基于不完美CSIT的MIMO系统线性预编码传输方案

使用一个基于统计信息的CSIT模型:动态CSIT模型(dynamic CSIT model).首先根据最小化平均误码率Pe的设计准则,建立凸优化问题,通过变量代换,使用标准的凸优化算法推导出最优的线性预编码器.在此基础上,提出一种正交STBC和线性预编码相结合的传输方案.仿真结果显示,该方案可获得良好的性能增益和强健的鲁棒性.     

Linear transmitter precoding design for downlink of multiuser MIMO systems

Presented is the design of a set of linear transmitter precoding vectors for the downlink of a multiuser MIMO system, using the maximum signal-to-jamming and noise ratio for each user criterion, subject to a transmit power constraint. The proposed scheme does not impose any restrictions on the number of transmit antennas as do many conventional methods. Simulation results have shown the superiority of the proposed scheme compared to the conventional transmitter precoding schemes.     

信道反馈延迟时MIMO中继系统的线性预编码算法

针对采用放大转发(Amplify and Forward, AF)中继技术的多入多出(Multiple Input Multiple Output, MIMO)系统, 考虑信道估计误差及反馈存在延迟的情况, 提出一种基于最小均方误差(Minimum Mean Squared Error, MMSE)准则的预编码设计方案.假设基站-中继端及中继端-终端的信道均存在估计误差与反馈延迟, 在基站和中继端功率都受限条件下, 以MMSE为准则, 推导得到了基站预编码矩阵、中继转发矩阵和终端解码矩阵的闭式解.数值仿真结果表明, 该方案所提出的预编码算法能有效地改善系统的误比特率与均方误差.     

多小区多用户TDD MIMO下行链路干扰抑制预编码算法

针对多小区多用户TDD MIMO下行链路,提出了一种基于预编码的联合干扰抑制算法。首先,利用广义MMSE信道逆的QR分解设计预编码矩阵抑制下行链路的多用户干扰(MUI)。然后,从信号能量泄露的角度设计第二个预编码矩阵抑制小区间干扰(ICI)和残留的多用户干扰。该算法能够利用TDD MIMO信道的互易性,不需要用户端的反馈。在市区微小区组成的多用户TDD MIMO系统中的仿真结果表明,该算法能有效地提高系统容量和用户端平均信干噪比(SINR)。     

MIMO中继系统中基于不完全信道信息的线性预编码算法

针对采用放大转发中继技术的多输入多输出系统,提出一种基于不完全信道状态信息的中继预编码设计方案.假设在中继端已知源-中继的全部信道状态信息,在中继-目的端的信道考虑信道估计误差及发射天线相关性,根据最小均方误差设计准则,推导获得目的端线性处理矩阵.在中继端最大发射功率约束条件下,通过理论推导求得中继端线性预编码矩阵的闭式解.数值仿真结果表明,在存在信道估计误差和天线相关性的条件下,所提方案能有效降低系统的误比特率和均方误差.     

Convex-optimization-based precoding for MIMO downlinks

In this paper,the design of linear leakage-based precoders is considered for multiple-input multiple-output(MIMO) downlinks.Our proposed scheme minimizes total transmit power under each user's signal-to-leakage-plus-noise ratio(SLNR) constraint.When the base station knows perfect channel state information(CSI),suitable reformulation of design problem allows the successful application of semidefinite relaxation(SDR) techniques.When the base station knows imperfect CSI with limited estimation errors,the desig...     

Trellis precoding for MIMO broadcast signaling

Channel Inversion, and its Minimum Mean Square Error (MMSE) variation, are low complexity methods for Space Division Multiple Access (SDMA) in Multiple Input Multiple Output Broadcast Channel (MIMO-BC). As the channel matrix deviates from orthogonal, these methods result in a waste of transmit power. This paper proposes a trellis precoding method (across time and space) to improve the power efficiency. Adopting a 4-state trellis shaping method from [1], the complexity of the proposed method, which is entirely at the transmitter side, is equivalent to the search in a trellis with 4N states where N is the number of transmit antennas. Numerical results are presented showing that the achievable gains, which depend on the channel realization, can be significantly higher than the traditional shaping gain which is limited to 1.53dB.     

Linear diversity precoding design criterion for finite block‐fading parallel MIMO channels

A novel optimal two stage coding for finite set of parallel flat‐fading MIMO channels with single common information source with specific constant rate requirement is derived. The optimality of suggested coding is achieved in terms of the capacity versus outage performance. The well‐known optimal coding rule relies on Gaussian codewords spanned over the whole available finite set of parallel channels. We prove that the equivalent preprocessing to the ideal interleaving is to re‐code independent parallel channels codewords by a linear inner precoder from a special class of unitary precoders complying with the optimality criterion derived in the paper. Performing such linear mixture of codewords sharing common Gaussian block‐wise codebook, the same capacity versus the outage is guaranteed without any interleaving over parallel channels. We utilize a virtual multiple access (VMA) channel approach to derive the optimality criterion. Selected precoders with various space‐time or time‐only domain span were tested against this criterion and we provide the optimality results on variety of the channel parameters. We showed that the temporal processing is the most important one to achieve the optimality of the precoder. A full space‐time precoding does not perform better than one which is temporal‐only. Copyright © 2010 John Wiley & Sons, Ltd.     

空间相关MIMO信道下的有限反馈预编码

对于独立同分布的瑞利衰落信道,Grassmann码本可以取得良好的系统性能,但是当MIMO信道存在空间相关性时,该码本不可避免的带来性能损失,本文针对空间相关的MIMO信道,通过用发送相关矩阵的平方根对传统Grassmann码本进行旋转,然后再量化,得到适用于空间相关信道下的新码本,并通过实验仿真阐释了新得到的码本对于传统码本在误码率和信道容量方面等方面的性能优势。     

大规模MIMO系统中低复杂度的预编码改进算法

针对大规模MIMO系统中线性预编码包含复杂的大维矩阵求逆运算,从而产生较大系统开销这一问题,提出了一种低复杂度的基于区域选择初始解的RZF-GS预编码算法.该算法是在RZF预编码的基础上,用Gauss-Seidel迭代算法代替矩阵的求逆运算,并将通常的零初始解向量优化为基于区域选择初始解的向量.实验结果表明,该算法使系统整体的复杂度降低一个数量级,同时,与Neumann级数预编码和零初始解的RZF-GS预编码相比,该算法均明显加快了其收敛速率,用较少的迭代次数就能逼近经典RZF预编码的最优误码率性能.     

Nonlinear iterative precoding algorithm for MIMO multiuser systems

A modification of the known linear precoding algorithm CLTD (closed-loop transmit diversity) intended for multiuser radio communication systems and using theMIMOtechnology has been proposed. The efficiency of the original precoding algorithm CLTD possessing a number of advantages as compared to earlier precoding methods based on complete information about the communication channel state is enhanced at the expense of introducing nonlinearity. The use of nonlinear procedure of ordered successive interference cancellation (OSIC) in forming the precoding matrix makes it possible to significantly increase the noise immunity of the entire system as a whole at the expense of a slight rise of algorithm computational complexity. In addition, the results of computer simulation are presented reflecting the efficiency of the proposed modification of the algorithm for forming a precoding matrix as compared to the original CLTD algorithm.     

基于毫米波大规模MIMO系统的混合预编码设计

大规模多输入多输出（MIMO）被认为是未来5G的关键技术之一。毫米波因其足够大的频谱带宽近来备受关注。针对部分连接结构、单用户下行链路毫米波大规模MIMO系统,提出了一种新型的混合预编码设计。利用分层设计思想,首先设计模拟预编码器,提出一种模拟预编码器算法;然后通过注水算法获得最佳数字预编码器;最后,将起始最优化问题转化为在每根天线功率分配约束下单个RF链路连接天线子阵列最优化问题,再根据迭代方法获得最佳混合预编码器。仿真结果表明,最佳混合预编码器性能接近纯数字预编码器的性能。     

Closed-form expression for optimal two-user MIMO unitary precoding

In this paper we investigate the problem of optimal unitary precoding for multiuser multiple-input multiple-output (MIMO) wireless communication systems. In the case that there exist two users, we derive a closed-form solution for the unitary precoder that maximizes the sum rate. To provide additional insight, the optimal precoder is also characterized in several asymptotic regimes. Monte Carlo simulation results are also provided.     

Penalty function-based precoding for downlink multiuser MIMO systems

In this paper, a novel linear precoding scheme is proposed for downlink multiuser multiple-input multiple-output (MIMO) systems. The new algorithm uses the penalty function method to mitigate the co-channel interference and is formulated as a convex problem with general linear constraints. The constraints can be sum power, per-antenna power or per-antenna-group power constraints, hence the new algorithm is general and can be used in both single-cell and fully cooperative multi-cell scenarios. Moreover, the famous block diagonalization (BD) precoding can be considered as a special case of our method when a very large penalty factor is used. We study the optimal solution of this convex problem and propose an iterative algorithm to obtain the optimum based on the Lagrange dual method. Simulation results show that the proposed method significantly outperforms the BD method at low and moderate SNR values in terms of the weighted sum rate.     

适用于大规模MIMO系统的低复杂度RZF-SOR预编码算法

在大规模多输入多输出(MIMO)系统中,为了降低传统预编码算法的复杂度,在原有正则化迫零(RZF)预编码算法的基础上,提出用超松驰迭代(SOR)法代替矩阵求逆的高复杂度运算,得到一种改进算法RZF-SOR,并应用随机矩阵原理得出其最优相关参数的近似表达式和取值的必要条件.实验仿真表明,提出的RZF-SOR预编码算法与RZF预编码相比有效地降低了一个数量级的复杂度,在很小的迭代次数下达到接近于RZF预编码的误码率性能,并且优于基于Neumann级数预编码算法的误码率性能.     

A novel zero-forcing precoding method for multi-cell MIMO systems

Precoding methods at the Base Station (BS) can be used to deal with the inter-cell interference and improve the signal quality of the user especially at the cell edge. In this paper, a novel Zero-Forcing (ZF) precoding method is proposed and investigated for multi-cell Multi-Input Multi-Output (MIMO) systems. We propose a relaxed ZF precoding method by relaxing the ZF criterion to some degree so that the inter-cell interference may not be zero. Complexity analysis shows that compared with the conventional ZF method, the additional computation complexity for the proposed method is trivial. Simulation results show that the proposed relaxed ZF method has better performance than the conventional ZF method in terms of the sum-rate, especially at low Signal to Noise Ratio (SNR).     

Simple iterative receivers for MIMO LP-OFDM systems

In this paper,Lp-ofdm is combined with differentMimo schemes in order to improve performance in terms of diversity gain and to exploit capacity brought by theMimo channel. The original contribution is the development of a generic iterative receiver designed forLp mimo transmission able to work whatever the antenna configuration and the spatial coding scheme. By using a globalMmse criterion, interference terms coming from space-time coding and linear precoding are jointly treated leading to a very good trade-off between performance and complexity compared to trellis based detectors particularly for high order modulations, high number of antennas and/or large size of precoding matrices.     

Low-complexity tensor-based blind receivers for MIMO systems

In the tensor-based MIMO receivers, the multidimensional MIMO signals first are expressed as a third-order tensor model, wherein the factor matrices of tensor model are corresponding time/frequency, symbols, code/diversity of signals. A algorithm then is used for fitting this tensor mode, in which the symbols are estimated as a independent factor matrix. Although the performance of tensor-based receivers strongly depends on the initializations of the factor matrices. However, due to the absence of a priori on channels, these initializations are done randomly in alternating least squares (ALS), a basic algorithm for fitting the tensor models. In order to avoid these random initializations, this paper proposes two algorithms for fitting the tensor models. The first one, called delta bilinear ALS (DBALS) algorithm, where we exploit the increment values between two iterations of the factor matrices, refine these predictions by using the enhanced line search and use these refined values to initialize for two factor matrices. The second one, called orthogonal DBALS algorithm that takes into account the potential orthogonal in factor matrix for the DBALS algorithm, to provide the initialization for this factor matrix. By this way, we avoid random initializations for three factor matrices of tensor model. The performance of proposed receivers is illustrated by means of simulation results and a comparison is made with traditional ALS algorithm and other receivers. Beside a performance improving, our receivers give a lower complexity due to avoid random initializations.     

一种基于子空间跟踪的认知MIMO预编码算法

针对多用户认知MIMO下行系统,提出一种适用于慢衰落信道环境的预编码算法。该算法基于子空间跟踪思想,利用信道时域相关性,通过递推方式自适应更新预编码矩阵来跟踪和适应慢衰落信道环境的变化。分别从算法收敛速度、收敛精度、跟踪性能以及计算复杂度四个方面进行了理论推导和仿真分析。结果表明,所提算法可以有效的跟踪信道环境的动态变化,与传统算法相比,在保证系统性能的同时显著降低了处理复杂度。     

MIMO中继系统中预编码的级联算法

在两跳MIMO中继通信系统的预编码相关研究中,提出了一种级联预编码算法,该算法把两跳系统的预编码分解成两个独立的部分,从而把预编码问题转化成为求源节点到中继节点的预编码过程以及中继节点到目的节点的过程。本文使用MMSE准则,在简化迭代算法复杂度的同时,与一种只在中继节点进行联合优化的算法进行比较,由仿真可以看出,本文算法有一定的性能提升。