调制与解调技术、调制解调器

Y2000-62410-40 0020386PSK 信号调制参数的改进的 Cramer-Rao 低边界= Modified CRLB on the modulation parameters of a PSKsignal[会,英]/Ho,K.C.//1999 IEEE MILCOM Vol.1.—40～44(HC)移相键控(PSK)是数字通信中常用的一种调制格式,本文研究了 PSK 信号调制参数的 Cramer-Rao 低边界(CRLB),所考虑的调制参数是载频、符号时间和信号幅度,结果说明,当 M22时,调制参数的 CRLB 与 M元 PSK 信号一样,而 BPSK 和 M 元 PSK 的 CRLB 非常接近,虽然它们不是完全相同,文中也研究了脉冲形状对调制参数 CRLB 的影响。参5     

激光多普勒测速参数估计的Cramer-Rao下限

针对固体运动目标高速度、高加速度的特点,研究了高斯白噪声背景下激光多普勒测速同波信号的参数估计问题.通过计算参数矢量的费希尔(Fisher)信息矩阵,分析了实同波信号的多普勒频率和频率变化率估计方差的克拉末-雷奥(Cramer-Rao)下限(CRLB),推导了采样点数较大时同波信号参数方差估计的CRLB计算公式,讨论了各参数的最大似然估计(MLE).指出同波信号参数估计方差的CRLB与采样点数、信噪比及初相有关,采样点数较大时,实信号参数估计方差的CRLB为对应复信号的2倍.在不同的采样点数和信噪比下仿真表明,提高回波信号的信噪比和增加采样点数可以减小各参数估计方差的CRLB,结果与理论分析吻合.     

一种新的超宽带脉冲波形设计方法

首先介绍了UWB成形脉冲的算法,然后基于Hermite矩阵和Chirp信号得到了UWB的成形脉冲。在对Chirp脉冲的带宽、中心频率等性能参数比较分析的基础上,将若干个Chirp脉冲信号进行线性叠加,通过仿真结果表明,随之产生的脉冲信号不仅满足FCC对UWB脉冲信号辐射功率要求,而且其脉冲信号的频谱利用率也很高,同时还能有效抑制对其他窄带系统的干扰。     

随机布局多天线信号联合时差估计Cramer-Rao下界

该文针对随机布局多天线信号联合时差估计Cramer-Rao下界（CRLB）开展研究,在深入研究多路联合参数估计和经典时差估计算法的基础上,首先建立信号模型,进而得到频域的联合概率密度函数,然后推导出Fisher信息矩阵和Cramer-Rao下界的解析表达式。最后,对结果进行了讨论分析,并同两路时差估计Cramer-Rao下界进行了对比。结果表明,多天线联合时差估计能够利用各信号的相同信息,有效提升时差估计性能,而且在低信噪比条件下估计性能改善更为明显。此外,可以看到增加天线数目不可能无限降低时差估计Cramer-Rao下界,其受待估时差的两路信号信噪比限制。      

基于频域数据采样和时域信号同步的超宽带时间反转成像

提出一种基于频域数据取样和时域信号同步的超宽带（Ultrawideband,UWB）时间反转（Time-Reversal,TR）成像方法.单个发射机发射UWB脉冲信号到探测区域,时间反转镜（Time Reversal Mirror,TRM）的每个天线单元对散射信号进行细频和粗频数据采样,得到各自单元的频率-频率-多站数据矩阵（individual-FF-MDM）.把所有单元的该矩阵堆砌起来,形成一个全体单元的频率-频率-多站数据矩阵（full-FF-MDM）,并对full-FF-MDM进行奇异值分解（Singular Value Decomposition,SVD）,得到耦合了目标位置信息的左奇异值向量.将每一个左奇异值向量变换成时域脉冲回传辐射,则来自TRM各单元的回传辐射信号在相应目标处同时到达波形的最大值,而在非该目标处则不能同时达到最大值.于是,定义各单元的回传信号乘积作为目标成像函数,可获得良好的横向和纵向分辨率.     

面向室内的基于异步UWB测距的椭圆位置估计算法

为了实现简单而精确的室内定位,并利用超宽带信号UWB(ultra-wide band)的特性,提出了基于异步UWB测距的椭圆室内位置估计方案AUREP(Asynchronous–UWB Range-elliptical indoor Position)。该方案由位置定位器locator、目标节点、参考节点组成。定位器先发射UWB信号,一旦接收该信号,目标节点进行转发。参考节点捕捉来自定位器、目标节点的信号,并通过计算这两不同路径的信号TOA(Time of arrival)差,最后,采用高斯-牛顿迭代算法估计目标节点的位置。与同步的球形定位系统SGPS(Synchronous-global position systems)不同,提出的方案无需同步机制。AUREP方案采用异步模式、无需同步设备,简化了系统。仿真结果表明提出的AUREP方案的定位精度高于双曲线定位系统SHPS(Asynchronous–Hyperbola Position systems),同时,AUREP的定位误差逼近于克拉美-罗下限CRLB(Cramer-Rao lower bound)。     

UWB通信技术最新进展及发展趋势

2002年2月14日美国联邦通信委员会（FCC）通过了将3．1～10．6GHz之间的频带分配给民用的法规，从而拉开了企业界和研发机构竞相研发超宽带（UWB）的序幕。按NFCC定义，只要信号在-10dB处的绝对带宽大于0．5GHz或相对带宽大于20％，并且中心频率大于500MHz，那么这种信号就是UWB信号。UWB直接对陡峭的时间脉冲进行调制，使信号具有吉赫兹级的带宽；因为时间脉冲持续的很短（大约10～100ps），大大降低了发射信号所需的功率，所以UWB信号具有很低的功率谱密度。     

利用光反馈半导体激光器产生超宽带混沌脉冲信号

提出了一种基于光反馈半导体激光器的混沌特性产生超宽带(UWB)信号的新方法。一个商用的通信波段半导体激光器在外腔光反馈下实现混沌振荡,输出连续波混沌激光,经由一个电吸收调制器后,被调制为一系列混沌脉冲信号。该混沌脉冲信号的频谱特性可通过调节半导体激光器的偏置电流和反馈强度进行控制。实验分别获得了中心频率为4.0 GHz、相对带宽为181%和214%的混沌脉冲UWB信号。进一步数值仿真了偏置电流和反馈系数对混沌脉冲UWB信号频谱特性的影响,实验结果与模拟验证相符。该方法实验装置简单,UWB信号频谱特性易控,可用作未来UWB光纤无线通信系统的光生微波信号发生装置。     

交替分离算法的Cramer-Rao界

该文推导了交替分离算法的Cramer-Rao界。交替分离算法的Cramer-Rao界涉及到矩阵的减逆,而矩阵减逆具有比通常Moore-Penrose广义逆更为宽松的定义条件,在理论上,一个确定矩阵有无数个减逆。为了建立分离算法的Cramer-Rao界,该文求出了一个确定矩阵的一个特定减逆矩阵。根据任一确定性定理,得到分离数据的密度分布函数,从而获得交替分离算法的Cramer-Rao界。交替分离算法的Cramer-Rao界将多信号对信号参数估计的影响能更直观反映出来。通过对交替分离算法的Cramer-Rao界的讨论,该文还给出了有关矩阵分离算子一些重要的性质。     

基于光注入半导体激光器的超宽带信号产生

提出一种基于光脉冲注入条件下半导体激光器腔 内交叉增益调制(XGM)效应的超宽带(UWB)信号产生方案,通过一个增益开关激光器(ML)、 一个半导体激光器(SL)和一个光带通滤波器(OBPF),在平衡探 测器(BPD)端口直接检测输出重复频率为2.5GHz的UWB一阶微分(Mo nocycle)和二阶微分(Doublet)信号, 而且通过引入马赫-曾德尔调制器(MZM),还可对产生的UWB信号实现开关键控(OOK)。 对所提系统 进行了全面的系统仿真分析,并进行了实验验证,实现了上述各种条件的UWB信号产生,并 实现了UWB信 号的40km光纤传输实验。实验结果表明:该方案获得的UWB信号的频 谱与美国联邦通信委员会(FCC)定制的EIRP标准吻合,同时经过调制的 UWB信号的波形经40km光纤传输之后基本保持不变。为了证明本文方 法产生的UWB信号的重复变化特点,还产生了频率为3.75GHz的UWB信 号。     

An ergodic approach for chaotic signal estimation at low SNR with application to ultra-wide-band communication

This paper proposes a novel method to estimate the parameters of chaotic signals corrupted by noise. By exploiting the ergodic property of chaotic signals, it is shown here that signal parameters can be estimated accurately from the noisy chaotic signal. The proposed estimator is proved to be consistent. The asymptotic variance of the proposed method and the Cramer-Rao lower bound (CRLB) are derived analytically to assess the estimation performance. Computer simulations confirm that the proposed ergodic estimation approach provides good parameter estimates even at low signal-to-noise ratio (SNR), and its performance is superior to conventional estimation techniques. This method is then applied to ultra-wide-band (UWB) communication by proposing a novel ergodic chaotic parameter modulation based UWB (ECPM-UWB) scheme. The ECPM-UWB scheme is analog and noncoherent. The communication performance of ECPM-UWB is found to be superior through theoretical mean-square-error (MSE) analysis and computer simulations. The ECPM-UWB scheme is shown to have good spectral characteristics. In addition, the proposed scheme is shown to be robust against channel estimation error and multipath fading using both theoretical and numerical analyses.     

Discrete spectral peak estimation in incoherent backscatterheterodyne lidar. I. Spectral accumulation and the Cramer-Rao lowerbound

The theory of the Cramer-Rao lower bound (CRLB) and maximum-likelihood (ML) estimators is summarized in the context of a heterodyne lidar. Numerical experiments are described that indicate the scaling of this CRLB with parameters such as the signal bandwidth and the level of noise. This CRLB is also compared with the CRLB of a highly idealized noiseless direct detection system using photon counting. It is found that the asymptotic bounds developed in the radar literature for the heterodyne CRLB should not be used as approximations for the correct expression in lidar applications at intermediate signal levels. Moreover, the variance of the ML estimator may be greater or even less than the heterodyne CRLB, depending on the mechanism leading to the departure from the bound     

Improved taylor-series location algorithm for cooperation networks

This article presents an iterative algorithm for estimating the location of the destination mobile station (DS) when some extra mobile stations around the DS are involved in and assist the base stations to complete the localization process. The proposed method is based on the taylor-series (TS) method and jointly estimates both the DS and the extra mobile stations, named reference mobile station (RS) in this article, positions simultaneously. Moreover, the time-differential-of-arrival (TDOA) measurements between DS and pairs of RSs are obtained by ultra-wide-band (UWB) signal, which is adept in accurate ranging application. According to the theoretic analysis, the Cramér-Rao lower bound (CRLB) of the modified TS algorithm reduces significantly. The actual performance, under a given simulation scenario, is enhanced by 25% at best.     

On the computation of an asymptotic bound for estimating autoregressive signals in white noise

The Cramer-Rao lower bound (CRLB) provides a useful reference for evaluating the performance of parameter estimation techniques. This paper considers the problem of estimating the parameters of an autoregressive signal corrupted by white noise. An explicit formula is derived for computing the asymptotic CRLB for the signal and noise parameters. Formulas for the asymptotic CRLB for functions of the signal and noise parameters are also presented. In particular, the center frequency, bandwidth and power of a second order process are considered. Some numerical examples are presented to illustrate the usefulness of these bounds in studying estimation accuracy.     

Cramer-Rao lower bound on locations of sudden changes in a steplikesignal

Estimation of locations of sudden changes in a steplike signal has many signal processing applications; e.g., well-log signal segmentation, ionic-channel signal classification, edge detection, and segmentation of images. In this work, the Cramer-Rao lower bound (CRLB) on locations of steps in one-dimensional (1-D) steplike signals is calculated. The calculation is based on the use of a sigmoidal function to model a sudden-change (step) in the signal. The introduced model has an adjustable parameter that can be used to fit the CRLB calculation to a particular class of steplike signals     

Analysis of wireless geolocation in a non-line-of-sight environment

We present an analysis of the time-of-arrival (TOA), time-difference-of-arrival (TDOA), angle-of-arrival (AOA) and signal strength (SS) based positioning methods in a non-line-of-sight (NLOS) environment. Single path (line-of-sight (LOS) or NLOS) propagation is assumed. The best geolocation accuracy is evaluated in terms of the Cramer-Rao lower bound (CRLB) or the generalized CRLB (G-CRLB), depending on whether prior statistics of NLOS induced errors are unavailable or available. We then show that the maximum likelihood estimator (MLE) using only LOS estimates and the maximum a posteriori probability (MAP) estimator using both LOS and NLOS data can asymptotically achieve the CRLB and the G-CRLB, respectively. Hybrid schemes that adopt more than one type of position-pertaining data and the relationship among the four methods in terms of their positioning accuracy are also investigated.     

多用户环境下定位精度的克拉美罗下限 与时延估计算法

本文针对码分多址(CDMA)系统,推导了基于到达时间(TOA)的移动台定位所具有的估计精度下限,给出了定位估计精度下限推导的具体步骤和下限表达式,分析了该下限所具有的物理意义,得到了定位精度下限与用户数无关的结论.同时,提出了在长码扩频条件下能够抑制多址干扰(MUI)的时延估计算法,进一步说明了精度下限的物理含义.最后在仿真的基础上对估计下限和新算法的性能进行了讨论.     

一种新的卫星导航信号码跟踪误差下限

卫星导航系统的精确定位是基于导航信号传输时延的精确估计,码跟踪误差是评估时延精度的重要参量之一。对信号的接收机码跟踪过程进行了理论研究,系统推导了相干延迟锁相环的跟踪误差。针对克拉美罗界(Cramer-RaoLower Bound,CRLB)只有在高信噪比时才能提供准确估计的问题,提出了一种新的码跟踪误差下限,称为MZZB(Modi-fied Ziv-Zakai Bound),该下限把码时延作为概率密度已知的随机变量,在更宽载噪比范围内提供更加紧密的下限。计算机仿真分析了BPSK-R(1)与BOC(1,1)信号的CRLB与MZZB异同,得出克拉美罗界只有在高信噪比时才能提供准确的估计,而MZZB在更宽范围信噪比下提供更加紧密的下限。     

Range Estimation in a Time Varying Multipath Channel

In this paper, range estimation in a time varying multipath channel is investigated, on the basis of which a multicarrier (MC) signal is compared with its pseudo-random (PN) counterpart in terms of the Cramer-Rao lower bound (CRLB) and the maximum likelihood estimator (MLE). The CRLB for range estimation in a time varying multipath channel is derived for three cases: (1) known channel state information (CSI); (2) unknown CSI; and (3) a special case of unknown CSI where the channel is modeled via Doppler shift. Furthermore, the MLE is developed for range estimation for each one of the above three cases and is investigated for a multipath Doppler channel with respect to the separability of its multipath components. Besides, the condition for a multipath Doppler channel to be separable is explored for a PN signal as well as for a MC signal. Simulation results show that range estimation with a MC signal outperforms its PN counterpart in a time varying channel, similar as that in a time invariant channel.     

Time-domain analysis of cross correlation for time delay estimationwith an autocorrelated signal

The estimation accuracy of the time difference of arrival (TDOA) of an exponentially autocorrelated signal at two sensors in white noise is analyzed. The estimate is obtained by cross correlating samples taken as short-term integrals of the noisy signals from the two sensors. This technique avoids ambiguities in the cross correlation, and it is shown that the best sampling rate is double the Nyquist rate, for which the Cramer-Rao lower bound (CRLB) is met in practice