MIMO多中继系统中基于不完全信道状态信息的预编码算法研究

针对配置多个中继节点的多输入多输出（Multiple-input Multiple-Output,MIMO）系统,提出一种不完全信道状态信息（Imperfect channel state information,CSI）下基于最小均方误差（Minimum Mean-Squared Error,MMSE）准则的预编码设计方案,该方案综合考虑各个节点天线之间的相关性及信道估计误差。由于各个中继端预编码矩阵之间可视为相互独立,故将约束优化问题转化为若干半正定规划问题,继而通过内点法或CVX工具箱求解预编码矩阵,然后采用求导法推导出接收端处理矩阵。最后利用迭代算法交替迭代来联合优化预编码矩阵和接收端处理矩阵,直到算法收敛。仿真结果表明,与未能综合考虑各个节点的预编码算法相比,本文提出的算法能明显改善系统BER性能。      

视距相关信道下考虑非理想CSI的MIMO收发联合设计

MIMO系统收发联合设计的性能依赖于信道状态信息(CSI)的质量。在较高通信频段(如6～8GHz)下,信道的视距分量相对于较低频段显著增加,采用传统的CSI模型无法反映实际的信道特点,从而影响联合设计算法的性能。本文在相关莱斯信道下,提出一种考虑高频段环境下非理想CSI的MIMO系统下行链路收发联合设计算法。论文推导出一种基于训练序列的信道估计误差模型代替传统误差模型,并在此基础上以最小化MSE为目标迭代求解最优预编码/解码矩阵。仿真结果表明,该算法在不同的子流数、视距分量、信道相关性以及信道估计误差环境下,具有较好的误码率性能。     

具有不完全信道状态信息MIMO系统的优化设计

 本文研究了不完全信道状态信息(CSI)对多输入多输出(MIMO)系统容量的影响.基于平均功率和平均误码率的约束条件,我们提出了一种利用不完全CSI进行功率自适应调制的优化设计方案.根据Wishart矩阵的统计分布,我们导出了该系统容量的封闭表达式.研究结果表明:在具有不完全CSI的MIMO系统中,利用不完全CSI进行设计可以显著地提高系统的容量.     

高速移动环境下基于动态CSI的MIMO系统改进模代数预编码

针对高速移动场景下信道快时变特性给多输入多输出（Multiple Input Multiple Output,MIMO）系统预编码带来的技术挑战,提出基于动态信道状态信息（Channel State Information,CSI）的MIMO系统改进模代数预编码（Tomlinson-Harashima Precoding,THP）算法.该算法利用信道统计量信息以及相关性构建动态CSI模型,更准确实时地体现当前信道状况;进一步地,提出一种基于循环遍历搜索的多用户调度算法,以最大化信干噪比为目标进行用户调度,且将多用户调度算法应用到THP中,提高了预编码精度.仿真结果表明,所提算法相比传统预编码算法具有更优的误码率性能和信道容量,验证了所提算法能有效地适应高速移动场景.     

基于信道状态的MIMO预编码算法

针对多输入多输出（MIMO）的应用需要,研究了一种利用发端信道状态信息（CSIT）进行预编码,增强系统性能的方法。该方法在发送端采用线性预编码器对CSIT进行预编码,合理分配不同天线的发射功率以提高系统性能;分别在低、高信噪比条件下,对进行预编码前后的容量比值差值进行了仿真分析。分析结果表明：进行预编码后,MIMO系统容量明显改善,以上研究结果对MIMO的工程应用有良好的参考意义。     

基于Khatri-Rao积的3D MU-MIMO预编码方法

为了解决下行三维(3D)多用户(Multi-User,MU)多输入多输出(MIMO)系统中的共信道干扰问题,提出了一种基于Khatri-Rao积的3D预编码方法。该方法首先产生离线码本,然后各用户分别选择与水平维和垂直维信道最匹配的的码字并将其反馈给基站端,最后,根据提出的KhatriRao积基站端构造3D预编码矩阵,对不同用户数据进行处理。理论分析和仿真结果表明,该方法可有效地匹配真实信道状态信息(CSI),而且可有效地抑制共信道干扰,提升系统误码性能,对系统的性能优化有一定的参考价值。     

基于非理想CSI的下行MU-MIMO鲁棒波束成形

在下行多用户多入多出（MU-MIMO）系统中,基站（BS）所获得的非理想信道状态信息（CSI）会导致频分双工（FDD）系统预编码性能变差.现有的MU-MIMO鲁棒预编码算法虽然可以对抗非理想CSI所导致的系统性能损失,但其只考虑其中一种或两种信道误差的鲁棒性,因此系统性能提升有限.本文通过建立包含信道估计误差、量化误差和延时误差的联合信道误差模型,推导出具有集中式特性的基于最小均方误差（MMSE）的鲁棒波束成形矩阵的闭式解;随后将这种信道条件应用到分布式通信系统,并推导出具有分布式特性的基于信号泄露的MMSE的鲁棒波束成形矩阵的闭式解.数值分析表明,本文所提的集中式和分布式MU-MIMO波束成形算法,与只考虑量化误差的鲁棒MMSE算法相比,具有更优的系统和速率与误码率,补偿了上述三种信道误差所导致的预编码性能损失.     

空间相关莱斯衰落信道下基于部分信道信息的多用户预编码与调度算法

在空间相关的莱斯衰落信道模型下,针对多用户MIMO(Multiple-Input Multiple-Output)系统潜在的多用户分集增益和空间分集增益,该文提出了一种基于部分信道信息的多用户预编码与调度算法。结合部分瞬时信道信息和统计信息,利用约束最大似然估计对各用户信道矢量进行估计,然后利用估计的各用户信道调度多个用户进行预编码。仿真结果表明,该方案以较少的反馈开销,获得了较大的性能增益。     

一种基于深度学习的FDD大规模MIMO系统CSI反馈方法

针对频分双工（Frequency Division Duplexing,FDD）大规模多入多出（Multiple-Input Multiple-Output,MIMO）系统中现有信道状态信息（Channel State Information,CSI）反馈方法复杂度高、反馈精度低的问题,本文提出一种基于深度学习的CSI压缩反馈方法.该方法首先采用卷积神经网络（Convolutional Neural Network,CNN）提取信道特征矢量,然后利用最大池化（Maxpooling）网络压缩CSI,最后考虑到大规模MIMO信道存在空间相关性的特点,分别对单用户和多用户场景使用双向长短期记忆（Bidirectional Long Short-Term Memory,Bi-LSTM）网络和双向卷积长短期记忆（Bidirectional Convolutional Long Short-Term Memory,Bi-ConvLSTM）网络对CSI进行重构.本文利用大规模MIMO信道数据对所提的深度学习网络进行离线训练,该网络学习到的信道信息能充分表征信道的状态.仿真结果表明,与已有的典型CSI反馈方法相比,本文所提方法反馈精度更高,运行时间更短,系统性能提升明显.     

基于SLNR与矢量扰动的毫米波大规模MIMO双层混合预编码算法

在多用户毫米波大规模多入多出（Multiple Input Multiple Output,MIMO）系统中，针对现有基于信漏噪比（Signal-to-Leakage-plus-Noise Ratio,SLNR）准则的混合预编码算法未考虑用户信道质量不同和信道矩阵具有病态性的问题，本文提出了一种联合SLNR与矢量扰动（Vector Perturbation,VP）的双层混合预编码算法.该算法分两层设计预编码矩阵.第一层，考虑用户信道质量不同，提出了基于SLNR准则的匹配加权算法.该算法充分考虑信道系数、预编码矢量和组合矢量的影响设计信道加权因子，利用加权因子对SLNR算法进行改进，从而设计更优的混合预编码器，消除用户间干扰.第二层，根据第一层获取到的等效基带信道，利用迫零（Zero Force,ZF）消除用户天线间干扰.考虑到信道矩阵具有病态性，采用VP算法进一步处理.通过在发射信号上添加扰动矢量减小发射端功率增强的影响.仿真结果表明，相较于同类混合预编码算法，所提算法可以获取更好的误码率（Bit Error Rate,BER）性能和频谱效率.     

Cellular Downlink Performance with Covariance-CSIT-Based MIMO Precoding

The nature of the trade-off between reduced overhead of channel state information (CSI) and resultant performance losses influences the design of frequency-division duplexed practical cellular systems. One candidate for CSI feedback reduction is the use of covariance-matrix-based CSI at the transmitter (CSIT) in conjunction with linear precoding techniques. This paper analyzes the performance of such systems in the downlink for both single-user (SU-) and multiuser (MU-) multiple-input multiple output (MIMO) in comparison to those using optimal perfect-instantaneous-CSIT-based precoding. In addition, the effectiveness of techniques enforcing frequency domain diversity versus those based on the maximal ergodic channel capacity criterion is evaluated. A novel precoding scheme using covariance matrix information that supports spatial multiplexing in both SU- and MU-MIMO is proposed. Simulation results show that the spectral efficiency loss from covariance-CSIT-based techniques from those utilizing perfect, instantaneous CSIT is shown to be about 1 dB in a highly correlated urban channel environment for both SU- and MU-MIMO, whereas for microcell environments it is between 3 and 4 dB.     

在空间相关Rice信道下的一种基于非码本的预编码方法在LTE下行系统中的应用

本文所提出的预编码生成方法适合在TD-LTE系统中工作，包括基于信道互易性获取信道状态信息模块，能量分配模块，波束形成模块。该方法充分利用了TDD系统的信道互易性特性，获取下行信道的信道状态信息，并使用基于非码本的预编码方式来增强传输的抗干扰性能，提升小区覆盖范围。与单纯考虑无视距LOS（Line-Of-Sight）分量的衰落信道不同，本文所提出的是在接收端天线之间存在空间相关的下行MIMO系统中，针对拥有LOS分量的莱斯（Rice）信道发射机的预编码设计方案。该方案可以保证非码本预编码算法的快速收敛，且保持较低的计算复杂度。     

Enhancing secrecy capacity of multi‐relay wiretap systems with partial channel state information

Distributed precoding has provento be capable of enhancing the secrecy capacity of the multi‐relay wiretap system. An iterative distributed precoding and channel state information (CSI) sharing scheme can be used to reduce the CSI overhead at each relay node. However, in practical applications, the CSI of each relay node cannot be perfectly known to themselves, especially that of the relay‐eavesdropper channels. Thus, partial CSI for the relay‐eavesdropper links is assumed, and the corresponding distributed precoding and CSI sharing schemes are investigated. Under the assumption that the average value of the relay‐eavesdropper channel is known at each relay node, an extended iterative distributed precoding and CSI sharing scheme is proposed. Simulation results demonstrate that with the increase of the power ratio of the constant part to the random part of the relay‐eavesdropper channels, the proposed scheme with partial CSI performs increasingly close to the one with perfect CSI in secrecy capacity. Copyright © 2014 John Wiley & Sons, Ltd.     

Transmission Scheme for 2D Antenna Array MIMO Systems with Limited Feedback

Three-dimensional (3D) multiple-input multiple-output (MIMO) systems exploit spatial richness and provide another degree of freedom to transmit signals and eliminate spatial interference. Currently, however, there is no 3D codebook for two-dimensional (2D) antenna array MIMO systems with limited feedback. In this paper, based on the existing 2D codebook, we present a limited feedback and transmission scheme for 2D antenna array MIMO systems. In this scheme, the mobile station (MS) has imperfect channel knowledge, and the base station (BS) only acquires partial information relating the channel instantiation. MS must feed back two channel state information (CSI) instances, i.e., the horizontal and vertical CSIs. After receiving the two CSI instances, the BS interpolates a new vertical precoding vector using the vertical CSI. Then, the BS re-constructs a 3D beamforming vector using horizontal and vertical precoding vectors and compensates the reported horizontal channel quality indicator. System level simulation is employed, and the simulation results show that the proposed method improves the system spectral efficiency and the cell-edge SE significantly.     

大规模MU-MIMO系统归一化预编码算法

针对大规模MU-MIMO系统中预编码技术性能不佳的问题,在不完善信道状态信息(CSI)的情况下,对迫零(ZF)和最大比发射(MRT)预编码技术提出了两种归一化算法：向量归一化与矩阵归一化。首先基站通过上行导频序列估计CSI,并在下行链路中用所提的算法对预编码矩阵进行归一化处理,然后将其与发送信号以及信道进行匹配。仿真结果表明,在高信噪比时,ZF预编码使用向量归一化算法实现了更好的系统性能;而在低信噪比时,MRT预编码使用矩阵归一化算法使系统性能得到了良好改善。     

Covariance-based linear precoding

This paper extends the self-contained theory of linear precoding to the field of covariance based spatio-temporal downlink processing for direct-sequence code-division multiple-access (CDMA) systems and shows the applicability to the release 6 of high-speed downlink packet access (HSDPA). To this end, a unifying theory is developed to formulate the three known linear filters, namely, the transmit matched filter, the transmit zero-forcing filter, and the transmit Wiener filter, as optimization problems even in systems, where only covariance knowledge is available at the transmitter. Second, the solutions of these transmit filters are given for such systems with partial channel state information (CSI). Finally, it is shown how covariance-based linear precoding can be employed in the new generation CDMA system HSDPA, i.e., how channel estimation on the secondary common pilot channel allows for optimum full rank linear precoding employing only partial CSI.     

The p -Sphere Encoder: Peak-Power Reduction by Lattice Precoding for the MIMO Gaussian Broadcast Channel

A vector precoding scheme has been recently proposed for the multiple-input multiple-output (MIMO) Gaussian broadcast channel. This technique minimizes the instantaneous transmitted power of linearly precoded signals, but does not take into account the peak-to-average-power ratio (PAPR). In this paper, we present a modified vector precoding scheme, where a perturbation vector is chosen in order to take into account both the instantaneous power and the instantaneous peak power of the transmitted signal. This is obtained by minimizing the p-norm of the transmitted signal for pges2. For this reason, the scheme is referred to as the p-sphere encoder. We demonstrate the performance of the proposed scheme applied to a MIMO independent, identically distributed Rayleigh fading downlink channel with simple channel inversion. We show that by choosing pges2, the proposed p-sphere encoder yields a tradeoff between power efficiency, PAPR reduction, and complexity. In particular, with eight antennas, the proposed algorithm significantly reduces the tail of the PAPR distribution, with very small degradation in terms of bit-error rate with respect to standard vector precoding