多基站协作系统中有限反馈策略及其码本设计

该文针对基于中央控制单元和大容量光纤骨干网连接而成的多基站集中调度协作系统所引起的高系统复杂度和高实现成本等问题,分析了一种可由现存蜂窝无线系统平滑过渡的多基站分布式协作MIMO系统结构及其信号传输特性。在此基础上,给出了该系统结构中基于信道量化码字索引信息的低速率有限反馈策略,讨论了对应的码本设计与构造准则,并提出了一种基于弦距离矢量量化准则的量化码本空间构造与实现算法。通过性能分析表明,该有限反馈策略获得的系统性能可明显优于模拟的导频重传方法,同时也好于基于欧几里德距离量化准则构造的码本空间性能。     

有限反馈预编码优化中基于性能准则的码字选择

多输入多输出(MIMO)空分复用系统中,采用有限比特反馈方式设计最优预编码矩阵,使用较少的反馈开销,可以有效地提高系统性能。对于有限反馈预编码设计方案,提出了一种基于Qos准则的码字选择方法,以最优化系统MSE性能和BER性能为目标选择最佳码字。仿真结果表明,与已有的码字选择方式相比,本文提出的方法更加直接,对于各种码本具有通用性,而且进一步改善了有限比特反馈预编码的性能,系统BER值降低了1.5 dB。     

基于码本的有限反馈非酉矩阵预编码多用户MIMO系统

该文提出了一种基于码本的有限反馈非酉矩阵预编码下行多用户MIMO系统。该方案根据用户反馈的信道信息SINR在发送端进行调度和预编码来提高系统容量。预编码的码本设计依据格拉斯曼空间装箱原理,并将码本中的向量按其相关性构成非酉矩阵来提高预编码增益和抑制多用户共道干扰。新方案反馈量少、复杂度低,在相同情况下比传统的单用户MIMO系统和基于码本的酉矩阵预编码多用户MIMO系统都具有更好的性能。     

空时相关MIMO信道下的空时联合Huffman有限反馈预编码

针对空时相关的MIMO信道,提出了一种新颖的Huffman空时联合有限反馈预编码方法,提高了系统性能,并减少了反馈量。从信道的空间相关性出发,推导了迫零准则下预编码的构成,从而设计了一种旋转量化码本,减小了空间相关性对系统性能的影响。另外,针对信道的时间相关性,利用基于邻域的有限反馈来降低慢衰落信道的反馈量。同时,由于领域内各码字被选中的概率不同,可以利用Huffman编码进一步减少反馈量。     

基于零向波束形成和旁瓣抑制的MIMO-OFDM系统码本设计

MIMO系统可提高通信系统的容量和频谱的利用率,支持高速数据传输,是下一代无线传输系统的关键技术。在MIMO系统中,当发射端已知信道状态信息时,利用有限反馈的预编码可提高系统的性能。已有的码本设计方法,有的实现较为复杂,有的受到信道的限制。根据零向准则波束形成器的原理,结合降低天线副瓣的方法,实现了一种MIMO—OFDM系统预编码码本的设计。将此码本用于MIMO—OFDM系统有限反馈的预编码中,经仿真结果验证了码本设计方法的有效性。该码本的设计复杂度低,具有较好的性能。     

MIMO-OFDM系统中基于簇的有限反馈方法

本文针对有限反馈MIMO-OFDM波束形成系统,研究了基于簇的有限反馈方法。利用簇内相邻子载波信道的频率相干性,提出了一种低复杂度的信道均值分簇法,该方法以平均信道响应在给定码本中选择最佳簇波束形成向量。此外,利用簇波束形成向量之间的剩余相关性,还提出了递归反馈和基于格的反馈两种反馈速率降低方法,即将前一簇码字的邻域内码字作为当前簇的新码本,从而大幅度降低反馈比特数。仿真结果表明信道均值分簇法能以较低的计算复杂度获得较佳的BER性能,反馈降低方法相对传统分簇方法能进一步降低反馈速率,递归反馈方法有一定性能损失,而基于格的反馈方法性能损失可忽略不计。      

LTE-A系统中预编码矩阵选择算法研究

该文是对第三代移动通信系统长期演进(3G LTE)及其增强版本(LTEAdvanced)下基于码本的MIMO预编码算法进行了研究。传统预编码算法可通过SVD分解获得,而该算法需要获知完整的信道状态信息,它的实现复杂度极高,因此该文在仿真SVD算法的基础上,对基于方程求解特征值获得预编码索引的方法和最大等效信道矩阵选择算法进行了研究,这两种算法在性能上较SVD算法没有损失甚至更优,但复杂度明显降低,基于EPA5、ETU70信道类型进行仿真,仿真结果验证了算法性能。     

3G LTE系统基于码本的自适应预编码方案

第三代移动通信系统长期演进(3G LTE)系统的下行链路传输中,基站端无法获知完全的信道状态信息(CSI),需要根据终端反馈的预编码序号从已有的码本中挑选合适的预编码矩阵进行信号处理。研究了多小区场景下基于有限信息反馈的码本选择算法,提出了一种单双流自适应的码本选择方案,分析了2×2天线情况下所提预编码算法的性能,通过计算机仿真给出了不同多天线预编码方案的性能对比。     

一种基于码本的SLNR算法

在有限反馈系统中,针对用户端向基站反馈完整的信道状态信息对上行链路传输能力要求较高、设备实现较为复杂的问题,给出一种基于码本的最大化SLNR及SFR的PF调度算法。该算法通过码本量化预编码矩阵,基站仅需用户端反馈码本编号即可获得预编码矩阵,从而大大降低了信息反馈量。仿真结果表明,算法保证了系统和边缘用户性能,但是,作为降低反馈量的代价,与引入码本前相比,算法性能略微下降。     

一种最大化系统用户速率下限的MIMO-MAC有限反馈干扰对齐算法

针对2小区MIMO-MAC中传统有限反馈干扰对齐码字选择方案的不足,本文提出了一种最大化用户速率下界的直接码字选择方案,并结合比特分配算法来减少和速率的损失,同时采用最大信干扰算法译码.不同于传统的基于最小弦距离或对齐度准则来选择码字,本文从最大化用户速率下界的角度来选择的码字;进一步地,在格拉斯曼空间中生成与期望预编码接近的码字集合,在该集合中只需简单的搜索便可找到优化的码字组合,同时实现了低复杂度和次优的全局搜索.仿真实验表明,相对于现有的典型算法,本文算法在提升系统和速率的同时,也提高了系统用户速率的下界.     

有限反馈MIMO下行系统中基于黄金码的传输方案与解码方法

针对有限反馈多输入多输出下行系统,结合黄金码与预编码技术,提出一种新的预编码设计准则、码字选择方案及新的传输方案和相应的低复杂度解码方法。事实上,在充分利用黄金码能够克服信道深度衰落这一特性的基础上,对所选预编码码字进行重新构造,得到一个二重预编码矩阵,将其作为发送信号,从而能够实现线性解码。与此同时,针对传统的MIMO下行系统传输方案提出了ML和MMSE的联合解码方法,使其能通过一个门限值动态地调节解码复杂度。数值仿真结果证明了本文所提方案性能的优越性。     

Limited feedback unitary precoding for orthogonal space-time block codes

Orthogonal space-time block codes (OSTBCs) are a class of easily decoded space-time codes that achieve full diversity order in Rayleigh fading channels. OSTBCs exist only for certain numbers of transmit antennas and do not provide array gain like diversity techniques that exploit transmit channel information. When channel state information is available at the transmitter, though, precoding the space-time codeword can be used to support different numbers of transmit antennas and to improve array gain. Unfortunately, transmitters in many wireless systems have no knowledge about current channel conditions. This motivates limited feedback precoding methods such as channel quantization or antenna subset selection. This paper investigates a limited feedback approach that uses a codebook of precoding matrices known a priori to both the transmitter and receiver. The receiver chooses a matrix from the codebook based on current channel conditions and conveys the optimal codebook matrix to the transmitter over an error-free, zero-delay feedback channel. A criterion for choosing the optimal precoding matrix in the codebook is proposed that relates directly to minimizing the probability of symbol error of the precoded system. Low average distortion codebooks are derived based on the optimal codeword selection criterion. The resulting design is found to relate to the famous applied mathematics problem of subspace packing in the Grassmann manifold. Codebooks designed by this method are proven to provide full diversity order in Rayleigh fading channels. Monte Carlo simulations show that limited feedback precoding performs better than antenna subset selection.     

毫米波大规模MIMO系统中低复杂度混合预编码方法

针对毫米波大规模多输入多输出(MIMO)系统混合预编码方案设计的难点,提出了一种低复杂度混合预编码方法。首先基于奇异值分解,构造初始射频(RF)预编码矩阵,然后构造数字预编码矩阵。进而将残差矩阵最大左奇异矢量构造的矢量添加到RF矩阵的最后一列,以更新初始RF矩阵。经过多次迭代,从而形成最终RF预编码矩阵。最后基于最小二乘准则设计数字预编码矩阵。理论分析和仿真结果表明,相比于基于正交匹配追踪(OMP)算法的混合预编码设计方法,该方法在计算复杂度大幅下降的同时,其性能远远优于基于OMP算法的混合预编码方法,同时在数据流数相对较小时,其性能接近最优的全数字预编码设计方法。     

Efficient QR-Based Multi-Mode Precoding for Limited Feedback Multi-User MIMO Systems

This paper proposes QR-based criteria for efficient selection of multi-mode precoders in multi-user multiple-input multiple-output (MU-MIMO) precoded systems with a limited feedback. In particular, a MU-MIMO QR based precoding scheme is developed which takes advantage of the overall precoder design among users in conjunction with QR detection. A selection criterion is developed to identify the precoder that yields the maximum free distance. Efficient mode selection and tree search strategies are adopted to reduce the complexity associated with the identification of the optimum precoder. To further improve the detection performance in correlated channels, an efficient QR-based MMSE V-BLAST detector is proposed. Computer simulations confirm that the proposed QR-based precoding scheme attains the performance of existing schemes with a significantly lower complexity level.     

MIMO系统中的一种码距分配矩阵构造方案

针对多输入多输出(MIMO)系统采用奇异值分解(SVD)预编码时最优码距分配矩阵的构造无闭式解且搜索复杂度高的问题,基于变形的Hadamard矩阵,以接收端成对错误概率最小化为准则,给出了一种易求解且为闭式构造的码距分配方案。同时,给出了与之相应的功率分配方案,进一步提高了系统的性能。仿真结果表明,该算法性能与现有方法近似,但复杂度降低。当推广到具有发射相关性的MIMO系统时,仍具有较好的性能。     

Grassmannian流形上基于高分辨率动态聚焦码本的MIMO信道预测

针对MIMO时变信道下,有限反馈发射预编码存在反馈延迟的问题,提出将多数据流空间复用传输的MIMO信道的主右奇异矩阵的列空间建模于n维复欧氏空间上p维子空间的集合Grassmannian流形Gn,p上,利用Grassmannian流形的测地线对时变信道进行跟踪预测,以补偿反馈延迟对于系统性能的影响。在此基础上,从Grassmannian流形的几何特性入手,针对Grassmannian流形的切空间提出了一种高分辨率动态聚焦的多维切空间码本。计算机仿真表明,Grassmannian流形上基于高分辨率动态聚焦码本的有限反馈预测预编码的系统性能明显优于存在反馈延迟的无记忆有限反馈预编码和采用固定码本的有限反馈预测预编码。      

存在估计误差的有限反馈MIMO性能分析

考虑的是利用有限反馈技术的下行多用户多天线系统。接收端通过信道估计获得信道状态信息,采用随机矢量量化信道信息并反馈码子的序号,发送端利用部分信道信息,采用波束成型的预编码技术实现多用户数据传输。考虑接收端信道估计存在误差,并对由此带来的系统性能影响进行分析,给出吞吐率损失的上界,以及使有限反馈系统保持固定空分复用增益,信道估计误差方差的限制条件和反馈比特数随发送功率的变化关系。     

Approximate Minimum BER Power Allocation for MIMO Spatial Multiplexing Systems

Precoding for multiple-input multiple-output (MIMO) spatial multiplexing generally requires high feedback overhead and/or high-complexity processing. Simultaneous reduction in transmitter complexity and feedback overhead is proposed by imposing a diagonal structural constraint to precoding, i.e., power allocation. Minimum bit-error rate (MBER) is employed as the optimization criterion, and an approximate MBER (AMBER) power-allocation algorithm is proposed for a variety of receivers, including zero-forcing (ZF), successive interference cancellation (SIC), and ordered SIC (OSIC). While previously proposed precoding schemes either require ZF equalization for MBER, or use a minimum mean-squared error (MMSE) criterion, we provide a unified MBER solution to power allocation for ZF, SIC, and OSIC receiver structures. Improved error-rate performance is shown both analytically and by simulation. Simulation results also indicate that SIC and OSIC with AMBER power allocation offer superior performance over previously proposed MBER precoding with ZF equalization, as well as over MMSE precoding/decoding. Performance under noisy channels and power feedback is analyzed. A modified AMBER algorithm that mitigates error propagation in interference cancellation is developed. Compared with existing precoding methods, the proposed schemes significantly reduce both transmit processing complexity and feedback overhead, and improve error-rate performance     

Low Complexity Suboptimal User Selection Algorithm for Multiuser MIMO Systems with Block Diagonalization

In downlink multiuser multiple-input multiple-output (MU-MIMO) systems, block diagonalization (BD) is a well-kown precoding technique that eliminates interuser interference. The number of simultaneously supportable users with BD is limited by the number of base station transmit antennas and the number of user receive antennas. The brute-force search for the optimal user set, however, is computationally prohibitive. Therefore, we propose a low complexity and suboptimal user selection algorithm based on block diagonalization for MU-MIMO systems. We introduce a strong tight upper bound of sum capacity as selection metric. Furthermore, we employ a substitution operation to improve system performance. The computational complexity analysis and simulation results show that the proposed algorithm achieves comparable throughput with low complexity compared to the existing algorithms.