28 GHz MIMO无线信道特性分析与研究

基于室内视距(Line-of-Sight,LOS)和非视距(Non-Line-of-Sight,NLOS)无线信道测量数据,研究了28 GHz多输入多输出(Multiple-Input Multiple-Output,MIMO)信道参数和容量特性.具体地说,分析了莱斯K因子、时延扩展、出发角和到达角的角度扩展等信道参数,研究了MIMO信道容量及空间相关性对容量的影响.结果表明:莱斯K因子、时延扩展以及角度扩展值取决于测量环境及场景;LOS条件下时延扩展的累积分布函数(Cumulative Distribution Function,CDF)曲线与正态分布拟合优于NLOS条件下的数据;MIMO天线空间相关性越大信道容量越小.本文结果可为28 GHz无线通信系统设计提供有用信息.     

基于SBR仿真研究粗糙度对室内MIMO电波传播特性的影响

入射及反弹射线法是研究MIMO信道的有效技术.基于入射及反弹射线法对室内环境中的MIMO信道电波传播特性进行研究,在不同粗糙度条件下,针对接收功率、均方根时延扩展、MI-MO系统信道容量的分布情况及其特点进行了比较分析.仿真结果与文献已知结论一致性良好.     

Linear dependence of double-directional spatial power spectra at 2.4 and 5.2 GHz from indoor MIMO channel measurements

Multiple-input multiple-output (MIMO) double-directional spatial channel responses for co-located indoor measurements at 2.4 and 5.2 GHz using eight element uniform circular arrays are compared. Correlation coefficients of the power spectra demonstrate a linear dependence, indicating similarity in propagation mechanisms at the two frequencies.     

Measurement and Analysis of Ultra-Wideband Time Reversal for Indoor Propagation Channels

The experiments of time reversal (TR) technique with ultra-wideband (UWB) signals are conducted in indoor propagation channel by using time-domain technique. The UWB propagation channel response of a typical indoor environment is measured and time reversal technique is applied for signal transmission. The characteristics of the TR scheme for different propagation scenarios, line-of-sight (LOS) and non-LOS with different wideband receiving antennas are evaluated. The measurement results of signals focusing gain, temporal sidelobes and average signal energy for different propagation scenarios are presented. The spectral analysis of TR-UWB signals is conducted and an inherent bandwidth limit of the classical TR-UWB scheme is observed. To overcome the bandwidth restrictions, novel design architecture is proposed. The new design adjusts the TR signal by a way to support ultra-wide bandwidth and provides better matching to the UWB spectral mask with better temporal focusing features.     

Wideband indoor channel measurements and BER analysis of frequencyselective multipath channels at 2.4, 4.75, and 11.5 GHz

Results from propagation measurements, conducted in an indoor office environment at 2.4, 4.75, and 11.5 GHz, are presented. The data were obtained in small clusters of six measurements, using a coherent wideband measurement system. The channel characteristics for the three frequencies are compared by evaluating path loss, rms delay spread, and coherence bandwidth. An analytical model for evaluation of the bit-error rate (BER) of the stationary frequency selective indoor channel is developed for a coherent binary phase shift keying (BPSK) receiver, based on the complex impulse response of the channel. Computational BER results are obtained for data rates up to 50 Mb/s, using the measured multipath channel impulse responses. The BER results for a number of clusters are presented and compared for the maximum reliable data rate as inferred by the measured rms delay spread of the channel     

A Stochastic Model of the Time-Variant MIMO Channel Based on Experimental Observations

This paper proposes a stochastic multipath model that is useful for generating multiple-input–multiple-output (MIMO) channel matrices in time-variant environments. The multipath model is developed by first extracting the relevant multipath cluster characteristics from measured indoor channel data and subsequently capturing these characteristics in an autoregressive stochastic model. This model is then used to generate channel matrices whose space–time characteristics closely match those of realistic scenarios, particularly when birth and death of multipath clusters are included in the stochastic representation. Computational examples reveal the applicability and the accuracy of the approach. While the current implementation is based on data taken assuming that propagation is confined to the horizontal plane, this paper also discusses the extension of the model to describe 3-D propagation, enabling its application to a wide range of physical scenarios and antenna characteristics.      

Indoor MIMO Channel Modeling by Rigorous GO/UTD-Based Ray Tracing

This paper presents a multiple-input-multiple- output (MIMO) channel model based on rigorous ray-tracing techniques, which is based on a full 3-D implementation of geometric optics and the uniform theory of diffraction (3-D GO/ UTD). Results obtained from measurements and simulations of the correlation matrix and capacity of a 2 times 2 MIMO system in specific indoor environments at a frequency of 2 GHz are presented. The channel capacity has been calculated for the different local areas considered in open- and office-area scenarios, starting from the measurements carried out there, as well as from the ray-tracing simulated channels. The rigorous and quantitative comparison between measurements and simulations shows that the model accuracy is sufficient for the analysis and design of the different aspects of the full MIMO system. The results from the ray-tracing model can also be used to extract general statistical characteristics and parameterize statistical models for different types of environments, without the need to carry out large and costly measurement campaigns. In addition, the measured data are used to study the impact of the channel on the achievable capacity of a 2 times 2 MIMO system in typical indoor scenarios at 2 GHz.     

MIMO Channel Capacity and Configuration Selection for Switched Parasitic Antennas

Multiple-input multiple-output (MIMO) systems offer significant enhancements in terms of their data rate and channel capacity compared to traditional systems. However, correlation degrades the system performance and imposes practical limits on the number of antennas that can be incorporated into portable wireless devices. The use of switched parasitic antennas (SPAs) is a possible solution, especially where it is difficult to obtain sufficient signal decorrelation by conventional means. The covariance matrix represents the correlation present in the propagation channel, and has significant impact on the MIMO channel capacity. The results of this work demonstrate a significant improvement in the MIMO channel capacity by using SPA with the knowledge of the covariance matrix for all pattern configurations. By employing the “water-pouring algorithm” to modify the covariance matrix, the channel capacity is significantly improved compared to traditional systems, which spread transmit power uniformly across all the antennas. A condition number is also proposed as a selection metric to select the optimal pattern configuration for MIMO-SPAs.     

Capacity Improvement for TDD-MIMO Systems via AR Modeling Based Linear Prediction

The quality of channel state information (CSI) affects the performance of multiple input multiple output (MIMO) systems which employ multi-elements antenna arrays at both the transmitter and the receiver. In a time division duplex (TDD) systems, the CSI for downlink can be obtained from uplink channel using reciprocity principal. However, the performance of a MIMO system can be degraded due to channel impairments especially in fast fading scenarios when the CSI obtained from uplink is used for downlink transmission. In this paper, we study performance of autoregressive (AR) modeling based MIMO channel prediction under varying channel propagation conditions (mobile speed, multipath number and angle spread) and prediction filter order. Our simulation results show that using the predicted CSI for downlink provides capacity improvement compared to conventional method.     

28 GHz室内毫米波信道路径损耗模型研究

毫米波信道建模是第五代（the 5th Generation,5G）移动通信系统的关键技术,而路径损耗是表征毫米波信道传播大尺度衰落影响的重要参数.为了更好地理解毫米波信道的传播特性,应进行广泛的信道测量与建模.因此,对28 GHz室内环境进行了信道测量,并给出了相应的毫米波信道路径损耗模型,同时基于入射及反弹射线法/镜像法仿真分析了路径损耗传播特性.研究结果表明:实测结果与仿真结果一致性吻合良好,从而验证了入射及反弹射线法/镜像法的正确性;自由空间邻近（Close-In,CI）参考距离路径损耗模型表达式更简洁,鲁棒性更强.最后,本文给出了一种普遍适用的用来表征室内视距（Line-of-Sight,LOS）与非视距（Non-Line-of-Sight,NLOS）环境28 GHz与60 GHz毫米波信道的路径损耗模型.     

非对称毫米波大规模MIMO系统信道特性研究

为了满足下一代无线通信的需求,基于最近提出的非对称毫米波大规模多输入多输出(multipleinput multiple-output, MIMO)系统架构,研究了非对称毫米波大规模MIMO系统信道特性——信道非对称性. 根据非对称毫米波大规模MIMO系统架构和影响毫米波信道非对称性的主要因素,提出了刻画上下行信道非对称性的新参数——非对称因子. 同时利用实验室自行研发的射线跟踪平台对非对称毫米波信道进行仿真分析. 结果表明,基站收发天线阵列配置不同是导致信道非对称性的根本原因,复杂的传播环境使得这种非对称性更加突出,严重情况下室内场景非对称因子可达到?30 dB左右. 同时室外视距(line-of-sight, LoS)和非视距(non-line-of-sight, NLoS)场景下的非对称因子累积分布函数(cumulative distribution function, CDF)与高斯分布拟合程度较好,而NLoS场景下明显比LoS场景下的非对称因子小. 因此,非对称因子能够直观地描述出不同场景中上下行信道的非对称程度,而且非对称毫米波大规模MIMO系统也应以场景为导向进行信道特性分析.     

A Novel Environment Characterization Metric for Clustered MIMO Channels

In this work we introduce a novel metric for characterizing the double-directional propagation environment and use this metric to assess the performance of a SAGE parameter estimator for MIMO channels. Using the IlmProp, a geometry-based MIMO channel modeling tool, we construct synthetic channels for three different scenarios showing: (i) well separated clusters containing dense propagation paths, and single-bounce scattering; (ii) partly overlapping clusters containing widely spread propagation paths, and single-bounce scattering; (iii) unclustered multipath components (“rich scattering”), and double-bounce-only scattering. We model the scatterers and the receiver in the environment as fixed, but the transmitter as moving. The Initialization and Search-Improved SAGE (ISIS) estimation tool is used to extract the propagation paths from the constructed channels. Both true and estimated paths are fed to the new system-independent metric which genuinely reflects the structure of the channel and the compactness of the propagation paths. We use this metric to decide on the accuracy of the channel estimator. The results show a convincing agreement between true and estimated paths.     

基于几何的高速铁路协作MIMO信道建模

协作MIMO技术通过协作发射或协作接收的方式可以将干扰信号转变为有用信号,在高铁无线通信中引入该技术,能解决回波信道响应和提高系统容量。为了掌握协作MIMO技术在高铁场景中的信道特性,该文基于几何随机散射理论,提出一个高速铁路协作MIMO信道模型,简单调整该模型中的几个关键参数即可适用于高速铁路的多种场景。基于该模型计算信道冲激响应,推导多链路空间相关函数,进行数值计算、仿真分析和实测数据验证。仿真结果显示,直射分量越强,散射分量的角度扩展越小,多链路的空间相关性越强。散射次数越少,散射分量空间相关性越强。使用北京-天津高铁段LTE专网的实测数据验证理论模型的正确性。这些结论有助于认知协作MIMO信道和进行有效的测量活动。     

基于测量的6 GHz频段大规模多天线信道容量的研究

目前,大多数大规模多入多出(Multiple-Input Multiple-Output,MIMO)系统信道特性的研究都是针对理想的独立同分布瑞利信道条件,其传播环境为"适宜的",即大规模MIMO系统中各子信道是正交的.但在实际的物理信道中,其传播条件是"非适宜的",对"非适宜"条件下大规模MIMO系统信道特性的研究尤为重要.文章基于校园室外场景在6 GHz频段下进行实地无线信道测量,利用奇异值分解,探讨了真实环境中各子信道的正交性,并进行了信道容量的计算和对比.分析结果表明,随着天线数的增加,正交性明显得到提升,当发射端天线数十倍于接收天线数时,容量值提升最为明显,相比于独立同分布的瑞利信道,真实的传播环境下,各子信道并非完全正交,容量值也存在一定的差距,说明在"非适宜"条件下,大规模多天线系统性能并没有获得满增益.     

6.0-6.4GHz室内MIMO无线信道测量与传播特性分析

工作在6GHz以上高频段的多输入多输出(Multi-Input-Multi-Output,MIMO)无线通信系统是下一代无线移动通信的有力竞争方案.目前,对制约无线系统性能的高频段空时无线信道特性研究仍较少见.针对这一现状,采用基于网络分析仪的信道测量平台对典型办公环境下6.0-6.4GHz MIMO无线信道特性进行测量和分析.为了明确高频段为系统设计带来的新问题,将测量得到的高频段MIMO信道特性参数与低频段对比.对比结果表明,6.2GHz频段与2.45GHz频段MIMO信道传播特性存在较大差异.在对6.0-6.4GHz室内覆盖MIMO无线通信系统进行设计和评估时,需要基于6.0-6.4GHz频段无线信道传播的新特性对系统的关键技术和方案进行调整.     

大规模MIMO信道测量与建模综述

归纳了国内外已开展的大规模多天线协作通信系统的无线信道测量活动,总结了国际标准化机构关于大规模多天线无线信道的相关提案和候选模型,分析了大规模多天线无线信道在实际测量环境中的传播特性,基于实际测量的问题,讨论了传统的建模方法以及基于大数据理论和人工智能理论的大规模多天线无线信道建模方法,最后提出了未来的研究方向。     

Channel Sounding System for MM-Wave Bands and Characterization of Indoor Propagation at 28 GHz

The aim of this work is to present a vector network analyzer based channel sounding system capable of performing measurements in the range from 2 to 50 GHz. Further, this paper describes an indoor measurement campaign performed at 26–30 GHz. The sounding system is capable of receiving two channels and transmitting one. Using this feature a channel measurement has been performed using both a directional horn antenna and a virtual uniform circular array (UCA) at the same time. This allows for comparative studies of measured channels with two different antennas in a simultaneous way. The measurement has been conducted with 42 measurement positions distributed along a 10 m long path through an indoor laboratory environment. The transmitter was positioned such that measurements were conducted both in line-of-sight and non-line-of-sight scenarios. The measurements showed good agreement between the measurement data collected with the horn antenna and the data collected with the UCA. The propagation environment was found to be sparse both in delay and angular domain for the given scenario. Based on the performed measurement campaign together with validation measurements of the system stability, it is found that the system works as expected.     

A stochastic multipath channel model including path directions for indoor environments

A novel stochastic channel model for the indoor propagation channel is presented. It is especially for, but not limited to future communication systems with multiple antennas like space division multiple access (SDMA), spatial filtering for interference reduction (SFIR), or multiple-input/multiple-output (MIMO). The model is designed for indoor scenarios, straight forward extendable to urban environments. It is based on physical wave propagation. The new approach describes the channel by multipath components, each characterized by its transfer matrix (including loss), delay, direction of arrival, and departure. The appearance and disappearance of multipath components over time is modeled as a birth and death process, a marked Poisson process. This enables first-time the correct modeling of spatial and temporal correlations. In each modeling step, path properties change according to the motion of transmitter and receiver. The changing delay times of propagation paths yield a realistic Doppler behavior of the channel. Deterministic ray tracing results are used to produce the huge data sets required for the statistical evaluation of the parameters of the proposed model. This method enables an automated parameter extraction for new environments or frequencies. The ray tracing tool has been verified by narrowband, wideband, and directional channel measurements. The novel stochastic spatial channel model allows the simulation of third-generation broadband radio systems including arbitrary antenna configurations and patterns. System simulations for the bit-error rate of radio links can be performed including intelligent antenna configurations like SDMA, SFIR, or MIMO. Furthermore, the capacity of complete systems can be investigated.     

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.