采用导频符号的短波OFDM同步捕获算法

分析了现有OFDM信号检测和同步捕获方案在低信噪比条件下存在的不足。针对短波信道的特点，提出了一种利用m序列作为导频符号的信号检测和同步捕获方案。方案利用时频联合估计来得到可靠的信号检测，并从导频符号估计时间和频率偏移。理论分析和仿真表明，该方案在短波信道低信噪比条件下工作性能良好。     

基于子空间的MIMO OFDM盲载波同步方法

针对MIMO OFDM系统,分析了多径信道与频域信号Hadamard积子空间的特点,构造了适合多天线条件下的基于子空间投影的频偏估计代价函数.该代价函数只和归一化频偏与接收数据有关,不需要信道信息和发送数据信息,因此是一种能有效提高数据传输效率的盲频偏估计方法.与已有盲同步方法相比,所提方法不需要使用虚子载波,因而频谱利用率可得到进一步提高.文中对算法的性能进行了仿真,验证了算法可对一个子载波间隔内的归一化频偏进行精确估计.结果表明,该方法性能优于已有文献提出的MIMO OFDM盲载波同步方法.     

OFDM系统中基于盲检测的低复杂度分块SLM算法

为了降低正交频分复用(orthogonal frequency division multiplexing, OFDM)系统中传统选择性映射(conventional selected mapping, CSLM)算法的计算复杂度,提高系统的频谱利用效率,提出了一种基于盲检测的低复杂度分块选择性映射(block selected mapping, BSLM)算法,发送端利用逆快速傅里叶反变换(inverse fast fourier transform,IFFT）性质仅需少量低维IFFT运算即可获得较多的备选序列,接收端采用低复杂度的盲检测方式。仿真分析了所提算法的峰均功率比(peak to average power ratio, PAPR)、立方度量(cubic metric, CM)和误比特率(bit error rate, BER)性能。结果表明,所提算法不仅明显降低了计算复杂度,而且有效抑制了OFDM信号的PAPR和CM,获得与已知边带信息的CSLM算法相近的BER性能。     

基于伪随机序列前导码的OFDM系统帧同步算法

在正交频分复用（orthogonal frequency division multiplexing, OFDM）系统接收端,错误估计快速傅里叶变换窗口起始点会导致OFDM帧偏差,从而造成严重的符号间干扰（inter symbol interference, ISI）以及子载波间干扰（inter carrier interference, ICI）。首先建立一个带有帧同步的OFDM系统模型,然后通过理论推导得到帧偏差对OFDM系统的影响。利用伪随机序列自身较好的相关特性,设计了一种基于伪随机序列前导码的帧同步算法,并分析了3种基于循环前缀（cyclic prefix, CP）的传统帧同步算法。通过仿真实验,结果表明所提出的基于伪随机序列前导码的帧同步算法与传统算法相比,即使在较差的信道条件下,如在较低的信噪比或存在较大的载波频率偏移（carrier frequency offset, CFO）时,其帧偏差估计结果更为准确、稳定以及节省资源。     

基于星座图统计的盲载波同步算法

卫星通信信号中90%以上采用相位或幅相联合调制方案,包括多进制相位键控（multiple phase shift keying,MPSK）,多进制正交幅度调制（multiple quadrature amplitude modulation,MQAM）,多进制幅相键控（multiple amplitude phase shift keying,MAPSK）等,此外短波通信、移动通信中MPSK也是最常用的信号类型之一。载波同步是信号解调中十分关键与核心的部分。针对非合作接收条件下幅相调制类信号星座图分布特性进行了深入研究,提出了一种基于星座图密度统计的载波同步算法,实现了一定信噪比条件下盲频偏消除与星座图恢复,此方案不需要预先进行调制识别,对数据量要求不高,复杂度低,抗噪性能好,可广泛应用于常规信号以及未知、猝发信号解调。仿真表明,在接近或高于解调信噪比的条件下,该方法频偏估计性能接近克拉美罗限,可应用于工程实践。     

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。     

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。     

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。     

改进的UPF算法在OFDM系统盲均衡中的应用研究

UPF滤波算法具有比PF算法更高的精度和抗噪声能力,但由于其计算复杂,不符合通信实时性的要求.为了改进算法的实时性,引入了平方根无迹粒子滤波算法(SRUPF),并对其进行改进,将改进算法应用于OFDM系统盲均衡中.最后经仿真表明,改进的UPF算法,在几乎不影响滤波效果的前提下,大幅减少了滤波所需计算量,并提高了数值稳定性.     

MIMO-OFDM系统多基站协作传输的盲定时同步算法

提出了一种用于多基站协作传输多输入多输出（multiple input multiple output, MIMO）正交频分复用（orthogonal frequency division multiplexing, OFDM）系统的分布式多天线盲定时同步算法,利用接收信号的循环平稳特性,根据天线间时延导致的接收信号循环自相关函数谱峰的偏移量得到天线间的时延差值。采用一种基于滑动窗的检测算法,得到各天线时延值。仿真结果表明,该算法在无须额外同步数据的情况下,能有效地解决分布式定时问题。     

Joint synchronization estimation based on genetic algorithm for OFDM/OQAM systems

This paper investigates the problem of synchronization for offset quadrature amplitude modulation based orthogonal frequency division multiplexing(OFDM/OQAM) systems based on the genetic algorithm. In order to increase the spectrum efficiency,an improved preamble structure without guard symbols is derived at first. On this basis, instead of deriving the log likelihood function of power spectral density, joint estimation of the symbol timing offset and carrier frequency offset based on the preamb...     

一种基于训练序列的OFDM时频同步新算法

针对正交频分复用(orthogonal frequency-division multiplexing,OFDM)系统性能对同步偏差的敏感性,提出了一种新的基于训练序列的OFDM联合定时和频率同步算法。基于新设计的训练序列结构,提出了新的定时度量函数,同时推导了小数倍频偏估计算法。新定时同步算法有效地克服了传统算法中的定时缺陷,新频偏估计算法具有和Schmidl算法相同的估计方差。理论分析与仿真结果表明,新算法在多径信道下具有较好的鲁棒性。     

Pseudo-noise preamble based joint frame and frequency synchronization algorithm in OFDM communication systems

Frame and frequency synchronization are essential for orthogonal frequency division multiplexing （OFDM） systems. The frame offset owing to incorrect start point position of the fast Fourier transform （FFT） window, and the carrier frequency offset （CFO） due to Doppler frequency shift or the frequency mismatch between the transmitter and receiver oscil ators, can bring severe inter-symbol interference （ISI） and inter-carrier interference （ICI） for the OFDM system. Relying on the relatively good correlation charac-teristic of the pseudo-noise （PN） sequence, a joint frame offset and normalized CFO estimation algorithm based on PN preamble in time domain is developed to realize the frame and frequency synchronization in the OFDM system. By comparison, the perfor-mances of the traditional algorithm and the improved algorithm are simulated under different conditions. The results indicate that the PN preamble based algorithm both in frame offset estimation and CFO estimation is more accurate, resource-saving and robust even under poor channel condition, such as low signal-to-noise ratio （SNR） and large normalized CFO.     

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.     

OFDM/OQAM系统中基于BEM信道模型的盲载波频偏估计算法

针对时频双选衰落信道下基于交错正交幅度调制的正交频分复用(orthogonal frequency division multiplexing with offset quadrature amplitude modulation,OFDM/OQAM)系统的频率同步问题,将双选信道建模为复指数基扩展模型,证明了存在载波频偏情况下OFDM/OQAM接收信号的二阶循环平稳特性,在此基础上,提出一种OFDM/OQAM系统载波频率偏差的盲估计算法。理论分析和仿真结果表明由该方法构造的估计器不仅能够有效地抵抗双选信道引起的衰落而且具有很好的抗噪性能,从而可以实现对载波频偏的稳健估计。     

Blind CFO estimation algorithm for OFDM systems by using generalized precoding and trilinear model

This paper discusses the blind carrier frequency offset (CFO) estimation for orthogonal frequency division multiplexing (OFDM) systems by utilizing trilinear decomposition and generalized precoding. Firstly, the generalized precoding is employed to obtain multiple covariance matrices which are requisite for the trilinear model, and then a novel CFO estimation algorithm is proposed for the OFDM system. Compared with both the joint diagonalizer and estimation of signal parameters via rotational invariant technique (ESPRIT), the proposed algorithm enjoys a better CFO estimation performance. Furthermore, the proposed algorithm can work well without virtual carriers. Simulation results illustrate the performance of this algorithm.     

Blind channel estimation for redundant precoded OFDM systems

Considering that channel estimation can play a crucial role in coherent detection of the information symbols in each data block, a blind channel estimation approach is proposed for redundant precoded orthogonal frequency-division multiplexing (OFDM) systems. A redundant linear frequency-domain precoder is applied to each pair of blocks before they enter the OFDM system. Because of the introduced structure, the frequency-selective channel can be identified at the receiver based on autocorrelation operations, singular value decomposition (SVD), and by resolving the scalar ambiguity. The proposed channel estimation method has low computational complexity and requires no prior statistical information on channel or noise. And the proposed blind method has high spectral efficiency owing to exploiting no training sequence. Computer simulations confirm that this proposed blind channel estimation method can identify the frequency-selective channels perfectly and obtain a good performance.     

接收分集OFDM通信系统的盲信道估计

提出一种新的利用接收分集技术的OFDM通信系统盲信道估计方法.所提出的算法根据单入多出系统模型,可直接在一个接收数据块内估计出各个接收分支所对应的多径信道,且不要求接收信号的二阶统计量等相关统计信息.由于采用频域相除抵消技术,各分支的信道参数可分离估计,因此降低了计算复杂度.仿真分析表明该算法的有效性.