新型基于几何的3D非平稳V2V MIMO信道模型

针对具有多种通信场景和收发端快速移动的V2V通信系统,提出一种基于几何的3D V2V MIMO信道模型.该模型首次结合双球模型和半椭球体模型,分别使用双球和半椭球体模型表征动态和静止散射体;考虑到收发端的运动状态,引入时变的出发角、到达角以及路径长度用于研究V2 V信道的非平稳特性;对所提出的信道模型,推导了空间互相关、时间自相关和多普勒功率谱密度等统计特性函数,分析了不同场景和参数下的V2 V信道统计特性.结果表明,不同场景下V2 V信道各统计特性有较大差异,信道相关性与时间变化和散射体分布密切相关.仿真结果与理论值的高度拟合验证了模型的正确性,为V2 V通信链路的设计提供了理论依据,拓展了基于几何的V2 V信道建模领域的研究.     

室外3D散射信道中ULA/UCA天线MIMO性能分析

为更好地解决室外三维(3D)空间域的移动通信问题,提出了一种新型室外3D空间域散射信道统计模型,主要研究MIMO多天线系统的接收性能。在宏蜂窝小区移动通信环境中,模型能够估计多径衰落信道的重要空间信道参数,首先推导了多径衰落信道的到达角(Angle of Arrival,AOA)概率密度分布。此外模型在设置多输入多输出(Multiple Input Multiple Output,MIMO)多天线的均匀线性阵列(Uniform Linear Array,ULA)和圆形阵列(Uniform Circular Array,UCA)的基础上,分析了波达信号不同方位角分布对散射信道中MIMO性能的影响因素,包括MIMO空间相关性、信道容量以及天线阵列配置。数值仿真结果与3D多径衰落信道模型对比,表明本模型的信道参数估计符合理论和实际的通信环境,为评估MIMO天线接收系统与仿真无线通信系统提供了创新性的研究。     

三维空间域多径信道模型的AOA和TOA特性分析

在三维空间域提出了一个几何模型,其散射椭圆半球体的中心在移动台(MS),基站(BS)被置于散射球体外部。该模型可以在方位角和仰角平面同时描述多径波的到达角度和到达时延,据此推导出电磁信号分别在MS和BS端关于到达角度的联合、边缘概率密度函数封闭式表达式。除此之外还推导出到达时延的联合概率密度函数的封闭式表达式。该三维模型适用于低MS天线和高BS天线且重要散射体分布在移动台附近的室外宏蜂窝通信环境。此外还对数值仿真实验获得的理论数据进行分析比较,进一步验证信道参数估计结果符合理论和经验。     

基于5G波段的V2V高速无线信道建模

高速移动的车车(Vehicle-to-Vehicle,V2V)信道与传统蜂窝系统的无线信道相比,其不同在于V2V无线信道的快速时变特性,主要体现在多径分量的快速变化、存在较大多普勒频移以及每条多径都具有动态生/灭特性。提出了一种高速无线信道建模方法,采用马尔科夫链模拟信道的动态生/灭特性,基于Nakagami分布仿真莱斯、瑞利等信道单径衰落,用抽头延时线模型完成高速多径信道建模。与传统无线信道建模方式相比,具有快速建模、动态改变和易于产生的特点,为高速移动无线接收机算法的开发奠定了基础。仿真结果表明,城市车内天线(UIC)信道多径数目最多,衰落最严重。     

双极化天线MIMO中SAST编码性能分析

为解决单极化天线中多输入多输出（MIMO）技术与移动终端有限体积之间的矛盾,将半正交代数空时（SAST）编码应用到配置双极化天线的MIMO系统中,并对SAST编码性能进行理论分析。将置换矩阵和交叉极化鉴别度（XPD）转换为等效信道的一部分,并使SAST编码在双极化天线中的传输模型等效转变为该编码在单极化天线中的传输模型,根据秩准则和乘积准则分析置换矩阵不同时,XPD对分集增益和编码增益的影响,并给出相应的译码方法。仿真结果验证了该理论分析的正确性。     

MIMO信道建模及仿真

本文研究了一种应用于移动通信系统中收发端皆为多天线系统的MIMO信道建模的方法，将功率延迟函数，空域相关以及时域衰落融入到信道模型中，充分考虑了时延扩散、多普勒效应、波达方向、角度扩展、到达角功率谱分布等多种信道参数。并且根据3GPP．25．996标准中的相关参数对此MIMO信道模型进行了仿真。结果表明，该模型得出的仿真值与理论值比较贴近。     

衰落信道下V2V通信系统性能分析

针对V2V通信的连接性能问题,将衰落引起的信道随机性纳入分析,提出了一种在衰落信道中对V2V连接性能的分析算法,并将物理层和MAC层相结合,分析了不同衰落模型下V2V通信系统性能,包括对包丢失率、吞吐量、平均延时等通信性能指标,并通过仿真验证。仿真结果表明,瑞利信道的连接性能比Nakagami-m信道高,但信号的传输性能Nakagami-m信道全面优于Rayleigh信道。     

基于IMT-Advanced信道模型的室内MIMO性能研究*

LTE-Advanced与多输入多输出（MIMO）技术的结合极大地改善了MIMO在不同信道环境下的传输质量和可靠性。为此,在基于IMT-Advanced几何分布统计信道模型基础上,建立LTE-Advanced通信系统的MIMO信道模型,深入研究室内多天线系统的性能。针对MIMO发射分集技术,研究在瑞利衰落信道下不同调制技术对系统误码率（BER）性能的影响,并通过理论验证仿真结果的可行性,进而在非视距（NLOS）情况下,结合不同载波频率的路径损耗,理论分析不同载波频率对系统误码率性能的影响。仿真结果表明,IMT-Advanced室内信道模型只适用于8 GHz以下的低载波频段通信。     

基于极化状态调制的无线通信物理层安全传输技术

针对无线通信系统中物理层信息安全风险问题,提出了一种基于极化状态调制的物理层安全传输技术。在无线通信中,引入极化状态调制,在经典的空域、时频域的基础上,增加了对信号极化域的描述。一方面,设计高维星座映射方案,利用信号的幅度、相位和极化状态共同承载信息,将传统调制技术和极化状态调制有效地结合在一起;另一方面,在高维星座映射方案的基础上,进一步设计基于去极化效应的信道预编码机制,通过增大Bob和Eve在极化域的信道差异实现物理层保密传输。安全性分析和仿真实验结果表明,利用该机制能够提升系统的保密容量,在接收信噪比为22dB时,窃听者接收到的星座图仍然是十分紊乱的,无法恢复出有效信息。     

降雨环境下的多阶散射蜂窝系统信号特性分析

为精确研究信道模型的空间和时间特征,提出一种基于椭圆几何并考虑降雨衰减效应的郊区密集乔木林区多阶散射信道模型。推导一阶与二阶散射系统波达信号的到达时间(TOA)和到达角(AOA)的联合概率密度函数(PDF),对该模型进行仿真。仿真结果表明,随着降雨强度的增加,经历多阶散射的波达信号到达时间将产生显著延迟,概率密度更加接近均匀分布,且阶数越高,降雨作用的影响越明显。仿真结果有利于进一步研究蜂窝通信系统功率延迟分布,推导降雨环境下的循环前缀,分析OFDM系统的性能。     

3D non-stationary vehicle-to-vehicle MIMO channel model for 5G millimeter-wave communications

Vehicle-to vehicle (V2V) is one of the most challenging scenarios in the fifth-generation (5G) millimeter-wave (mmW) mobile communication networks. Existing models cannot be utilized without development for compatibility with modern measurements, which have proved that the wide-sense stationary (WSS) modeling assumption is valid only for very short intervals. In this paper, a novel three-dimensional (3D) geometry-based stochastic model (GBSM) for non-stationary (non-WSS) narrowband V2V multi-input-multi-output (MIMO) channel with both 3D fixed and moving scatterers around the transmitter (Tx) and the receiver (Rx) is proposed. The azimuth angle of departure (AAoD), elevation angle of departure (EAoD), azimuth angle of arrival (AAoA) and elevation angle of arrival (EAoA) of the 3D moving scatterers have been considered as time varying angles, and this makes the model non-stationary. Based on the proposed model, the statistical properties, including space-time correlation function (STCF), space-Doppler power spectral density (SD-PSD), level crossing rate (LCR), and average fade duration (AFD) are derived and compared with those of measured data and state-of-the-art channel models. Finally, the close agreement between results reveal that the proposed 3D model with 3D moving scatterers reflects the real-world V2V channel characteristics, especially in 5G mmW networks.     

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。     

Computationally efficient 2D direction finding and polarization estimation with arbitrarily spaced electromagnetic vector sensors at unknown locations using the propagator method

This paper proposes a computationally efficient method for estimating angle of arrival and polarization parameters of multiple farfield narrowband diversely polarized electromagnetic sources, using arbitrarily spaced electromagnetic vector sensors at unknown locations. The electromagnetic vector sensor is six-component in composition, consisting of three orthogonal electric dipoles plus three orthogonal magnetic loops, collocating in space. The presented method is based on an estimation method named propagator, which requires only linear operations but no eigenvalue decomposition or singular value decomposition into the signal and noise subspaces, to estimate the scaled electromagnetic vector sensors' steering vectors and then to estimate the azimuth arrival angle, the elevation arrival angle, and the polarization parameters. Comparing with its ESPRIT counterpart [K.T. Wong, M.D. Zoltowski, Closed-form direction finding and polarization estimation with arbitrarily spaced electromagnetic vector-sensors at unknown locations, IEEE Trans. Antennas Propagat. 48 (5) (2000) 671–681], the propagator method has its computational complexity reduced by this ratio: the number of sources to sextuple the number of vector sensors. Simulation results show that at high and medium signal-to-noise ratio, the proposed propagator method's estimation accuracy is similar to its ESPRIT counterpart.     

街道环境V2V通信信道建模与容量分析

针对街道3D散射环境下的车载通信信道,考虑到道路两边高楼、树木等散射体,且收发两端处于移动状态,采用多天线技术,建立椭圆柱散射模型。运用几何分析法,推导了时间自相关函数（ACF）、空间互相关函数（CCF）,比较视距（LOS）和非视距（NLOS）情况下ACF和CCF的差异,验证仿真方法的可行性;研究了信道容量在不同天线阵列和散射环境下的区别,突出了3D模型更加精确。测量结果与理论分析的一致性表明该3D模型的可用性,拓宽了车载通信系统的研究。     

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.     

Multi-channel power allocation based on market competitive equilibrium in cognitive radio networks

Cognitive radios such as intelligent phones and Bluetooth devices have been considered essential goods in next-generation communication systems.Such devices will have to share the same frequency band owing to the limited bandwidth resource.To improve spectrum efciency,we formulate multi-channel power allocation as a market competitive equilibrium(CE)problem,and prove that its solution exists and is unique under the condition of weak interference.We then propose two distributed power allocation algorithms achieving CE,namely the fast convergent power allocation algorithm(FCPAA)and the social-fairness-aware FCPAA(SFAF).Theoretical analysis and simulation results demonstrate that the proposed algorithms lead to better system performance in terms of the guaranteed interference temperature constraint using the price mechanism instead of a strategy based on the Nash equilibrium.Moreover,it is shown that the FCPAA maximizes total utility,and converges more quickly than the method addressed in prior research with the help of improved round-robin rules.However,the FCPAA cannot ensure the same social fairness among secondary users as the SFAF scheme in both the non-fading channel and Rayleigh fading channel;the SFAF balances the individual utility by adjusting each user’s budget at the expense of a small quantity of system total throughput.     

移动通信宏小区信道模型的信道估计研究

为了有效地削弱无线通信环境中的多径效应并提高信道参数估计的准确性,在散射体非均匀分布下,引入了到达路径物理概念,提出了一种合理的改进型信道模型。此模型能够准确地描述出宏小区环境下的重要空时参数,如波达信号在基站(Base Station,BS)处的到达角(Angle of Arrival,AOA)和到达路径(Range of Arrival,ROA)。同时,由于移动台的移动特性,基站接收信号产生多普勒频移,从而推导出基站处多普勒频移概率分布。将此模型的数值仿真结果与其他信道模型仿真结果进行比较,结果表明参数估计结果符合理论和经验,证明了提出的信道模型更适用于宏小区移动通信环境,延伸了统计信道模型的研究与应用,为仿真无线通信系统提供了有力的工具。     

WSNs中一种新的编码协作通信方式

采用空间分集的方法可以有效地对抗无线信道中的衰落,由于受到体积、重量、成本等因素的限制,在无线传感器网络(W SNs)节点上实现多天线技术较为困难。在W SNs中提出了一种基于π旋转LD-PC码的编码协作通信方式,2个单天线节点通过共享自己的天线,形成了一个虚拟的多天线系统。LDPC码的不同部分通过不同节点的上行链路传输到基站,获得发送分集增益。在相同的系统带宽和发送功率下,与非协作通信方式相比,该编码协作方式可显著提高系统性能。