室内可见光通信MIMO信道相关性研究

多输入多输出(MIMO)技术是室内可见光通信发展的一个重要方向,信道相关性是影响其性能的一个重要因素。为此,研究了影响MIMO信道相关性的主要因素。首先,根据朗伯辐射模型,从理论上建立了MIMO信道模型并推导了MIMO信道相关性与空间距离参数的关系;在此基础上,建立了实验验证平台,通过实验验证了理论结果。理论及实验结果都表明:MIMO信道相关性随着发光二极管(LED)距离的增大而增大;随着光电探测器(PD)距离的增大而增大;随着LED平面与PD平面距离的减小而减小。研究结果对于室内可见光MIMO通信中LED及PD的布局有重要的指导意义。     

基于空时相关性的MIMO无线信道建模及仿真

针对多输入多输出无线信道的空时相关性，文章提出了一种改进的MIMO无线信道模型。该模型利用改进的Jakes模型仿真器来产生独立同分布零均值的复高斯随机变量，从而保证各个传播路径间的相关性很小。仿真结果表明改进的MIMO无线信道模型能够准确的描述出空时相关的MIMO无线信道的统计特性，即空间相关性随天线单元间距增大而战小，随散射信号角度扩展增大不是一致减小．     

三维粗糙面上的MIMO信道模型

多天线构成的多输入多输出MIMO（Multiple-Input Multiple-Output）信道是B3G/4G系统的关键技术之一。文章建立下垫三维粗糙面的MIMO信道模型,用基尔霍夫（KA,Kirchhoff approximation）近似随机粗糙面散射的数值计算方法研究下垫粗糙面产生的随机多路径传输对MIMO信道矩阵的影响,并数值地讨论接收、发射天线阵列位置以及下垫粗糙面几何参数对MIMO系统信道容量的影响。结果表明,双站距离大、天线高度低时,下垫随机粗糙面对MIMO信道容量的影响显著。当天线阵元间距小时,下垫粗糙面将显著增大MIMO系统信道容量;当天线间距大时,粗糙面减小MIMO系统信道容量。     

频率选择性衰落环境中MIMO系统信道容量研究

提出了一种频率选择性环境中多输入多输出系统信道容量的分析方法.该方法基于接收均匀圆阵构建了蕴含天线间距、散射角大小和多径数等模型物理参数的衰落空间相关模型。分析了MIMO OFDM系统信道衰落的统计特性。在此基础上利用Wishart分布的性质详细推导了任意天线数的MIMO OFDM系统的信道容量及其上下限。该方法回避了已有方法需要求取信道衰落相关特征值概率密度函数的问题，降低了运算量；并且可以有效地分析在频率选择性环境中模型物理参数对信道容量的影响。仿真结果表明，随着天线间距的增大，系统的平均信道容量也逐渐增大；但当天线间距增大到一定程度后,信道容量变化不明显，散射角越大，信道容量的增长速率越快，当接收信噪比较高时,平均信道容量的上下限接近于其实际值。     

极化分集时MIMO系统的信道容量

论文给出了MIMO系统采用极化分集时的信道模型,对接收信号空间相关性和信道容量进行了研究,并对其随接收天线极化夹角的变化情况进行了分析。研究表明,采用极化分集技术的MIMO系统具有良好的非相关衰落特性,信道容量得到显著提高。     

动态MIMO散射无线信道模型及性能分析

基于多入多出(MIMO)散射无线信道模型,提出一种动态MIMO散射无线信道模型,分析散射体及其收发多天线的运动对MIMO无线信道空域相关性及其容量的影响,得出这种影响是由收发天线的初始位置、运动速度及其传播环境决定的.数值模拟验证了这种影响,并指出空域相关性随天线单元间距增大而减小,随散射信号角度扩展增大不是一致减小,存在使相关性达最小的角度扩展值.     

3G LTE空间信道模型的三维修正及容量分析

空间信道模型SCM(Spatial Channel Model)是3GPP用于LTE系统仿真的MIMO二维信道模型。本文在SCM模型的基础上,综合考虑基站端和移动台端电波的离开角和到达角的三维特性,给出了三维MIMO信道模型的信道参数描述,提升了信道建模的准确度,并推导出该信道模型下包含极化特性的MIMO信道系数表达式。同时探究了天线间距、水平角扩展、俯仰角扩展等对MIMO信道空时相关性的影响。研究结果显示,随着俯仰角扩展从0°到60°增大,散射环境越来越强,信号在空间的色散度越高,不同天线单元接收到的信号之间的相关性越小,信道容量将会越大。     

相关Rician衰落信道下紧凑MIMO系统的容量分析

研究了Rician衰落信道下采用紧凑型双偶极子阵列的MIMO系统容量,建立了相关Rician衰落信道下紧凑MIMO系统的模型,深入分析了天线互耦、空间相关性、功率分配方案以及信道衰落环境对信道容量的影响。数值结果表明天线间距较小时,互耦和相关性会导致信道容量的损失,而在某些情况下互耦和相关性的影响会使信道容量有所增加。     

天线布局对于MIMO可见光通信的影响

针对多输入多输出(MIMO)的室内可见光 通信(VLC)系统,通过改变发光二极管(LED)及 光接收机的空间分布,分析了天线布局对于系统性能的影响。VLC系统采用基于朗伯辐射 的信道模型, 使用常见的重复编码(RC)、空间复用(SMP)和空间调制(SM)3种MIMO技术,分析了两 种系统。第1种为4×6系统,即发射端的4个LED采用正方形布局,光接收机的6个探测器采用正六边形、 矩形和三角 形布局。仿真结果表明,在室内中心处,对于RC,三角形布局的误码率(BE R)性能最好;对于SMP和SM,正六边形和三角形的性能相近,且优于矩形布 局。在室内非中心处,正六边形是3种技术的最优选 择。第2种为8×8系统,LED和光检测器分别采用正八边形、正方形布局。仿真结果表明, 发送端采用正方形布局时系统性能较好。     

同信道干扰下相关多输入多输出信道容量分析

在Rayleigh衰落环境下,研究了具有同信道干扰的多输入多输出(MIMO)信道容量问题,分析了通信用户发送端带有空间相关性的情况。假设接收端完美地知道信道状态信息而发送端不知道,基于矩阵变量分布理论,推导出MIMO信道互信息之矩生成函数的精确闭式表达式。利用该表达式进一步推导出MIMO遍历信道容量的精确表达式。用数值结果验证了分析结果的正确性,并给出各种参数对遍历信道容量的影响。     

Channel capacity of the distributed MIMO relay in visible light communication systems

Visible light communication (VLC) is a novel paradigm that uses light-emitting diode (LED) light as an information carrier and has several advantages over radio-frequency communication in terms of the bandwidth, security and multi-path fading. When the VLC system is considered in an indoor environment, LED lamps, which are placed at the ceiling to provide ambient light, can offer rich spatial resources for VLC as distributed intermediate relaying terminals. This paper introduces a novel distributed multiple-input multiple-output (D-MIMO)-relaying VLC scheme and analyzes its communication performance. Using the sum rate of the broadcasting and multiple access relay channels, a tight upper bound on the channel capacity was derived. The numerical results showed that the D-MIMO-relaying VLC scheme outperformed the direct-path-based scheme in terms of the channel capacity. For a given indoor environment, the capacity of D-MIMO-relaying VLC can be improved further by selecting the appropriate relay parameters, such as the number of LED–PD pairs in a relay, distance between relays and height of relays.     

Spatially and temporally correlated MIMO channels: modeling and capacity analysis

Wireless communication systems employing multiple antennas at both the transmitter and receiver have been shown to offer significant gains over single-antenna systems. Recent studies on the capacity of multiple-input-multiple-output (MIMO) channels have focused on the effect of spatial correlation. The joint effect of spatial and temporal correlation has not been well studied. In this paper, a geometric MIMO channel model is presented, which considers motion of the receiver and nonisotropic scattering at both ends of the radio link. A joint space-time cross-correlation function is derived from this model and variates with this joint correlation are generated by using the vector autoregressive stochastic model. The outage capacity of this channel is considered where the effects of antenna spacing, antenna array angle, degree of nonisotropic scattering, and receiver motion are investigated. When n transmit and n receive antennas are employed, it is shown that the outage capacity still increases linearly with respect to n, despite the presence of spatial and temporal correlation. Furthermore, analytical expressions are derived for the ergodic capacity of a MIMO channel for the cases of spatial correlation at one end and at both ends of the radio link. The latter case does not lend itself to numerical evaluation, but the former case is shown to be accurate by comparison with simulation results. The proposed analysis is very general, as it is based on the transmit and receive antenna correlations matrices.     

3×3多天线系统衰落相关与信道容量研究

为分析天线间距和散射角等信道物理参数对多输入多输出系统信道容量的影响,提出了一种相关衰落环境中信道容量的分析方法。该方法基于接收均匀圆阵构建了蕴含信道物理参数的衰落相关矩阵。并由此详细推导了3×3多天线系统信道容量的闭式表达。结果表明,相关矩阵特征值的个数和大小决定了系统信道容量的大小。该方法回避了已有算法需求取相关衰落信道特征值概率密度函数的问题,降低了运算量,可以被推广到任意收发天线数的多输入多输出和多输入多输出-频分复用系统。仿真结果表明,天线间距增大,信道容量随之增大。但是当天线间距增大到衰落相关的第一个过零点时,信道容量达到最大值,再增大天线间距对信道容量影响很小。散射角越大,信道容量收敛到最大值速率越快。     

Outdoor MIMO wireless channels: models and performance prediction

We present a new model for multiple-input-multiple-output (MIMO) outdoor wireless fading channels and their capacity performance. The proposed model is more general and realistic than the usual independent and identically distributed (i.i.d.) model, and allows us to investigate the behavior of channel capacity as a function of the scattering radii at transmitter and receiver, distance between the transmit and receive arrays, and antenna beamwidths and spacing. We show how the MIMO capacity is governed by spatial fading correlation and the condition number of the channel matrix through specific sets of propagation parameters. The proposed model explains the existence of "pinhole" channels which exhibit low spatial fading correlation at both ends of the link but still have poor rank properties, and hence, low ergodic capacity. In fact, the model suggests the existence of a more general family of channels spanning continuously from full rank i.i.d. to low-rank pinhole cases. We suggest guidelines for predicting high rank (and hence, high ergodic capacity) in MIMO channels, and show that even at long ranges, high channel rank can easily be sustained under mild scattering conditions. Finally, we validate our results by simulations using ray tracing techniques. Connections with basic antenna theory are made.     

阵元间距对室内MIMO系统信道容量的影响

引入散射体的随机分布模型,讨论了室内微微蜂窝4×4MIMO系统中接收端阵元间距对各子信道间衰落相关性及信道容量的影响.数值模拟结果说明在室内环境有丰富散射体存在且接收端放置天线的空间受限的情况下,阵元间距可做得很小（0.5λ）,便可以得到较大的信道容量,此时相关系数仅为0.1左右,对信道容量的影响很小.     

平坦衰落环境中多输入多输出系统衰落相关与信道容量研究

为分析模型物理参数和天线排列方式对多输入多输出系统信道容量的影响,提出了一种平坦衰落环境中信道容量的研究方法。该方法基于接收均匀圆阵和均匀线阵分别构建了蕴含模型物理参数的相关矩阵,并利用Wishart分布的性质推导了信道容量上下限。该方法回避了求取衰落相关矩阵特征值的概率密度函数,降低了运算量;可被推广到多天线-频分复用系统。仿真结果表明,天线间距较小时,采用均匀圆阵比均匀线阵的系统信道容量要高;天线间距增大到一定程度后,系统信道容量达到饱和。散射角越大,信道容量的增长速率越快且采用均匀线阵比均匀圆阵系统的信道容量高。接收信噪比较大时,平均信道容量上下限基本接近其实际值。     

基于射线跟踪法的73 GHz走廊环境MIMO信道特性研究

为了研究5G室内走廊环境的毫米波传输特性,通过射线跟踪仿真方法预测了室内走廊环境下73 GHz毫米波MIMO信道特性。介绍了实验的仿真环境和射线跟踪仿真预测的实验方法和具体参数设置。研究了室内走廊环境下73 GHz毫米波MIMO信道的路径损耗、RMS时延扩展和MIMO信道容量变化。发现了路径损耗斜率和RMS时延数值较小。研究MIMO容量随距离变化时发现,收发机沿走廊纵向方向中间处会产生容量峰值,主要是由于该处散射丰富,NLOS分量大。研究MIMO容量特性发现增大天线间距和增大天线阵列规模可以提升容量,但是采用4×64 Massive MIMO相对于采用4×4 MIMO时容量提升较为有限。实验证实了73 GHz毫米波MIMO可以用于室内走廊环境。     

MIMO信道在巷道中的GBDB模型分析

多输入多输出(MIMO)技术可以有效减弱无线传输多径衰落现象。建立矿井巷道环境下MIMO信道的三维GBDB模型,推导了该模型的空时相关函数,并对矿井下MIMO信道容量进行了数值仿真。结果表明,矿井巷道中的空间相关性对MIMO系统容量的影响很大,增加接收端天线数量、增大天线间距可以大幅度提高系统的信道容量。     

Impact of the propagation environment on the performance of space-frequency coded MIMO-OFDM

Previous work on space-frequency coded multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) has been restricted to idealistic propagation conditions. In this paper, using a broadband MIMO channel model taking into account Ricean K-factor, transmit and receive angle spread, and antenna spacing, we study the impact of the propagation environment on the performance of space-frequency coded MIMO-OFDM. For a given space-frequency code, we quantify the achievable diversity order and coding gain as a function of the propagation parameters. We find that while the presence of spatial receive correlation affects all space-frequency codes equally, spatial fading correlation at the transmit array can result in widely varying performance losses. High-rate space-frequency codes such as spatial multiplexing are typically significantly more affected by transmit correlation than low-rate codes such as space-frequency block codes. We show that in the MIMO Ricean case the presence of frequency-selectivity typically results in improved performance compared to the frequency-flat case.