预编码的反馈方式研究

本文主要对预编码的两种反馈方式进行研究.首先介绍了预编码技术,然后分别对1bit反馈法、随机矢量量化码本反馈法进行介绍和分析,比较不同反馈方式对于预编码性能的影响.1bit反馈法的系统性能可以接近完全信道信息反馈的系统性能,并能大大减少反馈数据量.     

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。     

基于HousehoJder码本的三维预编码码本设计

在LTE系统中,基于码本的有限反馈预编码码本设计是非常关键的一部分,本文以3GPP协议为标准,设计了该部分技术性问题的解决方案。文章介绍了LTEMIMOth的预编码技术和基于码本的有限反馈预编码技术,给出73GPP的预编码方案。本文在现有的研究基础上,提出了一种适合三维波束赋形的三维预编码技术的码本设计,并进行了性能仿真和分析。     

有限反馈MIMO系统中一种基于双码本的功率分配与预编码方案

研究表明，有限反馈预编码能有效利用信道信息提高MIMO系统频谱效率，在此基础上，在发射端进行功率控制将使频谱效率得到进一步提升．为了最大化有限反馈MIMO系统的频谱效率，本文提出了一种基于自适应调制的功率分配与预编码方案．为了减少反馈量，该方案通过双码本方式来反馈预编码矩阵和功率控制矢量，并给出了一种基于K-均值聚类的功率码本设计方法．仿真结果表明，该方案的反馈信息量少，且获得了较好频谱性能。     

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。     

一种用于MlMO系统的双码本预编码方法

时分复用(TDD)模式的通信系统可以通过有效利用信道的互易性,即通过上行链路对下行信道信息进行估计,并利用估计得到的信息对MIMO通信系统进行预处理或者预编码,从而进一步提升MIMO系统的信道容量和性能。然而,对于频分复用(FDD)的通信系统,由于上下行频段的不对称使得信道互易性原则不再适用,此时欲对信道进行预处理,则必须通过终端对下行信道信息进行上行反馈。反馈方式可分为直接对下行信道信息进行量化反馈的显式反馈和将量化后的信道空间以码本形式进行反馈的隐式反馈。对信道空间量化的隐式反馈进行研究,并在此基础上提出了一种双码本预编码的方法,并进一步对所提方案进行了理论分析和仿真验证。     

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。     

离散时间信号频域分析中的概念辨析

本文辨析了"信号与系统"课程中离散时间信号频域分析中的三个概念,提出了以离散傅里叶级数为切入点,顺序引出离散时间傅里叶变换和离散傅里叶变换的内容编排方式,其特点在于将离散傅里叶变换作为离散时间傅里叶变换在离散频点上的计算工具。这种编排方式避免了离散傅里叶级数与离散傅里叶变换的形式和概念混淆,适应了计算机仿真在"信号与系统"课程中广泛应用的趋势。对实现中的几个细节问题进行了具体分析,并给出基于门信号的信号仿真实例。     

基于OSTBC的有限反馈预编码设计

D.J.Love等在文献[7]中提出了基于正交空时码的有限反馈多天线系统,并且设计了至今保持最优性能的码本。这一系统已经被IEEE国际标准所采用。针对这一系统,本文基于文献[16]中的预编码设计准则,提出了新的预编码设计方案。相对于Love等在[7]中提出的码本,本文提出的新的码本在性能上有了提高。并且本文新的码本还具有快速选码方案,在其性能损失较小的情况下,有效降低了选码复杂度。     

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。      

Precoder Partitioning in Closed-loop MIMO Systems

We study unitary precoding for multistream MIMO systems with partial channel state information at the transmitter. We introduce a quantization scheme in which the full space of non-equivalent precoding matrices is partitioned into Grassmannian and orthogonalization parts. The Grassmannian part is used for maximizing the power after precoding and the orthogonalization part is used for removing cross talk between the data streams. We show that orthogonalization improves the attainable capacity when the receiver is linear. We give a parametrization for the non-equivalent orhogonalization matrices and a metric which measures the orthogonality of the transmission. Optimal orthogonalization codebooks for two-stream transmission are presented. When feedback is limited, the optimal partitioning of feedback bits between Grassmannian and orthogonalization parts becomes an issue. In correlated scenarios, the number of feedback bits may be significantly reduced by investing bits into the orthogonalization part.     

Quantized Principal Component Selection Precoding for Spatial Multiplexing with Limited Feedback

In this paper, for spatial multiplexing with limited feedback, a quantized principal component selection (QPCS) precoding scheme is proposed that achieves comparable capacity to the closed-loop multiple-input multiple-output (MIMO) and furthermore adapts to various fading channel conditions without any additional feedback bits and transmit channel state information (CSI). We propose a systematic design method for a codebook consisting of a finite number of unitary matrices based on a maximizing minimum distance criterion in the one- dimensional angular domain and show that the method outperforms the Grassmannian subspace packing method in various fading channel conditions. The proposed QPCS precoding scheme allows for adjustment of the precoding matrix based on limited feedback information on the principal vectors approximating a MIMO channel in the angular domain according to various channel conditions. Furthermore, for practical implementation of the QPCS precoding scheme, we propose a structured precoder optimization procedure and show that the proposed procedure induces a negligible capacity loss compared with the exhaustive precoder optimization, even with considerably reduced complexity.     

Optimized non-unitary linear precoding for orthogonal space-time block codes

This letter proposes a novel optimized non-unitary linear precoding design for orthogonal space-time block codes (OSTBCs). We dig out the transmission potentials by the analysis from eigen-space point of view according to the unique structure of OSTBCs. The proposed precoding form is proved to be theoretically optimized. Compared with the classical unitary Grassmannian codebook design, in the sense of restriction on the time average power of transmit signal, the proposed non-unitary codebook further improves the overall performance of practical systems. The new constraint on codebook size to guarantee full diversity order is given and proved. The advantages of our proposed design are verified in the numerical simulations.     

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.     

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。     

Recursive and Trellis-Based Feedback Reduction for MIMO-OFDM with Rate-Limited Feedback

We investigate an adaptive MIMO-OFDM system with a feedback link that can only convey a finite number of bits. We consider three different transmitter configurations: i) beamforming applied per OFDM subcarrier, ii) precoded spatial multiplexing applied per subcarrier, and iii) precoded orthogonal space time block coding applied per subcarrier. Depending on the channel realization, the receiver selects the optimal beamforming vector or precoding matrix from a finite-size codebook on each subcarrier, and informs the transmitter through finite-rate feedback. Exploiting the fact that the channel responses across OFDM subcarriers are correlated, we propose two methods to reduce the amount of feedback. One is recursive feedback encoding that selects the optimal beamforming/precoding choices sequentially across the subcarriers, and adopts a smaller-size time-varying codebook per subcarrier depending on prior decisions. The other is trellis-based feedback encoding that selects the optimal decisions for all subcarriers at once along a trellis structure via the Viterbi algorithm. Our methods are applicable to different transmitter configurations in a unified fashion. Simulation results demonstrate that the trellis-based approach outperforms the recursive method as well as an existing interpolation-based alternative at high signal-to-noise-ratio, as the latter suffers from "diversity loss"     

一种MIMO系统自适应码本设计方法

提出一种基于码本旋转的自适应码本设计方法,在不改变现有的码本基础矩阵的基础上,根据误码率(BER)和信干噪比(SINR)的统计和估计结果,生成一组新的旋转矩阵码本,并结合反馈开销考虑与原来基础码本矩阵构成双码本矩阵,根据信道的实时变化及时地调整码本的精度,从而能够在有限反馈的情况下更加有效地提高预编码的性能。     

基于算术傅里叶变换的小波变换快速算法

利用算术傅里叶变换(AFT)计算离散傅里叶变换(DFT)可使其乘法计算量仅为D(N）。文章根据这一特点，结合Mallat算法原理及离散傅里叶算法结构特征，提出了一种离散小波变换的快速算法，给出了数学推导过程，并对实验结果进行了分析。