基于虚拟仪器的数据链测试模拟器研制

针对传统数据链测试设备功能单一且不易重构的问题,借鉴虚拟仪器模块化的设计思想,设计实现了一种基于美国国家仪器公司（National Instruments,NI）通用软件无线电平台的数据链测试模拟器。该模拟器采用线性调频信号叠加（Sum of Linear Frequency Modulation,SoLFM）的方法高效产生具备连续相位的时变信道衰落,包括瑞利衰落、莱斯衰落和对数正态衰落等,并结合多相滤波思想能够精确模拟数据链长时延的多径传播场景。利用矢量网络分析仪对硬件模拟器输出的信道传递函数和信道冲激响应进行实测验证,并对各支路的随机信道衰落包络分布进行统计验证。实测结果表明,该数据链测试模拟器输出的信道函数和统计分布均与理论值吻合,因而可用于数据链装备的系统优化、验证和性能评估。     

Impact of clustering in statistical indoor propagation models onlink capacity

Explicit clustering in a statistical indoor propagation model is found to have significant effects on the capacity of an array-to-array link or matrix channel. Effects of antenna spacing, Poisson homogeneity, block size, and transmit power allocation strategies are also considered     

Evaluation and verification of the VHF/UHF propagation channelbased on a 3-D-wave propagation model

This paper is intended to increase and improve the knowledge concerning the characterization of digital VHF/UHF communication channels. This characterization of the propagation channel is based on the field strength-delay-spectrum (FDS) of the three-dimensional (3-D) multipath wave propagation. A statistical superposition of the predicted multipath signals yields the probability density function of the narrowband signal and the averaged channel impulse response of the wideband propagation channel. Thereof, the relevant parameters, e.g., standard deviations, mean values, delay spread, and correlation coefficients, are derived both in time and frequency domain. The angles-of-arrival of the multipath signals are used to calculate the Doppler spectra of moving receivers for the characterization the time-variant properties of the propagation channel. In total, a rather complete summary of derivations, algorithms and characteristics of the VHF/UHF propagation channel is presented. Narrowband and wideband measurements are included for verification     

利用LLR提高链路自适应准确性的满分集度网络编码策略

错误传播严重影响无线网络编码系统的分集阶数。针对此问题,本文设计了一种基于对数似然比的链路自适应智能网络编码策略,利用似然比代替背景噪声的统计特征参数,以提高中继的适应准确性。在等效信源-中继-信道虚拟模型下,利用接收信号的似然比计算信道后验条件误比特率,在此基础上换算得到等效接收信噪比,以此为依据对中继功率进行动态调整。通过理论分析证明了本方案能够获得满分集度。仿真结果表明,本方案能有效避免错误传播,保证系统获得满分集阶数,且性能优于现有链路自适应方案。      

Extension of the normalized two-ray transfer-function model to aspace-diversity line-of-sight link

Many methods for the prediction of multipath effects on the availability of a digital microwave line-of-sight link use a mathematical and statistical modeling of the propagation channel transfer function. Such a method, making use of the normalized two-ray model and adapted to a nonprotected hop, has been presented in a previous paper. In this paper we investigate the possibility to extend this model to a diversity channel, while keeping the statistical representation of the channel as simple as possible. Two theoretical possibilities, each leading to only one new statistical coefficient, are presented and validated on experimental data. From this result, a simple extension of the availability prediction method to a diversity channel seems to be feasible. Some problems remain to be solved however, which are discussed in the concluding section     

三维MIMO信道物理模型的统计特征

提出以散射矩阵来概括并简化电波传播过程中散射体对电磁波的影响,并对传统的距离分集和极化分集多入多出（MIMO）信道模型进行扩展,建立了一种可以应用于各种分集情况的三维通用MIMO物理信道模型。再以此模型为基础,对三维环境中的MIMO信道统计特征进行了研究,推导出任意情况下交叉极化鉴别度（XPD）和子信道间相关性的计算方法,并进行了仿真验证。仿真结果表明从文中所提出信道模型提取得到的统计特征与理论分析的结果是相符的。     

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     

室内走廊环境毫米波OAM信道特性分析与统计建模

针对自由空间传播模型仅能描述自由空间场景下携带轨道角动量(OAM)的涡旋信道传播特性,以及确定性稀疏多径涡旋信道模型严格依赖于传播环境而不能准确刻画真实多径场景下OAM信道传播特性的问题,该文提出毫米波OAM多径信道统计建模方法。在室内走廊环境下构建基于均匀圆形天线阵列(UCA)的OAM辐射传输系统,基于光学射线理论与UCA辐射特性,建立OAM多径信道模型。结果表明,在毫米波频段均匀分布和Nakagami-m分布能够准确地表征室内走廊多径环境下的OAM信道波前相位和幅度,视距(LoS)和非视距(NLoS)传播条件下传播距离较大时信道幅度服从瑞利分布,视距传播条件下传播距离较小时信道幅度服从莱斯分布。     

Indoor environments propagation simulation using a hybrid MoM and UTD electromagnetic method

Radio channel observation and characterization is indispensable in mobile communications systems development. Efficient propagation prediction is crucial for rapid and cost-effective systems deployment. On-site measurements, statistical models, propagation prediction and deterministic modeling are widely used for the qualification of radio channels. In this paper, a simulation tool for deterministic channel modeling in indoor environments is evolved. A hybrid combination of the Method-Of-Moments (MoM) and the Uniform Theory of Diffraction (Utd) is used. Statistical characteristics of a simple office room are calculated and the results are in excellent agreement with corresponding results of relative research on the field.     

A cluster-based analysis of propagation characteristics in MIMO relay channels based on wideband measurement

In this paper,the characteristics of clusters induced by a variety of propagation mechanisms in the link from the relay station(RS) to the mobile station(MS) are presented.Based on the results of high resolution channel parameter estimation,an automatic framework integrated with the manual intervention is utilized to perform the cluster identification and tracking.The power proportion and angular spread of clusters are investigated in both the line-of-sight(LOS) and non-line-of-sight(NLOS) scenarios.The measurement results indicate that the channel characteristics of clusters are different from the link from the base station to the MS due to the lower height of the RS antennas.     

A Detailed Experimental Study of the LEO Satellite to Indoor Channel Characteristics

General investigations and results from ratherextensive measurement campaigns are presented tocharacterize the propagation channel of SatellitePersonal Communication Systems; in the measurements the satellite was simulated by a helicopter andmeasurements at S band and L band were made. A newconceptual partitioning of the full link is introduced;the measrement equipment and the environment aredescribed. The major part of the paper deals withpresentation of the measurement results and theiranalyses. Measured and analyzed are average lossincluding satellite elevation and azimuth positiondependence, first-order statistics, Doppler characteristics, andwide-band characteristics. Finally, some rather generalconclusions are drawn.     

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     

基于抛物方程的无人机通信场景传播特性分析

摘 要：为提高无人机（unmanned aerial vehicle，UAV）毫米波通信场景传播特性的分析精度，基于抛物方程（parabolic equation，PE）理论建立了一种无人机通信场景传播特性分析方法，并针对都市和郊区两种典型无人机空地通信场景下的传播特性进行仿真。结果表明，提出的方法能够有效地反映地形地物变化对无人机空地通信信号传播产生的影响，对比ITU-R统计预测方法，两种场景下预测结果趋势均保持一致。该方法可实现毫米波无人机应用场景传播特性有效预测，对无人机毫米波通信系统设计、研制、测试等环节提供支撑。     

Experimental investigations of 60 GHz WLAN systems in office environment

This paper presents the results of an experimental investigation of 60 GHz wireless local area network (WLAN) systems in an office environment. The measurement setup with highly directional mechanically steerable antennas and 800 MHz bandwidth was developed and experiments were performed for conference room and cubicle environments. Measurement results demonstrate that the 60 GHz propagation channel is quasioptical in nature and received signal power is obtained through line of sight (LOS) and reflected signal paths of the first and second orders. The 60 GHz WLAN system prototype using steerable directional antennas with 18 dB gain was able to achieve about 30 dB baseband SNR for LOS transmission, about 15-20 dB for communications through the first-order reflected path, and 2-6 dB SNR when using second-order reflection for the office environments. The intra cluster statistical parameters of the propagation channel were evaluated and a statistical model for reflected clusters is proposed. Experimental results demonstrating strong polarization impact on the characteristics of the propagation channel are presented. Cross-polarization discrimination (XPD) of the propagation channel was estimated as approximately 20 dB for LOS transmission and 10-20 dB for NLOS reflected paths.     

Millimeter-Wave Propagation Channel Characterization for Short-Range Wireless Communications

This paper presents and analyzes the results of millimeter-wave 60-GHz frequency range propagation channel measurements that are performed in various indoor environments for continuous-route and direction-of-arrival (DOA) measurement campaigns. The statistical parameters of the propagation channel, such as the number of paths, the RMS delay spread, the path loss, and the shadowing, are inspected. Moreover, the interdependencies of different characteristics of the multipath channel are also investigated. A linear relationship between the number of paths and the delay spread is found, negative cross correlation between the shadow fading and the delay spread can be established, and an upper bound exponential model of the delay spread and the path loss is developed to estimate the worst case of the RMS delay spread at given path loss. Based on the DOA measurements that are carried out in a room [line of sight (LOS)] and in a corridor with both LOS and nonline-of-sight (NLOS) scenarios, radio-wave propagation mechanisms are studied. It is found that considering the direct wave and the first-order reflected waves from smooth surfaces is sufficient in the LOS cases. Transmission loss is very high; however, diffraction is found to be a significant propagation mechanism in NLOS propagation environments. The results can be used for the design of 60-GHz radio systems in short-range wireless applications.     

Modelling the transfer function in medium bandwidth radio channels during multipath propagation

A method to compute the effects of a multipath propagation channel on a line-of-sight link consists in establishing a statistical model of the channel transfer function. It is then possible to compute the outage time previsions for various communication systems, or to compare these systems by means of their signatures. To carry out this method, it is first necessary to choose a representation model of the transfer function, then to establish on an experimental basis the joint statistics of the model parameters. The authors discuss the various steps in the construction and validation of such a model and compare several proposed models from the point of view of their applications. These points are illustrated by means of results from the pacem Iexperiment.     

Measurement, modeling, and simulation of digital LOS microwavechannels with applications to outage prediction

A summary of prior work in the field of microwave line-of-sight (LOS) channel propagation measurements, channel models, and channel simulators is presented. The objective of these efforts is the reliable prediction of digital microwave radio performance on any specified link. Many digital radio outage prediction techniques are predicted upon the use of m-curves, which characterize a digital radio's performance in a simulated fading environment. These m-curves are generated by subjecting the radio under test to simulated multipath fading. This requires the use of a channel simulator that accurately emulates the fading conditions found on real LOS links. All parameters of an ideal channel simulator should be based on a model that has been validated through propagation measurements on a number of different paths. Although much progress has been made, some issues remain for further investigation. New channel propagation measurement, modeling, and simulation results that are directly applicable to these issues are given     

DS/CDMA closed-loop power control with adaptive algorithm

Closed-loop power control in the reverse link of a DS/CDMA system is analysed. The transmitter/receiver based on IS-95 and the radio propagation channel under mobile communication environments are modelled and a new power control algorithm is proposed. This algorithm utilises the burst error characteristics of the channel and can be directly applied to the current IS-95 system. The new power control algorithm, with respect to the SIR (signal to interference ratio), increases the service quality, and finally, enhances the system capacity