基于信号估计的扩频测控信号快捕方法

为进一步提高扩频测控系统的捕获速度,研究了借助辅助序列估计伪码相位的方法,分析了该估计算法的精度。针对该算法在高动态条件下估计偏差较大引起捕获概率骤降的问题,提出引入最大似然频偏估计修正相干载波的方法,显著提高捕获概率。设计了基于码相位估计和载波频率估计的快速捕获算法,仿真结果表明,该算法在载噪比较好的情况下可以有效完成捕获。为提高算法在较低载噪比时捕获的可靠性,提出将估计值作为部分匹配滤波辅助快速傅里叶变换( PMF-FFT )初值的综合捕获方法,与传统捕获方法相比,平均捕获时间显著降低,且并没有带来硬件复杂度的提高,具有一定的理论意义和工程应用价值。     

高动态弱信号环境下基于INS的GNSS捕获方法分析

为保证 GNSS 在挑战环境下的捕获性能，分析了高动态弱信号捕获存在的问题，提出了一种新的 INS 辅助并行码相位捕获方法，在频域利用 INS 辅助信息卫星星历/历书数据估计多普勒，缩小频率搜索范围，在码域利用码相位估计及并行码相位搜索的方法，减少码相位搜索时间，最后结合差分相干累积提高捕获灵敏度，实现高动态弱信号的快速捕获。仿真结果表明， 该算法能显著提升高动态、弱信号环境下 GNSS 接收机的捕获性能。     

基于LabVIEW的GPS信号捕获算法实现

简要介绍了GPS捕获原理以及并行码相位搜索捕获算法,并在此基础上编写了基于LabVIEW的GPS信号捕获程序.在考虑到算法实现所需时间和涉及计算量的前提下,采用了计算量较少,捕获时间较短的并行码相位搜索算法.基于LabVIEW的并行码相位捕获搜索算法实现的捕获程序不仅实现了粗捕获,而且加入了精捕获的程序,使得对载波频率的估计更加的准确.可扩展应用于北斗、伽利略等其它导航卫星的信号捕获.     

直序扩频系统中扩频码同步技术的研究

针对扩频通信中伪随机序列的快速捕获问题,文中提出了扩频信号快速捕获方法,来解决低信噪比条件下伪码序列的捕获问题.首先对直接扩频通信系统的基础理论做了探讨,而后重点研究了两种基带扩频信号同步捕获方案--序列相位搜索捕获法和不连续相位滑动相关法,序列相位搜索捕获法主要适用于m序列码周期较短的情况,而不连续滑动相关法则克服了...     

扩频通信中伪随机序列的捕获

１伪随机序列捕获的方法伪随机序列捕获的方法可分为串行搜索法和并行判决法两种。１．１串行搜索法串行搜索捕获是在本地伪随机序列和接收伪随机序列不同步的情况下，调整本地序列相位，逐一进行试验，直到发现某本地序列相位和接收序列相位基本一致为止，如图1所示。假设扩频系数为M，每码片两个采样时，需要进行2M次试验,则每次试验费时为伪随机序列一个周期的时间，即一个符号的时间。也就是说，在其它参量已同步且检测到无错误时，最多需要2M个符号后，才能对伪随机序列实现捕获。串行搜索捕获是以输入数据中伪随机序列相位为参考，…     

TDMA卫星通信系统突发同步的性能研究

突发载波捕获和同步是TDMA系统的关键技术,使用数据序列辅助判决可有效缩短该处理过程需要的时间;在低接收信噪比下使用CAZAC序列的相关处理能够获得较高的突发捕获性能;比较了CAZAC序列和"1010"序列的载波和时钟同步误差估计性能,分析了它们在低信噪比门限时对信号快速捕获能力的影响。提出了2种序列组合应用实现载波快速同步的方案,完成信号捕获和载波估计功能。     

基于前置三阶相关检测的高性能直扩伪码捕获

为了提高无线电导航系统长伪码序列的检测概率,同时降低捕获时间,提出了一种带前置三阶相关检测的伪码捕获算法,即根据伪随机码和高斯噪声的三阶相关特性,首先实现本地伪码与接收伪码序列的码元相位同步,再用传统捕获方法进行伪码相位同步.理论分析和仿真结果表明,该方法能够有效提高捕获过程的检测概率,并降低捕获时间.     

新息净积累量序列估计算法

 现有的伪随机序列捕获算法会重复积累历史错误信息,在低信噪比、高误码率下性能不理想,尤其是在初始相位未知的情况下.针对此问题,文中提出一种新息净积累量序列估计(INASE)算法,通过设计新息净积累方式,更有效地积累正确信息.仿真分析并与现有算法对比表明,INASE算法在极端恶劣的环境下仍能保持稳定收敛,最终捕获伪随机序列.     

北斗二号B1信号捕获方法研究

为了缩短北斗B1信号的捕获时间,提高多普勒频率和码相位的估计精度,针对北斗NH码对差分相干累积值的影响,改进了广义差分相干累积捕获方法。并采用二次频率-码相位捕获法来提高载波多普勒频率和码相位的估计精度。理论分析与仿真实验表明,改进的广义差分相干累积法能够克服NH码的影响。用4个1ms的相干累积值,改进的广义差分法可成功捕获信噪比为-27dB的信号。最后,用实测的北斗数据验证了算法的正确性。     

卫星导航中XFAST捕获的降计算量去模糊处理算法

卫星导航系统中,采用扩展复制重叠法(Extended Replica Folding Acquisition Search Tech-nique,XFAST)对长PN码进行直接捕获时,粗捕后得到的对齐码相位存在重叠模糊度.为减少去模糊处理的计算量,提高捕获速度,提出了一种新的去模糊处理算法.新算法在得到粗捕对齐码相位结果后,先对本地码序列重新按照对齐相位进行排列、分段、段内循环移位等操作,然后进行段间叠加,再与接收码序列通过FFT-IFFT运算实现循环相关运算,从而确定对齐码相位所在的子码段,得到无模糊度的捕获结果.理论分析与仿真结果证明,该算法可以在分段叠加段数和子段长满足一定关系的条件下,在检测性能满足系统要求下,大大降低去模糊处理的计算量和操作时间,从而提高捕获速度.     

PN acquisition for DS/SS using a preloop parallel binary search phase estimator and a closed-loop selective search subsystem

An acquisition method of long pseudo-noise (PN) sequences in direct-sequence spread spectrum (DS/SS) systems is presented. The concurrent cross correlation of locally generated auxiliary signals with the incoming PN sequence produces binary search estimates leading to an initial approximation of the input signal's PN offset. The PN receiver then uses a closed-loop subsystem to determine the true offset of the incoming PN signal. New phase estimates are generated from successive corrections of likely errors in the binary search. The acquisition scheme's average acquisition time and its variance are analytically determined. Simulation results show that the proposed acquisition scheme is faster than the conventional serial receiver. A hybrid serial/parallel PN acquisition receiver is used for comparing the acquisition performance given similar hardware complexity. The hybrid receiver used the same number of parallel correlators as used in the proposed receiver's input phase estimator. Simulation results show that the proposed system provides an improved performance under normal operating conditions.     

Rapid acquisition of PN signals for DS/SS systems using a phaseestimator

We propose a new scheme for rapid acquisition of PN signals in direct-sequence spread spectrum (DS/SS) systems by estimating the phase of the received PN signal with the use of an auxiliary signal. The auxiliary signal can be generated by a sum of the phase shifted PN signals. The phase of the incoming PN signal is estimated using the properties of cross correlation between the PN signal and the auxiliary signal. True phase alignment is detected using a conventional serial search scheme, where the initial phase of the local PN generators is set to a value obtained by the phase estimator. The performance of the proposed acquisition scheme is analytically evaluated in terms of the mean acquisition time. Numerical results show that the proposed scheme can achieve acquisition at least two times faster than the conventional scheme in the nominal operating condition     

一种快速的PN码同步捕获方法

针对直扩系统中长PN码同步捕获速度慢的问题,利用推导的串接短PN码与长PN码具有相似相关性的结论,对直扩系统中PN码同步捕获的并行匹配滤波捕获方法进行改进,得到了简单可行的串并结合捕获方法。然后,结合一个周期内PN码相关值,采用迭代的方式,选取简单、实用的自适应门限,实现了突发通信中PN码的快速同步捕获。采用该自适应门限的捕获方法无需估计噪声,计算量小。仿真实验表明所提方法捕获概率高,抗噪性能强。     

一种基于二分试探法的相干扩频快捕系统

利用辅助序列与接收PN码的线性相关性,在搜索方向判决准确的前提下,折半的查找范围对应折半的误差范围,达到应用二分法大步进缩小查找范围,从而有效的加快捕获速度,与常规步进滑动相关法相比,该捕获系统能够有效改善长PN码的捕获性能。     

Adaptive PN code acquisition using instantaneous power-scaled detection threshold under Rayleigh fading and pulsed Gaussian noise jamming

An adaptive serial search pseudonoise (PN) code acquisition scheme is proposed, in which the detection threshold is scaled by the instantaneous received power measured prior to PN code correlation. We observe that the proposed scheme achieves significantly improved mean acquisition times compared to the conventional nonadaptive schemes under Rayleigh fading and pulsed Gaussian noise jamming. Furthermore, the proposed scheme is shown to be optimum under pulsed Gaussian noise jamming in the sense that it forces the worst case jamming fraction to unity.     

A coherent acquisition method for a PN sequence using binary searchand an auxiliary sequence

Direct sequence spread spectrum systems require a local replica of the pseudonoise (PN) sequence to be synchronized with the received signal's spreading code. A method is proposed to improve the PN sequence acquisition time and decrease the acquisition time variability. The proposed method is based on a binary search algorithm. At each stage of the algorithm, an auxiliary signal is used to formulate a new search region within the PN sequence, and at each stage the search region is reduced by half. The region containing the incoming PN phase is therefore obtained within O(log₂ (N+1)) steps. A closed loop coherent PN acquisition algorithm presented by Salih and Tantaratana (1996) motivated the use of the auxiliary signal, and the algorithm of Salih et al. is also used for comparison. Results indicate the algorithm presented in this paper can achieve a factor of two to three times improvement in the mean acquisition time with a significant decrease in the acquisition time variability     

基于分段相关－视频积累方法的多驻留伪码捕获系统优化设计

针对载波多普勒下的伪码捕获问题,分析了基于分段相关-视频积累方法的多驻留伪码捕获系统的最优性能。推导了正交双通道检测器的检测概率和虚警概率表达式,给出了多驻留系统的捕获时间均值表达式;通过采用遗传算法对系统进行优化设计,增大了系统的多普勒容限,降低了捕获时间;分析了驻留级数、多普勒和载噪比等对捕获系统性能的影响。研究成果可用于指导扩频系统接收机伪码捕获模块的设计。     

一种面向深空测距的大多普勒频偏信号捕获算法

在深空测距任务中,高精度的伪码捕获是后续执行伪码跟踪的关键前提.传统基于时频二维搜索的频偏估计算法对于深空测距中频率偏移范围较大的情况难以满足伪码捕获实时性要求.为此,提出了改进的时频二维搜索算法,通过在传统时频二维搜索算法的前端引入快速傅里叶变换(Fast Fourier Transform,FFT)算法对多普勒频偏...     

A new approach to rapid PN code acquisition using iterative message passing techniques

Iterative message passing algorithms on graphs, which are generalized from the well-known turbo decoding algorithm, have been studied intensively in recent years because they can provide near-optimal performance and significant complexity reduction. In this paper, we demonstrate that this technique can be applied to pseudorandom code acquisition problems as well. To do this, we represent good pseudonoise (PN) patterns using sparse graphical models, then apply the standard iterative message passing algorithms over these graphs to approximate maximum-likelihood synchronization. Simulation results show that the proposed algorithm achieves better performance than both serial and hybrid search strategies in that it works at low signal-to-noise ratios and is much faster. Compared with full parallel search, this approach typically provides significant complexity reduction.