Investigation on the spatial-polarizational correlation based on 3GPP spatial channel model

The correlation among signals arriving at diferent elements of the antenna array has a significant impact on the performance of multiple-input multiple-output(MIMO)system.To investigate the inter-element correlation when slant polarized antennas are used,a general approach for calculating the correlation coefcient is proposed based on a model that incorporates the antenna configuration,namely the antenna spacing and the slant angle,as well as the channel parameters,such as the power azimuth spectrum(PAS)and the crosspolarization discrimination(XPD).By applying this method to the 3rd generation partnership project(3GPP)spatial channel model(SCM),the expression of the inter-element correlation when the PAS follows the Laplacian distribution is obtained.The approximate expressions are also given for two special cases,i.e.,the case where the angular spread(AS)of the PAS is small,and the case where the AS is so large that the PAS can be approximated by the uniform distribution.Using these expressions,the impact of the antenna configuration and the channel parameters on the correlation is analyzed.Following that,the trend of inter-element correlation with the slant angle is investigated.Finally,the equivalent relation between the slant angle and the antenna spacing is studied.The results can provide guidelines for the antenna configuration under diferent propagation conditions.     

建立巷道的MIMO信道几何模型仿真研究

研究了MIMO巷道几何建模技术。依据电磁波在矿井巷道环境中的特点且选用收发端水平角度功率谱作为拉普拉斯分布函数功率谱,仿真了巷道环境下MIMO天线放置角度、收发天线间距、巷道长度、莱斯因子、角度扩展和平均达到角等对空间相关函数的具体影响。仿真结果表明,巷道环境中天线放置角度对相关系数的影响较大;天线间距取较大值时,才能得到较小的相关性;相关系数还要受到天线间距和巷道长度以及角度扩展等的影响,比地面的相关性更大。     

基于特征值分布的自适应MIMO接收方法

多输入多输出(MIMO)系统性能优劣依赖于信道的相关特性,空分复用技术适用于低相关信道,而波束形成技术适用于高相关信道。依据上述信道相关特性,提出一种基于信道特征值分布的自适应MIMO接收方法。该方法以均匀圆形天线阵列结构为基础,能够根据信道相关情况动态选择接收方式:当角度扩展较大时,选用传统MIMO接收方式(称为天线MIMO方式);当角度扩展较小、多径独立时,选用基于智能天线的多波束接收方式(称为波束MIMO方式)。分析角度扩展、多径对信道特征值分布的影响,并给出自适应MIMO接收切换的条件。仿真结果表明,该方法能够适应复杂的无线环境,误码率较低,性能更加稳定可靠。     

微小区MIMO信道模型的相关性分析

根据微小区双散射的MIMO椭圆信道模型,分析发送、接收端阵元天线间的信道相关性,考虑到发射端与接收端周围存在大量散射体,且散射体服从非均匀分布,采用Von Mises分布函数描述散射角度的分布情况,从而得到信道相关函数的闭式表达式,并通过仿真分析影响信道相关性的主要因素。实验结果表明,相关系数随天线间距、角度扩展、扩展因子的增大而非单调性减小,为MIMO技术的应用提供了有效理论依据。     

Optimal array factor radiation pattern synthesis for linear antenna array using cat swarm optimization: validation by an electromagnetic simulator

In this paper, an optimal design of linear antenna arrays having microstrip patch antenna elements has been carried out. Cat swarm optimization (CSO) has been applied for the optimization of the control parameters of radiation pattern of an antenna array. The optimal radiation patterns of isotropic antenna elements are obtained by optimizing the current excitation weight of each element and the inter-element spacing. The antenna arrays of 12, 16, and 20 elements are taken as examples. The arrays are designed by using MATLAB computation and are validated through Computer Simulation Technology-Microwave Studio (CST-MWS). From the simulation results it is evident that CSO is able to yield the optimal design of linear antenna arrays of patch antenna elements.     

MIMO信道中衰落信号的多谱勒功率谱

MIMO系统中的角度功率谱有多种分布形式,所以经典多普勒功率谱不再适用。针对常用的均匀分布、余弦分布、高斯分布和拉氏分布的入射波角度功率谱,分别推导了多谱勒功率谱解析式。通过仿真比较了不同角度功率谱下的多普勒功率谱,并分析各种参数对其的影响。这些工作对MIMO信道中频率扩散的刻画做了拓展。     

Development of an Enhanced Ant Lion Optimization Algorithm and its Application in Antenna Array Synthesis

In order to design a highly effective communication system, antenna plays a vital role and antenna array adds to the performances. And to achieve such a goal, the crucial challenge is to determine the optimum spacing between the elements and their excitations. In order to address this issue a novel optimization technique named as enhanced ant lion optimization (e-ALO) algorithm has been developed by modifying the basic Ant lion optimization algorithm. Further, to validate the efficacy of the proposed algorithm, few benchmark functions have been successfully tested and significant improvement is obtained in comparison to other reported optimization approaches. The proposed scheme is applied to antenna array synthesis problem to optimize the inter-element spacing and excitation of the elements for different antenna geometries, with an objective to minimize the sidelobe levels while keeping other constraints within boundary limits. The encouraging results obtained from the study have emphatically placed the proposed e-ALO algorithm in the optimization arena as a dominant player.     

三维接收天线阵列信道模型下的空域相关性

建立三维接收天线阵列的空间信道模型,将以往的信道建模方向推广到空间域,给出该信道模型的通用数学表达式。针对该通用形式,将来波信号角度描述扩展到俯仰角和方位角,推导该信道模型下空域相关系数的数学表达式,显示接收天线阵的形状对空域相关系数的影响。分析当来波信号的功率谱(俯仰角和方位角)分别为均匀、高斯、拉普拉斯分布时的空域相关系数,给出了数值仿真结果。     

MIMO two-way relay channel with superposition coding and imperfect channel estimation

This paper deals with the superposition coding (SPC) scheme in multiple-input multiple-output two-way relay channels subject to imperfect channel estimation. In this scenario, two multiple antenna terminals, which are unable to communicate directly, exchange information with each other via a multiple antenna relay. We determine the impact of the channel estimation error degradation on the achievable rate region for two main SPC techniques: (a) SPC without channel state information (CSI) at the users, (b) SPC with an imperfect CSI at the users where a waterfilling power allocation is employed. We demonstrate that imperfect CSI significantly improves the achievable rate at low signal-to-noise ratios (SNRs) while it becomes less critical at high SNRs. In addition, a SPC power allocation technique that incorporates the average channel statistics and does not require any instantaneous CSI is also investigated. We show how the available power is split between the two bi-directional (superimposed) data flows in order to maximize the system performance and to support fairness as well as to maximize the achievable sum-rate.     

Golden angle‐inspired design of massive MIMO tapered slot array with less correlation for 5G lower band applications

In this article, for the first time, we come up with a nature‐inspired MIMO antenna configuration that could provide less correlated wireless channels for 5G lower band (3000‐4200 MHz). Essentially, the cross‐correlation among the antenna elements is reduced by incorporating the concept of golden angle into a cylindrical configuration of tapered slot antenna array. The golden angle helps in arranging the end‐fire radiating tapered slot antennas (TSAs) in such a way that there will not be any spatial overlap among the radiation fields of the individual antenna elements. The idea is validated with 24 TSA elements placed in a cylindrical fashion. The envelope correlation coefficient (ECC) is calculated from the simulations in ANSYS HFSS and verified with measurements. The ECC value is found to be less than 0.01 in the range of 3 GHz to 4.25 GHz. The impedance matching and mutual coupling between the elements are found to be very good in the above‐mentioned frequency range from the simulations and measurements. It is believed that the application of golden angle concept to MIMO antennas would open up the windows for implementation of dense massive MIMO.     

三维空间椭圆信道模型及其均匀矩形阵列研究

为研究无线多输入多输出(MIMO)系统信道特性,在考虑无线信道模型的信号传播复杂性与空间性的基础上,提出一种适用于户外环境的三维空间椭圆信道模型,并在其收发端设置均匀矩形阵列(URA)。利用该模型分析MIMO天线系统性能,推导出到达角、到达时间的概率密度函数表达式,并研究影响URA空间相关性与信道容量的因素。理论分析与实验结果表明,在基于URA的三维空间椭圆信道模型中,方位扩展角(AS)是影响URA空间相关性的主要因素,而收发端天线间距也会对URA信道容量产生一定影响,该结论对于无线信道模型的应用范围扩展及天线阵列灵敏度分析具有重要的参考和借鉴价值。     

Uplink spectral efficiency analysis of multi-cell multi-user massive MIMO over correlated Ricean channel

In this study, the performance of uplink spectral efficiency in massive multiple input multiple output (MIMO) over a spatially correlated Ricean fading channel is presented. The maximum ratio combining (MRC) receiver is employed at the base station (BS) for two channel estimation methods. The first method is based on pilot-assisted least minimum mean square error (LMMSE) estimation, whereas the second is based on line-of-sight (LOS). The respective analytical expressions of the uplink data rate are given for these two methods. Because of the existence of pilot contamination, the uplink data rate of the pilot-assisted LMMSE estimation method approaches a finite value (we call it the asymptotic rate in this study) when the BS antenna number is high. However, the data rate of the LOS method is linear with the number of BS antennas. The expression of the uplink rate of the LOS method also shows that for a Ricean channel, the spatial correlation between the BS antennas may either decrease the rate or increase the rate, depending on user location. This conclusion explains why the spatial correlation may increase rather than decrease the data rate of pilot-assisted LMMSE. We also discuss the power scaling law of the two methods, and show that the asymptotic expressions of the two methods are the same and both are independent of the antenna correlation.     

互耦宽带MIMO系统容量分析

研究了宽带通信系统中,互耦现象对多输入多输出（MIMO）通信容量的影响。首先分析了天线阵列间的互耦作用,并基于此推导出互耦条件下宽带通信系统的容量表达式。然后通过蒙特卡洛方法,仿真了不同天线阵列配置下的系统容量。结果表明,在天线阵列间距很近时,天线阵列间的互耦效应能够改善天线阵列之间的相关性,从而提高系统的容量。并且天线数目越多,系统容量改善越大。该结论对宽带MIMO通信系统的天线设计起到一定的指导作用。     

高速铁路环境下的MIMO信道建模及仿真

根据高速铁路环境下电波传播特性,基于多入多出(MIMO)无线散射信道模型,提出一种高速铁路无线环境下的MIMO无线信道模型,详细分析了其构建过程,并通过仿真得出MIMO信道的空域相关性随天线单元间距的增大而减小,拓展了MIMO信道衰落模型的研究。     

基于MIMO的对流层散射通信信道损耗研究

针对多输入多输出(Multiple-Input Multiple-Output,MIMO)场景下的对流层散射通信信道损耗进行了研究。在设计远距离MIMO通信系统时,链路损耗估计是其中的关键技术,而现有技术在损耗估计时都忽略了波束与散射体碰撞时的能量损耗。根据湍流非相干散射理论,首先将对流层建模为多条可微的曲线,从而与发射和接收天线阵列构成曲边梯形,根据此信道几何模型,计算入射角、反射角和散射角的角度关系;其次,建立了电磁波束射入散射体后散射波在散射体表面的能量分布模型;最后,根据波束传输距离,量化散射信道的损耗,推导得到基于MIMO对流层散射信道的衰落系数和信道矩阵。将仿真计算结果与实际数据进行对比,验证了所提模型在链路损耗估计问题上的有效性和准确性,同时根据仿真结果对接收天线的仰角设计提出了建议。     

Compact 2 × 2/4 × 4 tapered microstrip feed MIMO antenna configuration for high‐speed wireless applications with band stop filters

In this research, compact tapered feed 2 × 2/4 × 4 MIMO antenna are presented and investigated. The proposed MIMO antenna consists of a square patch and modified rectangular ground, which is chamfered at edges and etched with two semicircular slots. Likewise, obstruction caused by WiMAX and WLAN interfering bands is also taken care of by introducing notched filters. WiMAX is removed by embedding an rotated T‐type stub and a C‐type slot eliminates the WLAN band. The proposed antenna configuration covers the usable bandwidth of 3.07 to 11.25 GHz for 2 × 2 MIMO and 2.97 to 11.28 GHz for 4 × 4 MIMO. Also, both the MIMO antennas provide isolation <–20 dB. Proposed MIMO antennas are fabricated and characterized in near, far‐field, and diversity performance where envelope correlation coefficient, directive gain (DG), total active reflection coefficient (TARC), and channel capacity loss are simulated and measured. 4 × 4 MIMO antenna configuration provides stable gain with a maximum radiation efficiency of 91% and monopole radiation patterns.     

空域相关MIMO信道容量的研究

研究了在空域相关条件下MIMO通信系统的信道容量问题,利用Wishart矩阵的联合特征值概率密度函数显式给出了平坦性瑞利衰落信道的各态历经容量的可计算公式,利用Matlab所进行的数值计算表明：与已有的蒙特卡洛方法相比,公式提高了计算速度。数值计算结果还进一步表明了影响空间相关性的天线间距、来波角度和角度扩展这三个参数与信道容量之间的关系。     

结合天线选择的空间调制及性能仿真

提出了一种分组映射空间调制方案。每个时隙中有多个发射天线被同时激活,结合幅度相位调制技术,每根选中的天线发射不同的符号,并且所激活的特定天线序列也携带相应信息。相对传统空间调制技术而言,该方案可以有效地提高空间调制系统的频带利用率和传输速率。Rayleigh衰落信道的仿真结果表明,所提方案的误比特率（Bit Error Rate,BER）性能优于传统的空间调制与多输入多输出（Multi-Input Multi-Output,MIMO）技术。方案可进一步结合发射天线选择（Antenna Selection,AS）技术,提高系统的传输质量。实际多极化MIMO信道的测量和仿真结果表明,在发端天线选择数目均相同时,分组映射调制的性能明显优于空间调制,结合AS的调制系统性能明显优于未结合AS的系统。     

一种V2V多天线几何去极化信道建模

随着极化相关技术的发展,极化调制在V2V（vehicle-to-vehicle)通信系统中的应用越来越广泛。但由于V2V通信环境复杂,极化调制在V2V通信中会产生去极化效应,从而影响通信质量。为了能够识别去极化效应的大小,提出一种新的基于几何散射理论的V2V多天线极化信道模型。该模型可通过已知的多天线配置、极化场辐射模式及散射体的空间分布,建立去极化效应模型,从而将信道的去极化效应由交叉极化鉴别度——XPD(cross polarization discrimination)的值表示,以拓展极化调制在V2V系统中的使用范围,提高传输速率。实验结果表明,XPD的值受到车辆间距离影响存在阈值,并强烈依赖于到达方位角的分布常数,且当到达方位角的值不同时,改变到达仰角的最大值的大小,XPD值的变化呈固定趋势。因此,本文所提出的多天线几何信道模型,成功的将极化引入多天线的V2V通信,可以为极化域通信的进一步研究奠定基础。     

基于几何随机的无人机空地信道模型

针对传统无人机空地信道模型不支持三维飞行轨迹和三维天线的问题，通过引入空间旋转矩阵和轨迹参数，提出了一种基于几何随机的无人机空地三维信道改进模型。该模型结合无人机对地通信场景的特殊性，利用时变布尔变量描述视距路径、地面反射径和散射路径的动态生灭过程。同时，文中还给出了二维角度、时延和功率等模型参数的时间演进算法，用于复现无人机对地信道的时变统计特性。数值仿真结果表明，改进模型输出的空时相关特性和多普勒功率谱均与理论值吻合，并且自相关特性与实际测量结果基本一致，该模型可应用于辅助无人机空地无线通信设备的方案优化、算法验证和性能评估等领域。