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。     

互耦效应对双散射MIMO系统信道容量影响研究

多入多出(MIMO)传输技术是第四代移动通信系统的关键技术之一,而小尺寸间隔下天线阵元间的互耦效应则是有可能影响MIMO系统性能的一个重要因素。文中首先研究分析了一种接近实际电波传输环境的、收发端皆存在散射体的双散射MIMO信道传输模型,然后将天线互耦效应引入此MIMO传输系统;接下来通过建立多天线系统等效互耦效应网络模型,推导了互耦效应影响下空间相关系数和信道容量表达式;最后通过计算机仿真研究了双散射环境下天线阵元互耦对MIMO系统信道容量的影响。仿真实验表明:双散射环境下,互耦效应将降低MIMO系统信道容量。     

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.     

室内MIMO无线信道模型和信道容量研究

本文从工程的实际出发,首先提出一种修正的室内MIMO无线信道模型,该模型有效地修正先前室内MIMO无线信道模型的不足,具有明显吻合室内实际通信环境的特点,然后分析天线方向性以及天线单元间的互耦对室内MIMO无线信道容量的影响.数值模拟验证了这种影响,并得到在一定条件下互耦导致的天线方向图畸变产生角度分集,提高信道容量,互耦对空域相关性无影响的条件以及室内丰富的多径使天线方向性对信道容量的影响不明显等结论.最后,实验也证实理论分析.     

互耦对MIMO/SA系统误码率影响的分析

新一代无线移动通信系统采用多天线技术,多天线的互耦效应对系统的影响已越来越受到关注,成为研究热点。研究了互耦现象对MIMO/SA通信系统误码率的影响,首先建立了一种新型的MIMO和SA结合的天线阵列模型;其次通过网络等效分析法对天线模型进行简化分析,采用HFSS对MIMO/SA天线阵列模型仿真,得出阻抗矩阵和收发端的互耦矩阵;然后推导出考虑相关和互耦时采用QPSK调制的MIMO/SA系统的误码率;最后用MATLAB对系统误码率进行仿真。仿真结果表明：不考虑相关性和互耦效应时的系统误码率最低;当天线间距为0.5波长时,考虑互耦时系统的误码率变大;而当天线间距为0.2波长时,互耦效应又会降低系统的误码率。     

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。     

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.     

MIMO系统在空时二维相关莱斯快衰落信道下的性能

与准静态独立的瑞利衰落信道模型相比较,在MIMO(Multi-Input Multi-Output)系统中,实际信道更趋向于空时相关莱斯快衰落。考虑到MIMO系统的收发分集优势以及收发两端天线阵列的空时相关性,在简单论述了MIMO系统和信道模型的基础上,该文利用多变量统计学理论,推导出MIMO系统在空时相关莱斯快衰落信道下平均成对差错概率上界的闭合表达式,并探讨了信道特性对系统性能的影响,然后给出相应仿真结果。     

互耦效应对超大规模MIMO天线系统信道容量的影响

超大规模多输入多输出(Multiple-Input Multiple-Output,MIMO)天线系统是6G的关键技术,由于天线单元间距很小,多个天线单元的互耦效应是影响其性能的因素之一。建立了基于石墨烯基贴片天线阵列-子阵列架构的超大规模MIMO天线系统,推导出了互耦效应影响下的信道容量表达式。通过电磁场数值计算仿真了超大规模MIMO天线系统的信道容量,结果表明,在不考虑互耦效应时,超大规模MIMO天线系统的信道容量与子阵列天线单元数、子阵列数以及发射机功率正相关;在互耦效应的影响下,系统的信道容量降低,互耦效应的强弱与子阵列天线单元的间距有关,天线单元间间距越小,相邻天线间的互耦效应越明显,系统的信道容量越小。该仿真结果可以为6G中超大规模MIMO天线系统的设计提供参考。     

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.     

Achievable Performance of Orthogonal STBC Over Spatially Correlated Rician Channels

The effect of spatial correlation on the performance of orthogonal space-time block codes (OSTBCs) over multiple-input-multiple-output (MIMO) Rician fading channels is studied. Asymptotic error-rate formulas for OSTBC with high average signal-to-noise ratios (ASNRs) over arbitrarily correlated Rician MIMO channels are derived in terms of the diversity and coding gains. Our results show that, in correlated fading, the phase vector phi of the channel line-of-sight (LOS) components affects the effective Rice K-factor at the OSTBC receiver output and, hence, may result in a coding gain that is significantly higher than that for independent Rician MIMO channels. Furthermore, when the channel covariance matrix is rank deficient and under some additional mild conditions, the error and outage probabilities of OSTBC achieve those in a nonfading additive-white-Gaussian-noise channel. For both cases of full-rank and rank-deficient channel covariance matrices, analytical expressions of optimal and worst case phase vectors phi, and exact upper and lower bounds of OSTBC performance are derived. These results provide new insights into the achievable performance of OSTBC over correlated Rician MIMO channels and, if incorporated into future multiple antenna systems design, will bring about significant performance enhancement     

Capacity of MIMO Rician channels

This paper presents exact results on the capacity of multiple-input-multiple-output (MIMO) Rician channels when perfect channel state information (CSI) is assumed at the receiver but the transmitter has neither instantaneous nor statistical CSI. It first derives the exact expression for the average mutual information (MI) rate of MIMO Rician fading channels when the fading coefficients are independent but not necessarily identically distributed. The results for the independent and identically distributed (i.i.d.) MIMO Rician and Rayleigh fading channels are also obtained as special cases. These results are derived using a different approach than the one used by Telatar for the i.i.d. Rayleigh case. The complementary cumulative distribution function (CCDF) of the MI is also obtained using a Gaussian approximation. The CDF of MI can serve as an upper bound to the outage probability of nonergodic MIMO Rician channels. Numerical results confirm that for a fixed channel gain, a strong tine-of-sight component decreases the channel capacity due to the lack of scattering.     

Structures and performance of noncoherent receivers for unitary space-time modulation on correlated fast-fading channels

Fast fading used in this paper refers to multiple-input-multiple-output (MIMO) channels with channel gains changing from sample to sample, even within a block symbol. The impact of spatially correlated and sample-to-sample variant (SCSSV) fading channels on the design and error performance of noncoherent receivers is not yet clear in the literature. In this paper, we derive optimal and suboptimal noncoherent receivers for operating on SCSSV MIMO fading channels. The joint effect of spatial correlation and sample-to-sample variation of channel gains on various receivers in Rayleigh and Rician fading is investigated by the derivation of their pairwise error performance. Numerical and simulation results are also presented to illustrate the theory and to compare the performance of the optimal and suboptimal receivers.     

General Capacity Bounds for Spatially Correlated Rician MIMO Channels

This paper considers the capacity of spatially correlated Rician multiple-input multiple-output (MIMO) channels. We consider the general case with double-sided correlation and arbitrary rank channel means. We derive tight upper and lower bounds on the ergodic capacity. In the particular cases when the numbers of transmit and receive antennas are equal, or when the correlation is single sided, we derive more specific bounds which are computationally efficient. The bounds are shown to reduce to known results in cases of independent and identically distributed (i.i.d.) and correlated Rayleigh MIMO channels. We also analyze the outage characteristics of the correlated Rician MIMO channels at high signal-to-noise ratio (SNR). We derive the mean and variance of the mutual information and show that it is well approximated by a Gaussian distribution. Finally, we present numerical results which show the effect of the antenna configuration, correlation level (angle spreads), Rician$K$-factor, and the geometry of the dominant Rician paths.     

Mutual coupling in multi-element array antennas and its influence on MIMO channel capacity

The effects of mutual coupling between receive elements in a multi-element antenna on multiple-input multiple-output (MIMO) system capacity are reported. The results are based upon analysis of mutual coupling calculated for a measured linear array of five printed dipole elements with 0.56 of a wavelength spacing. It is shown that the presence of mutual coupling at the receive array antenna leads to additional correlation between spatial channels and results in a loss of MIMO system capacity.     

Genetic Algorithm Based MIMO Capacity Enhancement in Spatially Correlated Channels Including Mutual Coupling

Higher system capacities can be achieved if multiple antennas are used on both sides of the wireless link, thus creating a multiple-input-multiple-output (MIMO) system. In this work, the maximization of MIMO system capacity in Rayleigh fading, spatially correlated channels involving practical antenna arrays is challenged through inter-element spacing optimization. The system capacity is evaluated using a proposed formula that takes into account both antenna mutual coupling and signal correlation. Capacity values turn out to outperform the ones obtained considering the conventional antenna array geometries.     

Experimental Study on the Capacity of Compact MIMO Antennas for Portable Terminals

This paper presents the relationship between antenna structures and the performance of two kinds of compact MIMO antennas in order to find critical factors that affect the capacity of MIMO systems. The relationship between the channel capacity and some factors (antenna efficiency, mutual coupling, correlation) are analyzed based on experimental data under indoor Rayleigh fading environment. Antenna elements mounted in two different configurations (common and separated ground plane) with antenna spacing varying, were investigated at the frequency of 2.6 GHz band experimentally. The good characteristics in the case of separated ground plane show that the proposed antennas, even with small spacing, can still achieve high capacity to combat multipath fading and deliver higher data rates. It demonstrates that multiple antennas could be mounted onto small terminal devices without much loss of capacity. It is also found that mutual coupling has positive impact which could reduce channel correlation; negative effect which could degrade antenna efficiency. In the indoor multipath-rich environment, the negative effect is dominant.     

基于天线子集选择算法的DSTBC优化

为进一步提高空时码性能,在信道模型为瑞丽和莱斯慢衰落信道的情况下,文中提出了一种优化差分空时分组码的＂天线子集选择算法＂——假设发射信号为特定的Alamouti正交空时分组码,通过最大化信道参数矩阵F范数的方法,优化了MIMO系统的天线集。仿真结果表明：此方法可降低码元的比特错误率,并且可获得相当客观的分集增益和能量增益。此外,还讨论了该优化方法的适用范围。