Hierarchical space–time block codes signals classification using higher order cumulants

An efficient method for blind classification of space–time block codes(STBCs) based on fourth-order cumulants is proposed for a single receiver antenna.This paper presents a model of received STBCs signals in multiple input single output(MISO) communication systems and applies the characteristics of coding matrices to derive analytical expressions for the fourth-order cumulants to be used as the basis of an algorithm.The fourth-order cumulants at various delay vectors present non-null values that depend on the transmitted STBCs.Tests of nullity are accomplished by hypothesis testing.The proposed algorithm avoids the need for a priori information of modulation scheme,channel coefficients,and noise power.Consequently,it is well suited for non-cooperative scenarios.Simulations show that this method performs well even at low signal-to-noise ratios(SNRs).     

基于WVD的调频引信瞬时频率估计算法

针对传统的调频引信无法进行连续测距的问题,利用时频分析的方法,研究了引信差频信号瞬时频率估计算法.基于Wigner-Ville分布,分析了WVD最大值法、SPWVD最大值法及Viterhi-SPWVD算法用于提取信号瞬时频率的特点,通过Monte Carlor仿真试验,比较了几种算法的性能,给出了仿真结果.     

Detection of stochastic signals in the frequency domain

The optimum detector for a random signal, the estimator-correlator, is difficult to implement. If the power spectral density (PSD) of a continuous time signal is known, a locally optimum detector is available. It maximizes the deflection ratio (DR), a measure of the detector output signal-to-noise ratio (SNR). A discrete version of this detector is developed here, called the discrete-MDRD, which takes a weighted sum of the spectral components of the signal data as the detection statistic. Its derivation is applicable to nonwhite noise samples as well. A comparison of this new detector against three other common types, through their DR values and simulation results, reveals that the discrete-MDRD is near optimal at low SNRs. When the PSD of a signal is not known, a common test statistic is the peak of the PSD of the data. To reduce spectral variations, the PSD estimator first divides the data sequence into several segments and then forms the averaged PSD estimate. The segment length affects the DR values; the length that maximizes the DR is approximately the reciprocal of the signal bandwidth. Thus for unknown signal PSD, a detector that approaches the maximum DR is realizable from just the knowledge of the signal bandwidth, which is normally available. Examples and simulation results are provided to illustrate the properties and performance of the new detector     

Unintentional modulation evaluation in time domain and frequency domain

With the development of wireless communication technology, the electromagnetic environment has become more and more complex. Conventional signal identification methods are difficult to accurately identify illegal devices. However, electromagnetic signals have an unavoidable device-specific characteristic unintentionally generated by a transmitter, appearing in the form of an Un Intentional Modulation(UIM), namely Radio Frequency Fingerprint(RFF). RFFs can be used to uniquely identify an emitter ...     

Estimating the number of signals using reference noise samples

Criteria for estimating the number of signals in the case of small-sample populations are considered. The criteria introduced by M. Wax and T. Kailath (1985) do not work well in this case. Two new criteria based on information theoretic and eigenmode composition-based criteria are proposed, assuming a known noise covariance. Simulation results show a significant improvement in the performance of estimating the number of signals in the small-sample case, by the use of the new criteria combined with an estimate of the noise covariance obtained from reference noise samples     

使用低级音频函数实现音频采集与播放

随着多媒体技术的大量应用,需要对视频和音频数据进行处理,由于现实的网络状况难以满足较好的实时视频通讯的要求,因此对音频数据的处理就显得更加重要。音频数据的采集和播放可以通过三种方式实现:媒体控制接口、D irectSound和低级音频函数,三种方法各有优缺点。使用低级音频函数实现音频的采集与播放,能够根据需要对数据流进行灵活地控制,具有较高的实时性。     

利用一维像序列时域差分估计目标进动频率

针对弹道目标识别中目标运动特征参数估计问题,提出一种一维距离像（HRRP）序列时域差分目标进动频率估计方法,该方法首先对一维距离像进行归一化处理,利用峰值法对齐相邻一维距离像,然后计算相邻一维距离像之间的差分值,获得相邻一维距离像差分值序列,最后采用快速傅里叶变换（FFT）从该差分值序列中估计目标进动频率。该方法具有以下优点：利用相邻一维距离像差分值序列能够增强目标进动频率成份,降低其他频率成份,更有利于进动频率的估计;只需要对齐相邻2个一维距离像,而避免了对齐一维距离像序列所带来的问题。利用由FEKO软件计算的进动目标宽带一维距离像仿真数据进行了实验,结果表明所提方法比常规的加权累积法更有效,估计精度更高。     

Radar sensor using low probability of interception SS-FH signals

One of the best known weakness of radar sensors in defense and security applications is the necessity to radiate a signal, which can be detected by the target, so being possible (easy in fact) that the target is alerted about the presence of a radar before the radar is alerted about the presence of a target. In this context, Low Probability of Interception (LPI) Radars try to use signals that are difficult to intercept and/or identify. Spread spectrum signals are strong candidates for this application, and systems using special frequency or polyphase modulation schemes are being exploited. Frequency hopping, however, has not received much attention. The typical LPI radar at this moment of the technology is a CW-LFM radar. The simplicity of the technology is its best point. Polyphase codes, on the other hand have the inherent advantage of high instantaneous bandwidth regardless of observation time. But the complexity of the hardware is also higher. FH signals have traditionally been considered of lower performance but higher complexity, due to the difficulties to compensate the individual dopplers for the individual range cells in the receiver. One important point is that an FH radar must be clearly distinguished from an agile frequency radar. In the latter, a pulsed signal is transmitted using different frequencies from pulse to pulse. In an FH radar the frequency changes must be during the pulse. In fact, in an LPI FH radar, a CW frequency hopped signal is used. A radar system concept is proposed in which it shows how these problems can be overcome in a tracking application. Also, the signal format is analyzed under the scope of future decade digital interceptors, showing that, in fact, this kind of signal exhibits improvement in some performances and requires a hardware that is only slightly more complex than that needed for CW-LFM systems     

On-board regeneration of uplink signals using a blind multichannelestimator

We propose a restoration method to compensate distortions caused by cross-polarization interference (CPI) and multipath propagation when multichannel transmission is employed in the uplink of an on-board-processing (OBP) satellite. The proposed baseband signal processing architecture is numerically robust and efficient as vector operations are avoided by efficient orthogonal transformations. Since the algorithm is based on higher-than-second-order statistics, the method is very effective in severe distortion conditions where a traditional, perfectly trained Kalman multichannel filter obtains poor performance     

Performability analysis of avionics system with multilayer HM/FM using stochastic Petri nets

The integrated modular avionics (IMA) architecture is an open standard in avionics industry, in which the number of functionalities implemented by software is greater than ever before. In the IMA architecture, the reliability of the avionics system is highly affected by the software applications. In order to enhance the fault tolerance feature with regard to software application failures, many industrial standards propose a layered health monitoring/fault management (HM/FM) scheme to periodically check the health status of software application processes and recover the malfunctioning software process whenever an error is located. In this paper, we make an analytical study of the HM/FM system for avionics application software. We use the stochastic Petri nets (SPN) to build a formal model of each component and present a method to combine the components together to form a complete system model with respect to three interlayer query strategies. We further investigate the effectiveness of these strategies in an illustrative system.     

Three-dimensional target motion analysis using angle and frequency measurements

It is well known that passive target tracking by a single observer, commonly referred to as target motion analysis (TMA), can be done using angle and/or frequency measurements. Depending on the measurement set, different passive tracking procedures result: angle-only tracking (AOT), frequency-only tracking (FOT), and angle/frequency tracking (AFT). Whereas the two-dimensional passive tracking problem has been solved for a multitude of scenarios, thus giving a good insight into the parametric dependences, the three-dimensional problem has been discussed only in a few specific cases. To get a deeper insight into the parametric dependences of three-dimensional TMA, this work analyzes AOT and AFT in typical three-dimensional Airborne Warning and Control System (AWACS) scenarios. A Cramer Rao (CR) analysis of the problem reveals the parametric dependences of both methods and gives a clear idea of the increase in estimation accuracy by using AFT instead of AOT. The results obtained in this way are well confirmed by Monte Carlo simulations taking maximum likelihood (ML) as estimation procedure.     

Estimation of 3D angular motion using gyroscopes and linear accelerometers

The authors present a novel, real-time angular motion estimation technique using a linear Gaussian estimator, and the outputs of linear accelerometers and gyroscopes, to assess the actual angular velocity of a rigid body in three-dimensional (3D) space. The method obtains the covariances of the random actual 3D angular velocity, the angular velocity measurement, and the measurement noise from the time averages of the outputs of an array of nine linear accelerometers and the outputs of three orthogonal gyroscopes. These statistics are used by the estimator to calculate the angular velocity of the rigid body in 3D space. The multisensor technique performance is evaluated through a computer simulation. Results indicate that the method leads to more accurate angular velocity values than are obtained conventionally.<>     

Angle of arrival estimation of coherent signals using an arraydoublet in motion

Shown here is how the estimation of signal parameters via relational invariance techniques (ESPRIT) algorithm may be used with a single pair of antennas in motion to estimate angles of arrival (AOA) for coherent signals. The approach exploits the Doppler frequency shifts caused by the doubler in motion. With this estimator, the number of signals that can be handled is not limited by the size of the array, as in the usual ESPRIT application, but by an adjustable parameter. A theoretical performance analysis of the estimator and typical examples showing the use of this estimator are given     

Principle and Design of a Vernier FM Radar System

This paper describes the principle and the signal design of a proposed new FM radar system. In order to measure the surface characteristics of a small target at a long distance, or to discriminate among multiple targets, very accurate range or Doppler resolutions are necessary [1]. The proposed system satisfies the range resolution requirement by detecting the target with two different resolutions: coarse resolution for measuring range, and fine resolution for measuring the target details. The principal advantage of the system is in the vernier scale for the measurement of a distance. The system is just as easily realizable as conventional FM radar, requires no special filters in the receiver, and represents a saving in the required bandwidth for the same range resolution.     

Measurement of Pressures and Heat Transfer by FM Telemetry

A measurement system for obtaining pressure and heat-transfer data from models flying freely in hypersonic tunnel streams is described. Test models are either released from suspension threads or launched by low-velocity pneumatic launchers and have internal miniaturized frequency-modulated telemetry units. This technique permits the historically desired measurement of support-free afterbody pressure and heat-transfer rates. Base heating and pressure measurements for a cone and a sphere in free flight are included to illustrate application.     

Radar target classification using doppler signatures of human locomotion models

The problem of target classification for ground surveillance Doppler radars is addressed. Two sources of knowledge are presented and incorporated within the classification algorithms: 1) statistical knowledge on radar target echo features, and 2) physical knowledge, represented via the locomotion models for different targets. The statistical knowledge is represented by distribution models whose parameters are estimated using a collected database. The physical knowledge is represented by target locomotion and radar measurements models. Various concepts to incorporate these sources of knowledge are presented. These concepts are tested using real data of radar echo records, which include three target classes: one person, two persons and vehicle. A combined approach, which implements both statistical and physical prior knowledge provides the best classification performance, and it achieves a classification rate of 99% in the three-class problem in high signal-to-noise conditions.     

抗混叠时频域融合算法及在叶片响应分析中的应用

为解决现有的时频域融合算法中反复使用快速傅里叶变换而出现频谱混叠误差和频谱系数周期性重复的问题,采用快速抗混叠傅里叶变换取代原有的快速傅里叶变换,从计算精度和效率两个方面对时频域融合算法进行改进.使用改进后的抗混叠时频域融合算法对某真实叶片的非线性强迫振动响应进行了计算,并与原算法的计算结果进行了比较.计算结果表明:抗混叠时频域融合算法在保证精度的前提下,计算速度约为原算法的4倍.该算法适合于有限元模型、精度要求高的非线性系统的动力学响应分析.