一种基带GMSK信号相关器及其输出概率分布

该文提出一种基带GMSK信号相关器,并从GMSK解调信号的相位概率分布函数以及独立同分布随机变量和的概率分布函数出发,给出了该相关器的自相关峰和互相关峰的概率分布函数。从概率论与数理统计出发,推导了一种统一的数字相关器(数字匹配滤波器)的自相关峰和互相关峰的概率分布函数。数值计算结果表明,在相同条件下,该基带GMSK信号相关器的误检概率比数字相关器的低近一个数量级。     

BOC(1,1)信号处理方法研究和码跟踪精度分析

本文介绍了BOC（1,1）信号的调制原理、信号的频谱特性和自相关函数特性,分析了BOC（1,1）信号自相关结果的多峰值特性和由此特性造成的跟踪和锁定难度的增加。介绍了基于高精度测距技术的码跟踪环路的设计方案。实验表明,该环路设计可以可靠地跟踪BOC（1,1）信号并提供较高的测距精度。     

直接序列扩频谐波载波偏移调制

该文提出直接序列扩频谐波载波偏移(HOC)调制方法。HOC信号的扩频码流由成谐波关系的子载波调制扩频波形构成,其自相关函数是包络和阵因子的乘积。分析表明,HOC信号的相关函数具有窄主峰,主峰宽度为信号的撑张带宽的倒数。该文分别就理想随机码和周期性伪随机码给出HOC信号自相关函数的解析表示式。该文指出,类似二相载波偏移(BOC)调制信号的周期性子载波偏移调制的信号均可表示成HOC信号。HOC信号具有可分解性,可时分实现。HOC信号的窄主峰,次峰可控制以及可分解性,决定其具有更好的距离分辨力和抗多径干扰以及抗人为干扰性能。该文通过HOC信号的具体构成例,给出了峰值平均功率比抑制的找平法。该文最后特别讨论了大撑张带宽HOC信号的性质。     

Transverse flowmetry of carbon particles based on photo- acoustic Doppler standard deviation using an auto- correlation method

In order to measure the flow velocity of carbon particle suspension perpendicular to the receiving axis of ultrasound transducer, the standard deviation of photoacoustic Doppler frequency spectrum is used to estimate the bandwidth broadening, and the spectrum standard deviation is calculated by an auto-correlation method. A 532 nm pulsed laser with the repetition rate of 20 Hz is used as a pumping source to generate photoacoustic signal. The photoacoustic signals are detected using a focused PZT ultrasound transducer with the central frequency of 10 MHz. The suspension of carbon particles is driven by a syringe pump. The complex photoacoustic signal is calculated by Hilbert transformation from time domain signal before auto-correlation. The standard deviation of the Doppler bandwidth broadening is calculated by averaging the auto-correlation results of several individual A scans. The feasibility of the proposed method is demonstrated by measuring the spectrum standard deviation of the transversal carbon particle flow from 5.0 mm/s to 8.4 mm/s. The experimental results show that the auto-correlation result is approximately linearly distributed within the measuring range.     

A delay/Doppler-mapping receiver system for GPS-reflection remotesensing

A delay/Doppler-mapping receiver system, developed specifically for global positioning system (GPS)-reflection remote sensing, is described, and example delay/Doppler waveforms are presented. The high-quality data obtained with this system provide a more accurate and detailed examination of ground-based and aircraft GPS-reflection phenomenology than has been available to date. As an example, systematic effects in the reflected signal delay waveform, due to nonideal behavior of the C/A-code auto-correlation function, are presented for the first time. Both a single-channel open-loop recording system and a recently developed 16-channel recorder are presented. The open-loop data from either recorder are postprocessed with a software GPS receiver that performs the following functions: signal detection; phase and delay tracking; delay, Doppler, and delay/Doppler waveform mapping; dual-frequency (L1 and L2) processing; C/A-code and Y-code waveform extraction; coherent integrations as short as 125 μs; navigation message decoding; and precise observable time tagging. The software can perform these functions on all detectable satellite signals without dead time, and custom signal-processing features can easily be included into the system     

Correlation functions in a tapped delay line model of the orbital dipole channel

This paper considers the properties of the tap gain functions in a tapped delay line model of the orbital dipole channel. Specifically, auto-correlation and cross-correlation functions are computed for these tap functions in terms of assumed statistics for the motion of illuminated dipoles. It is demonstrated that when a certain inequality involving the transmitted signal bandwidth is satisfied, these correlation functions become identical to those which would arise from the corresponding tap gain functions of a suitably defined channel consisting of a continuum of motionless scintillating uncorrelated scatterers. In effect, this inequality sets an upper bound to the bandwidth of the transmitted signal, beyond which the orbital dipole channel may not be modeled as such a continuum of uncorrelated scatterers. Simplified expressions for tap gain correlation functions are derived for the case of large signal bandwidths, including the subcase in which the above mentioned inequality is satisfied. In the latter case the tap gain functions are shown to become mutually uncorrelated for all time shifts.     

On some bonds between autocorrelation and power spectra functions

Some bonds are established between values of the auto-correlation function of a signal and some parameters of the corresponding power spectrum, and vice versa. These relations are then detailed for band-limited signals, and some expressions for a rough evaluation of the signal bandwidth are deduced.     

On the distribution of positive-definite Gaussian quadratic forms

Quadratic signal processing is used in detection and estimation of random signals. To describe the performance of quadratic signal processing, the probability distribution of the output of the processor is needed. Only positive-definite Gaussian quadratic forms are considered. The quadratic form is diagonalized in terms of independent Gaussian variables and its mean, moment-generating function, and cumulants are computed; conditions are given for the quadratic form to bechi^{2}distributed and distributed like a sum of independent random variables having a Gamma distribution. A new method is proposed to approximate its probability distribution using an expansion in Laguerre polynomials for the central case and in generalizedchi^{2}distributions in the noncentral case. The series coefficients and bounds on truncation error are evaluated. Some applications in average power and power spectrum estimation and in detection illustrate our method.     

单信道混合数字通信信号的时延估计方法

单通道混合通信信号的参数估计是无线通信信号处理的热门方向。本文针对单信道两路数字通信信号混合的时延估计问题,根据混合信号的循环自相关函数与信号调制参数的关系,提出了两种基于循环自相关的时延估计方法。两种方法分别针对信道参数未知的情况和信道参数已知的情况,利用循环自相关函数构建关于两路时延参数的方程组,通过解方程组获得了两路信号时延的闭式估计。另外本文也对单通道混合数字通信信号时延估计的克拉美罗界进行了分析。最后利用计算机仿真实验,考察了不同条件下两种方法的性能,表明了它们的性能特点和适用的条件。      

双基地多载频MIMO雷达的同步误差提取方法研究

研究了双基地多载频MIMO雷达中由ADC采样引起的同步误差的3种提取方法。首先建立了同步误差的信号模型,仿真分析了同步误差对测距以及测角的影响,并将其归结为高精度频率估计问题。频谱连续细化法在较小范围内利用连续傅里叶变换来获得高精度的频率估计,既可以降低运算量又能获得较高的频域分辨率;自相关函数法通过对通道分离并补偿阵列延时差后的直达波信号的自相关函数做反正切运算求得同步误差值;MUSIC法首先构造时间同步误差的导向矢量,并利用其向噪声子空间投影,通过搜索空间谱的最大值来得到同步误差值。最后仿真比较了3种方法的性能,结果表明在低信噪比时可采用运算量较大的MUSIC法以取得较好的性能,而在信噪比较高时可采用运算量较小的自相关函数法或者频谱细化法以获得较快的处理速度。     

MATLAB中几种功率谱估计函数的比较分析与选择

功率谱估计是一种重要的频谱分析方法,通过分析比较MATLAB中几种常见的功率谱估计函数。从而选择最佳的频谱估计函数,减小实际的信号频谱分析误差。设计了仿真信号,并采用MATLAB中几种功率谱估计函数进行频谱估计;从频谱图出发,比较分析了谱估计结果,指出函数pwelch计算的功率谱估计在从宽带噪声中检测窄带信号应用过程中效果最好,对信号的频谱分析具有实际的应用价值。     

m值“复合”逻辑函数的Chrestenson循环谱、自相关函数及应用

该文利用反演公式求得了m值“复合”逻辑函数的Chrestenson循环谱的计算公式，并由此得到了m值“复合”逻辑函数的自相关函数的计算公式，进而运用这两个公式，给出了m值“复合”逻辑函数具备平衡性、相关免疫性的条件，并对m值“复合”逻辑函数的自相关函数及其性质进行了分析；此外该文还得到有限个m值“复合”逻辑函数的非零线性和函数的Chrestenson循环谱的计算公式。     

直扩信号抗多径能力分析

以二径模型为例,对直扩系统抗多径能力进行了分析。对几种实用扩频码序列特性进行了介绍,并对各种序列的自相关函数及加信息调制后扩频码序列与之的相关函数进行了仿真。最后得出结论:直扩系统中对多径信号的抑制能力小于系统的处理增益。从系统多址能力、抗白噪声能力及抗多径干扰能力综合考虑,对单址系统、多址系统伪码码型的选取提出了建议。     

Interpolating multipliers and related interpolators

Piecewise-linear and nonlinear interpolators (PLI and NLI) for the generation of a function of one variable produce an output signal from two or more input signals which represent tangents to the function. They have the additional property that an additive signal which is simultaneously applied to all input terminals is transferred through them. This property is made use of in order to facilitate the generation of functions of two variables that can be written in the form F(x, y) = f(u)+g(v), where u and v are linear functions of x and y. The method is particularly suitable when f and g are convex or concave functions; the major applications are interpolating multipliers for which this paper provides a simple theory of operation.     

加窗离散傅里叶变换性能分析和比对

离散傅里叶变换（DFT）是数字信号处理的常用方法,但通过加窗对信号进行时域截短会使频谱分析出现误差。不同窗函数对信号频谱产生的影响不同,对5种常用窗函数的特性进行了比较和适用性分析,通过仿真实验证明了针对不同信号特点和处理要求,应选择合适的窗函数,以减小频谱泄漏和栅栏效应对信号分析的影响。     

关于本原M序列的自相关函数

本文研究了本原M序列的自相关性能,首次获得了部份自相关函数的通解。这些通解的作用在于无需给出序列,只要知道反馈函数就可以获得相应的自相关函数值,大大降低了自相关函数的计算量。此外,还给出了自相关函数C(#em/em#)(n#em/em# 2n-1)的取值范围。     

Thresholding implied by truncated quadratic regularization

We address the problem of the estimation of an unknown signal that is known to involve sharp edges, from noisy data given at the output of a linear system. The sought solution is defined to be the global minimizer of an objective function combining a quadratic data-fidelity term and a regularization term. The latter term is a sum whose entries are obtained by applying a truncated quadratic potential function to every difference between adjacent samples. Such objective functions are naturally formulated either in a statistical framework, or in a variational framework, and they are customarily used in signal and image reconstruction. However, these objective functions are nonsmooth and highly nonconvex, and many questions related to their minimization, as well as to the features of the resulting solutions, remain open. We present some new facts characterizing the features exhibited by the minimizers of such objective functions. Our main result states that the magnitude of the differences between adjacent samples of a global minimizer are either smaller than a first threshold or larger than a second, strictly larger threshold. Conversely, no difference corresponding to a global minimizer of the objective function can be placed among these thresholds for any data. This explains how edges are recovered in a signal and estimated using truncated quadratic regularization. These thresholds are independent of the data but are related to the observation system and to the regularization parameters. They can be used to derive necessary conditions for the choice of the regularization parameters. We also show that the chance to get data for which the objective function has two or more global minimizers is . Numerical experiments corroborate the obtained theoretical results.     

The uncorrelated output components of a nonlinearity

Using his characteristic-function approach, Rice (1945) obtained a double series for the autocorrelation function of a sinusoidal signal and Gaussian noise after passage through a memoryless nonlinearity. It is shown here that the output of the nonlinearity can be expressed as the sum of uncorrelated terms whose auto-correlation functions are the terms of Rice's double series. Such a decomposition of the output is shown to be generally possible if and only if the bivariate probability density functions of the input signal and the input noise can both be expressed in the diagonal form studied by Barrett and Lampard (1955), though not necessarily involving polynomials, as they can in the sinusoidal and Gaussian cases. In addition, a more direct and meaningful equation is found for the coefficients in Rice's double series.     

Approximate information content of a signal with bispectral constraints

The information content of a signal constrained only by its autocorrelation function or by the total power at each of its Fourier frequencies is well known. This paper addresses the information content of a signal constrained by both the power at each Fourier frequency and by its bispectrum. It is found that the amount by which the information content of a signal with a known power spectrum is reduced when bispectral constraints are imposed is primarily determined by its bicoherence. Approximate solutions for the signal distribution function and signal entropy are obtained in the limit of small bicoherence values using a perturbation theory approach. In the limit of bicocoherence values approaching unity, approaches based on a "mean field" argument also yield expressions for the signal information content. Estimates of the reduction in information content by a quadratic distortion are made. Signal distribution functions are used to develop a non-linear signal detection algorithm similar to the North filter.     

Detection of the peak of an arbitrary spectrum

A new procedure is described for determining that frequency at which the spectrum of a signal has its absolute peak. The salient feature of the procedure is that it does not explicitly involve the estimation of the spectrum of the signal itself. Specifically, it is shown that the limit of the iterated normalized auto-correlation [see (8) and (9)] of a function,f(t), is a pure cosine wave whose frequency corresponds to the location of the peak of the spectrum off(t). Furthermore, if one is willing to accept an estimated peak frequency of maximum energy to within a given finite spectral resolution, then the procedure terminates after a specified finite number of iterations. Results from a computer simulation of the procedure are described. The areas of application of this procedure are discussed, and the results indicate that this method of detecting a signal (i.e., by the peak of its spectrum) merits further consideration. It is important to note that the consideration of random processes has not been undertaken in this initial study; the results apply to the spectral peak of a deterministic signal only.