基于中国余数定理的欠采样下余弦信号的频率估计

基于中国余数定理的重构算法的信号频率估计是近年来信号处理、电磁学以及光学等领域的前沿问题,但目前这些研究仅限于对复指数信号做粗略频率估计.因而,本文把基于中国余数定理的频率估计从复指数信号粗估计拓展到实余弦信号精细估计领域,其所提出的估计方案处理过程如下:1)对高频余弦波形进行过零点检测,确定信号的相位信息;2)对各路欠采样信号做快速傅里叶变换,并借助Candan估计器对各路谱峰值做频率校正以获取高精度余数估计,基于此算出频偏值以做相位校正;3)用提出的基于相位特征分类方法对校正得到的余数做筛选;4)将筛选出的频率余数代入闭合形式的中国余数定理得到原信号频率的高精度估计.此外,本文还推导出了频率估计方差的理论表达式.数据模拟实验验证了该表达式的正确性,实验结果还反映了本文提出的方案具有高精度和高抗噪性能.     

基于遗传算法的稀疏孔径两次离焦相位差法

稀疏孔径望远镜的子镜装调误差是影响光学系统成像质量的主要因素之一。研究了基于遗传算法的两次离焦相位差法,即在稀疏孔径望远镜系统的两个不同的离焦面上获得两幅图像数据,采用遗传算法,通过最大似然估计目标函数最优化的方法,恢复目标图像并计算出稀疏孔径光学系统的活塞误差和倾斜误差,分析了复原图像的信噪比和方差。结果表明:遗传算法与两次离焦相位差法的结合不但可以精确求得子镜的装调误差,而且能够算出两次离焦的距离。与传统相位差法相比,计算时间相当,实验难度降低。     

基于复合光栅投影的快速傅里叶变换轮廓术

在实际傅里叶变换轮廓术测量中,获取条纹图的零频分量对傅里叶变换轮廓术的测量精度和测量范围有很大影响,甚至妨碍三维面形的正确重建。π相移技术常被用来消除零频分量对傅里叶变换轮廓术测量的影响,但它需要采集两帧具有π相位差的条纹图。这影响了傅里叶变换轮廓术测量方法的实时性。提出采用复合光栅投影来实现从一帧条纹图中消除零频对傅里叶变换轮廓术测量的影响,该复合光栅是由两个不同频率的载频分别调制与其方向垂直的两帧具有π相位差的条纹并叠加形成的。实验表明,同传统的π相移方法相比,提出的新方法没有明显降低π相移傅里叶变换轮廓术的的测量精度,因此能真正实现实时高速测量。     

采用听觉滤波器的宽带MUSIC声源定位方法

在分析了采用短时傅里叶变换的宽带MUSIC声源定位算法(SF-MUSIC)存在问题的基础上,提出了一种采用听觉滤波器的宽带MUSIC声源定位算法(AF-MUSIC)。该算法使用听觉滤波器组对传声器阵列接收到的信号进行不等带宽分解后,在各个频率通道上使用MUSIC算法进行声源定位,并结合子区间频数估计法得出最终定位结果。对算法进行的实验评估表明,在不同声源类型条件下,相比SF-MUSIC算法,AF-MUSIC算法的平均估计误差减少2.5479°,有效地提高了声源波达方向估计的精度。      

两步法提高时延差估计精度的分析和实验验证

为提高短基线水声定位系统的定位精度,对利用两次估计提高时延差计算精度的方法进行了理论分析、仿真和实验验证,并给出了具体的实现步骤。该方法将时延差估计值分解成了时延差初测值和时延差修正值,前者直接利用相关函数包络求解,后者与相关函数相位差之间存在映射关系,通过频域的相位差估计获得。仿真和实验的结果显示,采用这一方法能够获得很高的时延差估计精度。两步法具有很强的实用性,可以有效的提高短基线水声定位系统定位精度。      

相关峰细化的精确时延估计快速算法研究

研究精确计算相关峰的方法,提高时延估计精度,改进传统的CZT算法,计算细化的频谱,降低了标准FFT计算带来的栅栏效应,利用互谱的前后两段计算相关函数的主峰波形,并建立了新的快速变换算法(FICP),相关峰可以任意“插值”而不增加计算量。采用该方法和模型,可以有针对性地利用有限范围频谱,抑制宽带噪声对时延估计的影响,提高相关峰的检测精度。     

基于Khatri-Rao子空间和传播算子的宽带声源波达方向估计算法

本文提出基于Khatri-Rao子空间和传播算子的宽带声源波达方向估计算法。该算法将声源不同频率处的协方差矩阵变换重排为一个高维矩阵,然后利用传播算子方法估计宽带声源波达方向。该算法计算复杂度介于聚焦Khatri-Rao子空间和相干子空间算法之间。仿真和实验结果表明,该算法在降低计算量的同时,估计误差与聚焦Khatri-Rao子空间算法相近,远小于相干子空间算法。     

浅海中运动声源径向速度与距离的无源估计

针对浅海波导中声源距离的无源估计问题,提出了一种环境参数和声场模型无关的、不依赖于引导声源的运动声源径向速度以及距离估计方法。该方法首先通过双水听器低频声场强度距离波数谱变换(R-K)的相位差获得干涉简正波水平波数,对水平波数轴定标来估计运动声源的径向速度。进一步地,对接收信号自相关函数进行WARPING变换得到运动声源距离的无源估计。对于反射类简正波为主的声场,在某一假定距离下根据某两时刻接收信号WARPING变换后干涉简正波谱峰频率与假定距离的关系估计距离;对于反射类或折射类简正波为主的声场,根据两个时刻接收信号的β-WARPING变换后干涉简正波的脉冲时延估计距离的值。数值仿真分析了等声速、负梯度以及温跃层3种水文环境下的噪声以及环境宽容性,结果表明径向速度与距离的估计不依赖于环境参数。利用2005年北黄海实验数据验证了方法的可行性,径向速度与距离的估计值与实际值符合良好。      

光频梳下变频信号光纤延时频率恢复方法

针对光频梳下变频信号接收过程中存在的频率信息丢失问题,提出了一种基于频率-相位映射的信号频率恢复方法,该方法使用可调光纤延迟线在两路光频梳变频链路之间产生一组固定已知的时延,时延在信号原始频率与下变频信号相位差之间建立映射关系,利用该映射关系可以从测得的相位差计算出信号的原始频率。分析了时延值等参数对频率恢复的影响,估计了该方法对相位测量不确定度的限值要求,最后给出了该方法具体实施方案中关键参数的设置策略。所有下变频信号的相位差可以通过快速傅里叶变换等数据处理一次性得出,因此该方法的时间代价和计算成本几乎不随着信号个数增加而增加。在不考虑下变频信号混叠的情况下,本文所提出的方法在理论上对处理信号的数量没有限制,因此相比于已有的光频梳下变频信号频率恢复方法,在多信号频率恢复方面更具有优势。     

多速率STFT超宽带信号瞬时频率估计研究

提出多速率短时傅里叶变换(Multi Rate Short Time Fourier Transform,MR-STFT)瞬时频率估计算法,提高了超宽带信号瞬时频率估计精度。该方法将多速率信号处理算法与短时傅里叶变换(STFT)技术相结合,兼顾采样频率和被测频率,将宽频范围进行分段采样,对分段处理结果进行拟合,构成多速率STFT算法,实现超宽带信号瞬时频率的高精度测量。论文通过对仿真信号和实测信号进行处理,研究了方法的可行性和频率估计精度,结果表明MR-STFT算法较大提高了超宽带信号瞬时频率估计精度,尤其对低信噪比的超宽带信号效果显著。     

单次空时域并行欠采样下的频率和到达角联合估计

随着应用频段的不断升高,空时域欠采样下的入射信号的频率和到达角的联合估计变得愈加困难.为解决此难题,本文提出了一种基于互素稀疏阵列的联合估计器.首先,结合互素稀疏阵列和闭式中国余数定理,建立了频率估计和到达角估计的理论模型;其次,将频谱校正理论和中国余数定理结合起来,导出了频率估计算法;再次,将相位差校正和中国余数定理结合起来,导出了到达角估计算法.该估计器不仅可降低现有估计器的硬件成本,而且仅需对单次并行采样的快拍做并行处理即可获得联合估计结果,无需对单阵元做多次采样,数据处理效率较高.仿真实验表明,该估计器具有较高的鲁棒性估计精度,因而在雷达、遥感等被动感知领域具有较广阔的应用前景.     

ECM and SAGE based joint estimation of timing and frequency offset for DMIMO–OFDM system

Distributed multiple-input multiple-output (DMIMO) technology is a key enabler of coverage extension and enhancement of link reliability in wireless networks through distributed spatial diversity. DMIMO employs classic relay channels in between the source and the destination to opportunistically form a virtual antenna array (VAA) for emulating cooperative diversity. Use of multiple antennas at the relays further increases capacity and reliability of the relay–destination channel through multiplexing and diversity of MIMO antennas respectively. In such network, the signal received at the destination is characterized by multiple timing offsets (MTO) due to different propagation delay and multiple carrier frequency offsets (MCFO) due to independent oscillators of the relays. Hence, synchronization becomes a crucial issue in DMIMO in order to realize the distributed coherence. In this paper, we address joint estimation of MCFO and MTO in DMIMO orthogonal frequency division multiplexing (OFDM) with MIMO configuration at the relays for estimate-and-forward (EF) relaying protocol. Two iterative algorithms, based on expectation conditional maximization (ECM) and space alternating generalized expectation–maximization (SAGE) are proposed for joint estimation in presence of inter carrier interference (ICI). The robustness of both the estimators to ICI is evaluated by mathematical analysis and supported by extensive simulations. The performance of the proposed estimators is assessed in terms of mean square error (MSE) and bit error rate (BER). The theoretical Cramer–Rao lower bound (CRLB) of estimator error variance is also derived.     

多谐波脉冲星信号时延估计方法

针对脉冲星导航技术中延时估计这一关键问题, 提出了频域上直接使用脉冲星信号测量到达时间集合进行时延估计的方法——多谐波脉冲星信号时延估计(MHSPE)方法. 该方法建立在频域上相位时延的极大似然估计的基础上, 通过高次谐波对脉冲星观测信号提取出各谐波相位的极大似然估计, 然后取频谱上各谐波的幅值进行归一化作为各谐波相位的权值, 最后取各谐波相位的加权平均作为该时刻的相位估计. 理论上证得MHSPE算法对相位的估计是无偏、一致的, 相比于频域上一次谐波的极大似然估计, MHSPE方法的信噪比随谐波数m的增加而增加, 当各谐波幅值相同时, 信噪比可提高m_1/2倍; 与脉冲星信号时延的克拉美罗界比较, 脉冲星信号时域的导数在频域上的反映就是各谐波分量的数量, 因此随着谐波次数的增加脉冲星信号时延估计可极大趋近克拉美罗界. 采用RXTE航天器对Crab脉冲星的实测数据检验MHSPE方法的性能, 实验结果表明, 针对低信噪比的脉冲星信号, MHSPE可获得高精度的相位估计, 随观测时间增加, 估计精度快速收敛于克拉美罗界.     

一种基于最优频段的X射线脉冲星累积轮廓时延估计方法

为提高X射线脉冲星导航中累积脉冲轮廓的时间延迟估计精度, 分析了X射线脉冲星累积脉冲轮廓的频谱特性和现有Taylor快速傅立叶变换时延估计算法的缺陷, 提出了一种基于最优频段的累积轮廓时延估计算法, 并通过建立不同信噪比下时延估计误差与所采用频段之间的关系以确定最优频段. 数值及实测数据实验结果表明: 在短时观测或光子流量较小时, 该算法优于常用的近似最大似然 (FAML)、相关 (CC)、最小二乘 (NLS) 及加权最小二乘 (WNLS) 方法; 在观测时间较长或光子流量较大时, 该算法的估计精度与CC及NLS方法相当, 但其运算量低于NLS, FAML 及WNLS方法. 本文所提算法适用于短时观测脉冲轮廓或低流量脉冲星的高精度时延估计.     

Improved dichotomous search frequency offset estimator for burst-mode continuous phase modulation

A data-aided technique for carrier frequency offset estimation with continuous phase modulation(CPM) in burstmode transmission is presented. The proposed technique first exploits a special pilot sequence, or training sequence, to form a sinusoidal waveform. Then, an improved dichotomous search frequency offset estimator is introduced to determine the frequency offset using the sinusoid. Theoretical analysis and simulation results indicate that our estimator is noteworthy in the following aspects. First, the estimator can operate independently of timing recovery. Second, it has relatively low outlier, i.e., the minimum signal-to-noise ratio(SNR) required to guarantee estimation accuracy. Finally, the most important property is that our estimator is complexity-reduced compared to the existing dichotomous search methods: it eliminates the need for fast Fourier transform(FFT) and modulation removal, and exhibits faster convergence rate without accuracy degradation.     

Iterative Joint Estimation Procedure of Channel and PDP for OFDM Systems

The power-delay profile (PDP) estimation of wireless channels is an important step to generate a channel correlation matrix for channel linear minimum mean square error (LMMSE) estimation. Estimated channel frequency response can be used to obtain time dispersion characteristics that can be exploited by adaptive orthogonal frequency division multiplexing (OFDM) systems. In this paper, a joint estimator for PDP and LMMSE channel estimation is proposed. For LMMSE channel estimation, we apply a candidate set of frequency-domain channel correlation functions (CCF) and select the one that best matches the current channel to construct the channel correlation matrix. The initial candidate set is generated based on the traditional CCF calculation method for different scenarios. Then, the result of channel estimation is used as an input for the PDP estimation whereas the estimated PDP is further used to update the candidate channel correlation matrix. The enhancement of LMMSE channel estimation and PDP estimation can be achieved by the iterative joint estimation procedure. Analysis and simulation results show that in different communication scenarios, the PDP estimation error of the proposed method can approach the Cramér–Rao lower bound (CRLB) after a finite number of iterations. Moreover, the mean square error of channel estimation is close to the performance of accurate PDP-assisted LMMSE.     

Digital detection and processing of multiple quadrature harmonics for EPR spectroscopy

A quadrature digital receiver and associated signal estimation procedure are reported for L-band electron paramagnetic resonance (EPR) spectroscopy. The approach provides simultaneous acquisition and joint processing of multiple harmonics in both in-phase and out-of-phase channels. The digital receiver, based on a high-speed dual-channel analog-to-digital converter, allows direct digital down-conversion with heterodyne processing using digital capture of the microwave reference signal. Thus, the receiver avoids noise and nonlinearity associated with analog mixers. Also, the architecture allows for low-Q anti-alias filtering and does not require the sampling frequency to be time-locked to the microwave reference. A noise model applicable for arbitrary contributions of oscillator phase noise is presented, and a corresponding maximum-likelihood estimator of unknown parameters is also reported. The signal processing is applicable for Lorentzian lineshape under nonsaturating conditions. The estimation is carried out using a convergent iterative algorithm capable of jointly processing the in-phase and out-of-phase data in the presence of phase noise and unknown microwave phase. Cramér-Rao bound analysis and simulation results demonstrate a significant reduction in linewidth estimation error using quadrature detection, for both low and high values of phase noise. EPR spectroscopic data are also reported for illustration.     

Closed-form CRLB and LPI power allocation strategies for MIMO radars with unneglectable clutter

This paper studies clutter’s effect on MIMO radar performance through obtaining closed-form Cramer Rao lower bounds (CRLBs) for the range and velocity parameters versus the powers assigned to the transmit antennas which resulted in more calculation’ complexity. To verify extracted CRLBs, the maximum likelihood estimation’s error variance (MLEEV) of range and velocity were derived in attendance of clutter. Based on obtained closed-form CRLBs, four optimized power allocation (PA) strategies are proposed which consider measurement error statistics as the objective function or constraints to improve radar performance. So, the calculated closed-form CRLBs are simplified to the closed-forms versus assigned powers to the transmitters. Simulation results verify the proposed CRLBs’ accuracy, and improvements have been made by proposed power allocations.     

基于窗口傅里叶变换剪切干涉法波前检测

提出了一种利用二维窗口傅里叶变换从径向剪切干涉条纹中准确得到波前的重建技术。首先对剪切干涉条纹做二维窗口傅里叶变换,设置阈值和频率积分范围后,进行二维窗口傅里叶逆变换,然后对包裹相位做去载频和相位展开处理得到相位差分布,最后使用波前迭代算法从相位差中复原实际波前。模拟计算表明,使用该方法最大相位复原误差为0.82%,均方根值为0.020 9 rad,实验结果验证了该方法的有效性。同时也对窗口傅里叶变换的关键参数,如窗函数的选择、窗口大小的确定以及阈值的选取等进行了简要讨论。与传统傅里叶变换法(FFT)相比,基于窗口傅里叶变换的剪切干涉波前检测法有更高的精度和稳定性,为波前检测提供一种新的处理方法。