算法的研究.