基于广义周期性的单通道多分量正弦调频信号分离和参数估计

针对噪声条件下的单通道多分量正弦调频(SFM)信号,该文提出一种信号分离和参数提取方法。利用正弦调频信号的广义周期性进行奇异值分解,以求出分量信号的调制频率;通过离散点搜索,估计出分量信号的调频(FM)初始相位、调制指数及载频,并对这些估计值利用信赖域算法进行优化,减小误差;利用内积计算,估计分量信号的幅度和初始相位。此外,还利用自相关矩阵特征值分解估计混合信号的信噪比(SNR),并根据信噪比确定停止分解的阈值。在仿真与分析中,针对具体的信号详细说明了该方法的各步骤,并在不同信噪比条件下分析了该方法的参数估计精确度。     

多径条件下的时差估计研究

研究了多径条件下的时差估计问题。在多径条件下,运用谱相干校正法（SPECCOA）和多径多信号环境下的时差估计去模糊（DATEMM）算法相结合的方法进行信号到达时差（TDOA）的参数估计,该方法能够从估计出的多个峰值中提取出真实TDOA值,消除多径带来的估计模糊,得到正确的估计值。最后的计算机仿真结果验证了文中的结论。     

单通道混合信号的幅度估计算法

针对非协作通信场合中同调制参数的MSK单通道混合信号的幅度估计问题进行研究。在MSK混合信号的循环谱推导的基础上,通过搜索零频率处循环频率轴上的大强度谱线进行混合信号的幅度估计,利用循环谱算法中的泄漏谱包络辅助来消除谱线选择时存在的模糊问题,并通过大强度谱线位置的泄漏谱包络值来修正相应位置的循环谱幅度,以提高估计精度。仿真结果表明在信噪比大于?15dB时,该方法对功率差异不大的混合信号幅度具有较高的估计精度。该算法无需任何先验信息,适用于低信噪比环境,具有实用价值。     

单信道多信号分量分离

提出了一种单信道多信号分量的分离方法,该方法利用能量算子对单信道的各个信号分量的瞬时频率、幅度进行估计,从而对2个或3个信号分量进行分离。仿真结果表明该方法在信噪比大于25dB时,对重叠的3个信号分量分离误差小于7.5%。     

线性调频信号时/频差快速联合估计方法

提出了一种线性调频(Chirp)信号时/频差估计算法。首先估计Chirp信号互模糊函数中脊线的位置,再通过频率补偿使脊线通过原点,进而通过搜索信号在分数阶傅里叶变换域上的相关峰来代替沿脊线搜索模糊函数峰值的过程,最终获得时/频差的估计。该算法由于采用一维搜索,并且可用快速傅里叶变换实现,因此所需运算量显著降低。对于多分量Chirp信号,根据脊线位置的不同,算法能够分别估计出各分量信号的时/频差。仿真实验表明,该算法能够精确估计Chirp信号的时/频差,并且随着信噪比的提高,时/频差估计值的均方根误差逐渐接近克拉美罗下界。      

基于多分量LFM信号时频分析的水声多普勒和时延估计研究

在水声多普勒因子和时延估计研究实用化的进程中,利用多分量线性调频(LFM)信号实现估计的算法研究越来越普遍。针对多分量LFM信号时频域存有交叉项时各分量参数估计不准确的问题,提出基于非完全残差与脊线段匹配的自适应模态分解方法。该方法采用非完全残差函数保留了交叉点处的部分时频信息,利用脊线段匹配方法提供更精确的预设时频脊线,改进了各分量LFM信号调频斜率和起始频率的估计精度。联合两个估计量进一步给出了多普勒因子和时延估计的算法。仿真结果表示,较现有模态分解算法,所提改进方法有效解决了估计分量过程中交叉区间断裂带来的估计误差;水声多径的条件下,该方法的多普勒因子和时延估计精度优于对比的现有方法。     

基于包络拟合的Chirplet分解算法

针对信号自适应Chirplet分解未知参数多、分解算法运算量大的问题,提出了一种基于包络拟合的Chirplet自适应分解算法。该方法利用二次相位函数在时间上的积分估计调频率,通过对包络主瓣峰值的幅度拟合估计标准差和时间中心,并利用包络主瓣峰值的相位信息对调频率与初始频率估计值进行修正,提高参数估计精度。给出了单分量和多分量情况下的Chirplet参数估计流程。推导了一般高斯环境下Chirplet信号参数估计的CRB界。仿真及实测数据处理结果验证了算法的有效性。      

一种改进的基于奇异值分解的信源数目估计算法

信源数目估计问题在盲源分离中具有重要的意义。研究了传感器数目大于信源数目时的源数估计问题。首先分析了用奇异值分解法进行信源数目估计的优势与不足,然后提出了一种改进的基于奇异值分解的信源数目估计算法。该算法首先对含噪混合信号进行奇异值分解,然后检测信号分量与噪声分量之间的转折点,将信号分量与噪声分量区分开来,从而得到信号源的数目。实验仿真表明,该算法在低信噪比以及采样点数较少时仍然具有好的性能。     

高斯混合噪声中弱信号的Rao检测方法

期望最大化(Expectation Maximization,EM)算法是求解参数最大似然估计(MLE)的最优迭代算法,但若参数初始化不恰当,会使估计值落入"初值陷阱",导致错误的参数估计值.为此,本文提出了估计高斯混合噪声参数的矩 - EM算法,即先求参数的矩估计,并用矩估计值初始化参数,再通过EM迭代算法估计参数.在此基础上,经高斯化滤波,导出了高斯混合噪声背景下未知幅度弱信号的Rao检验统计量.仿真结果表明,矩 - EM算法可以更准确地估计噪声参数;基于矩 - EM算法的Rao检测性能优于基于EM算法的Rao检测性能.     

基于积分二次相位函数和分数阶Fourier变换的多分量LFM信号参数估计

针对高斯白噪声中多分量线性调频信号参数估计问题,提出了一种基于积分二次相位函数（IQPF）和分数阶Fourier变换的新方法。分析了IQPF估计线性调频信号调频率的原理,指出IQPF有压制弱信号的缺点。为解决强度相差较大的多分量线性调频信号中弱分量信号的参数估计问题,提出利用分数阶Fourier变换域的信号分离技术,逐次估计强信号分量的参数并将其消去,来提高多分量信号参数估计的可靠性。最后通过计算机仿真,验证了该方法的有效性。这种方法与Radon-Winger变换法、Radon-Ambiguity变换法和单纯的分数阶Fourier变换法相比,极大的简化了计算。因此,该方法非常适合于多分量LFM信号的快速参数估计。      

Prediction of Gain Expansion and Intermodulation Performance of Nonlinear Amplifiers

A mathematical model for the input‐output characteristic of an amplifier exhibiting gain expansion and weak and strong nonlinearities is presented. The model, basically a Fourier‐series function, can yield closed‐form series expressions for the amplitudes of the output components resulting from multisinusoidal input signals to the amplifier. The special case of an equal‐amplitude two‐tone input signal is considered in detail. The results show that unless the input signal can drive the amplifier into its nonlinear region, no gain expansion or minimum intermodulation performance can be achieved. For sufficiently large input amplitudes that can drive the amplifier into its nonlinear region, gain expansion and minimum intermodulation performance can be achieved. The input amplitudes at which these phenomena are observed are strongly dependent on the amplifier characteristics.     

基于周期谱包络的线性调频信号特征参数估计

线性调频信号是二阶循环平稳信号,其周期谱幅度包含了信号的最小载频、最大载频以及调制斜率等信息。本文提出了利用非零循环频率处谱峰的位置与大小估计这三个参数的算法,该算法不需要信号参数的先验信息;对参数的估计是在非零循环频率处进行一维搜索,可减小平稳噪声和干扰的影响,适用于低信噪比情况,且避免了多维搜索;文中给出了算法的实现过程,分析了其估计性能,最后进行了计算机仿真实验。     

Efficiency of frequency transformation on MOS transistors with a built-in channel under intensively handicapped radioreception

An algorithm and a technique are developed for finding the maximum values of the target current components in a MOS transistor with an n-type built-in channel depending on the submicron and nanoscale topological norms for a frequency transformer in the presence of intensive noise at its input. The spectral making components of the intermediate frequency are evaluated and analyzed for the given amplitudes of the generator, signal, and handicap. The behavior of the n-MOS transistors designed according to the GPDK045 and GPDK0990 technological norms is investigated.     

GMSK with limiter discriminator detection in satellite mobilechannel

Formulas are derived to find the error probability of partial-response frequency-shift keying with limiter discriminator detection, with and without decision feedback, for a satellite-mobile channel. The special cases of a Gaussian channel and a land-mobile channel are discussed. The formulas are applied to Gaussian minimum shift keying, and the error probability is computed as a function of energy-to-noise ratio, Gaussian filter bandwidth, Doppler frequency, maximum Doppler frequency, the ratio of powers in the specular and diffuse signal components, and the time delay between specular diffuse components     

K-vector determination of whistler mode signals by using amplitudedata obtained by a spacecraft borne instrument

A straightforward method for determination of k-vector (wave normal) direction of a whistler mode signal observed onboard spacecraft consists in measuring three components of the wave magnetic field with their instantaneous amplitudes and phases. In that method, one needs to send by telemetry a total wave form of a signal, which requires much larger bandwidth than for sending amplitudes only. The present study develops another method of determination of the wave normal direction based only on the amplitude data; the method is checked using Omega signal observations by the Akebono satellite. It should, however, be noted that the sense of k-vector is not determined by this proposed method     

New single-parameter models for electronic circuits with even symmetry nonlinearity

In this paper single-parameter models are presented for the instantaneous characteristics of electronic circuits/systems exhibiting even-symmetry nonlinearities. The models can easily provide closed-form expressions, in terms of the ordinary Bessel functions, for the amplitudes of the second-harmonic and second-order intermodulation components at the output of the nonlinear circuit/system excited by a multisinusoidal input signal. Moreover, by combining the proposed models with the previously published models for instantaneous characteristics exhibiting odd-symmetry nonlinearities, a new method and apparatus are proposed for characterizing nonlinear circuits/systems exhibiting both even- and odd-symmetry nonlinearities. The proposed method and apparatus use the amplitudes of the measured output second- and third-order intermodulation components resulting from a two-tone equal-amplitude input signal.     

Optimal detection of a BPSK signal contaminated by interference andnoise

The problem of detecting a desired binary phase-shift keying (BPSK) modulated bit in the presence of a second BPSK modulated interfering signal and additive white Gaussian noise is considered. Given knowledge of the amplitudes and phases of the unmodulated signals received from the two transmitters, the minimum achievable bit error rate is obtained and compared with that for a conventional matched filter detector. It is shown that the performance difference can be quite large when the interfering signal is strong     

Null steering using the minimax approximation by controlling only the current amplitudes

A linear programming technique using the minimax approximation to steer the nulls of an array by controlling the current amplitudes is presented. The technique determines the current amplitudes that produce the minimum sidelobe level for a given beam width and prescribed nulls in arbitrary directions. The results show the ability of this technique to steer the nulls in the sidelobe region while maintaining the main beam directed towards the desired signal. This technique also allows the number of controlled nulls to attain the full degrees of freedom for the array.     

正交多载波调制中峰值因子的一种减小方案

在多载波调制系统中，通常调制信号的平均功率恒定，且和实际发送的信息符号向量无关，此时，由N个子载波组成的多载波信号的峰值因子(PF)等于10lgN(dB)。提出了减小多载波调制系统中PF的一种方案，对于瞬时包络功率的最大值超过所给门限值的信息符号向量，所有子载波的幅度被降低至门限值，而对于瞬时包络功率的最大值低于门限值的信息符号向量，所有子载波的幅度被增大至门限值。采用这种方法，整个调制系统的PF被减小，而净比特速率保持不变，但系统的误比特率(BER)略为增加。