原子钟性能对卫星导航系统定位精度的影响分析

星载原子钟是卫星导航系统的关键设备,原子钟主要通过影响卫星钟差对定位精度产生影响,分析了GNSS星载原子钟性能对定位精度的影响.通过原理分析,建立了原子钟稳定度与卫星导航系统定位精度的关系.在不考虑控制段对星钟校准误差的前提下,将原子钟噪声与星上工作环境因素作为主要因素,分析了GPS-IIF铷钟和铯钟对钟差/定位误差的影响,并给出了分析结果.最后,利用iGMAS提供的钟差产品数据,对比了北斗和GPS部分原子钟的稳定度及其对定位精度的影响,为后续星载原子钟的发展与选择提供了一定参考.     

不同GNSS星载原子钟周期特性分析

高精度的卫星时钟修正是全球卫星导航系统实时精密单点定位和授时服务的重要基础。为了提高GNSS钟差预报精度，需要对GNSS星载原子钟的周期特性进行分析。基于2016年全年的GNSS精密卫星钟差数据，利用中位数方法进行了数据预处理，使用多项式拟合模型分析了卫星钟的拟合残差，利用频谱分析法分析了BDS、GPS卫星钟差的周期特性，全面分析了BDS、GPS星载原子钟的周期特性。分析结果表明：除Cs钟外，其他卫星钟差都表现出较好的周期特性，BDS、GPS的主周期项基本在12h、24h、6h附近；同时不同的轨道、原子钟，其钟差周期项不同，而相同的轨道类型，其钟差周期项也存在一定差异；卫星的钟差主周期分别近似为其卫星轨道周期的1/2倍、1倍、2倍。     

Characterization of NAVSTAR GPS and GLONASS on-board clocks

Investigation into navigation satellite on board clock frequency references and performance are reported. The focus is on the stability of the clocks aboard the NAVSTAR GPS (Global Positioning System) and GLONASS satellites as well as those used by their respective maser control stations and associated time scales. Allan-variance techniques have been applied to determine the long-term time-domain behavior of satellite clocks in an attempt to identify different regions of power spectral density. Coupled with analysis of relative-frequency drift over a period of many weeks, this behavior allows the type of satellite onboard standard to be tentatively identified. The known nature of the GPS clocks has shown that the different types of clocks aboard the satellites (crystal, rubidium, and cesium) are distinguishable given a sufficient sample time. The same approach has been applied to the GLONASS satellites, and a comparison of the results obtained from GPS has allowed conjecture on the type of clock used by the GLONASS satellites. It appears that GLONASS has used clocks of the quality of rubidium atomic oscillators since at least 1986, and that the quality and performance of onboard standards have increased steadily with time. Some current satellites perform well enough in terms of frequency drift, flicker FM noise floor, and long-term stability to compare favorably with the cesium beam standards carried on NAVSTAR GPS satellites launched in 1983-84     

Frequency steering of spaceborne clocks based on XPNAV-1 observations

Due to high stable rotations, timing of pulsars provides a natural tool to correct the frequency deviation of spaceborne atomic clocks. Based on processing the observational data about a year of Crab pulsar given by XPNAV-1 satellite, we study the possibility of correcting the frequency deviation of spaceborne atomic clocks using pulsar timing. According to the observational data in X-ray band and the timing model parameters from radio observations, the pre-fit timing residuals with a level of 6...     

Galileo卫星星钟故障前后信号质量分析

星载原子钟是卫星导航系统的核心器件,是影响导航信号质量的重要因素。2016年11月,Galileo系统利用一箭四星发射升空4颗新一代Galileo卫星。根据观测显示,截至2017年7月,仅能接收到其中1颗卫星发射的导航信号。在2017年1月,欧洲航天局通告称多颗卫星原子钟大规模故障。针对此,40m 大口径高增益天线系统设备对不同批次和星钟故障情况的3颗Galileo卫星E5频点信号进行了数据采集处理,对各信号分量的功率谱、星座图、码片波形、相关损失、相关峰、S曲线偏差等信号质量指标进行了分析评估。结果表明,此次星载原子钟的大面积故障并未影响Galileo卫星信号的可用性,足够的星载备份钟避免了信号质量的严重恶化。     

磁场对冷镱原子光钟稳定度影响的仿真分析

在光晶格钟运行时，不停起伏的杂散磁场会引入一阶塞曼频移和二阶塞曼频移，从而影响光晶格钟的频率不稳定度。此外，突变的磁场可能导致激光频率参考到钟跃迁频率的伺服闭环过程发生不可恢复的失锁，从而阻碍光钟的持续运行。在实验中，光钟进行频率闭环锁定前，通常通过控制三维线圈对光钟主腔中心原子处的杂散磁场进行补偿。首先使用三维磁强计，对真空主腔附近的磁场进行监测和记录，以分析杂散磁场对光钟性能的影响。然后利用正态分布模型和二项分布模型等，对光钟频率伺服锁定过程的阿伦偏差进行仿真拟合。在引入实际磁场监测数据的基础上，模拟光钟频率的伺服锁定过程，分析其仿真结果可以得出：减小杂散磁场起伏和控制磁场漂移，在提高冷镱原子光钟的短期稳定性和长期稳定性方面具有重要意义。     

Receiver clock-based integrity monitoring for GPS precision approaches

The errors in the vertical position and clock bias estimates obtained from GPS pseudo-range measurements are highly correlated. Therefore, the error in a vertical position estimate can be predicted if we know the clock bias estimation error. The latter can be estimated if the clock bias changes smoothly and, therefore, predictably. The current technology appears capable of manufacturing clocks which can meet this smoothness requirement for airborne use within the constraints of size, weight, and cost. We discuss the theoretical basis and present empirical data from laboratory and field experiments with a commercial rubidium standard to explore the benefits of integrity monitoring for precision approaches based on the receiver clock.     

光抽运小铯钟及其在PNT应用

对比分析了大小铯原子钟及其在PNT中的应用,在此基础上介绍了基于光抽运技术方案实现的国际上第一台商用小铯钟。在研制原理样机和工程样机的过程中,解决了激光稳频、铯束准直等关键技术和工作温度、振动、EMC等环境难题,技术状态满足小批量生产要求,频率稳定度可达10-15,频率准确度优于10-12,技术指标达到国际同类小铯钟5071A水平。分析了光抽运小铯钟作为守时原子钟如何应用于时间频率基准实验室、数字通信同步网、卫星导航地面站、长波导航路基站等PNT体系。     

运输类直升机仪表飞行规则下的设备和系统的适航验证方法研究

直升机按照驾驶和领航条件可划分为目视飞行规则和仪表飞行规则。我国现有已取得型号合格证的直升机大都是目视飞行规则,使用受限制较多。综合分析了直升机仪表飞行规则的适航要求,提出验证方法以及在AC313型机的验证结果,对直升机申请仪表飞行规则以及目视飞行规则升级到仪表飞行规则具有一定的指导意义,对新型号研制也具有参考价值。     

Experiments with numerically controlled atomic clocks

Long term timing stability of present atomic clocks can be considerably improved by simple numerical algorithms which correct both the inherent frequency bias and the effects of supply voltage variations and outside temperature. Rubidium units are demonstrated to operate with less than 100 ns errors per week or any sensible longer interval corresponding to relative uncertainties of 10^-13. Often a linear subtraction of frequency offset which can be realized by a microprocessor controlled digital delay line is sufficient. A cesium clock could be run at 10^-15 level, but reliable and reasonable real-time measurement techniques do not yet exist     

The time delay of a solar grazing photon

Moving clocks and clocks in a gravitational field slow down, not due to the effects of special relativity nor to the space-time curvature of general relativity, but due only to the principle of equivalence and the conservation of energy. However, some might argue that there has been a further “test” of the effect of gravity on time, namely, the measurement of the time-delay of a round-trip, solar-grazing radar beacon performed by Shapiro in the 1960s. In this test, Shapiro bounced a radar pulse off Mars at superior conjunction (a feat in itself for the time), and compared the measured round-trip travel time of this pulse with the expected round-trip time of a signal traveling at c for the entire trip, as determined from highly accurate planetary ephemerides. Shapiro had predicted this time-delay long before being technologically able to make such a measurement. While general relativity can be used to correctly obtain the magnitude of this delay, it is not the only explanation. As earlier with the analysis of clocks in motion and of clocks in a gravitational field, this paper derives the same result without invoking the space-time curvature of general relativity     

差分码偏差对PPP授时精度影响的研究

论文分析了不同机构差分码偏差(DCB)产品的天稳性.选取了2个外接氢原子钟的测站进行实验,以国际GNSS服务组织(IGS)发布的接收机钟差为参考值,分析了不同机构DCB产品对2个测站PPP授时精度的影响.实验结果表明:1)不同机构DCB产品的天稳性差异不大,中国科学院天稳性略优于德国宇航中心;2)2个测站使用不同机构的DCB产品估计钟差的均方差(RMS)和时间偏差(Bias)均优于0.4ns,其中中国科学院产品精度最高,RMS和Bias均优于0.2ns;德国宇航中心和欧洲定轨中心精度略差,但也能够达到亚纳秒级,可为下一步推广PPP授时应用提供一定的参考.     

导航星座的自主导航技术--卫星自主时间同步

基于星载原子时钟频率稳定性的Allan方差表达,建立系统状态方程,并以星间双向测量伪距差作为基本观测量,组成系统测量方程,从而可以设计适用于导航星座卫星时间同步的Kalman滤波算法。系统仿真结果表明：通过对星间双向测量数据的滤波处理,能够实现星座卫星时间精密同步。     

Space time clock: An on-chip clock with 10−12 instability

High precision and stable clock is extremely important in communication and navigation. The miniaturization of the clocks is considered to be the trend to satisfy the demand for 5G and the next generation communications. Based on the concept of meter bar and the principle of the constancy of light velocity, we designed a micro clock, Space Time Clock (STC), with the size smaller than 1 mm × 1 mm and the power dissipation less than 2 mW. Designed in integrated circuit of 0.18 μm technology, the instability of STC is assessed to be 2.23 × 10^?12 and the trend of the instability is reversely proportional to τ. With the potential ability to reach the level of 10^?16 instability on chip in the future, the period of the STC’s signal is locked on the delay time defined by the meter bar which keeps the time reference constant. Because of its superior performance, the STC is more suitable for mobile communication, PNT (Positioning, Navigation and Timing), embedded processor and deep space application, and becomes the main payload of the ASRTU satellite scheduled to launch next year and investigate in space environment.     

GNSS实时卫星钟差估计技术进展

不依赖实体基准站增强信息的GNSS实时精密单点定位服务将逐渐成为主流定位模式。实时卫星钟差产品作为实时精密单点定位的关键先决条件之一，其精度直接决定实时精密定位服务的性能。计算实时卫星钟差的GNSS实时卫星钟差估计技术成为实时精密定位的核心技术之一，其主要包括两种解算模式：非差解算模式和差分解算模式。由于对卫星模糊度等未知参数处理策略的不同，卫星钟差估计技术又可细分为非差、历元差分、星间差分、混合差分等策略类型。针对不同实时卫星钟差估计技术的原理方法、算法效率、适用性等问题，综合目前已有相关研究成果的基础上，对GNSS实时卫星钟差估计的研究现状、关键技术和面临的挑战进行了较为系统的总结综述，并对未来卫星钟差预报产品和实时估计产品的关系进行了展望。     

Pulsar Timing and Its Application for Navigation and Gravitational Wave Detection

Pulsars are natural cosmic clocks. On long timescales they rival the precision of terrestrial atomic clocks. Using a technique called pulsar timing, the exact measurement of pulse arrival times allows a number of applications, ranging from testing theories of gravity to detecting gravitational waves. Also an external reference system suitable for autonomous space navigation can be defined by pulsars, using them as natural navigation beacons, not unlike the use of GPS satellites for navigation on Earth. By comparing pulse arrival times measured on-board a spacecraft with predicted pulse arrivals at a reference location (e.g. the solar system barycenter), the spacecraft position can be determined autonomously and with high accuracy everywhere in the solar system and beyond. We describe the unique properties of pulsars that suggest that such a navigation system will certainly have its application in future astronautics. We also describe the on-going experiments to use the clock-like nature of pulsars to “construct” a galactic-sized gravitational wave detector for low-frequency (\(f_{GW}\sim 10^{-9} \text{--} 10^{-7}\) Hz) gravitational waves. We present the current status and provide an outlook for the future.     

时钟模型辅助的惯性/卫星紧组合导航算法研究

针对卫星信号受到遮挡或者干扰、卫星接收机收星数不足的问题,提出了一种时钟模型辅助的惯性/卫星紧组合导航算法。通过正常紧组合状态下的钟差、钟漂估计值建立钟差和钟漂的数学模型,在可见卫星少于4颗时,用时钟模型计算得到的钟差和钟漂作为系统钟差、钟漂的真实值引入观测信息中,并省去状态变量中的钟差和钟漂项,增加了系统的可观测性。最后,通过采集跑车试验数据进行了离线数据仿真试验。试验结果表明,提出的时钟模型辅助的惯性/卫星紧组合导航算法在可见卫星不足的情况下取得了良好的效果。     

Comparison of Bit Synchronization Schemes Using AM and Summed Clocks

This paper considers bit synchronization through the use of a separate clock signal which is either amplitude modulated onto or summed with the data signal. For continuous data transmission, such schemes are known to be inferior, in the sense of efficient use of power, to schemes which derive synchronization directly from the data signal. However, these techniques have application in burst systems such as spacecraft command systems, and in systems where receiver simplicity is more important than power conservation. For systems in which the composite data-clock signal subsequently modulates an RF carrier, it is shown that the summed clock signal performs slightly better than the AM clock signal, and that for both signal types, the optimum allocation of power between data and clock is approximately 9:1.     

芯片原子钟的工作原理及其研究进展

作为导航设备的重要部件,芯片原子钟可作为战术导弹、卫星接收机、小型无人机等所用导航设备的时钟源,也可与陀螺仪和加速度计组合实现微型定位、导航与授时。介绍了相干布局囚禁(Coherent Population Trapping, CPT)现象,以及芯片原子钟的发展历程,阐述了CPT实现方案的缺点(产生极化暗态、降低原子利用率),并给出了优化方案。此外,分析了微机电系统(Micro Electro Mechanical System, MEMS)加工工艺等用于芯片原子钟制造的关键技术,并对芯片原子钟的发展趋势进行了展望。