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针对低信噪比条件下,罗兰C天波信号延迟时间估计的准确性和有效性问题,提出基于优化包络的相关系数时域法。通过分析标准罗兰C信号包络的特征,分别采用微分和二次微分方法对罗兰C信号包络进行优化,形成陡峭的包络信号上升沿;利用相关系数法对接收信号包络和参考信号包络进行匹配,形成的匹配峰值分别对应地波和天波信号到达的时刻,由此可获得天波信号的延迟时间;通过仿真分析和实测信号试验验证,证明该方法能满足数字化接收机的实际要求,并具有更高的抗干扰能力、估计准确性和自动识别功能的特点。估计的结果还可以作为判别相位跟踪和周期识别正确率的辅助依据。 相似文献
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为了降低卫星导航的使用风险,美国和一些导航大国都积极加强其陆基无线电导航系统特别是罗兰C系统的进一步研究。这说明在开发应用卫星导航系统的同时,还必须继续发展陆基无线电导航系统。因此,我国在大力发展双星导航系统的同时,还应继续加强罗兰C系统的研究,积极开发双星/罗兰C组合导航的潜力。对双星/罗兰C组合导航技术的数据组合方法进行介绍,比较了不同组合方式的导航精度及工作性能。 相似文献
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中国区域导航定位系统(CAPS)是我国一种具有自主知识产权的新型卫星导航系统.基于卫星转发地面产生的导航信号的工作模式,实现卫星导航功能.导航综合基带是CAPS主控站的重要终端设备.利用无线电软件设计思想,设计了导航综合基带总体架构.采用标准面向仪器系统的PCI扩展(PXI)机箱结构,基于总线设计,可扩展性强.基带的关键技术包括发射信号的频率补偿技术,高精度接收技术,设备高稳定时延保持技术.实际测试结果表明:该导航综合基带性能良好,伪码测量精度优于0.20 ns,通道时延稳定度优于0.25 ns,频率补偿精度优于0.8 Hz,满足CAPS的需求. 相似文献
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将GPS的卫星接收仪与左旋与右旋极化天线结合,接收来自水面微弱的GPS反射信号,并对该信号进行提取和分析。同时应用右旋圆极化及左旋圆极化天线分别接收GPS发射和反射信号,并微调接收天线提高GPS正、反信号的分辨率,获得天线的有效接受频率范围及近似的方位,根据几何方法,进一步利用各卫星与接收仪天线所在位置形成的投影,反推计算所接收各组微弱反射信号的虚拟地面及水面发射点。通过对比信号强度、时间修正延迟量、大气修正延迟量,完成求解反射点的位置与高度,在利用这些精确的高度数据,反推波形模式、波浪特性与形态,为河海与港湾工程及潮汐观测提供有效依据。 相似文献
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卫星导航信号模拟源为用户终端设备的设计、验证、测试提供输入信号源,是用户终端设备研发和卫星导航信号系统验证的重要工具.早期的射频合成技术产生的信号的精度和通道一致性较差,随后的模拟中频合成技术存在通道间偏差的问题,而目前常用的数字中频合成技术存在相位抖动问题,所以本文基于PXI Express(PXIe)总线的软件无线电架构,设计并实现了一款采用数字基带合成技术的软硬件结合模拟源.模拟源上位机数学仿真软件采用图形化编程语言LABVIEW开发,实现简单,开发效率高,最终生成数字基带合成信号;模拟源硬件则使用美国国家仪器公司(NI)模块化的虚拟仪器,接收并处理上位机产生的数字基带合成信号,最终产生用户终端设备可以接收的全球定位系统(GPS)射频信号.利用频谱分析仪观察模拟源输出信号的频率和带宽,验证了GPS模拟源仿真信号的正确性;利用商用接收机进行定位解算,分析静态和动态场景下的信号质量、定位结果及三轴定位误差,验证了GPS模拟源仿真信号的准确性和有效性. 相似文献
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A major challenge in using GPS guidance for aircraft final approach and landing is to reject interference that can jam reception
of the GPS signals. Antenna arrays, which use space–time adaptive processing (STAP), significantly improve the signal to interference
plus noise ratio, but at the possible expense of distorting the received signals, leading to timing biases that may degrade
navigation performance. Rather than a sophisticated calibration approach to remove biases introduced by STAP, this paper demonstrates
that a relatively compact calibration strategy can substantially reduce navigation biases, even under elevated interference
conditions. Consequently, this paper develops an antenna bias calibration strategy for two classes of adaptive array algorithm
and validates this method using both simulated and experimental data with operational hardware in the loop. A proof-of-concept
system and an operational prototype are described, which implement the adaptive antenna algorithms and deterministic corrections.
This investigation demonstrates that systems with adaptive antenna arrays can approach the accuracy and integrity requirements
for automatic aircraft landing, and in particular for sea-based landing on board aircraft carriers, while simultaneously providing
significant attenuation of interference. Evidence suggests that achieving these goals is possible with minimal restrictions
on system hardware configuration—specifically, limitations on the permissible level of antenna anisotropy and the use of sufficient
analog-to-digital converter resolution. 相似文献
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Metop-GRAS in-orbit instrument performance 总被引:2,自引:1,他引:1
The GRAS instrument on the Metop-A satellite provides more than 600 radio occultation measurement profiles per day. The instrument
is characterized by its wide antenna coverage, high signal-to-noise ratio and an ultra-stable clock reference. The conventional
dual-frequency tracking of GPS signals is under dynamic atmosphere conditions complemented by open loop tracking with sampling
of the signal at a 1 kHz rate, providing an unprecedented view of the signal spectral environment. This paper presents the
instrument performance as derived from analysis of in-orbit measurement data. We show that the noise figure is low enough
to enable mapping of external radio noise variations over the earth’s surface. An error propagation model is presented to
relate instrument characteristics to bending angle performance. This model is also used to illustrate the relation between
filter bandwidth, resolution and measurement noise. The Doppler model, guiding open loop measurements, is found to be accurate
to better than 20 Hz with a possibility for improvement to 10 Hz. The high performance at low altitudes enables the presence
of surface reflections at the −20-dB level to be identified in more than 50% of the occultations. The potential performance
improvements for next generation receivers are discussed. 相似文献
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Antenna thrust is a small acceleration acting on Global Navigation Satellite System satellites caused by the transmission of radio navigation signals. Knowledge about the transmit power and the mass of the satellites is required for the computation of this effect. The actual transmit power can be obtained from measurements with a high-gain antenna and knowledge about the properties of the transmit and receive antennas as well as losses along the propagation path. Transmit power measurements for different types of GPS, GLONASS, Galileo, and BeiDou-2 satellites were taken with a 30-m dish antenna of the German Aerospace Center (DLR) located at its ground station in Weilheim. For GPS, total L-band transmit power levels of 50–240 W were obtained, 20–135 W for GLONASS, 95–265 W for Galileo, and 130–185 W for BeiDou-2. The transmit power differs usually only slightly for individual spacecraft within one satellite block. An exception are the GLONASS-M satellites where six subgroups with different transmit power levels could be identified. Considering the antenna thrust in precise orbit determination of GNSS satellites decreases the orbital radius by 1–27 mm depending on the transmit power, the satellite mass, and the orbital period. 相似文献
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In order to enhance the acquisition performance of global positioning system (GPS) receivers in weak signal conditions, a high-sensitivity acquisition scheme aided by strapdown inertial navigation system (SINS) information is proposed. The carrier Doppler shift and Doppler rate are pre-estimated with SINS aiding and GPS ephemeris, so that the frequency search space is reduced, and the dynamic effect on the acquisition sensitivity is mitigated effectively. Meanwhile, to eliminate the signal-to-noise ratio gain attenuation caused by data bit transitions, an optimal estimation of the unknown data bits is implemented with the Viterbi algorithm. A differential correction method is then utilized to improve the acquisition accuracy of Doppler shift and therefore to meet the requirement of carrier-tracking loop initialization. Finally, the reacquisition experiments of weak GPS signals are implemented in short signal blockage situations. The simulation results show that the proposed scheme can significantly improve the acquisition accuracy and sensitivity and shorten the reacquisition time. 相似文献
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载波数字振荡器(NCO)是导航接收机中对接收信号进行载波剥离处理的关键部分. 在接收机的基带数字信号处理模块中,NCO通过量化位宽和地址字长分别对本地载波信号的幅值和频率进行量化,即通过存储器数据的位宽和深度设计本地载波. 在给定输入信号/干扰动态范围下,根据本地载波的特点,优化设计了载波NCO中只读存储器(ROM)的幅值量化位宽和地址字长,使其适应实际工程需求,在保证信噪比(SNR)损耗和频率误差的条件下避免了本地载波存储的冗余. 实验结果表明:从需求出发设计导航接收机本地载波的最优位宽和深度,可保证数字下变频SNR损耗小于0.1 dB,本地载波实际输出频率相对误差小于0.1%,且最优位宽和深度小于优化前,减小了存储资源占用率,有效地提高了本地载波输出信号在动态信号和干扰下的适应性. 相似文献
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北斗卫星导航系统(BDS)极易受到空中或地面干扰的影响,信号质量因此发生改变,导航性能大大降低.评估干扰对BDS信号质量的影响,可以为干扰监测技术奠定基础.借助矢量信号源发出不同类型的干扰信号,通过时频分析设备获取其信号特性,并将干扰叠加到由高增益天线接收到的实际BDS信号中,对叠加数据进行离线处理,从频域及调制域两方面分析信号质量.结果表明:空间环境的干扰恶化了BDS信号,不同类型的干扰对信号质量影响程度不同,功率谱及星座图处理结果可作为分析干扰环境中BDS信号质量的基本依据. 相似文献
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为满足组合导航系统在高动态环境下的性能要求,设计基于矢量跟踪的GNSS/SINS相干深组合导航方法。利用矢量跟踪环路将所有可视卫星的跟踪和导航解算融为一体,增强通道间的辅助;高动态对载波跟踪影响更大,在通道预滤波中将码环载波环分别用独立的滤波器处理,组合滤波中采用通道间差分降低滤波状态维数,提高计算效率。引入惯导的加速度辅助本地信号参数预测,较精确地测量卫星视线方向的加速度,减小接收机在高动态时段的剩余动态,提高本地信号参数的预测精度。基于矢量跟踪软件接收机搭建相干深组合仿真系统,实验表明该方法在高动态等环境下能提高信号跟踪性能,改善系统的精度、可靠性。 相似文献