一种利用信号幅度信息的光学传感器像平面GM-PHD滤波算法

针对光学传感器像平面多目标跟踪应用,基于有限集统计学理论(Finite Set Statistics, FISST)提出一种利用信号幅度信息的高斯混合概率假设密度(Gaussian Mixture-Probability Hypothesis Density, GM-PHD)滤波算法。该算法通过建立信号幅度似然函数将幅度信息引入到PHD的递推公式中,首先根据光学传感器的特点对输出的信号幅度进行建模,然后分别计算来源于目标和杂波的信号幅度似然函数,在目标信噪比未知的情况下给出一种替代计算方法,最后采用高斯混合方式实现该算法。仿真结果表明,本文提出的算法相比仅利用量测位置信息的PHD滤波器能够显著提高多目标跟踪性能和计算效率,而且在目标信噪比未知时同样具有稳定的性能。     

遥测数据压缩算法的设计与实现

介绍遥测数据在数据存贮过程中的特点 ,分析对遥测数据进行压缩的必要性 ,特别地还分析了数字信号处理方法在遥测数据压缩中的应用。设计了自适应的遥测数据压缩算法。系统中使用多种压缩算法 ,包括预测编码、Huffman编码、游程编码、1- 9编码等 ,通过使用快速傅里叶变换、离散余弦变换、小波理论 ,将遥测数据信号转换到频域 ,再通过一般压缩算法进行压缩 ,在符合数据处理精度要求的前提下 ,引进有损压缩算法 ,达到最高压缩比。实践证明 ,使用多种压缩算法相结合 ,能使数据压缩率提高十多倍 ,远远高于压缩软件的压缩比。     

连接单元干涉测量技术应用于嫦娥二号卫星测轨实验

为了支持月球、火星等探测任务,我国正在组织开展深空干涉测量信号处理中心的建设工作。在嫦娥二号卫星在轨运行期间,利用连接单元干涉测量系统对卫星下行的数传信号进行采集记录,应用自行开发的数据处理软件获得了清晰的干涉条纹,同时时延计算结果与理论轨道具有较高的一致性,精度优于纳秒级。测轨实验验证了数据处理算法的正确性,证明了应用连接单元干涉技术进行卫星测轨的可行性。文章的分析和结论可为后续深入开展深空干涉测量信号处理中心建设提供技术储备。     

Multipath fading analysis of telemetry signals power fluctuations from Universitetsky microsatellite

The article deals with the results of the fading fluctuations analysis for telemetry signals in the 2 m and 70 cm bands from the first Moscow State University microsatellite better known as “Universitetsky”. Radio telemetry signals were received from the microsatellite for around 2 years, collecting and recording the power signal data of almost 7500 satellite overpasses. The received signals from about 2300 satellite overpasses had a very low signal to noise ratio (SNR) that caused high transmission losses. The rest of the signals had a SNR high enough to complete the transmission without losses. The main objective of this paper was to find the fading fluctuations caused both by diffusion and by the presence of Gaussian and non Gaussian noise in telemetry signal power data. The purpose was both to characterize the communication channel as well as to elaborate solutions both to improve the communication quality as well as to identify no homogeneous zones in the ionosphere environment. The signal power analysis was based in the observation of statistical characteristics from different power signal components, in particular the components influenced by diffusion and non Gaussian noise. The employed methodology follows the next steps: removing the power signal envelope; taking away the Gaussian noise; obtaining the statistical characteristics from non Gaussian noise, Gaussian noise and envelope; finally identifying the LOS and NLOS signal fading components. For this purpose, the wavelet technique was used to perform the signal decomposition. In particular, the discrete wavelet transform DWT was utilized to carry out the signal de-noising. Then, the results were statistically treated in order to obtain a diffusion index for Rician fading, which are associated with fading in atmosphere and ionosphere layers. In this way the communications channel among satellite and ground station was characterized and a BER parameter was obtained for every satellite overpass, which means an outstanding result when considering that just few papers describe such results for satellite systems. The obtained results are valid not only for satellite communications systems but also for wireless communications systems. These results are the basis for future communications system design, which in our case pursues to reduce the BER parameter in the satellite link. The referred system will employ adaptive error coding schemes as well as channel analyzer algorithms based in the theory exposed in this paper.     

一种非周期调制直扩信号扩频码估计方法

对卫星测控中一类扩频码周期与信息码周期之比为非整数的直扩信号进行了研究,得出这类信号可建模成非周期调制直扩信号,提出并讨论了一种基于差分主元分析（D PCA）的非周期调制直扩信号扩频码估计方法,该方法通过计算与差分序列协方差矩阵的最大特征值对应的特征向量完成信息码个数、子序列、信息码同步点等参数的估计,解决了传统矩阵分解方法在估计码序列时码序列相位模糊问题,理论分析和仿真结果表明该方法可以在低信噪比下进行有效估计。     

连续波雷达目标回波信号参数估计的克拉美-罗界

现代雷达、导航和通信系统几乎无一例外地采用了先进的信号处理技术 [1～ 3 ] 。目前 ,最大似然估计 (ML E)方法是获得雷达目标回波信号参数估计的常用方法。它给出信号参数的无偏渐近有效估计。克拉美 -罗 (CR)界是由样本数据的联合概率密度函数导出的无偏估计量的性能界 ,它可以作为所有参数估计方法的比较标准。任何雷达关于信号参数的测量精度都不可能优于 CR界。文中给出了雷达目标回波信号参数的 CR界的详细而严格的推导过程 ,得出的 CR界公式非常简洁 ,易于计算。实验结果证明了该理论公式正确     

What should we say to extraterrestrial intelligence?: An analysis of responses to “Earth Speaks”

If scientists engaged in the Search for Extraterrestrial Intelligence (SETI) detect a signal from an extraterrestrial civilization, one of the most pressing issues facing humankind will be “Should we reply, and if so, what should we say?” Building on an infrastructure that the SETI Institute used to gather over 50,000 messages from around the world to send onboard the Kepler mission, Earth Speaks invites people to submit online their text messages, pictures, and sounds, as they ponder what they would want to say to an extraterrestrial civilization. Participants for the study have been recruited from 68 nations, from all walks of life. By tracking demographic variables for each person submitting a message, we have identified commonalities and differences in message content that are related to such factors as age and gender. Similarly, by tracking the date on which messages were submitted and the location from which the message was sent, we have also identified the way in which message content is related to time and geographic location. Furthermore, when we compare previous themes derived from textual messages to our current categorical analysis of submitted images, we find our textual themes to be concurrently validated. In doing so, we find the Earth Speaks Website not only allows for the construction of interstellar messages, but also functions as a projective psychological assessment of species-level human identity. We next proceed to demonstrate the generative power of our method by showing how we can synthesize artificial messages from the Earth Speaks messages. We then discuss how these artificially generated messages can be tailored to represent both commonality and diversity in human thought as it is revealed through our data. We end by discussing our method's utility for cross-disciplinary research in the social sciences and humanities.     

Survey of convective blockage for planetary entries

During a planetary entry, the decomposition of the thermal protection system material resin by the pyrolysis process produces strong blowing gases that are injected into the boundary layer. Induced by the blowing gas, the blockage phenomenon has a strong effect on the level of heat-fluxes. For some entries, such as Earth super-orbital re-entries characteristic of sample return missions, blockage is one of the key issues that have to be addressed. Additionally, this phenomenon is strongly linked to turbulence and to the porous aspects of the ablative material. Here, experimental, numerical and flight data available for different missions, involving high level of heat-fluxes, are gathered and discussed. The models for convective blockage found in the literature have been reviewed in order to select a generic way to estimate this phenomenon. It appears from this study that the convective blockage is still not fully understood and that there is no established approach for its accurate modelling since most of the existing correlations possess a high degree of empiricism.     

基于卷积神经网络的雷达和通信信号调制识别

雷达和通信信号的调制识别是电子侦察对抗的一项关键技术,通过搜索、截获敌方电子设备发射的电磁辐射信号,经过电子侦察系统分析、识别,从而获取敌方战术、技术特征参数等情报。人工神经网络中的深度学习网络由于具有强大的表征学习能力,可以自动从原始数据中提取出各种复杂的特征。介绍了一种差分自相关预处理结合深度学习进行中频信号调制识别的方法,结合工作的实际需求,对深度学习在信号调制识别中提出了一些展望,如进一步提高在低信噪比下的识别率和研究深度学习调制识别混合架构。     

The DISC Quotient

D.I.S.C: Decipherment Impact of a Signal's Content.The authors present a numerical method to characterise the significance of the receipt of a complex and potentially decipherable signal from extraterrestrial intelligence (ETI). The purpose of the scale is to facilitate the public communication of work on any such claimed signal, as such work proceeds, and to assist in its discussion and interpretation.Building on a “position” paper rationale, this paper looks at the DISC quotient proposed and develops the algorithmic steps and comprising measures that form this post detection strategy for information dissemination, based on prior work on message detection, decipherment. As argued, we require a robust and incremental strategy, to disseminate timely, accurate and meaningful information, to the scientific community and the general public, in the event we receive an “alien” signal that displays decipherable information. This post-detection strategy is to serve as a stepwise algorithm for a logical approach to information extraction and a vehicle for sequential information dissemination, to manage societal impact.The “DISC Quotient”, which is based on signal analysis processing stages, includes factors based on the signal's data quantity, structure, affinity to known human languages, and likely decipherment times. Comparisons with human and other phenomena are included as a guide to assessing likely societal impact. It is submitted that the development, refinement and implementation of DISC as an integral strategy, during the complex processes involved in post detection and decipherment, is essential if we wish to minimize disruption and optimize dissemination.     

Rapid model-based inter-disciplinary design of a CubeSat mission

With an increase in the use of small, modular, resource-limited satellites for Earth orbiting applications, the benefit to be had from a model-based architecture that rapidly searches the mission trade-space and identifies near-optimal designs is greater than ever. This work presents an architecture that identifies trends between conflicting objectives (e.g. lifecycle cost and performance) and decision variables (e.g. orbit altitude and inclination) such that informed assessment can be made as to which design/s to take on for further analysis. The models within the architecture exploit analytic methods where possible, in order avoid computationally expensive numerical propagation, and achieve rapid convergence. Two mission cases are studied; the first is an Earth observation satellite and presents a trade-off between ground sample distance and revisit time over a ground target, given altitude as the decision variable. The second is a satellite with a generic scientific payload and shows a more involved trade-off, between data return to a ground station and cost of the mission, given variations in the orbit altitude, inclination and ground station latitude. Results of each case are presented graphically and it is clear that non-intuitive results are captured that would typically be missed using traditional, point-design methods, where only discrete scenarios are examined.     

Search for extraterrestrial life using chiral molecules: mandelate racemase as a test case

We have investigated an enzymatic racemization reaction as a marker for extraterrestrial life, which resulted in a change in optical rotation of a mandelic acid over time, as measured by polarimetry. Mandelate racemase was active in aqueous buffer in a temperature range between 0 degrees C and 70 degrees C and also in concentrated ammonium salt solutions and water-in-oil microemulsions in a temperature range between -30 degrees C and 60-70 degrees C; however, the enzyme was not active in several organic cryosolvents. Thus, we have demonstrated that concentrated ammonium salt solutions and water-in-oil microemulsions, both of which are able to form on extraterrestrial planets and moons in the presence of liquid water, are suitable media for enzyme reactions at subzero temperatures. Kinetic data for the mandelate racemase reaction obtained by polarimetry, while reproducible and internally consistent, differed significantly from several sets of data obtained previously by other methods such as chromatography and hydrogen-deuterium exchange. However, we conclude that reactions yielding a polarimetric signal, such as the racemizations employed in this work, are suitable mechanisms by which to utilize a change in chirality over time as a tool to detect signs of life.     

一种基于降调频的宽带LFM信号DOA估计算法

传统的宽带LFM信号DOA估计算法,是直接对信号进行估计,为满足采样定理,需要很高的采样频率,数据量和运算量巨大。针对这一问题,提出一种基于降调频的宽带LFM信号DOA估计算法,采用基于改进谱形熵的自适应降调频技术,通过若干次降调频,将宽带LFM信号带宽降到接收机可以处理的范围内,再利用窄带LFM信号DOA估计算法估计...     

Positive consequences of SETI before detection

Even before a signal is detected, six positive consequences will result from the scientific search for extraterrestrial intelligence, usually called SETI. (1) Humanity’s self-image: SETI has enlarged our view of ourselves and enhanced our sense of meaning. Increasingly, we feel a kinship with the civilizations whose signals we are trying to detect. (2) A fresh perspective: SETI forces us to think about how extraterrestrials might perceive us. This gives us a fresh perspective on our society’s values, priorities, laws and foibles. (3) Questions: SETI is stimulating thought and discussion about several fundamental questions. (4) Education: some broad-gage educational programs have already been centered around SETI. (5) Tangible spin-offs: in addition to providing jobs for some people, SETI provides various spin-offs, such as search methods, computer software, data, and international scientific cooperation. (6) Future scenarios: SETI will increasingly stimulate us to think carefully about possible detection scenarios and their consequences, about our reply, and generally about the role of extraterrestrial communication in our long-term future. Such thinking leads, in turn, to fresh perspectives on the SETI enterprise itself.     

On orbit fabrication and assembly of large space structural subsystems

The evolving use of large space systems, with accompanying large truss-like structures, creates the need to develop an on-orbit fabrication and assembly capability for producing structural elements and structural subsystems. Such a capability is a basic necessity for extremely large structural subsystems because of the economy of operations resulting from the on-orbit conversion of high-density material stock into low-density structural elements. This paper discusses the development of large space structural subsystems; in particular the role a generic structure plays in that development. This generic structure embodies the key issues of the structural subsystems of various classes of large space systems and as such, when its development is completed a proof-of-capability will have been accomplished for a wide variety of large space structures.     

基于PDW的雷达信号环境建模与仿真研究

在雷达电磁环境仿真系统中,需要模拟生成描述雷达信号环境的脉冲描述字(PDW)数据,以引导系统生成干扰信号环境数据。采用PDW对雷达信号环境进行描述,结合雷达信号环境的PDW数学模型,给出了基于PDW的模型框架,并设计了雷达电磁环境仿真流程。最后归纳了生成PDW数据的处理方法,给出了载频、重频和脉宽的模拟生成示例。     

卫星导航信号畸变导致的测距偏差的估计方法

为定量评估导航信号的测距性能,本文研究了在轨卫星导航信号畸变导致的测距偏差估计问题。基于Vernier采样原理利用大口径抛物面天线采集在轨卫星导航信号,经数据处理获得一个伪码周期的脉冲波形。在此基础上,对该波形起点位置进行精确估计,然后根据延迟锁定环工作原理产生超前本地波形和滞后本地波形,获得E-L鉴别器曲线,最后估计鉴别器曲线的零交叉点偏差,该偏差即为卫星导航信号畸变导致的测距偏差。利用北斗卫星采集信号,获得了B1频点I支路信号的测距偏差,验证了该估计方法的正确性。     

应答式目标旋转运动对雷达速度测量的影响

携带应答机的飞行目标,若除了沿其某一轨道运动外,还作自旋运动,应答机天线辐射相位空间分布的不均匀性会使应答机转发信号产生附加的相位调制,因而导致多卜勒测量雷达的测量误差。本文分析了对称安装三天线园柱形应答式目标回波的多卜勒频率调制。得出了附加多卜勒频率及其各阶导数的解析式。研究了目标旋转速度、方向角(目标旋转轴线与雷达视线的夹角)和回波谱线宽度的关系,以及对雷达多卜勒测量精度的影响,它对于研究自旋再入体测量问题具有实用价值。文章给出了一个典型的三天线园锥目标模拟旋转试验结果。试验中在不同目标转速下由相参雷达跟踪测量目标回波,同时记录中频信号、多卜勒跟踪回路鉴频器输出等有用信息。对试验数据的分析得出了明确的结论:目标旋转使回波信号的谱线展宽、测速误差增大,谱线宽度与目标转速成正比,同时谱线宽度随目标方向角增大而加宽,方向角为90°时旋转影响最大。理论分析得出了与试验相同的结果。虽然试验是在静态下进行的,但问题的分析对质心运动的目标也同样适用。     

激光雷达系统仿真软件

从激光雷达约束条件入手 ,研究了通用激光雷达仿真模型 (GL M) ,其中包括大气传输模型、探测器噪声模型、发射与接收模型、目标反射数据库。着重分析、讨论了各种天气和系统条件下 ,对激光雷达性能的影响。根据模型 ,研制了通用仿真软件 ,最后给出了计算机仿真结果。