天线互耦对MIMO无线信道性能的影响

基于多天线系统等效网络模型,导出通用耦合系数矩阵,进一步推导天线单元平均接收功率以及空域相关系数的解析式,分析互耦对平均接收功率以及互耦与平均到达角对MIMO无线信道空域相关性及其容量的影响,并给出互耦无影响与天线单元功率平衡以及互耦解相关的条件,最后给出一些数值结果以指导MIMO多天线设计.     

接收天线阵列三维空域相关性快速评估算法

针对任意三维到达波角度分布时,接收天线阵列的空域相关性评估比较复杂,通常只能采用数值积分方法的问题,本文提出了一种基于角谱域脉冲采样的三维空域相关性评估快速算法。该算法首先利用特定采样脉冲对三维入射波功率角谱进行二维采样,然后根据采样脉冲的空域相关系数加权叠加获得不同天线接收信号之间的空域相关性,大大降低相关性计算的复杂度。同时,文中还推导获得基于最小均方误差准则的采样脉冲表达式及其对应的空域相关系数精确解析式和近似表达式。仿真和分析结果表明,当角谱域采样间隔小于10度时,该快速算法的最大误差小于0.01,但运算时间远远小于数值积分方法及其它评估方法,可满足信道估计和天线阵列设计等实际需求。      

空间衰落相关性对MIMO多天线信道特性研究

文中对常用的波达信号在拉普拉斯(Laplace)角谱分布函数进行深入的研究。分析MIMO阵列多天线系统在波达信号角功率谱分布下的衰落相关系数并推导出了其通用精确和近似表达式。阐明了波达信号分布与MIMO阵列间的内在机理及近似算法的优越性和使用限制条件,进而提出了改进型的空间散射体分布模型的波达信号角谱分布。研究结果为未来5G MIMO多天线布局和设计提供了理论指导和研究基础。     

基于空间信道模型的MIMO系统建模与仿真

研究了基于空间信道模型(SCM)的空域相关矩阵,搭建了MIMO通信信道仿真平台,同时考虑时延扩散、多普勒效应、波达方向及角度扩散等多种信道参数,通过蒙特卡罗方法计算了MIMO系统的信道容量、空时相关性、衰落特性及功率延迟分布特性.指出了在信道的去极化作用下,无线通信系统的多径衰落可以采用极化分集和天线分集等技术进行克服,平均入射角对系统性能起着关键的作用.     

一种新的MIMO信道模型

实际无线通信环境中发送天线之间以及接收天线之间存在相关性.针对以上特点,从多径MIMO信道的特性出发,首先建立发射天线相关系数矩阵和接收天线相关系数矩阵,并将它们引入无线信道的莱斯MIMO信道模型中.最后通过分析LOS MIMO信道相关模型和瑞利衰落MIMO信道相关模型,给出了具体的建模步骤.仿真结果表明采用本文方法产生的信道模型的MIMO系统误码率更低,从而验证了该信道模型能够较好地模拟MIMO系统的空间信道.     

多输入多输出信道空域相关性评估简化模型

针对任意散射环境的多输入多输出(MIMO)信道,提出一种基于角度域脉冲采样的空域相关性评估简化模型,推导常见采样脉冲空域相关系数的近似简化解析式,并详细分析简化模型中采样脉冲数目和加权系数的选取依据,大大降低MIMO衰落信号空域相关性分析的复杂度.仿真结果表明:当到达波角度扩展为5到20度且采样脉冲数目大于36时,本文...     

三维空间多天线相关性及互耦影响研究

针对三维传播环境下多天线系统空域相关性评估问题,首先将达波信号二维角度谱建模为更为通用的von Mises-Fisher（vMF）分布,并推导了不同阵列流型天线空域相关系数的解析式和近似表达式;然后分析互耦机理及其对接收信号矢量的影响,据此推导了互耦效应下天线空域相关性的闭式表达式,并给出了存在互耦的相关性与无互耦相关性之间的内在关系.仿真结果表明,本文推导的天线相关性表达式与数值计算结果非常吻合.另外,小角度扩展时,考虑互耦效应的天线空域相关曲线围绕着无互耦时的相关性曲线上下波动,且面型阵列具有更好的抗互耦能力.     

窄带波束信道MIMO系统的容量分析

最近的研究表明,多输入多输出(MIMO)技术在不增加功率和带宽消耗的情况下具有大幅提高无线通信速率的潜力.在传统的MIMO系统(称为天线信道MIMO系统)中,多个接收天线的输出被直接选作多输出信号.提出了波束信道MIMO系统的结构.在波束信道MIMO系统中,多个波束的输出被选作多输出信号.基于阵列方向响应矢量,提出了窄带MIMO信道冲激响应矩阵的仿真算法.基于提出的信道冲激响应矩阵算法,给出了天线信道MIMO系统和波束信道MIMO系统容量极限的分析算法.理论分析和仿真结果都表明:波束信道能够提高信噪比(SNR),降低信道间的互相关性,因此波束信道MIMO系统比天线信道MIMO系统具有更大的容量极限.     

三维空间MIMO信道接收天线阵列互耦效应及系统容量分析

针对非频率选择性瑞利衰落MIMO(multiple-input multiple-output)信道,建立了接收天线阵列的三维空间信道模型,将MIMO的一般信道建模推广到三维空间域。在建模过程中利用天线阵列在互耦效应下的等效网络模型,推导出三维空间域模型下的互耦相关性的通用表达式,阐明了互耦效应下相关性与无互耦相关性之间的关系。应用通用表达式分析了当接收端为不同的天线阵列结构时,入射信号的中心到达角和角度扩展分别对于在互耦效应下信道容量的影响。分析结果验证了不同的角度扩展对于互耦相关性的影响,揭示了在互耦效应下影响系统容量的主要因素为入射信号的平均中心到达角。     

MIMO信号周期平稳特性研究

基于无线移动衰落信道下的多天线系统(Multiple Input Multiple Output,MIMO)传输模型和信号周期平稳特性理论,研究了基于垂直分层空时码(Vertical Bell Laboratories Layered Space Time,V-BLAST)技术的MIMO信号的周期平稳特性。理论分析和仿真结果显示:衰落信道下的MIMO系统接收信号具有周期平稳特性,如果对接收信号进行过抽样,则可以获得具有周期平稳特性的接收序列,从而可以利用周期平稳特性理论进行数字化的信号处理。     

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.     

Pre-Coding for MIMO Systems in Frequency-Selective Fading Channels

Multiple input multiple output (MIMO) systems showed good utilization of channel characteristics. In MIMO systems multiple signals are transmitted using multiple antenna system. This provides each receiver the combined signals and hence, array processing techniques helps in reducing the effects of interference among them. In this paper we devise the use of pre-coded MIMO system to reduce the effects of frequency selectivity and hence, enhance the systems capacity and/or reduce the bit error rate. In this technique we introduce a temporal pre-coder on each antenna signal; this creates a deterministic multi-path signals similar to signals received when the channel is multi-path fading channel. The same antenna signal will arrive at each receiver forming orthogonal sub-space and the receiver will be simple add and delay of the received signals. Ant colony optimization is used in this paper to select the best pre-code. Results showed that we can diagonalize the channel matrix and practically eliminate the interference for frequency selective fading channel. Simulation of two transmitting two receiving antennas pre-coded MIMO system showed that the capacity can be doubled.     

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。     

机舱内分布式MIMO系统信道容量分析

采用自主搭建的信道测量平台测得了机舱环境下分布式MIMO系统的信道冲击响应矩阵。根据实测的信道矩阵分别计算了4种具有不同收发天线数目的分布式MIMO系统的信道容量。为了便于比较,SISO系统的信道容量也通过实测数据进行了计算。计算结果表明：在机舱环境下,采用分布式MIMO系统和采用SISO系统相比能够显著提高系统信道容量,说明分布式MIMO系统可以充分满足未来机舱内无线通信高速率数据传输的需求。     

Effect of Signal and Noise Mutual Coupling on MIMO Channel Capacity

In this paper we analyze the impact of mutual coupling on MIMO channel capacity, considering its effect on both signal and thermal noise. We calculate noise correlation matrix in the multi-antenna system with closely spaced antenna by applying Nyquist’s thermal noise theorem. Then, we employ the noise correlation matrix in the channel capacity formula, which enables the identification of thermal noise correlation contribution on the MIMO channel capacity. In addition, we examine the variations in the mean branch signal-to-noise ratios (SNR) due to the noise correlation. Our simulation results corroborate the theoretical analysis that mean and outage MIMO channel capacity is underestimated if noise correlation due to mutual coupling effect is not accounted for.     

On the Capacity and Design of Limited Feedback Multiuser MIMO Uplinks

The theory of multiple-input–multiple-output (MIMO) technology has been well developed to increase fading channel capacity over single-input–single-output (SISO) systems. This capacity gain can often be leveraged by utilizing channel state information at the transmitter and the receiver. Users make use of this channel state information for transmit signal adaptation. In this correspondence, we derive the capacity region for the MIMO multiple access channel (MIMO MAC) when partial channel state information is available at the transmitters, where we assume a synchronous MIMO multiuser uplink. The partial channel state information feedback has a cardinality constraint and is fed back from the basestation to the users using a limited rate feedback channel. Using this feedback information, we propose a finite codebook design method to maximize the sum rate. In this correspondence, the codebook is a set of transmit signal covariance matrices. We also derive the capacity region and codebook design methods in the case that the covariance matrix is rank one (i.e., beamforming). This is motivated by the fact that beamforming is optimal in certain conditions. The simulation results show that when the number of feedback bits increases, the capacity also increases. Even with a small number of feedback bits, the performance of the proposed system is close to an optimal solution with the full feedback.      

Analysis of macroscopic diversity combining of MIMO signals in mobile communications

In this paper, the system model and performance analysis of macroscopic diversity combining (MDC) multiple-input multiple-output (MIMO) systems are presented for mobile cellular communication applications. The channel capacity of MIMO systems will deteriorate if the dual antenna array (DAA) spacing is insufficient or the scattering environment does not provide completely uncorrelated channels. In addition, the shadowing component of the directional signal is a common factor among the scattered channels, resulting in significant reductions in obtainable channel capacity. Therefore, in this paper, a macroscopic diversity topology is applied to maximize the spatial multiplexing gain while combating the shadowing phenomena. The channel capacity as well as its upper and lower bounds are derived for MIMO-based MDC systems. Additionally, the outage capacity for the proposed MDC system topology has been analyzed. Compared to a single communicating MIMO system pair, the results show that the macroscopic diversity MIMO communication topology enables a larger number of uncorrelated shadowed and scattered channels to exist, and therefore, improvements of enhanced channel capacity and reduced outage is obtained.     

Interference Mitigation in MIMO Systems by Subset Antenna Transmission

This paper investigates subset antenna transmission (SAT) for multiple-input multiple-output (MIMO) systems in the presence of strong dominant co-channel interferer. The capacity gain from SAT is investigated in the context of optimal antenna subset selection and power allocation. The SAT does not require channel state information of the co-channel interference, and achieves capacity gains by distributing the transmit power equally over a selected subset of the transmit antennas. The capacity gain of the SAT method is analyzed in terms of transmit power and eigenvalues of channel matrix, and its performance in V-BLAST MIMO systems with various signal constellations is evaluated by computer simulation.     

基于信号共轭周期平稳特性的MIMO信道估计方法

MIMO系统中,由于各天线间干扰以及码间干扰等问题的存在,信道估计性能成为影响系统性能的决定性因素。直接利用接收信号的二阶统计特性进行信道估计是目前比较通用的方法之一。本文基于信号的二阶共轭周期平稳特性。提出了一种适用于MIMO系统的信道估计方法,该方法直接利用接收信号的共轭周期自相关函数间的关系,消除了系统的码间干扰(ISI)和信道间的互扰(CCI),分离出信道矩阵的各个元素分别加以估计。该估计算法不需要事先知道信道的准确阶数,整个估计结果不受信道阶数过估计的影响。由于一般的信号不具有共轭周期平稳特性,因而本文同时还提出了一种在MIMO系统中构造和处理二阶共轭周期平稳特性信号的方法。本文最后给出的仿真结果显示所提的估计方法具有良好的估计性能。     

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。