余弦BOC信号伪相关函数无模糊跟踪方法

二进制偏移载波 (binary offset carrier,BOC) 调制方式实现了频谱分离和频段共享,被应用于全球导航卫星系统中;但由于BOC信号自相关函数的主峰和副峰幅度差异较小,容易引起捕获和跟踪模糊,导致较大的测距误差;余弦相位BOC(Cosine-phased BOC,CosBOC)信号自相关函数形式相对复杂,给其无模糊处理带来了挑战;基于伪相关函数法(pseudo correlation function, PCF)思想,针对CosBOC信号设计本地参考信号的特殊码片波形,与接收信号相关后经过非线性组合可获得单峰无模糊相关函数,消除了跟踪模糊性;仿真结果表明:参数取值合适时该方法的跟踪和抗多径性能均优于同等条件下的BPSK-like方法。     

主动声呐信息过程的实验研究——声呐信号综合分析仪在信道研究和声呐设计中的应用

本文介绍声呐信号综合分析仪(简称SZY)在主动声呐信道特性的实时测量和声呐设计中的应用原理和方法,并给出部分实验结果.内容包括:1.声呐信号分析:相关、模糊度和谱以及随机数据的统计测量;2.主动声呐信道(水声传输信道、目标散射和混响)特性的测量:时变谱和时变相关、时空相干性和散射函数;3.声呐检测和最佳设计:定位、跟踪、波形设计和信道匹配.     

GNSS导航卫星抛物面天线系统建设与测试

导航卫星的信号质量是影响卫星导航系统精度、连续性和可靠性的关键因素,为实时监测上海地区可见GNSS导航卫星的信号质量,建成了GNSS导航卫星抛物面天线系统;该系统可以对包括北斗导航卫星系统在内的GNSS导航卫星的空间信号进行监测,分析导航卫星空间信号的质量;GNSS导航卫星抛物面天线系统主要由3.2m抛物面伺服跟踪天线、GNSS信号中频采集器、数据存储装置、监测控制平台以及相关监测设备组成;介绍了导航卫星抛物面天线系统的建设及其测试情况,测试结果表明,所建成的抛物面天线系统可以对观测范围内的各卫星导航系统的各颗卫星的导航信号进行实时信号跟踪与监测,相关技术指标达到了预期要求。     

任意复包络信号的匀速运动目标回波脉间补偿及相干积累

现代声呐、水下制导等水声探测系统常常使用窄带脉冲、调制、编码、伪随机等种类繁多的发射信号波形来满足低信噪比检测、高分辨估计、抗干扰、主动隐蔽探测的应用需求.针对这一情况,本文研究了任意信号的长时间积累问题,给出了一种任意复包络信号的匀速运动目标回波脉间补偿及相干积累检测方法.通过构建任意发射信号波形的广义模糊函数,将匹配滤波器输出表示为所构造的广义模糊函数,使得任意复包络信号的脉压波形不仅能够用统一的数学模型来表述和计算,而且能够提供多脉冲回波的距离走动信息和多普勒频移信息,为多脉冲距离位置对齐和Fourier变换(FFT)积累提供了依据.对于用广义模糊函数表示的匹配滤波器输出,采用Keystone变换将复包络对齐,消除了距离走动,采用FFT补偿多普勒频移项,实现了任意复包络信号的长时间相干积累.对于水下探测中使用的连续波信号、线性调频信号以及复杂的m序列编码信号、Costas跳频编码信号波形进行了信号积累及检测的计算机仿真,验证了任意复包络信号的匀速运动目标回波脉间补偿及相干积累的正确性.消声水池实验验证了该方法的有效性.     

宽带多普勒技术中模糊速度处理方法改进

宽带多普勒剖面仪(BBADCP),利用复相关测频技术和伪随机码性质,测得各水层散射波的多普勒频率偏移,从而得到水流剖面图.复相关算法由于采用反正切函数.测频范围受到限制,会产生速度模糊问题.本文对接收信号作自相关运算,在以前研究者利用时延估计解决速度模糊的基础上,利用复相关测频结果与模糊边界的关系,设计了一种更准确更稳定的解模糊算法.     

高速电影摄影机的一种新装置——反射镜快速扫描跟踪器

本文介绍了一种单反射镜快速扫描跟踪系统,它是一种通用跟踪系统,可以同时配备一台高速摄影机、一台跟踪测量电视(或彩色录相机)。跟踪方式有三种:计算机内引导;单杆半自动;电视自动跟踪。本文论述了固定式摄影系统的局限性和反射镜快速扫描跟踪的优点。文中还给出了几种反射镜跟踪方案,以供读者参考。     

一种通用的卫星导航信号码时延估计误差评估方法

卫星导航信号的码时延估计误差是决定系统服务性能的关键因素,迫切需要对多种不同调制与复用方式的导航信号进行全面的码时延估计误差性能评估,从而为后期的系统应用提供重要的选择依据.为此,本文提出了通用的码时延估计误差评估方法.首先,概括了导航接收机的码跟踪环路模型,根据是否匹配接收以及是否相干处理,将目前的导航接收机归纳为四种类型.其次,在假设码时延估计误差非常小的条件下,分别给出了匹配接收下相干处理和非相干处理时的估计误差以及相互之间的关系;推导了非匹配接收下非相干处理时的估计误差,并讨论了与相干处理时的关系.最后,推导了码时延估计误差的齐夫-扎凯界限,解决了估计误差不满足非常小这一假设条件时的评估.本文提出的评估方法均以导航信号的功率谱密度表示,为信号设计和接收机的研制提供了重要的理论指导,同时也给具体信号的评估带来了极大便利.仿真实验中对新一代典型导航信号的码时延估计误差做了有效评估.     

激光干涉仪应用于无导轨测距的研究

本文提出了一种使用外差激光干涉仪实现无导轨测距的方法.该方法动态跟踪测量反射镜,使测量信号不中断,实现反射镜在一定范围内的非直线运动.这样,拥有双频激光干涉仪的用户,再添置一台比较简单的跟踪装置,即可用于无导轨测距,测量精度可远高于通用测距仪,为大型设备现场组装和安装提供了新方法.本文介绍了工作原理及实验情况.     

同步水声跟踪定位系统软件抗距离模糊技术研究

同步水声跟踪定位系统通过时延测量进行定位,当信号传播时延大于脉冲重复周期时,就会出现距离模糊。距离模糊是远程高帧率定位系统不可避免的问题。以往多采用硬件方法抗模糊,使得系统趋于复杂。本文提出了两种软件抗模糊方法:举手表决法和参考位置标示法,前者利用真解的一致性抗模糊,无需任何先验信息;后者利用目标的参考位置抗模糊,需要目标初始就位点这一先验信息。文中给出了算法原理和适用条件。软件抗模糊方法简化了系统设备,海试结果验证了算法的有效性。     

基于自适应EKF的弱GNSS信号跟踪算法

弱GNSS信号跟踪技术是卫星导航接收机关键技术之一,跟踪技术的好坏将直接影响卫星导航接收机在弱信号条件下的跟踪性能;在动态环境和先验信息不充分的情况下,由于扩展卡尔曼滤波(EKF)的固定设计使其不能满足要求,针对此不足引入一种自适应扩展卡尔曼滤波(AEKF)的信号跟踪算法;该自适应滤波算法能够实时监测残差或滤波器新息的动态变化,来修正观测噪声方差和状态噪声方差,以此调整滤波器增益,观测值和控制预测值在滤波结果中的权重;理论分析和结果表明,该算法能够充分利用观测信号的统计特性,克服了传统EKF算法不足,获得更好的跟踪性能。     

Navigation signal structure based on complex carrier modulation

Signal structure design is an important part of satellite navigation system research,which directly affects navigation performance.Signal performance parameters are analyzed and performances of BPSK modulated signals and BOC modulated signals are compared.Aiming at requirements of high navigation precision and high anti-jamming ability,a new navigation signal structure based on complex carrier modulation is proposed and performances of the signal are researched with different parameters.A synchronization al...     

基于VSLMS-Rake模型的高阶多径BOC信号捕获方法*

针对高阶多径BOC信号捕获存在模糊性的问题,提出了一种基于VSLMS-Rake模型的捕获方法。该方法首先将接收的多径BOC信号经过VSLMS-Rake模型,然后再对处理后的信号进行功率谱估计。通过二者结合,不仅可以抑制多径干扰增强信号能量,还可以减小估计误差提高捕获概率,最终实现对高阶多径BOC信号的精确捕获。理论和仿真表明,在较低信噪比下,该方法优于现有其它捕获算法。     

A signal optimization strategy for next generation navigation and communication integration applications

For 6G and future communication technologies, integration of navigation and communication has become a hot research topic, which can greatly improve the transmission data rate and can be applied to self-driving vehicles. In former research, a novel integrated navigation and communication signal has been designed by combining traditional global navigation satellite system (GNSS) and cyclic code shift keying (CCSK) signals. In this paper, we design an enhancement strategy for this signal, optimizing the number of cyclic shifts of the CCSK signal, which can make larger values of cross-correlation function align with the peak value of self-correlation function to overcome the cross-correlation interference and improve communication performance. Simulation results validate that the proposal not only can avoid interference between navigation and communication signals, but also can improve the signal detection probability and reduce the transmit error rate. Taking Beidou B1I signal as an example, when the signal to noise ratio (SNR) is set to -27 dB, the detection probabilities for the navigation and communication signals increase about 11.4% and 13.5%, respectively, while the symbol error rate (SER) for the navigation and communication signals decrease about 16.3% and 17.8%, respectively.     

Comparison between direct-sequence and multicarrier spread-spectrum acoustic communications in time-varying channels

Underwater communication experiments have been conducted in the Norwegian Oslofjord. Two modulation schemes are compared in a 7-kHz frequency band on a 14-kHz center frequency. The first scheme is direct-sequence spread spectrum (DSSS), using a 7-chip spreading code to achieve a raw data rate of 1000 bps on a single carrier. The second scheme is multicarrier spread spectrum (MCSS) and accomplishes spreading by using seven subbands. The DSSS receiver equalizes on the chips prior to explicit symbol despreading, whereas MCSS features joint multiband equalization and despreading. Four channels are examined, from nearly static to overspread. In slowly varying channels, MCSS offers the best performance. DSSS has the best tracking potential for rapidly varying channels, where the challenge is to obtain reliable chip decisions before symbol despreading. The tracking potential can be realized to some extent by hypothesis-feedback equalization. It is further shown that adaptive equalizers are capable of code conversion, i.e., the DSSS receiver can demodulate the MCSS waveform, and vice versa. Neither receiver requires knowledge of the spreading code in order to despread the data.     

Signal structure of the Chinese Area Positioning System

Proper signal structure is very important in the navigation, positioning, and time services of a satellite navigation system. In this paper, the carrier wave characteristics, ranging code functions, BOC modulation, navigation data rate, the error-correcting methods, and signal channel resource allocation are discussed in terms of the technical characteristics of the transforming satellite navigation system and the resources of communication satellites. The results show that dual-frequency of C band in the Chinese Area Positioning System (CAPS), compound ranging code, a combination of the coarse code and precise code, BOC modulation, separate-channel transmission of different users are compatible with the satellite navigation system at present. The experiments show that the current signal structure can meet the demand of CAPS. Supported by the Major Knowledge Innovation Programs of the Chinese Academy of Sciences (Grant No. KGCX1-21), the National High Technology Research and Development Program of China (Grant No. 2004AA105030), the National Natural Science Foundation of China (Grant No. 10453001), and the Major State Basic Research Development Program of China (Grant No. 2007CB815502)     

Chaotic secure communication based on strong tracking filtering

A scheme for implementing secure communication based on chaotic maps and strong tracking filter (STF) is presented, and a modified STF algorithm with message estimation is developed for the special requirement of chaotic secure communication. At the emitter, the message symbol is modulated by chaotic mapping and is output through a nonlinear function. At the receiver, the driving signal is received and the message symbol is recovered dynamically by the STF with estimation of message symbol. Simulation results of Holmes map demonstrate that when message symbols are binary codes, STF can effectively recover the codes of the message from the noisy chaotic signals. Compared with the extended Kalman filter (EKF), STF has a lower bit error rate.     

基于云计算的嵌入式人脸识别系统建构与研究

在捕获北斗信号的过程中,接收机根据预先设定好的信号搜捕策略和门限值来捕获信号。欺骗干扰源通过产生虚假的相关峰和增加噪声基底,可以有效地干扰普通型北斗接收机正常的捕获工作。欺骗信号会增加噪声基底使得真实的卫星信号埋没,同时欺骗信号相关峰可以诱导接收机捕获到欺骗信号。针对欺骗信号检测问题,在分析欺骗信号入侵对接收机噪声基底影响的基础上,提出了在捕获阶段利用信噪比(SNR)检测技术识别欺骗干扰信号的方法,并对其有效性进行了分析。仿真结果表明,采用该方法的接收机具有一定程度的欺骗干扰识别能力,为提高GNSS接收机抗干扰能力提供了有益的参考 。     

一种基于强跟踪滤波的混沌保密通信方法

提出了一种基于强跟踪滤波器的混沌保密通信方法. 在发送端, 混沌映射和信息符号被建模成非线性状态空间模型, 信息符号被加性混沌掩盖或乘性混沌掩盖调制, 然后通过信道输出. 在接收端, 驱动信号被接收, 使用带有贝叶斯分类器(信息符号估计)的强跟踪滤波器算法动态地恢复信息符号. Logistic混沌映射的仿真表明, 当信息符号为二进制编码时, 不管是加性混沌掩盖调制还是乘性混沌掩盖调制, 强跟踪滤波器均能较好地从混沌信号中恢复信息符号. 与扩展卡尔曼滤波器相比, 由于卡尔曼滤波器对于离散的信息符号跟踪能力差, 混沌映射中信息符号难以恢复, 比特误码率高. 因此, 这种基于强跟踪滤波器的混沌保密通信方法是有效的.