Direct P-code acquisition algorithm based on bidirectional overlap technique

According to the signal-to-noise ratio （SNR） loss of average algorithms in direct P-code acquisition method, this paper analyzes the SNR performance of the overlap average algorithm quantitatively, and derives the relationship of SNR loss with overlap shift value and initial average phase difference in the overlap average algorithm. On this basis, the bidirectional overlap average algorithm based on optimal correlation SNR is proposed. The algorithm maintains SNR consistent in the entire initial average phase difference space, and has a better SNR performance than the overlap average algorithm. The effectiveness of the algorithm is verified by both theoretical analysis and simulation results. The SNR performance of the bidirectional overlap average algorithm is 5 dB better than that of the direct average algorithm, and 2 dB better than that of the overlap average algorithm, which provides the support for direct P-code acquisition in low SNR.

Improved direct P code acquisition technique

P code direct acquisition is an important technology in satellite navigation system. As the P code has a long period, it is hard to directly acquire. The traditional average method can process multiple code phases in a time to shorten the acquisition time. But with the increase of average phase error of the input signal and the local code, the correlation signal-to-noise ratio （SNR） loss increases. To reduce the SNR loss, an improved average method is introduced. A new sequence is generated with a summation of phase shifting sequences to decrease correlation peak loss. Simulation results show that compared with direct average method, the improved average method effectively increases correlation SNR.

High-Sensitivity Acquisition of Ultrahigh Dynamic Direct Sequence Spread Spectrum Signals in Space Communications

According to the requirements of the high-sensitivity acquisition of Direct Sequence Spread Spectrum(DSSS) signals under ultrahigh dynamic environments in space communications, a three-dimensional joint search of the phase of Pseudo-Noise-code(PN-code),Doppler frequency and its rate-of-change is presented to achieve high sensitivity in sensing high-frequency dynamics. By eliminating the correlation peak loss caused by ultrahigh Doppler frequency and its rate-of-change offset,the proposed method improves the acquisition sensitivity by increasing the non-coherent accumulation time. The validity of the algorithm is proved by theoretical analysis and simulation results. It is shown that signals with a carrier- to-noise ratio as low as 39 dBHz can be captured with high performance when the Doppler frequency is up to ±1 MHz and its rate-of-change is up to ±200 kHz/s.

Research on Estimator and Testing Acquisition Schemes in Direct Sequence Spectrum Spreading Systems

Serveral methods for the pararrel acquisition of a PN sequence in a baseband direct sequence spread spectrum system are investigated. Four different kinds of schemes are considered: the optimal estimation scheme, the locally optimal estimation scheme, the optimal testing searches and the locally optimal testing scheme. In the four kinds of parallel acquisition schemes, the expressions for the probability of error are given and compared with the actual error probabilities obtained via Monte Carlo simulation. We also outline a technique that can be suboptimal because of a large amount of hardware and computation when using the parallel acquisition schemes.

New Acquisition Algorithm for Direct Sequence Spread Spectrum Signals

Aiming at improving acquisition performance for direct sequence spread spectrum （DSSS） signals, a new acquisition algorithm based on fast Fourier transform （FFT） is proposed. The code phases are parallel searched throughout the Doppler frequency domain. Since the influence of Doppler frequency errors on peak-to- average ratios of correlation power shows a pattern similar to the sinc function, it is our belief that by judging on peak-to-average ratios for different Doppler frequency errors false alarm probabilities should be lowered. Analyses have supported the underlying principle of this new algorithm. Simulation results have also indicated that the new algorithm can effectively improve the acquisition performance for DSSS signals.

A Study on the Second Language Acquisition for Chinese Simple Directional Complement

Complement is a typical feature of Chinese grammar, and it seldom appears in other languages. Because of its complexity, it is very difficult for Chinese learners all over the world. The paper takes seven groups of simple directional complement （SDC）, ＂V-Shang＂, ＂V-Xia＂, ＂V-Jin＂, ＂V-Chu＂, ＂V-Kai＂, ＂V-Qi＂, and ＂V-Hui＂, as research goals. The investigation on second language acquisition （SLA） is carried out in terms of different native languages. The conclusion can be drawn that native language has a close relationship with SLA, because of their difference in Semantic Incorporation. In addition, the category of SDC is also an important factor influencing SLA.

Study on Fast Acquisition of Hybrid DS/FHSS

In hybrid Direct Sequence/Frequency Hopping Spread Spectrum （DS/FH SS） system, the fast acquisition is a key technique. A combined fast scanning and waiting method for FH acquisition is introduced, and a neural network for DS acquisition is presented also. Using these two methods, the fast acquisition of the hybrid DS/FH SS system can be realized.

New acquisition decision algorithm for multiple access interference suppression in DSSS system

For decreasing the multiple access interference of weaker signal acquisition in direct sequence spread spectrum（DSSS） systems,a new single decision algorithm is presented.The maximum value of correlation results is conventionally detected.However,there may be not only one strong peak among correlation results when the cross-correlation noise is strong enough to affect the correlation results.The proposed algorithm decreases the false alarm probability through the decision of the ratio of the maximum value and the second maximum value of the correlation results.Theoretical analysis and simulation results indicate that the proposed algorithm effectively suppresses the acquisition problem of multiple access interference in DSSS system.

大庆油田地球物理勘探技术现状及发展方向

大庆油田地球物理勘探技术(简称为物探技术)以高效支撑油田勘探开发为宗旨,通过引进吸收和自主创新相结合的方式快速发展。针对各领域勘探开发的需求,已形成适用配套的地震资料采集、处理和解释技术系列,并自主创新研发了具有国际先进水平的黏弹性叠前偏移技术和薄互层波阻抗直接反演技术,有力支撑了大庆油田各领域油气勘探开发,为油田“稳油增气”作出了积极贡献。但随着油田勘探开发持续向非常规油气藏、复杂油气藏、深部油气藏等领域延伸,勘探开发对象日趋复杂,对物探技术的支撑能力提出了新的挑战。围绕当前大庆油田主要勘探开发领域,在梳理技术现状的基础上,详细分析了松辽盆地北部、海拉尔-外围盆地、四川盆地矿权流转区、塔里木盆地塔东区块在常规油、致密碎屑岩油气藏、页岩油、火山岩气藏、碳酸盐岩油气藏等领域面临的地质难题,厘清物探技术需求和差距,提出了未来在推广完善成熟技术、创新研发核心技术、加快构建大数据平台、探索储备新能源物探技术等方面的发展方向,以促进大庆油田物探技术的持续快速进步,为大庆油田高质量发展再作新贡献。

基于SoC的软件定义宽带信号采集回放系统设计

为提高宽带信号采集系统开发的简便性和灵活性,提出了基于SoC的软件定义宽带信号采集回放系统的设计及实现方法,采用直接射频采样和数字信号处理技术实现对信号的高速采集和回放,在可编程数字域中灵活完成下变频和信号处理,且具备软件无线电二次开发功能,解决了传统宽带信号采集系统中采用超外差中频采样的模拟化方案设计复杂、灵活性差的问题。系统实验结果表明,本信号采集回放系统输入输出信号频率范围1 MHz~4 GHz、信号带宽不小于80 MHz、采样时钟频率不小于200 MHz,回放信号功率输出范围-90~0 dBm,输出功率调节步进1 dB,具有较高的灵活性。

一种整数抽取结合小数插值重采样技术研究

射频直采技术近年来在雷达、通信、电子对抗尤其是一体化接收等领域得到了广泛的应用。然而射频采样数据率极高,导致后续信号传输与实时处理难度变大。数字重采样技术能够在数字域降低采样率,从而减轻射频直采带来的信号处理压力。本文针对数字重采样技术开展研究,提出一种整数抽取结合小数插值重采样方法,推导了理论模型,给出了相应的参数递推解算方法,仿真验证了方法的有效性。采用本文所提方法,既可解决在射频高采样率下,直接进行小数插值带来的数字信号实时处理压力,又可在保证信号质量的情况下,解决特殊场景下精确变采样率处理的需求,进而实现对大范围任意分数倍抽取。

基于圆周相关扩频信号的快速捕获改进方法

针对大多普勒频偏、低信噪比条件下长周期伪码的扩频信号捕获问题,提出了一种基于圆周相关扩频信号的快速捕获改进方法。该算法对圆周相关后的结果利用快速傅里叶变换(FFT)进行频率估计,扩大了传统圆周相关法的扫频步进,使扫频步进不再受跟踪环路带宽的限制。理论分析及仿真结果表明,在信噪比为-34 dB、多普勒频率为500 kHz条件下算法可以正确地估计出伪码相位和多普勒频偏。在达到相同的灵敏度条件下,所提算法的平均捕获时间与传统的圆周相关法相比缩短了约47%,与基于FFT的并行频率搜索法相比缩短了约88%。另外,用于频率估计的FFT点数仅占圆周相关点数的1%,故额外增加的硬件资源很少。算法逻辑控制简单,尤其适用于大多普勒频偏、低信噪比及长周期伪码的卫星通信系统。

一种改进的高灵敏度长码直接捕获算法

针对微弱卫星导航信号条件下捕获难度大、概率低的问题,提出了多段信号叠加累积的长码直接捕获算法。该算法在典型PMF-FFT的基础上,结合了相干累积和非相干累积,获得了额外的非相干累积增益,从而有效提升了微弱信号条件下的捕获概率。改进算法采用N中取M的方式有效降低了由于非相干累积引入的存储器资源消耗,通过捕获策略优化,采用GEO卫星辅助MEO卫星捕获的方式,大大缩短了信号捕获时间。经应用验证表明,该算法在捕获微弱卫星导航信号时消耗存储器资源少,捕获性能提升较为显著。

煤矿井下定向钻孔随钻测量数据综合采集系统研究

当前煤矿井下定向钻孔随钻测量装备与系统之间相互独立,导致孔底随钻测量数据形式各异,形成数据孤岛的问题。基于B/S系统架构模式,通过对比随钻测量方式、测量数据格式,分析数据综合采集系统需求模块;搭建综合采集系统后台数据库,开发了煤矿井下定向钻孔随钻测量数据综合采集系统。验证表明,数据综合采集系统满足多种随钻测量数据统一汇总处理和整体分析评价功能,并完成数据实时上传,为煤矿井下定向钻孔数据监管平台提供数据网络传输保障,提高煤矿井下钻探智能化水平。

基于观测系统退化的气云区地震资料采集参数分析与建议

渤海湾浅层气云广泛发育,气云影响区在地震剖面上多表现为模糊带,无法准确描述构造和储层特征,但学术界针对气云区地震资料采集方面的研究较少。文中以渤海湾X油田先后采集的三套关键采集参数存在较大差异的地震数据为基础,通过对实际采集观测系统进行退化处理,在保证其他采集参数一致的前提下,分别研究采集方向、面元尺寸、覆盖次数等单一采集参数对气云区地震成像的影响规律。得到能够指导海上气云区地震资料采集设计的三点认识:①采集方向对条带状气云成像影响非常大,沿气云短轴方向采集时气云内部成像品质相对更好,而沿气云长轴方向采集时气云平面影响范围相对更小,对于方向特征比较明显的条带状气云,宜采用双方位采集及融合处理改善气云区成像;②不同面元尺寸气云区成像品质及气云平面影响范围差异均较小,缩小面元尺寸对气云区成像贡献不大,建议气云区地震资料采集时采用常规面元尺寸,不必过分追求小面元;③覆盖次数增加到一定程度,继续增加对非气云影响区成像贡献不大,但对气云区成像仍然很有意义,建议地震资料采集时增加气云区的有效覆盖次数。

人工智能与中国企业跨国并购:新一轮技术红利存在吗?

人工智能发展产生的新一轮技术红利开始显现,成为构筑我国企业跨国并购竞争优势的核心模块之一。本文结合Zephyr全球并购交易数据库、国际机器人联合会数据库和国泰安上市公司财务数据库,并采用二元选择Probit模型就人工智能与企业跨国并购之间的关系展开系统分析。研究发现,人工智能是推动我国企业跨国并购的重要因素。异质性分析表明,人工智能发展能够促进技术红利替代人口红利,对不同企业跨国并购行为带来差异化影响。并且,机器代人能够促进企业劳动力结构优化,产生资源配置的倒金字塔效应。机制分析显示,用工成本削减效应、管理效率提升效应、聚集知识溢出效应是人工智能作用于企业跨国并购的具体机制。此外,本文在考虑跨国并购样本选取、核心指标稳健性、计量模型设定等多方面问题后进行稳健性检验,以及控制内生性问题后,人工智能发展对跨国并购的促进作用依然显著。

基于复杂网络的本土汽车企业逆向跨国并购发展与对策研究

随着我国综合国力的提升,中国自主汽车品牌纷纷开始进行海外并购,并且不断尝试逆向跨国并购,以获取先进技术促进国内汽车产业发展。本文以中国2001—2022年本土汽车企业逆向跨国并购事件为基础,建立逆向跨国并购网络,运用社会网络分析方法,对其现状进行可视化分析,并且基于逆向跨国并购发展存在的问题,提出本土汽车企业逆向跨国并购发展路径。研究发现,本土汽车企业逆向跨国并购规模较小,并购对象集中于美国和德国,网络呈现“核心-外围”结构。基于此,本文将考虑政府方面的政策引导、本土企业与被并购企业的区位优势和协同发展,提出逆向跨国并购发展路径,以期促进本土汽车产业创新发展。

一种基于无线链路监测的手机直连卫星业务捕获系统实现及应用

手机直连卫星技术的发展将带来10亿量级的用户,给人们带来便利通信的同时,也给信息安全带来严重考验。针对此,设计了一套无线链路监测的卫星业务捕获系统,用以获取商用手机的卫星话音、短消息等业务。与地面移动系统DU-CU模式相似,系统射频和基带处理部分以分布式形式安装在室外信号塔,业务处理部分集中安装在机房,可完成多个无线接收点的业务处理。测试表明,系统能够正常截获卫星手机通话业务,并能存储和回放。

基于Direct X和PCI总线的光栅扫描显示系统

对国内外雷达光栅扫描显示技术的研究现状进行分析 ,提出了新一代基于 Direct X和 PCI总线技术的雷达光栅扫描显示系统。该雷达光栅扫描显示系统具有高性能、低成本、功能强、易于维修和功能扩展等特点。

Direct GPS P-Code Acquisition Method Based on FFT

Recently, direct acquisition of GPS P-code has received considerable attention to enhance the anti-jamming and anti-spoofing capabilities of GPS receivers. This paper describes a P-code acquisition method that uses block searches with large-scale FFT to search code phases and carrier frequency offsets in parallel. To limit memory use, especially when implemented in hardware, only the largest correlation result with its position information was preserved after searching a block of resolution cells in both the time and frequency domains. A second search was used to solve the code phase slip problem induced by the code frequency offset, Simulation results demonstrate that the probability of detection is above 0.99 for carrier-to-noise density ratios in excess of 40 dB. Hz when the predetection integration time is 0.8 ms and 6 non- coherent integrations are used in the analysis.