随机桥过程分析街道拐角的无线传播特性

使用随机桥过程研究街道拐角的小尺度衰落和大尺度传播的特性.首先介绍模型,随机桥过程的理论基础,从随机桥过程引入随机射线的概念,利用随机射线建立无线信道分析街道拐角的多径传播特性和大尺度传播特性.然后给出信道的时延分布、多径分量的幅度特性、功率延迟分布,接收机接收波的到达角分布等多径特性参数,并给出路径损耗.仿真结果与参考文献中无线信道测量结果吻合较好,表明使用随机桥过程可以有效地分析街道拐角的无线传播特性.     

散射环境下宽带移动通信衰落信道扩展模型

介绍了采用高精度信道测试设备进行室外100 MHz宽带无线信道测试;针对传统多径衰落无线信道测量模型中易忽略的漫散射效应,提出了包含漫散射指数衰落特性的宽带无线信道扩展模型;基于实测数据提取了相应的扩展模型参数和更准确的时延特性,验证了宽带扩展模型的有效性和必要性.宽带移动通信信道扩展模型能够高精度地描述宽带信道衰落特性,对第四代宽带移动通信系统的设计乃至实际散射环境下的现场试验均有重要意义.     

无线信道

与有线通信中良好的信道状况(一般可以用加性白色高斯噪声信道来仿真)完全不同，移动通信中的无线信道状况非常恶劣，信道是多径、时变的，从而使无线信号在短时间或短距离传播后幅度快速衰落。即产生小尺度衰落现象。     

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.     

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。     

无线局域网信道特性的研究

无线信道是整个现代数字无线移动通信研究的基础,从电磁波传播方式、无线信道对传输信号的影响以及等效低通信道的时变冲激响应等几个方面对无线信道的特性进行了研究。结果表明,信号通过无线信道传播时,会产生各种形式的衰落,衰落对无线移动通信系统传输性能的影响是很大的,在实际中应设法消除。     

基于FDTD方法的无线信道衰落特性模拟研究

为了表述无线信道衰落的时变及远区分布特性，提出了利用时域有限差分(FDTD)方法研究由多径效应引起的时变无线信道衰落的方法。在此将无线信道的衰落建模为随机过程，而不是通常的确定性随机变量。首先基于Clarke统计模型，利用FDTD方法研究了时变无线信道的小尺度平坦衰落特征；然后利用Monte Carlo方法和FDTD方法产生了具有信道多普勒功率谱特性的色高斯随机过程，再基于无线信道的时变统计特性建模，用Suzuki模型研究了时变无线信道的快衰落；最后将无线信道衰落特性分布和理论分布做了比较，验证了方法的有效性。     

基于FPGA的无线信道模拟器设计

为了缩短研发周期,需要在实验室模拟出无线信道的各种传播特性,无线信道模拟器设计必不可少。采用基于频率选择性信道Jakes仿真器模型,使用Xilinx公司的Virtex-2p模拟实现了频率选择性衰落信道,最后将数据通过串口上传到Matlab分析信道的统计特性。     

不同衰落下的并行信道建模与容量分析

无线信道的分析与建模是无线通信研究的基础的工作,信号在传输过程中会受到不同衰落环境的影响,例如频率选择性衰落、时间选择性衰落和空间选择性衰落。为了分析无线传播环境在这三种衰落条件下的信道特性,分别对三种衰落信道进行并行信道建模,在此基础上将注水原理分别应用于这三种衰落信道中,即分别在频率、时间和空间上进行最佳功率分配,只对信道状况良好的子信道分配功率,最后得到不同衰落信道下的信道容量。     

多径衰落信道的多重分形模型

本文研究多径衰落信号的多重分形性质,分析并指出了信号多重分形维数是描述无线信道传播特性的重要参数;计算了多径衰落信号的多重分形维数及其分形参数;在此基础上提出了一种新的无线信道模型;结合分形插值方法,对多径衰落信号的重构进行了研究.仿真结果表明,无线信道的多重分形模型与传统的统计模型相比更有效、更准确.     

Analytical outage evaluation of TDMA local radio systems withcoding and diversity

A completely analytical approach is presented in order to evaluate outage probability of TDMA (time-division multiple access) local radio systems using coding and diversity to combat frequency selective fading. First, starting from a multiray model for multipath propagation, performance sensitivity is tested by suitably simplifying the channel model. An analytical expression is obtained of the probability that BER may exceed a fixed value in the presence of a simplified channel model. A suitable upper bound formulation is given to express the same probability in the presence of coding and diversity techniques. Finally, some application examples are proposed both with reference to slow frequency hopping and space diversity systems     

Autoregressive modeling of wide-band indoor radio propagation

Based on frequency domain measurements in the 0.9-1.1-GHz band, an autoregressive model for the frequency response of the indoor radio channel is introduced. It is shown that a second-order process is sufficient to represent the important statistical characteristics of the channel both in the frequency domain and the time domain where each pole identifies the arrival of a cluster of paths. A comparison is made between the statistical characteristics of the empirical data and of the channel responses regenerated from the second-order AR processes. Four methods to regenerate the indoor radio channel responses from a second-order AR model are proposed. The accuracy of the methods is examined by comparing the cumulative distribution functions of the RMS delay spread and the 3-dB width of the frequency correlation function with that of the measurements performed in global, local, and mixed indoor radio propagation experiments     

A UHF channel simulator for digital mobile radio

A device to simulate the channel propagation characteristics of the ground mobile environment at UHF has been designed, built, and characterized. This device provides a flexible, easily changed set of simulated channel characteristics, which allows the performance of a mobile radio unit to be evaluated in the laboratory under controlled conditions. The channel simulator was designed to simulate mobile platform speeds up to 675 mi/h and multipath components having differential delays approaching 10 µs. The channel simulator can provide up to four easily selectable, independently fading, multipath components, having calculated time delay spreads of up to 3.5 µs. The adjustable fading bandwidths and the exceptional long delays were implemented using the relative new signal processing technologies of charged-coupled devices and surface wave devices. Envelope statistics such as fading distributions and level crossing rates produced by the channel simulator show excellent agreement with theoretical prediction and documented experimental data.     

城市地形对电波传播的影响研究

随着科技的日新月异,我国通信技术得到飞速的发展,无线电波在人们的工作和生活中发挥越来越重要的作用。怎样提升无线电波的应用质量,是相关部门一直探索的课题。为了掌握无线电波在移动通信中的传播规律以及无线信道的特征,文章进行了城市地形对电波传播影响的试验,测量的对象是距离基站2.5 km处8个不同的测量点,测量目的是研究接收的信号电平状态和规律,并对城市地形对电波传播的影响进行研究。     

A characterization of the frequency selective fading of the mobile radio channel

An experiment has been designed to determine the frequency selective behavior of a mobile radio channel for a medium bandwidth (maximum of 128 kHz). The measurement technique uses a multitone approach. The transmitted signal consists of several tones (five) with fixed phase and amplitude relationships. Coherent demodulation and separation of each tone is performed at the receiving end. Quantification of the mobile radio channel is conveniently described by its frequency correlation function. Measurements for several types of environments (rural, suburban, urban) were taken and analyzed. The results characterize the amplitude and phase behaviors of a signal for each type of environment. Finally, the computations of the probability of error for a differential phase shift keying (DPSK) modulation scheme in the presence of frequency selective fading show the dominance of this factor as the signal-to-noise ratio (SNR) increases.     

Statistical AR models for the frequency selective indoor radio channel

A statistical model of the indoor radio channel is proposed that is derived from a second order autoregressive process representation of the channel frequency response. The accuracy of the statistical model is examined by comparing the cumulative distribution functions of the RMS delay spread and the 3 dB width of the frequency correlation function computed from the regenerated data with that of the measurements performed in two indoor radio propagation studies in the 0.9-1.1 GHz band.<>     

A flexibly configurable spatial model for mobile radio channels

The application of multiple directive antennas, i.e., directional diversity, may lead to significant capacity benefits in cellular mobile radio systems. A flexibly configurable statistical channel model for mobile radio systems using directional diversity is presented. The parameters of this model, which is available as a FORTRAN77 program, can be easily adjusted to various propagation areas such as, for example, rural, urban, microcellular, and picocellular environments. Therefore, the model is well suited to perform simulations, evaluations, and comparisons of mobile radio systems. Simulation results concerning a code-division multiple-access (CDMA) mobile radio system which uses multiple directive base station (BS) antennas in combination with joint detection illustrate the application of the presented channel model     

A channel model for multipath interference on terrestrialline-of-sight digital radio

A comprehensive system model for characterizing the effects of multipath propagation on digital radio systems in the 4-6-GHz band is shown in this paper. The effects of terrain-induced multipath propagation in the presence of atmospheric anomalies are studied using data from experimental microwave links in the field and in the laboratory. This technique, which treats multipath propagation as digital signal distortions caused by interference from ground reflections, has not been shown previously. A forward multipath propagation model is used to identify the critical propagation parameters for a quadrature amplitude modulated (QAM) signal. A normalized two-ray channel model is developed to approximate the frequency response produced by interference from a ground reflection in a narrow band. The effectiveness of this channel model is evaluated using measured data from the test radio link in the laboratory and in the field     

Channel estimation and compensation for preamble-assisted DAPSKtransmission in digital mobile radio system

This paper presents a novel channel estimation and compensation technique, combining fading estimation and frequency offset estimation, for preamble-assisted differentially encoded amplitude- and phase-shift keying (DAPSK) transmission in a digital mobile radio system. The received preamble symbols are used to estimate the combined distortions caused by multipath fading and frequency offset. The detected data symbols as well as preamble symbols are used to enhance the accuracy of the estimation process. The combined distortions can be compensated in the data symbols at the same time. The storage-delay time of the estimation process is only several symbols long. A series of computer simulations have been carried out to investigate the bit error rate performance of the preamble-assisted 16-DAPSK signals with uncertain frequency offset in the frequency-nonselective and frequency-selective Rayleigh fading channels