Differential Code Bias (DCB) is the time delays between two different GNSS signals, which is crucial for GNSS positioning. Previous studies have shown that it can be significantly affected by the flex power operations in satellites. This study proposes a 15-min short-term DCB estimation method to analyze flex power's impact on DCB variations. The method jointly estimates satellite DCB, receiver DCB, and ionospheric parameters using over 300 MGEX stations. We examined three representative flex power events in 2024, achieving average internal RMS values of 0.042 ns and 0.0068 ns for inter-frequency and intra-frequency scenarios respectively. Results show that intra-frequency DCB exhibits clear shift biases synchronized with flex power state transitions while maintaining stability within 0.20 ns during non-transition periods. No definitive impact on inter-frequency DCB was observed at current estimation precision levels.

The third-generation BeiDou Navigation Satellite System (BDS-3) has commenced global service, establishing a service architecture characterized by ‘global coverage, regional enhancement, and distinct features,’ which deeply integrates navigation and communication capabilities to provide users worldwide and regionally with diverse, specialized services. This paper systematically reviews the key theoretical and technological innovations of BDS-3; clarifies the operational principles and coverage areas of its global and regional services. In light of the onset of the 25th solar cycle maximum, a comprehensive evaluation of the performance metrics of various BDS-3 services is conducted based on data and products from the International GNSS Monitoring and Assessment System (iGMAS) in 2024, along with findings from recent relevant publicly available literature. Additionally, current research hotspots and key directions are summarized, offering valuable references for the technological evolution and development of global satellite navigation systems in the future..

With the rapid development of low Earth orbit (LEO) constellations for navigation, using LEO satellites to augment the global navigation satellite system (GNSS) has become an effective method for enhancing positioning performance. In LEO navigation augmentation systems, constellation design is a multi-objective optimization problem that must trade off positioning performance against overall cost. To mitigate the particle swarm optimization (PSO) algorithm's tendency to converge to local optima, this study develops an adaptive genetic algorithm-PSO (AGA-PSO) framework tailored to the multi-objective design of LEO constellations for precise point positioning (PPP) augmentation. The proposed algorithm optimizes key orbital parameters-including the number of satellites, orbital altitude, and orbital inclination-while considering both navigation performance and system cost, to determine the optimal configuration. Simulation experiments were conducted to evaluate the performance of the optimized LEO constellation in augmenting GNSS. The results demonstrate that the improved AGA-PSO framework achieves higher optimization efficiency, avoids local optima more effectively, and yields a constellation with significantly improved navigation performance compared to the PSO. Utilizing LEO satellites substantially reduces the three-dimensional positioning error for both single- and multi-GNSS PPP solutions and markedly shortens the convergence time. These findings confirm the feasibility and effectiveness of LEO navigation augmentation in enhancing GNSS PPP performance and highlight its considerable potential for improving precise positioning capabilities.

Flex power is a capability of GNSS satellites that enables programmable output power redistribution. Detecting these changes is crucial, as they significantly influence the satellite hardware-related bias estimation and positioning accuracy. Previous methods rely on the baseline modeling of historical data for difference detection or on using sliding window approaches to capture step edges. These detection methods need either amount of labeled data or are time-consuming. We propose a novel flex power detection method, Adaptive Flex Power Detector–Dynamic Time Warping (AFPD-DTW), based on inter-day differences. Taking advantage of the Dynamic Time Warping (DTW), it addresses the temporal misalignment caused by GNSS orbital periodicity based on diurnal patterns in carrier-to-noise density ratio (C/N0). Our method requires as few as eight stations to achieve high accuracy in both post-processing (99.83 https://github.com/BlackiePiggy/AFPD.git ).

In recent years, the flex power of the global positioning system (GPS) Block IIR-M and Block IIF satellites has frequently been activated and deactivated. Ground-based GPS flex power monitoring faces several challenges, including uneven receiver distribution, multipath error arising from complex environments, and significant fluctuations in low-elevation carrier-to-noise ratio data. To overcome these challenges, we propose a novel GPS flex power detection method by introducing a detection metric, CN0el. Spaceborne receiver data from 15 low earth orbit (LEO) satellites and historical data from February 2022 to December 2023 are utilized to train an extreme gradient boosting (XGBoost) machine learning model. The detection model achieves an accuracy exceeding 99

The navigation signal received by the Inclined Geo-Synchronous Orbit (IGSO) satellite is often blocked by the Earth, and the signal strength is weak due to the long propagation distance, which makes the carrier phase data processing complicated. Using pseudorange data is a convenient and efficient method for determining the orbit of IGSO satellites. Code hardware delays are non-negligible errors in pseudorange data processing. This study investigates the precise orbit determination (POD) result using only pseudorange data corrected by four types of Differential Code Bias (DCB) products and Observable-specific Signal Biases (OSB) products, with the LT4A satellite as a case study. The results show that the correction of code hardware delay can effectively improve the orbit quality. After correcting the code hardware delay, using only GPS pseudorange observations, using only BDS pseudorange observations, and using GPS + BDS combined pseudorange observations to determine the orbit, the pseudorange residuals RMS are about 1.82 m, 1.09 m, and 1.53 m, respectively. Compared with the uncorrected code hardware delays results, the residuals RMS is better by 21.8 %, 79.5 %, and 53.0 %, respectively. As the length of the POD arc increases from 24 h to 72 h, both the quality and stability of the orbit are observed to improve. For the 72 h arc, the orbit overlap RMS with the three data types is 3.4 m, 3.0 m, and 2.8 m, respectively, with the improvement of about 10.5 %, 77.6 %, and 59.4 %, respectively, compared with no code hardware delays correction. Compared with the precise reference orbit, the comparison RMS are 6.3 m, 4.8 m, and 4.4 m, increased by 24.0 %, 78.9 %, and 51.6 %, respectively. The results demonstrate that the comparison RMS of the IGSO satellite with only pseudorange data can be better than 5 m in position, and correcting the code hardware delays can improve orbit quality obviously, especially for BDS pseudorange data. (c) 2024 COSPAR. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

In recent years, the Global Positioning System has commonly activated flex power, including global flex power and regional flex power. The activation and deactivation periods of satellite flex power are distinguished, and the impact of flex power on the estimation of the differential code biases (DCBs), ionospheric delays and positioning are analyzed. The results indicate that the DCBs are more stable when taking flex power into account. The impact of flex power on the inter-frequency DCBs is 0.19 ns, and on ionosphere estimation is 0.68 TECU. The impact of flex power on the intra-frequency DCBs for L1 and L2 is 0.17 ns and 0.25 ns, respectively. Single point positioning is affected by flex power in the E, N and U components by 0.04 m, 0.12 m and 0.17 m, respectively. (c) 2024 Published by Elsevier B.V. on behalf of COSPAR.

Aiming at the problem that the Cubature Kalman filter (CKF) algorithm has a non-positive definite of the covariance matrix in GNSS/SINS integrated navigation, which leads to the failure of Cholesky decomposition and the inability to estimate GNSS measurement noise, a backward smoothing adaptive CKF integrated navigation algorithm based on Singular Value Decomposition (SVD) is proposed. Backward smoothing adaptive CKF based on Singular Value Decomposition (BS-A-SVDCKF) algorithm replaces the Cholesky decomposition in standard CKF with SVD, constructs the test threshold for backward smoothing by using the relatively stable noise of the SINS system, and adaptively estimates based on different measurement characteristics when the GNSS measurement noise changes abruptly. Experimental results show that compared with adaptive SVDCKF (A-SVDCKF), backward smoothing SVDCKF (BS-SVDCKF) and SVDCKF, the average positioning accuracy of the proposed algorithm is improved by 32.12%, 57.07% and 68.66%, the average operating efficiency is reduced by 2.19% compared with SVDCKF, and 0.57% and 3.60% higher than that of BS-SVDCKF and A-SVDCKF, which improves the positioning accuracy of the integrated navigation system and ensures real-time.

A Low Earth Orbit (LEO) constellation augmenting satellite navigation is important in the future development of Global Navigation Satellite System (GNSS). GNSS augmented by LEO constellations can improve not only the accuracy of Positioning, Navigation, and Timing (PNT), but also the consistency and reliability of secure PNT system. This paper mainly analyzes the diverse demands of different PNT users for LEO augmented GNSS, including the precision demand in real-time, the availability demand in special areas, the navigation signal enhancement demand in complex electromagnetic environments, and the integrity demand with high security. Correspondingly, the possible contributions of LEO constellations to PNT performance are analyzed from multiple aspects. A particular attention is paid to the special PNT user requirements that cannot be fulfilled with existing GNSS, such as the PNT service demand in the polar regions and the onboard GNSS orbit determination demand of some LEO satellites. The key technologies to be considered in the constellation design, function realization, and payload development of the LEO-augmented navigation system are summarized.

为了进一步提升北斗卫星导航系统(BDS)克洛步伽(Klobuchar)电离层模型(BKlob)在亚太以外区域的服务性能,提出利用遗传算法(GA)优化反向传播神经网络(BP)对 BKlob模型进行改进:对BKlob模型残差进行相关性分析和周期性检测;然后采用遗传算法优化BP神经网络(GA-BP)算法对模型残差进行 7、30 和 150 d的预测,以实现对 BKlob 模型的改进;最后,分别以全球电离层格网图(GIM)产品为参考和单频单点定位精度提升,评估改正精度.实验结果表明:BKlob模型残差不同格网点处具有较强的相关性,且受地理纬度影响较大,受地理经度影响较小;改进的BKlob模型改正性能有明显提升,在高纬度地区和全球范围,改正率可提升 50.0%、30.0%以上;采用改进的BKlob模型进行伪距单点定位(SPP)解算,三维方向均方根误差(RMSE)可提升 14.84%,北(N)、天(U)方向定位精度明显提升.

This paper comprehensively analyzes the kinematic positioning performance of the third-generation BeiDou Navigation Satellite System (BDS-3) in car-borne, ship-borne, and air-borne scenes. Specifically, this work collects three types kinematic data, i.e., car-borne, ship-borne, and air-borne in three scenes including a real experimental scene, a simulated urban canyon or forest-covered scene, and a simulated regional interference or covered scene. Based on these datasets, the kinematic positioning performance of the BDS-3 interoperable signals of B1C and B2a is systematically analyzed and compared with GPS. The results demonstrate that the BDS-3 has slightly more visible satellites than GPS in the Asia-Pacific test area, and the positioning performance indexes for the B1C and B2a new signals are comparable to GPS in terms of the single point positioning (SPP), precise point positioning (PPP), and real-time kinematic (RTK) positioning.

脉冲星导航试验卫星(X-ray pulsar-based navigation-1,XPNAV-1)是我国首颗致力于探索X射线脉冲星导航技术的空间试验平台,已在轨运行七年多,获得大批观测数据,本文收集了该卫星三年多的空间观测数据,开展了一些有益的技术探索.首先处理分析了卫星对Crab脉冲星观测数据,得到Crab脉冲星的每轨、每天和总脉冲轮廓,结果表明,在时间维度上脉冲轮廓是稳定的,与国内外观测结果一致性较好;其次得到Crab脉冲星不同能段脉冲轮廓,分析了脉冲轮廓随能量变化特征;在能量维度上,得到了Crab脉冲星在不同脉冲相位区间的能谱,发现能谱与相位区间的脉冲强度成正比,表明我国自主研制的聚焦型X射线探测器具备良好的技术状态,也实现了卫星精确地"看得见"脉冲星的试验目标.最后利用XPNAV-1 卫星的三天观测数据,实现基于最小二乘算法的脉冲星导航试验解算,得到卫星轨道确定精度约为 56.93 km,分析发现XPNAV-1 星对Crab脉冲星观测误差和初始轨道误差对当前导航解算精度影响较大.

为探究差分码偏差(DCB)对准天顶卫星系统(QZSS)伪距单点定位(SPP)的影响,推导了QZSS伪距单点定位时间群延迟(TGD)和DCB改正模型,并选取 6 个MGEX(Multi-GNSS Experiment)测站连续 7d的观测数据按照两种不同方案进行实验.结果表明:DCB产品月稳定度较好,无明显波动,各颗卫星月稳定度优于 0.2 ns,与TGD互差值优于 2.5 ns;TGD/DCB改正对SPP精度影响为米级,经TGD/DCB改正后水平方定位精度可从 4～9 m提升至 3～6 m,高程方向可从 7～9 m提升至 5～7 m,提升率为 10％～46％.可见DCB改正对单点定位精度影响较大,在定位解算中不可忽略.

星载原子钟作为导航卫星的时间基准,其性能直接影响GNSS的导航、定位和授时服务.采用德国地学中心(GFZ)提供的多系统精密钟差产品,对GNSS卫星钟时域性能和中长期(τ=10 000 s)稳定性进行分析,并提出了基于重叠采样的自相关法对卫星钟噪声进行识别.结果表明,稳定性方面,BDS氢钟、Galileo氢钟和GPSⅢ-A铷钟性能相当且优于其他类型的卫星钟,GLONASS卫星钟存在略微老化的现象,而BDS与Galileo在轨卫星钟进入稳定运行期.噪声特性方面,BDS与Galileo卫星钟主要受3种调频噪声的影响,GPS铷钟主要受调频白噪声、调相闪烁噪声和调相白噪声的影响,GPSIIF铯钟和GLONASS铯钟主要受调频白噪声的影响,提出的基于重叠采样的自相关法能准确识别受相对频率漂移影响较小的GPS和GLONASS卫星钟噪声.

Aiming at Cholesky decomposition failure caused by non-positive definite covariance matrix of cubature Kalman filter（CKF） in GNSS/SINS integrated navigation and inability to perform adaptive estimation of GNSS measurement noise, a improved adaptive SRCKF algorithm for GNSS/SINS integrated navigation based on measurement characteristics is proposed. QR decomposition is applied to update CKF covariance matrix to improve filtering stability. The short-time high precision of SINS is used to estimate the GNSS measurement noise adaptively, so as to reduce the influence of the abrupt change of measurement error. The detection threshold is constructed, and the adaptive estimation is not performed to reduce the amount of calculation when the GNSS measurement error is stable. Simulation and integrated navigation experiment results show that the proposed algorithm has high adaptability to GNSS measurement noise under the condition of abrupt change of GNSS measurement error. Compared with SRCKF and Sage-Husa adaptive SRCKF algorithm, the average positioning accuracy is improved by 19.31% and 4.56% respectively, which improves the anti-jamming ability of integrated navigation system.

Satellite navigation systems are vulnerable. To guarantee the positioning, navigation and timing (PNT) safety of core infrastructure, it is necessary to establish a secure PNT system with hybrid physical principles. In this paper, the augmentations of the BeiDou satellite system (BDS) itself are analysed, namely augmentations through the BDS inter-satellite link, BDS geostationary orbit (GEO) and inclined geostationary orbit (IGSO) satellites, and BDS PNT services supported by low earth orbit (LEO) satellites. Then, taking BDS as the core component, the comprehensive PNT infrastructure seamlessly covering deep space and deep ocean is described, consisting of the deep space PNT constellation, the sea-floor PNT sonar beacon network, and the ground-based low frequency and very low frequency (VLF) long wave radio stations. Moreover, the key technologies of resilient PNT application matching comprehensive PNT and various autonomous perception PNT information are discussed, such as resilient PNT sensor integration, the resilient PNT functional model and the resilient stochastic model. As a future development direction, the key factors of intelligent PNT services are analysed, including the intelligent perception of PNT application scenes, the intelligent optimization of PNT functional and stochastic models and the intelligent fusion of multisource PNT information.

Low Earth orbit (LEO) satellites have high signal strength and faster geometry changes over short periods, offering unique advantages in navigation augmentation. Integrating LEO satellites into the navigation system can help augment the performance of the global satellite navigation system and break the dilemma of the existing navigation system with limited services in challenging environments. Constellation design is the key before establishing a complete LEO navigation augmentation platform. Therefore, in this study, two LEO navigation augmentation constellations, Polar/Walker (S1) and Walker/Walker (S2) with different inclinations, are designed and optimized using the non-dominated sorting genetic algorithm III (NSGA-III). The global average geometric dilution of precision (GDOP) of BDS-3 is reduced from 1.56 to 0.92 and 0.95, and the average visible satellite number is improved from 11.74 to 27.83 and 25.72 with the navigation augmentation of the optimized constellations. To further validate the navigation augmentation effect of two LEO constellations on BDS-3 precision point positioning (PPP), nine stations at different latitudes were selected for LEO augmented BDS-3 PPP simulation experiments. The results show that after adding S1 and S2 constellations to BDS-3, respectively, the convergence times of the nine stations are reduced by 35.5%∼96.5% and 43.7%∼96.2%, and the positioning accuracy is improved by 5.7%∼71.9% and 24.2%∼69.5%, respectively. Overall, each S1 and S2 constellations can significantly improve the global service performance and PPP performance of BDS-3.

Magnetic storms and solar flares cause anomalous changes in ionospheric electron content, during which the performance of the broadcast ionospheric model correction decreases. In this paper, we use the CODE GIM (Center for Orbit Determination in Europe global ionosphere maps) product as a reference to evaluate the BDGIM (BeiDou global ionospheric correction model) BDS Klobuchar (BKlob), GPS Klobuchar (GKlob), and NeQuick G models in terms of its correction performance and the adaptability to magnetic storm and flare events. The analysis of the measured data shows that (1) during the magnetic storm, the BDGIM model does not show significant changes at low and mid-latitudes, while the correction rate is less than 20.0

卫星导航系统具有脆弱性,为了确保核心基础设施定位、导航和定时（PNT）的安全,必须构建多物理原理混合的安全PNT体系.本文首先分析了现有北斗卫星导航系统自身能力增强途径,包括北斗星间链路的能力增强,北斗静止轨道（GEO）、倾斜同步轨道（IGSO）卫星的能力增强和低轨卫星配合的北斗系统PNT服务能力增强;其次,以北斗卫星导航系统为核心,描述了无缝覆盖深空、深海的综合PNT基础设施建设的主要内容,包括深空PNT星座、深海PNT声呐信标网络和地基低频/甚低频长波台网PNT体系.在此基础上,论述了与综合PNT和各类自主感知PNT信息配套的弹性PNT应用关键技术,包括弹性PNT传感器集成、弹性PNT函数模型和弹性随机模型.作为未来PNT应用的发展方向,文章最后论述了PNT应用的环境智能感知、PNT函数模型和随机模型智能优化以及多源PNT信息智能融合等智能PNT核心要素.

为探究BDS-3单、双频SPP TGD改正对定位的影响,选取10个MGEX测站连续30 d的观测数据进行SPP实验.结果表明,BDS-3 DCB产品在1个月内的日解值稳定,未出现明显跳变,月稳定性优于0.2 ns.TGD参数与DCB产品的符合度较高,大部分卫星差异优于2 ns.单、双频SPP经TGD校正后水平和高程方向上的精度均大幅提升,其中单频SPP提升率为17％～70％,双频SPP提升率为66％～90％,可见硬件延迟偏差对单点定位的影响较大,在定位解算中不可忽视.