Estimation of the inter-frequency clock bias for the satellites of PRN25 and PRN01

We present two efficient approaches,namely the epoch-differenced(ED) and satellite-and epoch-differenced(SDED) approaches,for the estimation of IFCBs of the two Block IIF satellites.For the analysis,data from 18 stations from the IGS network spanning 96 d is processed.Results show that the IFCBs of PRN25 and PRN01 exhibit periodical signal of one orbit revolution with a magnitude up to 18 cm.The periodical variation of the IFCBs is modeled by a sinusoidal function of the included angle between the sun,earth and the satellite.The presented model enables a consistent use of L1/L2 clock products in L1/L5-based positioning.The algorithm is incorporated into the MGPSS software at SHAO(Shanghai Astronomical Observatory,Chinese Academy of Sciences) and is used to monitor the IFCB variation in near real-time.

Developing an Innovative High-precision Approach to Predict Medium-term and Long-term Satellite Clock Bias

A new prediction method based on the nonlinear autoregressive model is proposed to improve the accuracy of medium-term and long-term predictions of Satellite Clock Bias(SCB).Forecast experiments for three time periods were implemented based on the precision SCB published on the International GNSS Server(IGS)server.The results show that the medium-term and long-term prediction accuracy of the proposed approach is significantly better compared to other traditional models,with the training time being much shorter than the wavelet neural network model.

Clock-based RAIM method and its application in GPS receiver positioning

Because the signals of global positioning system （GPS） satellites are susceptible to obstructions in urban environment with many high buildings around, the number of GPS useful satellites is usually less than six. In this case, the receiver autonomous integrity monitoring （RAIM） method earmot exclude faulty satellite. In order to improve the performance of RAIM method and obtain the reliable positioning results with five satellites, the series of receiver clock bias （RCB） is regarded as one useful satellite and used to aid RAIM method. From the point of nonlinear series, a grey-Markov model for predicting the RCB series based on grey theory and Markov chain is presented. And then the model is used for aiding RAIM method in order to exclude faulty satellite. Experimental results demonstrate that the prediction model is fit for predicting the RCB series, and with the clock-based RAIM method the faulty satellite can be correctly excluded and the positioning precision of GPS receiver can be improved for the case where there are only five useful satellites.

基于不同模糊度固定产品的PPP-AR定位性能评估

基于CODE、GFZ、CNES、武汉大学PRIDE实验室和内部估计的模糊度固定产品,从收敛时间、首次固定时间及定位精度等方面进行PPP-AR固定性能的研究。实验选用2022年40个IGS测站7 d的观测数据和各模糊度固定产品配套使用的精密产品,结果表明,在置信度为95%的静态解算模式下,5种产品在解算时间为1 h时固定解较浮点解定位精度提升最明显,分别提升46.58%(3.4 cm)、41.10%(3.0 cm)、45.21%(3.3 cm)、34.25%(2.5 cm)和41.10%(3.0 cm)。仿动态解算模式下,5种产品E、N方向的定位精度都能达到mm级,U方向较浮点解精度提升较小,其中使用GBM产品的精度提升最小,E、N、U方向分别提高72.73%(2.4 cm)、47.37%(0.9 cm)、5.41%(0.2 cm);提升效果较好的是WUM和COM产品,分别为81.82%(2.7 cm)、63.16%(1.2 cm)、24.32%(1.1 cm)和81.82%(2.7 cm)、63.16%(1.2 cm)、15.58%(0.8 cm)。

Impact of receiver inter-frequency bias residual uncertainty on dual-frequency GBAS integrity

Dual-Frequency Ground-Based Augmentation Systems(GBAS)can be affected by receiver Inter-Frequency Bias(IFB)when Ionosphere-Free(Ifree)smoothing is applied.In the framework of the proposed GBAS Approach Service Type F(GAST-F),the IFB in the Ifree smoothed pseudorange can be corrected.However,IFB residual uncertainty still exists,which may threaten the integrity of the system.This paper presents an improved algorithm for the airborne protection level considering the residual uncertainty of IFBs to protect the integrity of dual-frequency GBAS.The IFB residual uncertainty multiplied by a frequency factor is included in the Ifree protection level together with the uncertainty of other error sources.To verify the proposed protection level algorithm,we calculate the IFB residual uncertainties of ground reference receivers and user receiver based on BDS B1I and B3I dual-frequency observation data and carry out a test at the Dongying Airport GBAS station.The results show that the proposed Ifree protection level with IFB residual uncertainty is 1.48 times the current protection level on average.The probability of Misleading Information(MI)during the test is reduced from 3.2×10^(-4)to the required value.It is proven that the proposed protection level can significantly reduce the integrity risk brought by IFB residual uncertainty and protect the integrity of dual-frequency GBAS.

论精密单点定位整周模糊度解算的不同策略

由于GPS非差相位观测值的相位偏差(initial phase biases,IPB)与整周模糊度难以分离,精密单点定位(PPP)估值均为模糊度浮点解。首先对GPS原始观测方程的秩亏问题进行分析,从参数整合的角度,推导卫星IPB估计的满秩函数模型,形成一种新的PPP-AR算法。以此为基础,对已有两种算法的特点进行对比分析。研究表明,分解法是一种观测信息的最优利用,且与传统的星钟估计方法具有一致性,但未发掘卫星IPB较为稳定的有利约束;非整法对所采用的组合观测值之间的相关性未加考虑,是一种次优估计,实时性较差,且较依赖于高精度的码观测。推导的新算法可有效克服已有算法的不足,便于施加部分参数的合理时变性约束,提高卫星IPB估计的可靠性。

一种采用常跨导偏置技术的高速多相时钟发生器

介绍了一种基于电荷泵型锁相环的高速多相时钟发生器。采用常跨导偏置技术,使锁相环的频率响应对工艺、电源电压和温度的变化不敏感;在压控振荡器中采用镜像偏置,使该时钟发生器无需外部精确的偏置电压或电流。电路采用UMC0.18μmN阱CMOS工艺实现。仿真结果显示,在SSS、TTT和FFF三种条件下,环路带宽变化仅为12%,相位裕量只变化0.1°。

高速CMOS钟控比较器的设计

基于预放大锁存理论,设计了一种高速钟控比较器,它包括三个主要部分:预放大器、判断级电路、输出缓冲器。在SMIC 0.18μm CMOS工艺模型和1.8 V电源电压下,采用Hspice对比较器电路进行仿真,结果表明在500 MHz的时钟频率下,精度可达0.3 mV,功耗仅为26.6μW。该电路可以应用在高速Flash ADC电路中。

改进的非组合精密单点定位模型(MPPP)与实时授时研究

【目的】基于精密单点定位(Precise Point Positioning,PPP)的时间传递技术因其高精度、广覆盖而成为GNSS时间传递中的优势性方法。然而,实践过程中发现接收机码偏差天内短时变化是影响接收机钟差估值精准度的主要偏差之一。【方法】因此,本文提出了一种改进的非组合精密单点定位(Modified Precise Point Positioning,MPPP)模型,将接收机码偏差作为时变参数估计,并基于模拟与实测数据进行了方法验证。【结果】结果表明:同等条件下,MPPP授时精度可达0.1~1ns,相较于PPP精度提升30%以上,【结论】可有效克服接收机码偏差变化对实时授时的影响。

Estimation of fractional cycle bias for GPS/BDS-2/Galileo based on international GNSS monitoring and assessment system observations using the uncombined PPP model

The Fractional Cycle Bias(FCB)product is crucial for the Ambiguity Resolution(AR)in Precise Point Positioning(PPP).Different from the traditional method using the ionospheric-free ambiguity which is formed by the Wide Lane(WL)and Narrow Lane(NL)combinations,the uncombined PPP model is flexible and effective to generate the FCB prod-ucts.This study presents the FCB estimation method based on the multi-Global Navigation Satellite System(GNSS)precise satellite orbit and clock corrections from the international GNSS Monitoring and Assessment System(iGMAS)observations using the uncombined PPP model.The dual-frequency raw ambiguities are combined by the integer coefficients(4,−3)and(1,−1)to directly estimate the FCBs.The details of FCB estimation are described with the Global Positioning System(GPS),BeiDou-2 Navigation Satellite System(BDS-2)and Galileo Navigation Satellite System(Galileo).For the estimated FCBs,the Root Mean Squares(RMSs)of the posterior residuals are smaller than 0.1 cycles,which indicates a high consistency for the float ambiguities.The stability of the WL FCBs series is better than 0.02 cycles for the three GNSS systems,while the STandard Deviation(STD)of the NL FCBs for BDS-2 is larger than 0.139 cycles.The combined FCBs have better stability than the raw series.With the multi-GNSS FCB products,the PPP AR for GPS/BDS-2/Galileo is demonstrated using the raw observations.For hourly static positioning results,the performance of the PPP AR with the three-system observations is improved by 42.6%,but only 13.1%for kinematic positioning results.The results indicate that precise and reliable positioning can be achieved with the PPP AR of GPS/BDS-2/Galileo,supported by multi-GNSS satellite orbit,clock,and FCB products based on iGMAS.

应用于FPGA芯片时钟管理的锁相环设计实现

设计了一种嵌入于FPGA芯片的锁相环,实现了四相位时钟、倍频、半整数可编程分频、可调节相位输出功能,满足对于FPGA芯片时钟管理的要求.锁相环采用了自偏置结构,拓展了锁相环的工作范围,缩短了锁定时间,其阻尼系数以及环路带宽和工作频率的比值都仅由电容的比值决定,有效地减小了工艺、电压、温度等对电路的影响.锁相环采用0.18μm CMOS数字工艺,嵌入复旦大学自主研发的FPGA芯片FDP-Ⅱ,经过流片验证,实现了工作频率范围10~600 MHz,整体电路功耗仅为29 mW,锁定时间小于4μs,峰峰值抖动小于±145 ps.

Extraction of line-of-sight ionospheric observables from GPS data using precise point positioning

Here we propose a method for extracting line-of-sight ionospheric observables from GPS data using precise point positioning(PPP).The PPP-derived ionospheric observables(PIOs) have identical form with their counterparts obtained from leveling the geometry-free GPS carrier-phase to code(leveling ionospheric observables,LIOs),and are affected by the satellite and receiver inter-frequency biases(IFBs).Based on the co-location experiments,the effects of extracting error arising from the observational noise and multipath on the PIOs and the LIOs are comparatively assessed,and the considerably reduced effects ranging from 70% to 75% on the PIOs with respect to the LIOs can be verified in our case.In addition,based on 26 consecutive days' GPS observations from two international GNSS service(IGS) sites(COCO,DAEJ) during disturbed ionosphere period,the extracted PIOs and LIOs are respectively used as the input of single-layer ionospheric model to retrieve daily satellite IFBs station-by-station.The minor extracting errors underlying the PIOs in contrast to the LIOs can also be proven by reducing day-to-day scatter and improving between-receiver consistency in the retrieved satellite IFBs values.

Multi-GNSS products and services at iGMAS Wuhan Innovation Application Center:strategy and evaluation

Over the past years the International Global Navigation Satellite System(GNSS)Monitoring and Assessment System(iGMAS)Wuhan Innovation Application Center(IAC)dedicated to exploring the potential of multi-GNSS signals and providing a set of products and services.This contribution summarizes the strategies,achievements,and innovations of multi-GNSS orbit/clock/bias determination in iGMAS Wuhan IAC.Both the precise products and Real-Time Services(RTS)are evaluated and discussed.The precise orbit and clock products have comparable accuracy with the precise products of the International GNSS Service(IGS)and iGMAS.The multi-frequency code and phase bias products for Global Positioning System(GPS),BeiDou Navigation Satellite System(BDS),Galileo navigation satellite system(Galileo),and GLObal NAvigation Satellite System(GLONASS)are provided to support multi-GNSS and multi-frequency Precise Point Positioning(PPP)Ambiguity Resolution(AR).Compared with dual-frequency PPP AR,the time to first fix of triple-frequency solution is improved by 30%.For RTS,the proposed orbit prediction strategy improves the three dimensional accuracy of predicted orbit by 1 cm.The multi-thread strategy and high-performance matrix library are employed to accelerate the real-time orbit and clock determination.The results with respect to the IGS precise products show the high accuracy of RTS orbits and clocks,4–9 cm and 0.1–0.2 ns,respectively.Using real-time satellite corrections,real-time PPP solutions achieve satisfactory performance with horizontal and vertical positioning errors within 2 and 4 cm,respectively,and convergence time of 16.97 min.