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.     

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.     

多径信道下MIMO系统发送天线数估计

为了解决认知无线电或信号截获中多径信道下MIMO系统发送天线数估计问题,首先分析了现有模型在多径信道下失效的原因,将MIMO多径信道模型等效变换出一种虚拟信道矩阵,从而建立多径信道下MIMO系统发送天线数估计模型;然后,利用随机矩阵理论中协方差矩阵最小特征值分布的相关研究结果,证明了时不变瑞利信道的协方差矩阵最小特征值收敛于第二类Tracy-Widom分布,分析了该特点对发送天线数估计的影响,并提出一种改进的RMT估计算法来估计多径信道下MIMO系统发送天线数.最后对改进算法进行了仿真验证,结果表明在低信噪比和小数据条件下,改进算法的估计性能相比RMT算法有较大提升.     

基于宽带电力线载波通信的信道相关性研究

研究电力线信道的MIMO通信系统中子信道之间的相关性具有重要意义,以此提出了电力线信道的MIMO系统模型,并在此模型的基础上提出子信道之间的相关性,给出电力线信道MIMO模型信道之间相关系数的CDF曲线,并推导出相关信道模型。实验测量和仿真结果表明:电力线信道的MIMO系统中信道间的确存在一定的相关性,且相关系数基本满足均匀分布。     

一种基于无人机MIMO信道的容量分析方法

针对无人机通信环境特点以及多天线系统(Multi-Input Multi-Output,MIMO),建立了具有直射、反射以及散射分量的无人机MIMO三维GBSBCM信道模型,给出了无人机空时频信道相关函数的简要形式;采用信道矩阵分解、信道系数归一化的方法,推导了无人机的MIMO信道相关矩阵的计算方法;根据信道相关矩阵中参数定量分析法,仿真分析了在发射端信道未知条件下的多天线间隔对无人机MIMO信道容量的影响。通过容量的影响分析,对无人机MIMO天线间隔的合理配置具有一定的理论参考价值和实际应用价值。     

MIMO信道中衰落信号的空域相关性评估

将MIMO(多输入多输出)信道建立为Nakagami衰落信道,进一步推导单元天线接收多径衰落信号的空域相关系数的通用解析式,并在均匀分布、余弦分布、高斯分布和拉式分布的来波功率角谱下分别进一步评估接收信号的空域相关性,分析各参数对相关系数的影响,比较各种来波功率角谱下相关性的数值结果,这些对于准确分析MIMO系统性能与设计MIMO多天线系统是十分必要的.     

航空图像回传系统中MIMO信道的容量分析

多入多出技术同时采用多天线发射和多天线接收,能够大大提高无线通信系统的容量和频谱利用率。在空一地无线传输MIMO信道模型的基础上,讨论了在航空图像传输链路中应用MIMO系统的理论基础,结合数值模拟分析的方法对MIMO信道的平均容量和容量互补累积分布函数进行了分析。研究表明:在不相关Ricean信道中MIMO系统的容量随着天线数目的增加渐近线性增加;而在相关情况下渐近对数增加。     

基于球面波的非平稳性MIMO信道建模

提出了一种新的无线通信物理信道模型，可用于研究多输入多输出(Multiple-Input Multiple-Output, MIMO)系统中天线与传播信道之间的相互作用。利用球矢量波系数展开、天线散射矩阵和非平稳性建模，推导出了信道矩阵的扩展形式。引入了剥离天线影响的信道矩阵，并将其协方差统计量表示为共极化分量和交叉极化分量的双边功率角谱(Double-Directional Power-Angular Spectrum, DD-PAS)的函数。模型对于研究指定传播信道中天线设计具有重要价值，对MIMO系统在典型的传播环境中的应用进行了仿真分析，验证了所提出信道的准确性，结果表明提出的模型可以用于未来无线通信系统建设中。     

天线匹配对莱斯信道下紧凑MIMO系统性能的影响

深入研究了存在天线互耦和空间相关时,天线匹配网络对莱斯信道下多输入多输出MIMO系统性能的影响,建立了包含相关莱斯信道、天线互耦和匹配网络的(MIMO)系统模型.通过仿真分析了匹配阻抗、天线互耦、空间相关性以及信道衰落环境对包络相关性和信道容量的影响.实验结果表明:莱斯信道下匹配阻抗对MIMO系统的影响与瑞利信道情况下有所不同,适当地选择天线匹配阻抗可以改善MIMO系统的性能.     

大规模MIMO相关信道下的联合天线分组和天线选择

在大规模多输入多输出系统中,针对密集部署的大型天线阵列之间的强相关性会抑制天线选择增益效果的问题。在系统下行链路场景下建立空间相关信道模型,提出了基于天线分组的天线选择算法。根据瞬时信道相关矩阵将天线阵列划分为若干组,保证各组内天线之间相关性较强。在完成天线分组的基础上,基于信道矩阵列范数准则在各组发射天线与接收天线之间构成的子信道矩阵中选择天线,进而构造有效发射天线与接收天线之间的信道矩阵。仿真分析了所提天线选择算法对系统遍历和速率的影响,结果表明,在基站天线数为32、接收天线数为2、选择天线数为2、天线相关因子为0.9的假设下,当信噪比为10 dB时,与基于相邻天线分组的天线选择算法相比,所提算法使系统和速率约提高了27.5%,且所提算法若要与最优天线选择算法达到相同的和速率,仅需将其信噪比提升1～2 dB即可。     

关于MIMO系统的天线子集选择性能的研究

讨论了有关 MIMO 无线系统中的天线子集选择性能的问题。首先建立了 MIMO 信道模型,对信道模型进行了分析,接着对信道矩阵为非满秩的情况进行了研究,分别采用几种组合对发射、接收天线进行选择,得出不同组合对信道容量的影响。仿真结果表明,选择发射天线可以增加信道容量,选择接收天线虽然无助于增加信道容量,但在不会严重降低信道容量的前提下,可以降低系统的成本。     

空时频MIMO信道建模与实现

该文根据角度功率谱、多普勒谱、功率时延谱及收发两端天线的结构,建立了一种多抽头的宽带MIMO信道模型。在建模过程中提出了一种改进的成形滤波器法,通过加入随机相移来消除各条路径的相关性,从而能够更好地仿真出独立的衰落信道。利用Matlab软件,创建了一个无线MIMO信道仿真平台,并针对3GPP标准MIMO信道模型进行了仿真。仿真结果表明用该文方法产生的信道特性与理论结果十分接近,从而验证了改进信道模型能够较好地模拟MIMO系统的空间信道。     

Impact of spatial correlation on the performance of orthogonal space-time block codes

We analyze the impact of transmitter and receiver spatial correlation on the performance of a multiple-input multiple-output (MIMO) system which applies an orthogonal space-time block code with no channel state information at the transmitter and perfect channel state information at the receiver. We derive a general formula for the bit error rate of a MIMO system with arbitrary number of transmit and receive antennas as a function of the correlation at the transmitter and the receiver. We prove that the diversity advantage is given by M/spl middot/N if M is the rank of the transmit correlation matrix and N the rank of the receive correlation matrix, respectively.     

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.     

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。     

Spatial precoder design for space–time coded MIMO systems: based on fixed parameters of MIMO channels

In realistic channel environments the performance of space–time coded multiple-input multiple output (MIMO) systems is significantly reduced due to non-ideal antenna placement and non-isotropic scattering. In this paper, by exploiting the spatial dimension of a MIMO channel we introduce the novel idea of linear spatial precoding (or power-loading) based on fixed and known parameters of MIMO channels to ameliorate the effects of non-ideal antenna placement on the performance of coherent (channel is known at the receiver) and non-coherent (channel is un-known at the receiver) space–time codes. Antenna spacing and antenna placement (geometry) are considered as fixed parameters of MIMO channels, which are readily known at the transmitter. With this design, the precoder is fixed for fixed antenna placement and the transmitter does not require any feedback of channel state information (partial or full) from the receiver. We also derive precoding schemes to exploit non-isotropic scattering distribution parameters of the scattering channel to improve the performance of space–time codes applied on MIMO systems. However, these schemes require the receiver to estimate the non-isotropic parameters and feed them back to the transmitter. Closed form solutions for precoding schemes are presented for systems with up to three receive antennas. A generalized method is proposed for more than three receive antennas.     

Ergodic channel capacity of the spatial correlated rayleigh MIMO channel

The theoretical capacity of the spatial correlated Rayleigh multiple input multiple output (MIMO) channel is an important issue in MIMO technology. In this article, an ergodic channel capacity formula of the spatial correlated rayleigh MIMO channel is provided, which is deduced when two antennas exist at either the transmitter or the receiver. The multi-dimensional least-squares fit algorithm is employed to narrow the difference between the theoretical formula capacity and the practical capacity. Simulation results show that the theoretical capacity approaches the practical one closely.     

二进制猫群算法在大规模MIMO天线选择中的应用

在多输入多输出(MIMO)系统中,天线选择技术平衡了系统的性能和硬件开销,但大规模MI-MO系统收发端天线选择复杂度问题一直没有得到很好的解决.基于信道容量最大化的准则,采用两个二进制编码字符串分别表示发射端和接收端天线被选择的状态,提出将二进制猫群算法(BCSO)应用于多天线选择中,以MIMO系统信道容量公式作为猫群的适应度函数,将收发端天线选择问题转化为猫群的位置寻优过程.建立了基于BCSO的天线选择模型,给出了算法的实现步骤.仿真结果表明所提算法较之于基于矩阵简化的方法、粒子优化算法具有更好的收敛性和较低的计算复杂度,选择后的系统信道容量接近于最优算法,非常适用于联合收发端天线选择的大规模MIMO系统中.     

MIMO系统信道容量研究

针对单用户MIMO系统信道的容量特性展开研究。首先详细推导了无衰落信道下信道容量表达式,然后重点分析了瑞利衰落信道下,接收端已知信道状态信息,发射端已知信道状态分布时的容量特性。最后分别针对瑞利衰落信道下,采用发射分集、接收分集以及BLAST传输结构的系统容量进行仿真。仿真结果表明:给定发射功率,独立的瑞利衰落信道条件下,MIMO系统容量随最小天线数目的增加而线性增加,极大地提高了系统容量。     

Multiple-input-multiple-output measurements and modeling in Manhattan

Narrowband multiple-input-multiple-output (MIMO) measurements using 16 transmitters and 16 receivers at 2.11 GHz were carried out in Manhattan. High capacities were found for full, as well as smaller array configurations, all within 80% of the fully scattering channel capacity. Correlation model parameters are derived from data. Spatial MIMO channel capacity statistics are found to be well represented by the separate transmitter and receiver correlation matrices, with a median relative error in capacity of 3%, in contrast with the 18% median relative error observed by assuming the antennas to be uncorrelated. A reduced parameter model, consisting of 4 parameters, has been developed to statistically represent the channel correlation matrices. These correlation matrices are, in turn, used to generate H matrices with capacities that are consistent within a few percent of those measured in New York. The spatial channel model reported allows simulations of H matrices for arbitrary antenna configurations. These channel matrices may be used to test receiver algorithms in system performance studies. These results may also be used for antenna array design, as the decay of mobile antenna correlation with antenna separation has been reported here. An important finding for the base transmitter array was that the antennas were largely uncorrelated even at antenna separations as small as two wavelengths.