空间相关信道下分布式MIMO系统中的STBC-VBLAST组合方案

在空间相关信道下分布式多输入多输出(D-MIMO)系统中,提出了一种新的空时分组编码(STBC)和垂直分层空时编码(VBLAST)组合方案.为充分利用D-MIMO系统的拓扑结构和空间相关信道的特性,在下行D-MI-MO系统的每个分布式天线(DA)簇内采用STBC,而在不同DA簇之间采用VBLAST.同时,为了降低系统复杂度并节省总发射功率,采用了基于最小传播路径衰落准则的天线选择方案.仿真结果证明,对比于传统VBLAST方式,所提出的STBC-VBLAST组合方案能显著降低系统误比特率(BER)并提高空间相关信道下BER性能的鲁棒性.因此,该组合方案是实现空间相关信道下D-MIMO系统下行分集与复用的折衷的一种有效方案.     

用于有限反馈MIMO系统中的统计多模发射天线选择算法

利用多输入多输出（MIMO）系统中的发射端天线选择算法,可以在降低复杂度的同时,有效地提高系统性能。考虑到基于线性接收机的空间复用系统,在通过已选择的发射天线上采用等功率分配等增益传输可以减少反馈信息量。因此,文章提出了空间相关衰落信道下可提升系统容量的统计多模发射天线选择方法。     

八天线TD-LTE系统的波束赋形算法分析

多天线是天线技术的发展趋势,TD-LTE引入了8发2收的天线配置.基于小间距多天线阵列,利用TDD系统信道互易性,波束赋形技术可以根据上行导频获得信道信息,形成对基带(中频)信号的最佳组合或者分配,补偿无线传播过程中由空间损耗、多径效应等因素引入的信号衰落与失真,同时降低同信道用户间的干扰.EBB(Eigen-based Beamforming)算法是波束赋形主要算法之一,该算法中在整个波束空间中,找到使接收信号功率最大的赋形权矢量.通过仿真,对EBB算法在各种应用场景下的性能进行了分析,结果表明八天线EBB波束赋形算法可以正确实现波束合成,在低速或上行信道信息估计误差较小情况下能够明显提高系统性能.     

协同信道空时优化MIMO无线传输系统

该文提出一种基于虚拟信道的空时优化多输入多输出(MIMO)无线传输系统。通过在发射端产生不同的空时虚拟信道,与实际空间无线信道级联,构成系统的整体传输信道即协同空分信道。系统可以根据接收端的反馈信息采用模拟退火算法来优化虚拟信道,改善误码率(BER)性能。利用虚拟信道方法,可以使一根MIMO发射天线在同一时间、同一频段传输多路叠加合并后的数据信号,从而可以使发射的不同数据信号的总路数超过发射天线的数量,突破了现有MIMO系统在同一时间、同一频段最多只能发射与发射天线数量相等的不同数据信号的传统方式,可以显著提高系统的频谱效率。仿真结果和基于ZC706和AD9361硬件平台的微波暗室实际测试结果充分验证了新MIMO系统的有效性。     

波束成形在TD-LTE-A系统中的性能优化

TD-LTE系统中的波束成形(Beam Forming)会受到收、发天线不对称性的影响。TD-LTE-Advanced(TD-LTE-A)系统中使用上行多天线发送可以解决天线不对称性的问题,因此需要对其分析以优化Beam Forming的性能。通过对上行多天线的信道状态信息(CSI)做特征值(SVD)分解,指出了Beam Forming对下行信噪比(SNR)的改善。针对Beam Forming模式下SNR和链路质量指示(CQI)的差异,提出了一种优化链路自适应的方法。数值仿真验证了优化后的TD-LTE-A相比TD-LTE的Beam Forming吞吐率最大提高了24%,其结论对商用TD-LTE网升级到TD-LTE-A具有显著价值。     

多径信道下基于空时分组码的发送分集技术

文章在多径信道下,提出了一种基于RAKE接收机的空时分组编码(STBC)方案.该方案将空时分组编码(STBC)与RAKE接收机的多径叠加相干检测的方法相结合,从而可以在频率选择性衰落信道下采用多发射天线实现发送分集.此方案获得的分集增益与由采用相同数量接收天线的最大比接收合并(MRRC)方案得到的接收分集增益接近,能够较大地提高传榆系统的可靠性.     

信道差错对多发射天线选择性能的影响

对于多发单收天线(MISO)通信系统,考虑发射端信道状态信息的差错(ECSI).研究正交空时分组码的MISO系统的多天线选择,提出了一种CSI差错的选择性信道序统计特性求解方法.在独立的平坦瑞利衰落信道和多进制相移键控(MPSK)调制下,推导了一种较准确的系统比特误码率(BER)切诺夫上界解析式.最后系统BER性能上界的数值结果和仿真结果研究表明:多发射天线选择技术能极大地提高系统的传输质量,能有效地抵抗ECSI的影响.     

一种移动终端多天线方向图重构快速选择算法与基于滑动时间窗的加速实现

 多输入多输出(MIMO)系统中,天线选择技术可以在降低复杂度的同时,有效地提高系统的性能.但对于天线安装空间受限的小型终端,天线的数目将受到很大限制,本文结合方向图可重构技术,考虑基于线性接收机的空间复用系统,通过在已选择的发射天线上采用等功率分配等增益传输以减少反馈信息量.在此条件下,推导出空间相关衰落信道下自适应发射天线选择的统计容量公式下限,然后,在此基础上提出基于方向图重构的发射天线快速选择方法以最大化该容量值.此外,在实现中提出了一种基于滑动时间窗的梯度更新估计模型,缩短了算法所需时间.     

Alamouti方案在不同信道状态信息下的仿真与性能分析

介绍了Alamouti方案的编译码原理。在发送端已知信道状态信息下,构建瑞利平衰落信道和频率选择性衰落信道,分别对该方案中2发1收和2发2收传输系统的性能进行仿真分析。利用Alamouti方案的正交特性求得了发送端未知信道条件下平均误符号率(SER)的一般解,并与发送端已知信道条件下的系统性能进行比较。通过系统仿真,证明了该方案的分集增益可以有效对抗多径效应和多普勒扩展,且分集重数决定Frobenius范数平方的数值进而影响系统的误符号率。     

无线通信系统中的闭环MIMO技术

多入多出（MIMO）技术被认为是下一代无线通信的关键技术之一,本文主要讨论能够进一步提升多天线系统容量的闭环MIMO技术,即带有反馈的MIMO系统。反馈的信道信息既可以提高单链路的传输性能,也可以优化多用户之间的调度问题。本文给出了几种在未来无线通信系统中可能采用的闭环MIMO方案,包括基于SVD分解和基于码本的预编码技术,分析并比较了它们的性能。仿真结果表明,闭环MIMO技术将有效地提高通信系统的性能。     

A DSFBC-OFDM for a Next Generation Broadcasting System With Multiple Antennas

In this paper, we propose a differential space-frequency block code-orthogonal frequency division multiplexing (DSFBC-OFDM) scheme as a multiple-input multiple-output (MIMO) transmission technique for next generation broadcasting system. A linear decoding method for DSFBC, which performs comparably to the ML decoding method, is derived for the cases of two or four transmit antennas. A simple table lookup method is proposed to improve the efficiency of the encoding/decoding process of DSFBC for the case of non-constant modulus constellations. This not only reduces the computational load, but also removes the necessity of channel estimation. Also, synchronization techniques with a DSFBC-encoded phase reference symbol (PRS) are discussed. Finally, an MIMO channel model for the next generation broadcasting system is developed by extending the 3GPP MIMO model to fit broadcasting environments. The MIMO channel model is then used to compare BER performances of differential space block code schemes for various channel environments. Simulation results show that the DSFBC-16QAM scheme using either four transmit antennas with one receive antenna or two transmit antennas with two receive antennas achieves a performance gain of 12 dB, with a data rate twice faster than that of the conventional DQPSK scheme     

联合波束域分解和SVD的多用户大规模MIMO系统信道估计

针对TDD(Time Division Duplex)模式下的多用户大规模MIMO(Multiple-Input Multiple-Output)系统,本文研究了将波束域分解和SVD(Singular Value Decomposition)同时用于该系统的信道估计。当基站天线数目较多时,信道估计误差、导频开销、信道估计算法的复杂度等问题将成为影响大规模MIMO系统性能的关键因素。运用波束域分解理论,将多用户的大规模MIMO系统分解成多个单用户的大规模MIMO系统,同时从波束域对信道建模,该方法降低导频开销的同时也减小了信道估计误差。另外运用SVD对信道自相关矩阵优化,可以进一步降低信道估计算法的复杂度。基于以上两点,本文提出了一种联合波束域分解和SVD的大规模MIMO信道估计方案,并推导出了估计误差协方差矩阵的闭式表达式。仿真结果表明,与同类方案相比,本文提出的方案具有更好的信道估计性能。      

MIMO-OFDM技术

多进多出(MIMO)系统在发射端和接收端分别设置多副发射天线和接收天线,采用MIMO技术可以提高信道容量和信道可靠性,降低误码率。正交频分复用(OFDM)是一种特殊的多载波传输方案,各子载波在整个符号周期上正交,各子载波信号频谱可以互相重叠,子载波正交复用技术大大减少了保护带宽,提高了频带利用率。MIMO-OFDM技术是OFDM与MIMO技术结合形成的一种新技术,该技术是在OFDM传输系统中采用阵列天线实现空间分集,提高了信号质量。MIMO-OFDM技术将成为下一代移动通信核心技术的解决方案。文中全面介绍了MIMO技术和OFDM技术及两者的结合,分析了实现MIMO-OFDM技术的关键,展望了发展前景。     

Exact bit error probabilities and packet error statistics for SVD transmission over time-varying dual-branch MIMO systems obtained by a Markov model

Using a finite state Markov channel model, we develop an analytical method for evaluation of the packet error structure in multiple-input multiple-output (MIMO) systems based on singular value decomposition (SVD). We consider dual-branch MIMO systems, with either two transmit and arbitrary number of receive antennas, or arbitrary number of transmit and two receive antennas. The corresponding Markov model parameters are obtained using a novel closed-form expressions for probability density function and level crossing rate of the signal-to-noise ratio at the output of eigenchannels in a MIMO system, derived for a case of Rayleigh propagation, imperfect channel state information and any fixed power allocation. The exact bit error rate for the transmission of quadrature amplitude modulated (QAM) symbols through the eigenchannels is derived in polynomial closed form. Furthermore, by using the developed Markov model, the packet error statistics in the corresponding eigenchannels are determined, and the closed-form analytical expression for the system throughput is derived when ‘go-back-N’ automatic repeat request procedure is applied in time-varying eigenchannels. The analytical results are validated by using Monte Carlo simulations.     

Degrees of freedom of MIMO interference channel with distributed space-time interference alignment

In the context of K-user MIMO interference channel (IC),achievable degrees of freedom (DoF) were investigated with distributed space-time interference alignment (DSTIA).By precoding with distributed current and outdated channel state information at the transmitters (CSIT),new tradeoff regions between achievable DoF and CSI feedback delay/frequency were achieved for MISO system.The impact of the number of transmit antennas on achievable DoF in the MISO system was analyzed,revealing that DoF results approach to the outer bound as the number of transmit antennas increases.Further,the impact of the number of receive antennas on achievable DoF was characterized,deriving the range of CSI feedback delay that preserves achievable DoF in the MIMO system.Theoretical and numerical analyses show that,the proposed DSTIA scheme can achieve better sum-DoFs by eliminating inter-user interference perfectly,tighten the gap between achievable DoF and outer bound,as well as improve the achievable rate of the system.     

Capacity and performance of lattice reduction aided linear processing with lattice encoding and decoding in limited feedback systems

Linear processing for multi-input multi-output (MIMO) antenna systems is preferred to non-linear ones for computational efficiency. Using channel state information (CSI) at the receiver, channel matrix can be decomposed via singular value decomposition (SVD), and if the transmitter can be fed back with the right-unitary-matrix of the SVD from the receiver, the maximum channel-capacity can be achieved with linear processing in point-to-point wireless MIMO communications. However, if the transmitter receives no-feedback, the optimal linear detector at the receiver is the minimum-mean-squareerror- estimator, of which capacity is far below the channelcapacity. In practice, reducing the amount of feedback information to achieve a "reasonably close channel-capacity" is an important issue in point-to-point wireless communications. In this paper, we propose a limited feedback system employing linear processing, which achieves near-channel-capacity. The feedback information is only an integer matrix, which is much less than that of the right-unitary-matrix of the SVD. Key ideas of the proposed scheme are the lattice reduction and modulo operation. Moreover, the amount of feedback information can be further reduced to a binary matrix using multi-level/multi-stage encode and decode. Under the turbo channel code the proposed scheme shows excellent performance at high data rates. We compare our simulation results with Shannon capacity limits for ergodic MIMO channels.     

MIMO-OFDM for wireless communications: signal detection with enhanced channel estimation

Multiple transmit and receive antennas can be used to form multiple-input multiple-output (MIMO) channels to increase the capacity by a factor of the minimum number of transmit and receive antennas. In this paper, orthogonal frequency division multiplexing (OFDM) for MIMO channels (MIMO-OFDM) is considered for wideband transmission to mitigate intersymbol interference and enhance system capacity. The MIMO-OFDM system uses two independent space-time codes for two sets of two transmit antennas. At the receiver, the independent space-time codes are decoded using prewhitening, followed by minimum-Euclidean-distance decoding based on successive interference cancellation. Computer simulation shows that for four-input and four-output systems transmitting data at 4 Mb/s over a 1.25 MHz channel, the required signal-to-noise ratios (SNRs) for 10% and 1% word error rates (WER) are 10.5 dB and 13.8 dB, respectively, when each codeword contains 500 information bits and the channel's Doppler frequency is 40 Hz (corresponding normalized frequency: 0.9%). Increasing the number of the receive antennas improves the system performance. When the number or receive antennas is increased from four to eight, the required SNRs for 10% and 1% WER are reduced to 4 dB and 6 dB, respectively. Therefore, MIMO-OFDM is a promising technique for highly spectrally efficient wideband transmission.     

一种MIMO中继系统的自适应自干扰消除方法

为节省频率资源,全双工中继一般采用相同的频率接收和发射信号。由于收发天线之间无法充分隔离,接收天线容易受到自身发射天线的回波干扰。针对宽带全双工多输入多输出( MIMO)中继的自干扰问题,提出了一种基于梯度下降自适应算法的自干扰消除方法。该方法利用中继反馈的已知信号进行自干扰信道估计,并产生一个对自干扰信号的估计信号,从而在接收端将干扰抑制。仿真结果表明,该方法在自适应滤波器的跟踪性能、收敛分布和不同 MIMO 配置下的均方误差( MSE)性能等方面均取得良好效果。     

瑞利衰落信道下最大比发射联合选择接收技术的性能分析

本文设计了一种新的MIMO传输技术,它在发射端(基站)按最大比发射(MRT),接收端则基于信噪比最大的原则仅选择一根接收天线来处理信号,记MRT/RAS.其目标就是为了提高系统性能并降低接收端(移动台)的硬件复杂度.根据随机矩阵和排序统计的最新理论,推导出瑞利衰落信道下MRT/RAS系统的中断概率、误码率(BER)等性能指标的确切表达式.仿真结果表明MRT/RAS系统可以取得很好的阵列增益及满分集增益.仿真试验也证明了分析结果的正确性.     

Coordinated beamforming with limited feedback in the MIMO broadcast channel

In this paper, we propose a new joint optimization of linear transmit beamforming and receive combining vectors for the multiple-input multiple-output (MIMO) broadcast channel. We consider the transmission of a single information stream to two users with two or more receive antennas. Unlike past work in which iterative computation is required to design the beamformers, we derive specific formulations for the transmit beamformers for two active users via a power iteration and a generalized eigen analysis. To enable practical implementation, a new limited feedback algorithm is proposed that exploits the structure of the algorithm to avoid full channel quantization. The feedback overhead of the proposed algorithm is independent of the number of receive antennas. Monte Carlo simulations are used to evaluate the bit error rate and the sum rate performances of the proposed algorithm. Simulation results show that the proposed method performs close to the sum capacity of the MIMO broadcast channel even with limited feedback.