基于循环平稳特性的MIMO-OFDM符号定时和载波频率联合盲同步算法

提出了一种基于接收信号循环平稳特性(CS)的多输入多输出正交频分复用(MIMO-OFDM)系统符号定时和载波频率联合盲同步算法。该算法通过初始信号检测与符号定时粗同步、符号定时精同步、载波频率粗同步、载波频率精同步四个步骤完成MIMO-OFDM系统符号定时和载波同步。理论分析表明算法适用于无导频符号或训练序列、任意数目收发天线、任意分布加性平稳噪声条件下的同步。仿真结果验证了算法精度可满足MIMO-OFDM系统的符号定时和载波同步要求,并在低信噪比下性能保持稳定。     

MIMO-OFDM系统中基于CS-ESPRIT算法的多频偏盲估计

提出了一种基于接收信号循环平稳特性(CS)和基于旋转不变技术的参数估计方法(ESPRIT)的多输入多输出正交频分复用(MIMO-OFDM)系统多频偏盲估计算法。理论分析表明,算法无需训练序列或导频符号,可估计每对收发天线间频偏,适用于任意分布加性平稳噪声下的频偏估计。计算机仿真验证了算法在低信噪比下仍可取得稳定性能,并在传统单入单出(SISO)OFDM系统中也可获得较好的性能。     

分布式MIMO-OFDM系统中的时频同步

针对分布式多输入多输出〖CD*2〗正交频分复用系统,提出一种新的训练序列及时频同步方案。在定时同步方面,它首先利用训练序列的时域共轭对称性完成粗定时同步,在此基础上进一步通过接收信号与本地时域训练序列移动相关完成细定时同步;在频率同步方面,它首先在时域利用接收信号相位差估计小数倍频偏,然后在频域利用训练序列良好的自相关性估计整数倍频偏。该方案不仅能够同时估计出各收发天线对之间的定时偏移和频率偏移,而且估计性能良好。     

一种鲁棒的OFDM系统的定时算法

提出了一种新的定时同步的估计的方法。本同步方法采用了一种新的前导,可以避免Schmidl和Minn方法的不足,通过计算机仿真比较了三种方法的定时估计的均值和标准方差,结果表明文中算法的定时估计的均值与实际值一致,标准方差非常小。     

多频带OFDM超宽带系统同步及信道估计算法

针对标准多频带正交频分复用超宽带系统,基于前导训练序列研究其同步及信道估计算法。相关检测用取中点来减小粗定时误差范围。细定时利用系统零保护间隔的特点找相邻窗口最小能量比,对频偏不敏感且抗多径干扰。对定时位置进行修正,避免了信息数据的丢失及符号间串扰。采用基带数字域跳频解跳的机制,使载波频偏的影响归结为与单频带系统一致,简化了同步算法。仿真表明,在较恶劣的信道条件下,残余定时误差仍很小,并由信道估计及均衡有效的吸收,频率同步及系统差错性能良好。     

基于联合特征参数和一维CNN的MIMO-OFDM系统调制识别算法

针对当前非协作通信中多输入多输出正交频分复用(multiple-input multiple-output orthogonal frequency division multiplexing, MIMO-OFDM)系统子载波的调制识别问题,提出了一种基于一维卷积神经网络(one-dimensional convolutional neural network, 1D-CNN)的调制识别方法。首先,利用特征矩阵的联合近似对角化(joint approximate diagonalization of eigenvalue matrix, JADE)算法从接收端的混合信号中恢复发送信号;然后,提取恢复信号的循环谱切片和四次方谱作为浅层特征;最后,利用1D-CNN对特征进行训练,使用测试样本对所提出的调制识别方法进行仿真验证。仿真结果表明,所提方法对MIMO-OFDM系统中的5种信号可以进行有效识别,在信噪比为10 dB时的识别精度即可达到100%。     

IEEE802.11a接收机符号定时算法研究

IEEE802.11a是无线局域网中最重要的标准之一，它采用的是OFDM技术。由于IEEE802．11a系统特殊的前导信号，接收机可以利用IEEE802．11a前导信号的周期性而产生的自相关或者是接收信号和已知训练符号的互相关来进行符号定时估计。阐述了三种IEEE802．11a接收机的符号定时算法：一种是基于短训练序列的自相关符号定时算法；第二种是基于短训练序列的双自相关符号定时算法；第三种是基于长训练序列的互相关符号定时算法。通过仿真和性能分析比较说明了这三种符号定时算法的优缺点，这在实际应用中有很重要的意义。     

利用时域相关的MIMO-OFDM信道估计算法

提出了一种适用于多入多出正交频分复用(MIMO-OFDM)系统的信道估计算法,详细说明了导频符号的特殊设计算法以及信道估计算法的原理,并对该算法的均方误差性能以及复杂度进行分析;该算法能够在信道多径时延信息准确已知或不准确时带来良好的估计精度,从而保证系统性能。将该算法应用于超三代-时分双工(B3G-TDD)系统中并在室外和室内环境下仿真,均方误差和系统误码率性能结果说明了该算法的有效性;该算法能够大大增强系统的鲁棒性。     

多天线OFDM系统的线性优化

从Jakes信道模型出发,用KKT优化方法,从信道部分特性已知的情况推导了多天线OFDM系统中发射机与接收机的线性最优化设计问题。仿真比较了多天线OFDM系统的各个子载波之间采用合作的线性优化与非合作的线性优化两种方法在不同最大多普勒频移和反馈时延下发送符号的均方误差。仿真结果表明,当信道特性部分已知时,子载波之间合作的线性优化较之非合作的线性优化有更小的均方误差。可为存在反馈时延的多天线OFDM系统设计提供指导     

基于EM的MIMO-OFDM系统MAP信道估计算法

最大后验概率（maximum a posteriori, MAP）信道估计算法应用于MIMO-OFDM系统时将带来大规模矩阵求逆和乘积运算,且OFDM符号的数据传输效率随着发送天线的增多逐渐下降。针对这些弊端,提出一种基于期望最大化（expectation maximum, EM）的MAP信道估计算法,并分析了算法的性能。该算法利用EM算法把多输入输出信道估计问题化简为一系列独立的单输入输出问题,避免了大规模矩阵运算,降低了MAP算法的计算复杂度;为进一步改善MAP算法的数据传输效率及其估计性能,可通过对多个连续的OFDM符号进行联合信道估计。通过仿真实验证明了该算法的有效性。     

非数据辅助的OFDM系统联合同步算法设计

研究了正交频分复用(orthogonal frequency division multiplexing, OFDM)系统中非数据辅助的同步问题,通过对OFDM时域信号延时相关函数进行分析,设计了一种非数据辅助且具有较低复杂度的联合采样频率、载波频率及符号定时同步算法。算法根据延时相关函数以OFDM符号率为周期的周期特性,首先从延时相关函数的模中提取OFDM符号的周期标记,通过对收端和发端在相同时间内的采样点数之比进行采样频率偏差(sampling frequency offset, SFO)估计;然后通过对延时相关函数的模进行分段平均,从中提取去除循环前缀(cyclicprefix,CP)的开始时刻,从而进行符号定时同步和载波频率偏差(carrier frequency offset, CFO)估计。仿真结果表明,算法性能受累积时间长度和CP长度影响较大,而受OFDM基带调制方式影响较小;与其他同类文献相比,本文的联合同步算法具有较低复杂度和较好的性能。     

基于波达方向矩阵的MIMO-OFDM系统载频偏移估计

MIMO-OFDM系统中设置虚拟子载波后,时域接收符号向量与经频域信道系数加权的频域发射符号向量之间通过一个范德蒙矩阵相互联系,且该矩阵的列向量的结构决定于载频偏移量。基于此,提出了一种采用波达矩阵方法、利用范德蒙矩阵的移不变结构完成载频偏移估计的闭式频偏估计方法。该方法综合地利用了多收发天线的空域分集效应,降低了信道零点对频偏估计性能的影响,有效地提高了估计的均方误差性能。仿真结果验证了不同天线配置情况下所提出算法的性能。     

Blind channel estimation for multiple antenna OFDM system subject to unknown carrier frequency offset

The problem of channel estimation for multiple an- tenna orthogonal frequency division multiplexing （OFDM） systems subject to unknown carrier frequency offset （CFO） is addressed. Multiple signal classification （MUSIC）-Iike algorithm, which generally has been used for direction estimation or frequency estimation, is used for channel estimation in multiple antenna OFDM systems. A reduced dimensional （RD）-MUSIC based algorithm for channel estimation is proposed in multiple antenna OFDM systems with unknown CFO. The Cramer-Rao bound （CRB） of channel estimation in multiple antenna OFDM systems with unknown CFO is derived. The proposed algorithm has a superior performance of channel estimation compared with the Capon method and the least squares method.     

Joint timing synchronization and frequency offset acquisition algorithm for MIMO OFDM systems

For multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) sys-tems, a joint timing synchronization and frequency offset acquisition algorithm based on fractional Fourier transform (FRFT) is proposed. The linear frequency modulation signals superimposed on the data signals are used as the training signals. By performing FRFT on the receiver signals and searching the peak value of the FRFT results, the receiver can realize timing synchronization and frequency offset acquisition simultaneously. Compared with the existing methods, the proposed algorithm can provide better timing synchronization performance and larger frequency offset acquisition range even under multi-path channels with low signal to noise ratio. Theoretical analysis and simulation results prove this point.     

Hybrid pilots assisted channel estimation algorithm for MIMO-OFDM systems

Abstract: A hybrid pilots assisted channel estimation algorithm for multiple input multiple output (MIMO) orthogonal frequency division multiplexing (OFDM) systems under low signal-to-noise ratio (SNR) and arbitrary Doppler spread scenarios is proposed. Motivated by the dissatisfactory performance of the optimal pilots (OPs) designed under static channels over multiple OFDM symbols imposed by fast fading channels, the proposed scheme first assumes that the virtual pilot tones superimposed at data locations over specific subcarriers are transmitted from all antennas, then the virtual received pilot signals at the corresponding locations can be obtained by making full use of the time and frequency domain correlations of the frequency responses of the time varying dispersive fading channels and the received signals at pilot subcarriers, finally the channel parameters are derived from the combination of the real and virtual received pilot signals over one OFDM symbol based on least square (LS) criterion. Simulation results illustrate that the proposed method is insensitive to Doppler spread and can effectively ameliorate the mean square error (MSE) floor inherent to the previous method, meanwhile its performance outmatches that of OPs at low SNR region under static channels.     

基于目标不变信息量的模糊航迹对准关联算法

探讨了在组网雷达存在系统误差情况时的目标航迹对准关联问题。通过将探测系统误差对目标航迹的影响表示为各目标航迹数据的旋转和平移,从而说明了目标之间的相对拓扑关系不受系统误差影响;由此提出了一种雷达组网模糊航迹对准关联算法,该算法通过提取包括目标间拓扑信息在内的各种不受系统误差影响的目标不变信息量,采用模糊信息处理理论来解决目标航迹的对准关联问题,从而较好地实现了误差配准前的准确航迹对准关联。     

Improved H-infinity channel estimator based on EM for MIMO-OFDM systems

H-infinity estimator is generally implemented in timevariant state-space models,but it leads to high complexity when the model is used for multiple input multiple output with orthogonal frequency division multiplexing (MIMO-OFDM) systems.Thus,an H-infinity estimator over time-invariant system models is proposed,which modifies the Krein space accordingly.In order to avoid the large matrix inversion and multiplication required in each OFDM symbol from different transmit antennas,expectation maximization (EM) is developed to reduce the high computational load.Joint estimation over multiple OFDM symbols is used to resist the high pilot overhead generated by the increasing number of transmit antennas.Finally,the performance of the proposed estimator is enhanced via an angle-domain process.Through performance analysis and simulation experiments,it is indicated that the proposed algorithm has a better mean square error (MSE) and bit error rate (BER) performance than the optimal least square (LS) estimator.Joint estimation over multiple OFDM symbols can not only reduce the pilot overhead but also promote the channel performance.What is more,an obvious improvement can be obtained by using the angle-domain filter.     

基于内插结合MMSE均衡消除OFDM系统相位噪声的算法

针对正交频分复用（orthogonal frequency division multiplexing, OFDM)系统对相位噪声的敏感特性,提出一种基于内插结合最小均方误差(minimum mean square error, MMSE)均衡消除OFDM系统相位噪声的算法,通过在发射端的IFFT之前,对符号进行零子载波的内插,可有效地降低OFDM系统相位噪声造成的子载波间干扰（inter carrier interference, ICI）,提高信干比。通过MMSE均衡方式,可消除OFDM系统相位噪声造成的公共相位误差（common phase error, CPE）。仿真结果表明,本算法可以消除CPE引起的整个信号星座的旋转,同时大大降低ICI引起的信号星座点的云状发散,OFDM系统的相位噪声在高斯信道和多径信道下都能够得到有效抑制,且复杂度低、实现简单,具备良好的实用价值。