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.     

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.     

MIMO中继系统中基于失真信道的联合收发机设计

在MIMO中继系统中,基于完全信道状态信息的基站、中继节点和终端联合收发机设计方案能够改善系统的误比特率性能,在放大转发(AF)中继的基础上提出了一种基于不完全信道状态信息的联合收发机设计方案.新方案在基站和中继节点的功率都受限条件下,将信道估计误差建模为高斯随机变量,以最小均方误差(MMSE)为准则,采用迭代算法,得到了基站预编码矩阵、中继转发矩阵和终端解码矩阵.该方案与不考虑信道估计误差的方案相比,能够有效地改善系统的均方误差和误比特率性能.     

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的多用户MIMO收发联合设计

在FDD模式多用户MIMO(Multi-input Multi-output)系统下行链路中,由于信道估计、反馈信道等存在误差,使得发送端获取理想信道状态信息(CSI,channel state information)十分困难。针对获得非理想CSI的多用户MIMO系统,考虑在基站和各用户的天线分别具有相关性并引入视距分量的信道条件下,提出了一种新的基于块对角化的MMSE准则收发联合设计算法。该算法首先通过块对角化消除用户间的共信道干扰,然后针对存在信道估计误差的用户信道依据MMSE准则分别迭代求解每个用户预编码和解码矩阵。论文设计出一种基于训练序列的信道估计误差算法,并获得等效信道模型,使得收发端获得的信道状态信息更有实际意义。本文假设反馈信道理想,发射端可以完整得到信道估计矩阵。在MMSE准则下,推导获得了Lagrange乘子的解析解,避免了求解非线性方程的复杂过程,显著降低了计算复杂度。和已有算法相比,该算法不仅可以获得良好的误码性能还可以对各用户进行独立优化,处理更加灵活。仿真分析了视距分量、信道相关性以及信道估计误差对算法性能的影响。仿真结果表明,该算法误码性能良好,算法收敛快,并且对信道估计误差带来的影响有较好的抑制作用。      

基于人工噪声的多用户MIMO系统加密算法

当多用户MIMO系统中的用户数多于或等于发射端天线数时,现有的基于人工噪声的物理层加密算法会导致合法用户无法正常接收。为提高此时的多用户MIMO系统的安全性,该文提出一种新的基于人工噪声的多用户MIMO系统加密算法。首先,发送端对多个合法用户进行联合处理,建立多用户联合信道状态矩阵;然后,将联合信道状态矩阵进行奇异值分解,并根据最小的奇异值进行预编码,以消除人工噪声对合法用户的影响;最后,提出一种优化功率分配的方案。仿真结果表明,该算法将多用户MIMO系统的保密容量平均增加了0.1 bit/(s?Hz),从而提高多用户MIMO系统的安全性。     

一种多用户多中继MIMO通信系统迭代预编码方案

该文针对多中继MIMO通信系统多用户传输时的用户间干扰问题,提出了一种可以有效抑制多用户干扰的发射端与中继端迭代预编码的方案。该方案首先在中继端进行多中继联合的迫零预编码,然后将基站与多用户之间等效为一个点到多点的MIMO信道,采用最大化信漏噪比的预编码方法,在发射端进一步消除用户间的干扰,同时避免了噪声放大的影响,进而通过中继端预编码与发射端预编码的多次迭代,更好地保持了多中继并行传输引入空间分集所带来的性能优势,有效地抑制了用户间干扰,获得了更高的系统和容量。     

双向中继系统用户联合预编码与检测算法研究

双向中继协同通信系统的两用户节点通过中继节点相互交换信息,显示了其在频谱效率上的优势。在系统装备多天线的情况下,为进一步改善误比特率性能,论文提出一种基于格规约算法的用户联合预编码与检测算法。该算法通过一次复数域格规约处理来提高信道增益矩阵的正交性,预编码和检测算法联合应用处理后的矩阵,中继节点仅需要对接收信号进行求模运算和放大转发,算法的复杂度主要集中在两用户节点上。仿真结果显示:相比于传统的预编码和检测算法,用户联合预编码与检测算法在计算复杂度仅增加了对信道增益矩阵一次格规约计算的前提下,可显著降低系统的误比特率,提高分集增益,具有工程实用价值。     

基于双向MIMO中继系统的一种预编码策略

为了克服已有的双向MIMO中继系统模型中预编码技术计算量大的缺点,提出了一种基于双向MIMO系统的三时段预编码策略,给出了该策略的模型和算法。该模型的中继节点预均衡各信道状态信息影响(CSI)后将合并信号分时段发送给不同通信节点,简化了传统中继转发矩阵对多信道信息的联合设计。理论计算和仿真结果表明,该策略在性能和复杂度之间得到了良好的折衷     

多用户毫米波MIMO系统中基于信道互易性的混合模数预编码算法

本文针对多用户毫米波多输入多输出(Multiple Input Multiple Output,MIMO)系统,首次提出了分离子阵列MIMO混合模数预编码架构毫米波系统的一种模拟接收方案。将最大化和速率求解混合模数预编码的三元联合优化问题分成模拟和数字两部分求解,进一步提出了基于信道互易性的混合模数预编码算法。该算法通过最大化下行各个用户和上行各个子阵列的接收信干噪比分别求解模拟合并矢量和模拟预编码矢量;优化模拟部分后,设计发射端数字预编码器消除多用户数据流之间的干扰。数值仿真表明所提算法收敛速度快,且可获得接近最优纯数字预编码算法的性能。      

协同OFDM系统中继节点发送训练序列的功率分配算法

考虑到在复杂街区环境中由于距离太远或者障碍物阻挡等原因,造成源节点和目的节点之间没有直接链路,而是利用多个中继进行协同传输的情景,本文针对空间相关信道下的协同OFDM系统,提出了一种中继节点发送训练序列的功率分配算法,从窄带协同信道模型矩阵表示出发,推导得到了宽带协同OFDM信道模型。在已知信道协方差信息情况下,利用LMMSE（Linear Minimum Mean Square Error）准则对中继节点发送的训练序列进行了功率分配。仿真结果表明,该功率分配算法在空间相关信道下具有良好的均方误差性能;与未考虑空间相关性的功率分配算法相比,该算法的估计精度更接近于Cramér Rao界（CRB）。      

Robust Tomlinson-Harashima Precoding for Two-Way Relaying

Most of the non-linear transceivers, which are based on Tomlinson-Harashima (TH) precoding and have been proposed in the literature for two-way relay systems, assume perfect channel state information (CSI). In this paper, a novel and robust TH precoding scheme has been investigated for two-way relay systems, with multiple antennas at the transceiver and relay nodes. We assume imperfect CSI and the channel uncertainty is bounded by a spherical region. The minimum mean square error at the destinations is used as the design criterion and we develop an iterative method to solve this nonconvex problem to obtain TH precoding matrices at the transmitter, linear precoding matrix at the relay and linear equalizer at the destination nodes, where each subproblem is convex. Simulations are provided to evaluate the performance and to validate the efficiency of the proposed scheme.

     

基于导频信号的MIMO-AF协作中继信道估计

提出一种在2个时隙内对MIMO-AF协作两跳中继信道进行估计的方法.重点研究在信源发送功率和中继发送功率受限的约束条件下,运用MMSE准则构建信源至中继节点信道估计的优化问题,采用矩阵分解的方法将信号分解成酉分量和对角分量,简化代价函数.最后用二分法求出最佳的导频信号和中继放大系数.仿真结果表明,本方法能够得到确定的、精度较高的信道估计值,并分析了信道相关性、天线数目对信道估计的影响.     

Array Calibration for CDMA Smart Antenna Systems

In this paper, we investigate array calibration algorithms to derive a further improved version for correcting antenna array errors and RF transceiver errors in CDMA smart antenna systems. The structure of a multi‐channel RF transceiver with a digital calibration apparatus and its calibration techniques are presented, where we propose a new RF receiver calibration scheme to minimize interference of the calibration signal on the user signals. The calibration signal is injected into a multichannel receiver through a calibration signal injector whose array response vector is controlled in order to have a low correlation with the antenna response vector of the receive signals. We suggest a model‐based antenna array calibration to remove the antenna array errors including mutual coupling errors or to predict the element patterns from the array manifold measured at a small number of angles. Computer simulations and experiment results are shown to verify the calibration algorithms.     

MMSE‐based transceiver design for distributed MIMO amplify‐and‐forward cooperative networks in correlated channels

In this paper, the source‐precoder, multiple‐relay amplifying matrices, and destination‐equalizer joint optimization is investigated in distributed MIMO amplify‐and‐forward multiple‐relay networks with direct source–destination transmission in correlated fading channels. With the use of taking both the direct link and spatial correlation between antenna elements into account, the cooperative transceiver joint design is developed based on the minimum mean‐squared error criterion under individual power constraints at the source and multiple‐relay nodes. Simulation results demonstrate that the cooperative transceiver joint design architecture for an amplify‐and‐forward MIMO multiple‐relay system outperforms substantially the noncooperative transceiver design techniques on the BER performance under the spatial‐correlation channels.Copyright © 2012 John Wiley & Sons, Ltd.     

New Solutions for Distributed Realization of 8 × 1 MISO channel with QOSTBC

We proposed new solutions for distributed realization of the quasi orthogonal space-time block coding (QOSTBC), which is designed for 8 × 1 multiple input–single output (MISO) system. The first proposed solution assumes that base station and relay stations are equipped with 2 antennas, while for the second solution base station is equipped with 4 antennas and relay stations are with one antenna. In both scenarios mobile unit is equipped with single antenna. The proposed solutions are compared with distributed QOSTBC which is used for 4 × 1 MISO system. The simulation results show BER performances improvements provided with the proposed solutions in comparison with distributed QOSTBC designed for 4 × 1 MISO. It was shown that the first proposed scheme provides lower BER values than the second solution. Also, beside ideal channel estimation, influence of real estimation errors on BER performances is considered.     

Channel estimation technique in multi-antenna AF relay communication systems

The channel estimation technique is investigated in OFDM communication systems with multi-antenna Amplify-and-Forward (AF) relay. The Space-Time Block Code (STBC) is applied at the transmitter of the relay to obtain diversity gain. According to the transmission characteristics of OFDM symbols on multiple antennas, a pilot-aided Linear Minimum Mean-Square-Error (LMMSE) channel estimation algorithm with low complexity is designed. Simulation results show that, the proposed LMMSE estimator outperforms least-square estimator and approaches the optimal estimator without error in the performance of Symbol Error Ratio (SER) under several modulation modes, and has a good estimation effect in the realistic relay communication scenario.     

Space-time channel estimation and performance analysis for wireless MIMO-OFDM systems with spatial correlation

This paper treats channel estimation in multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems with correlation at the receive antenna array. A two-step channel estimation algorithm is proposed. Firstly, the iterative quadrature maximum likelihood based time delay and spatial signature estimation is presented by utilizing special training signals with a cyclic structure. The receive spatial correlation matrix of the vector valued channel impulse response is formulated as a function of the spatial signature, the time delay, and the pulse shaping filter. The joint spatio-temporal (JST) filtering based minimum mean squared error channel estimator is derived by virtue of the spatial correlation. In addition, the effect of channel estimation errors on the bit error probability performance of the space-time block coded OFDM system over correlated MIMO channels is derived. The Cramer-Rao lower bound on the time delay estimate is provided for a benchmark of the performance comparison. The performance of proposed algorithms is illustrated based on analysis and computer simulations. The JST channel estimator achieves significant gains in the mean squared error compared to the temporal filtering. It also enables remarkable savings in the pilot symbol power level.