MC V-BLAST系统的MIMO信道盲估计

本文研究多载波垂直分层空时(MC V-BLAST)系统的下行频率选择性衰落多输入多输出(MIMO)无线信道估计问题.本文首先为MC V-BLAST系统提出了一种新颖的移不变性编码方法.利用上述移不变性性质,本文进一步提出了相应的下行频率选择性衰落MIMO无线信道的盲估计方法.仿真结果表明了本文移不变性编码方法的有效性和信道盲估计方法的性能.     

阵列天线多载波DS-CDMA系统基于子空间的信道估计

阵列天线多载波DS-CDMA系统在未来移动通信中具有重要的应用前景。本文研究了阵列天线多载波DS-CD MA系统基于子空间的信道盲估计方法。通过在阵列天线多载波DS-CDMA系统下构造统一的信号模型,实现了基于子空间的信道盲估计。仿真结果表明所提出的方法可有效地对阵列天线多载波DS-CDMA系统的信道参数进行估计,并可抵抗适度的远近效应。     

一种基于子空间分解的IIR信道盲辩识算法

本文证明了对IIR信道输出进行过采样 (采样率是输入码率的整数倍 )可以转化成单输入多输出的多信道模型 ,并且不同的信道有相同的AR系数 .基于这一特性本文提出一种基于子空间分解的信道参数盲辩识方法 ,即不同信道的MA系数可以由输出信号的噪声子空间唯一确定 ,而AR系数则可以通过求解YW方程得到     

循环前缀块传输系统中的一种MIMO盲信道估计算法

信道估计一直是无线通信领域的研究热点之一,信道参数估计的好坏对系统的整体性能有着至关重要的影响。针对采用循环前缀的多输入多输出(MIMO-CP)系统,本文提出了一种基于子空间的盲信道估计方法,该算法利用了循环前缀所引起的冗余信息。基于子空间的盲信道估计算法都是通过对接收块的自相关矩阵进行奇异值分解(SVD)来实现信道估计的,因此需要利用尽可能多的接收块来得到准确的自相关矩阵的估计值,这就意味着会产生过久的判决延迟以及不能准确对快变信道进行跟踪。利用MIMO-CP系统中系统矩阵特有的块循环特性,对于连续的两个接收数据块以及对应的循环前缀部分组成的向量,可以重新构造一组新的向量而不改变系统的信道矩阵,因此可以通过较少的接收块来得到准确的自相关矩阵的估计值,该方法十分适用于对快变信道的盲估计。文章通过仿真分析了在不同的重复系数以及不同的接收块下该算法的性能并且比较了该算法与现有的“预编码”、“虚拟子载波”等盲信道估计算法的性能。仿真结果表明,提出的算法利用较少的数据块个数就得到了一个可靠的信道估计值和很好的误码率性能。      

一种基于子空间分解的IIR信道盲辨识算法

本文证明了对IIR信道输出进行过采样（采样率是输入码率的整数倍）可以转化成单输入多输出的多信道模型，并且不同的信道有相同的AR系数。基于这一特性本文提出一种基于子空间分解的信道参数盲辨识方法，即不同信道的MA系数可以输出信号的噪声子空间唯一确定，而AR系数则可以通过求解YW方程得到。     

具有周期调制和循环前缀的块传输系统中MIMO信道的盲辨识

在块传输系统中,可通过添加块前缀来辅助信道识别。一种针对具有循环前缀和周期调制的块传输系统的盲辨识方法,利用了信道矩阵的块循环特性来求解信道系数。该文将该算法推广到了多用户系统,并给出了算法的辨识条件。同样是基于二阶统计量的方法,新算法克服了基于子空间分解类算法对噪声,对信道阶数误估计,对信道零点位置敏感的缺点。文中仿真证明了在较低信噪比条件下,利用新算法仍可对多输入多输出信道进行较好的估计。     

一种不受信道阶数估计影响的SIMO直接盲均衡算法

针对单输入多输出（Single-Input-Multiple-Output, SIMO）模型提出一种完全不需要信道阶数估计的直接盲均衡算法。文章利用接收数据的截短协方差矩阵和信号子空间的关系设计一种零延迟均衡器,并通过信道矩阵和均衡器系数的合响应特性克服了算法相位偏转的问题,最后得到一种对信道阶数估计鲁棒并且没有相位偏转的盲均衡算法。该算法不同于一般子空间类算法,不需要直接对接收信号的协方差矩阵进行信号子空间和噪声子空间的分解,因此对信道阶数估计具有很强的鲁棒性。文章给出了算法的Batch实现过程,同时为更好适应一般时变信道环境和实现实时处理的要求,通过递归迭代得到算法的自适应实现过程。仿真实验表明该算法几乎不受信道阶数过估计或欠估计的影响,同时该算法具有良好的均方误差（Mean Square Error, MSE）和误符号率SER（Symbol Error Rate, SER）性能,并且具有很快的收敛速度。      

CDMA信道的盲均衡和多用户检测

把码分多址（CDMA）信道等效为一多输入多输出（MMO）信道模型,用子空间分解的盲估计方法进行信道估计,而且估计出信号子空间特征向量,利用信道参数和信号子空间的特征向量构建解相关和最小均方误差（MMSE）两类线性检测器,能同时消除码间干扰（ISI）和多址干扰（MAI）。     

MIMO-OFDM的通信系统模型设计

为了达到更高的信息传输速率,提出了一种基于MIMO-OFDM的通信系统的实际模型。主要利用正交频分复用(OFDM)各子载波的频谱可以重叠、技术频带利用率高的特点,再配合多输入多输出(MIMO)系统,在通信速率上相比普通单输入单输出(SISO)系统有大幅提升。具体表现为对MIMO信道的估计方案进行改良,主要针对稳定环境下的MIMO信道进行估计,避免了快速时变环境下信道估计性能低劣的缺点。并在符号误差(STO)估计技术的基础上,针对性地找到一般条件下的系统偏差,由此可以得到更为精确的STO估计值。相对于常规方案,该方案性能更为稳定和优异。     

发射分集MC-CDMA系统盲干扰抑制

研究了多载波码分多址(MC-CDMA)系统的盲干扰抑制,采用基于空时分组码的发射分集。考虑对应于子载波的衰落系数是信道冲激响应的离散傅里叶变换,通过研究多径信号频域码空间和数据矢量空间,采用噪声子空间技术进行盲信道估计。为了抑制多址干扰(MAI),提出一种基于投影的辅助矢量算法(PAV),该算法计算复杂度低,在低输入信号干扰噪声比(SINR)时能提供有效的干扰抑制,在高输入SINR时具有稳健的性能。     

V-BLAST OFDM系统的频率选择性信道盲估计

研究下行频率选择性衰落环境中垂直分层空时正交频分复用(V-BLAST OFDM)系统的信道盲估计问题。为V-BLAST OFDM系统提出了一种新颖的贴标签型延迟分集结构。该结构能够巧妙赋予V-BLAST OFDM系统以旋转不变性性质。利用上述旋转不变性，进一步为下行V-BLAST OFDM系统提出了一种多输入多输出(MIMO)频率选择性无线信道的盲估计方法。仿真结果表明了新颖贴标签型延迟分集结构的有效性和信道盲估计方法的性能。     

Closed-form space-time channel blind estimation for space-time coded MC-CDMA sytems with uniform linear array

This paper proposes a closed-form joint space-time channel and Direction Of Arrival （DOA） blind estimation algorithm for space-thne coded Multi-Carrier Code Division Multiple Access （MC-CDMA） systems equipped with a Uniform Linear Array （ULA） at the base station in frequency-selective fading environments. The algorithm uses an ESPRIT-like method to separate multiple co-channel users with different impinging DOAs. As a result, the DOAs for multiple users are obtained. In particular, a set of signal subspaces, every one of which is spanned by the space-time vector channels of an individual user, are also obtained. From these signal subspaces, the space-time channels of multiple users are estimated using the subspace method. Computer simulations illustrate both the validity and the overall performance of the proposed scheme.     

DSSS-MIMO结构的标签延迟发射分集方法

针对频率选择性衰落多输入多输出(Multiple-Input Multiple-Output,MIMO)结构,提出在各发射天线通道引入直接序列扩频(Direct-Sequence Spread-Spectrum,DSSS)操作以便实现信道的矢量化,然后提出了一种标签延迟发射分集方法和相应的实现频率选择性衰落无线信道估计的盲方法.仿真结果表明了上述标签延迟发射分集方法的有效性及其信道盲估计方法的性能.     

Blind RLS-Based Detection Using GSC with DF for STBC MC-CDMA Systems Under Mismatched Channel Estimation

Under Rayleigh fading channels, a common problem with blind multiuser space-time block coded (STBC) multicarrier code division multiple access (MC-CDMA) detectors is that their performance is very sensitive to the signature waveform mismatch (SWM) induced by channel estimation distortion. This paper presents a robust detector using the generalized sidelobe canceller with a double-feedback filter that effectively mitigates the channel estimation distortion for the STBC MC-CDMA system during multipath fading. Numerical simulations show that the proposed detector substantially provides robustness against small-to-medium SWM scenarios for a downlink STBC MC-CDMA system.     

MUI-free receiver for a synchronous DS-CDMA system based on blockspreading in the presence of frequency-selective fading

We discuss a synchronous direct-sequence code division multiple-access (DS-CDMA) system based on block spreading in the presence of frequency-selective fading. Note that block spreading, which is also known as chip interleaving, refers to a spreading of a data block sequence, which is obtained by dividing a data symbol sequence into consecutive blocks. For such a system, we develop a simple new receiver that completely removes the multiuser interference (MUI) without using any channel information. The MUI-free operation is obtained by the use of a shift-orthogonal set of code sequences on which this receiver is based. Within the framework of the MUI-free receiver, we further present a subspace deterministic blind single-user channel estimation algorithm. As a benchmark for the MUI-free receiver and the corresponding subspace deterministic blind single-user channel estimation algorithm, we consider the linear multiuser equalizer and the corresponding subspace deterministic blind multiuser channel estimation algorithm developed by Liu and Xu (1996) for a standard synchronous DS-CDMA system in the presence of frequency-selective fading. We show that the complexity of the MUI-free receiver using the corresponding subspace deterministic blind single-user channel estimation algorithm is much smaller than the complexity of the linear multiuser equalizer using the corresponding subspace deterministic blind multiuser channel estimation algorithm. We further show that the performance of the MUI-free receiver is comparable with the performance of the linear multiuser equalizer. This is for the case in which the channels are known as well as for the case in which the channels are estimated with the corresponding subspace deterministic blind channel estimation algorithm     

Blind adaptive MIMO receivers for space-time block-coded DS-CDMA systems in multipath channels using the constant modulus criterion

We propose blind adaptive multi-input multi-output (MIMO) linear receivers for DS-CDMA systems using multiple transmit antennas and space-time block codes (STBC) in multipath channels. A space-time code-constrained constant modulus (CCM) design criterion based on constrained optimization techniques is considered and recursive least squares (RLS) adaptive algorithms are developed for estimating the parameters of the linear receivers. A blind space-time channel estimation method for MIMO DS-CDMA systems with STBC based on a subspace approach is also proposed along with an efficient RLS algorithm. Simulations for a downlink scenario assess the proposed algorithms in several situations against existing methods.     

Space-Time Coded Beamforming for DS CDMA Downlink

1　Introduction　 In 3G mobile system, Code Division Multiple Access(CDMA) is a promising multiple access techniques. It iswell know that BeamFormin ( BF), Space Time Coding(STC) and Multiuser Detection(MUD) techniques in CDMAsystem can effectively resist Multi Path Interference (MPI),MAI and near far effects. So the system capacity will be im proved greatly by employing these techniques[1,2,8]. In Ref.[3] introduces Water Filling(WF) theory into STC to assignth…     

LS—CMA在MIMO—OFDM频域盲信源分离中的应用

源分离(SS)是M IMO系统接收的关键技术,而盲源分离(BSS)又是其中的一个研究热点。目前最小二乘常模(LS-CM)BSS算法[1~3]都是针对频率非选择性衰落的时域M IMO信道。本文提出了LS-CMA在M IMO-OFDM系统频选信道频域盲源分离中的应用,计算机仿真表明,M IMO-OFDM系统频域盲信源分离的最小二乘常模算法能够获得很好的性能以及较快的收敛性。     

Equalization and semi-blind channel estimation for space-time block coded signals over a frequency-selective fading channel

In this paper, we investigate the equalization and channel identification for space-time block coded signals over a frequency-selective multiple-input multiple-output (MIMO) channel. The equalization has been considered by taking into account the cyclostationarity of space-time block coded signals. The minimum mean square error (MMSE) solutions have been derived for the linear and decision feedback (DF) equalizers. The channel estimation is required for the equalization. With known symbols (as pilot symbols), MIMO channels can be estimated. In addition, due to the redundancy induced by space-time block code, it is possible to identify MIMO channels blindly using the subspace method. We consider both blind and semi-blind channel estimation for MIMO channels. It is shown that the semi-blind channel estimate has fewer estimation errors, and it results in less (bit error rate) performance degradation of the MMSE linear and DF equalizers.