China Satellite Navigation Conference (CSNC) 2015 Proceedings: Volume III

The precision of broadcast ephemeris of navigation satellite is one of the important factors, which determines the performance indicator of navigation satellite system. However, the result of precise orbit determination and orbit prediction affected the precision of broadcast ephemeris. It’s a very complex task to calculate the precise orbit of satellite. The in-orbit satellite is effected by several kinds of perturbations, that are Earth’s non-spherical gravitation, Sun and Moon gravitation, solar radiation pressure (SRP), tidal acceleration and other little perturbing acceleration. Compared with the other pressure, SRP is the most important error source for medium-earth-orbit satellites. On the basis of engineering parameter and attitude control modes of a certain navigation satellite, this paper had constructed the composite SRP model including direct SRP, thermal radiation pressure (TRP), Earth radiation pressure (ERP). The influence of SRP model parameters had been analyzed in precise orbit determination by long arc orbit calculation. According to the analyzed result, the adjust strategy of the parameters of SRP model had been given for long arc orbit determination, thus the result of orbit determination could be improved further.

BeiDou Navigation Satellite System (BDS) is constructed and operated by China independently. It has important significance in researching the real-time kinematic precise point positioning (PPP-RTK) based on BDS. The fusion of multi-GNSS in data processing can increase satellites observed, improve the geometric configuration of satellites constellation, enhance the accuracy, continuity and reliability in real-time kinematic positioning. This paper deduced the mathematical model of BDS/GNSS PPP-RTK, studied the theories and methods of BDS/GNSS un-difference ambiguity resolution, and realized multi-GNSS PPP-RTK by fixing the un-differenced ambiguities of BDS-only, GPS-only, both BDS and GPS satellites, respectively. Multi-GNSS data of reference stations from Crustal Monitor of Network of China (CMONOC) were processed. The experiment results showed that the values of fractional cycle bias (FCB) of BDS IGSO and MEO satellites kept stable; The precision were less than 1 cm in plane direction and 3 cm in vertical direction after the fusion of BDS, GPS and GLONASS even without ambiguity resolution, respectively; It not only raised the precision of positioning but also quicken the convergence speed after fixing the un-differenced ambiguities of BDS IGSO and MEO satellites; The performance of multi-GNSS PPP-RTK improved further after fixing the un-differenced ambiguities of both BDS and GPS satellites.

Melbourne-Wübbena (MW) combination, which has characteristics of geometry-free and ionosphere-free (first-order), has been often used for cycle slip detection and facilitating ambiguity resolution in GNSS dual-frequency data processing. The constellation of BeiDou Navigation Satellite System (BDS) is different from that of GPS. GPS constellation includes only Medium Earth Orbit (MEO) satellites, while BDS constellation is composed of three types of satellites: Geostationary Orbit (GEO), Inclined Geosynchronous Orbit (IGSO) and MEO satellites. We studied the characteristics of BDS MW combinations of different types of satellites with static observations. The results indicated that: all un-differenced MW combinations of BDS observations show obvious systematic biases. These biases cannot be cancelled out by single-differencing between satellites. On the contrary, they are amplified due to the superposition of the systematic biases of two satellites observations. By single-differencing between receivers, different characteristics are shown for different types of satellites and different baseline distances. The systematic biases of IGSO and MEO MW combination series can be cancelled out by single-differencing between receivers over short and medium baselines, however, they cannot be cancelled out over long baselines. For GEO MW combinations series, their systematic biases cannot be cancelled out over both short and long baselines. The further analysis of the DD (Double-differenced) MW combinations indicated that the systematic biases which cannot be cancelled out by single-differencing between receivers also cannot be cancelled out by double-differencing between both receivers and satellites. By summing up these results, we analyzed the sources of the systematic biases of BDS MW combination: the systematic biases of IGSO and MEO MW combination series mainly originate from multipath errors of satellite; the systematic biases of GEO MW combination series also originate from multipath errors, however, it is not sure that they originate from satellite multipath, receiver multipath, or the combined influence of both satellite and receiver multipath.

The differential code bias (DCB) in Global Navigation Satellite System (GNSS) satellites should be precisely determined using real ground GNSS data when designing certain applications, such as precise positioning, navigation and timing. This paper analyzed the relationship between satellite elevation angle with DSNR (difference signal to noise ratio) of BDS (BeiDou Navigation Satellite System) different orbital satellite. The experimental results showed that the DSNR of IGSO satellite was less than 5dBHz and more stable, much better than the other satellites; the change of GEO satellite DSNR was small, but the absolute value was large; MEO satellite DSNR changed frequently and big. A new algorithm to get the BDS observation weight is introduced by considering the distance between the satellite and the Earth and DSNR. The results indicated that the new weight algorithm improved the DCB accuracy and enhanced the stabilities, which improved GEO satellites 1–15 %, IGSO satellites 4.5–16 %, MEO satellites 20–22 %.

The rapid development of the Beidou navigation satellite system (BDS) accelerates the user demands for high-precision position and navigation. International GNSS Monitoring and Assessment System (iGMAS) built by China independently provides a good platform for GNSS high-precise real-time products. In this paper, the precise satellite clock error resolving model and strategy are studied, the feasibility of real-time precise clock error estimation on the premise of guarantee accuracy is researched, and the precision of real-time precise clock error using iGMAS site resources (built and planning) is verified. The results show: There is convergence process in the Un-difference mode to realize real-time clock estimation and the convergence RMS accuracy comparing to IGS is about 0.2 ns; Epoch single-difference model eliminates the continuous ambiguity, so there is no convergence process, the precision is better than 0.2 ns; On the whole, the precision of Un-difference mode and epoch single-difference model is quite; From the calculation efficiency and high-precision clock error application, the epoch single-difference model is adapt to GNSS real-time precise clock estimation because of less resolved parameters; Using iGMAS site resources (built and planning) recently, the precision of clock estimated by epoch single-difference model is about 0.2 ns.

Due to the precision of BDS orbits and satellites clock, BDS PPP need long time to convergence to centimeter accuracy than GPS PPP. Combined BDS/GPS PPP can benefit from more visible satellites and enhanced satellite geometry distribution, which can accelerate the convergence speed of PPP. In this contribution, Combined BDS/GPS PPP and its integer ambiguity resolution were investigated. Using data set of 8 MGEX stations, the visible satellites and PDOP between GPS constellation and BDS/GPS constellations were analyzed. The results show combined BDS/GPS constellations can increase visible satellites and reduce PDOP. The improvement rate of visible satellites and PDOP is 89 and 31 %. Then, the positioning accuracy and convergence speed of single system PPP and combined BDS/GPS PPP were compared. For PPP hourly solutions, the positioning accuracy and convergence time of combined GPS/BDS PPP is better than single system PPP solutions. For PPP daily solutions, however, the positioning accuracy is not significantly improved. Finally, the integer ambiguity resolution of PPP was conducted. Only the GPS ambiguities were fixed and leaved BDS ambiguities as float values. The experiment results with MGEX BDS/GPS data indicate that combined GPS/BDS PPP with GPS integer ambiguity resolution can further improve positioning accuracy of PPP hourly solutions. Comparing with float solutions, the positioning accuracy is improved by 59.1 % in N component, 87.0 % in E component and 39.1 % in U component.

In order to the study of BeiDou navigation satellite system (BDS) precise orbit determination, a suit of satellite precise orbit determination software named Orbit Study is developed under VC6.0 platform. Object-oriented programming ideas are used. The implementation of each module is carried out by the corresponding c++ class. This software currently processes undifferenced phase and pseudorange measurements. The Extended Kalman Filter (EKF) is used to estimate parameters. It can satisfy the need of post or real time orbit determination. Firstly, the basic modules of Orbit Study are introduced. The data management mode and the optimization algorithm of improving the computational efficiency are also been introduced in the first part. Secondly, the observation model, dynamic model and EKF orbit determination process are introduced. Thirdly, BDS orbit determination experiment is processed based on the observation of Compass Experimental Test Service network (CETS). Two types for comparison for BDS orbit determination accuracy are used, which are inner and outer consistency test. Although the results show that the accuracy of Orbit Study is 10 cm worse than PANDA in radial direction, it has orbit determination ability of BDS preliminary. At last, the reasons of this result are analyzed and the next plans are proposed.

In this contribution, quality control which includes number of visible satellites, PDOP and multipath of BDS+GPS integrated system in varying cut-off elevations is analyzed by a lot of real datasets, and then the performance of BDS+GPS multi-frequency RTK positioning over short baseline is evaluated. The following conclusions can be drawn: more satellites are visible in the combined BDS+GPS system, which ensures the spatial geometry intensity even in case of high cut-off elevations; With the cut-off elevation increases, the impact of the multipath effects on BDS and GPS is significantly weakened, so the AR success rate is mainly affected by the spatial geometry intensity in case of high cut-off elevations; The triple-frequency BDS-only or combined system can perform as well as that of dual-frequency, but it is not much beneficial to positioning performance; The AR success rate and positioning accuracy of BDS+GPS combined system in case of high of cut-off elevations still remain high, which will significantly improve the availability and reliability of the current RTK positioning under some challenging conditions.

In order to improve the prediction accuracy of LEO, it is essential to build up an accurate atmospheric model for density prediction. However, most existing atmospheric models belong to the type of semi-empirical model, thus the data sets are not of homogeneous quality and have limited geographical and temporal coverage. Since the space-borne accelerometer could measure the total non-conservative accelerations acting on LEO directly, the atmospheric drag component could be isolated with the help of the solar and earth albedo radiation pressure models, then the atmospheric density can be calculated, which provides necessary data for making evaluation and improvement of the existing atmospheric models. This paper describes the method to retrieve the upper atmospheric density from accelerometer in detail, 3 months of observations spanning from May 2013 to July 2013 are selected to do the experiment, we use the dynamical orbit determination strategy to calibrate the accelerometers, and then retrieve the air density at the altitude of GRACE Mission. The results show that prediction models cannot exhibit the density variation in high frequency, and the in situ measurements are very useful in density analysis, in addition, it is validated that atmospheric density has a positive correlation with the solar activity intensity.

The single epoch deformation monitoring method based on the relative positioning principle was analyzed and its limitations were investigated. This paper presents an intensive study on the deformation features of monitoring objects using a deformation transformation matrix from the rectangular space to topocentric Cartesian coordinates and proposes a dynamic PPP deformation estimation method that includes prior information regarding the deformation features of the monitoring objects. The method was applied to a case study using high-rate data from four international GNSS service (IGS) sites located in a magnitude-9.0 earthquake zone in Japan. The results showed an effective improvement on the precision and convergence of the deformation solution and were in agreement with current results, proving that our method is effective and reliable.

Based on PANDA software, GPS and Beidou observation data of four Beidou continuous operation tracking network (iGMAS/BETS/CMONOC/MGEX) are calculated in precise point positioning mode, while GPS and Beidou positioning accuracy and observation residuals of each tracking station are analyzed, which can provide reference for the establishment of centimeter-level reference coordinate frame using Beidou system. The results are as follows: single day positioning repeatability with Beidou are 11.06, 7.33, 30.13 mm in E, N, U directions respectively; the STD of differences between GPS and Beidou are 11.36, 7.43, 31.73 mm in E, N, U directions, which indicates that Beidou system can achieve centimeter-level precision positioning at service area; the average of differences between GPS and Beidou are 4.87, 2.65, 29.38 mm in E, N, U directions, which demonstrates an obvious systematic bias of precision positioning between GPS and Beidou; according to tracking network, GPS and Beidou positioning accuracy and residuals are statistically analyzed, which shows that CMONOC tracking network has the best positioning accuracy, while MGEX and BETS tracking network are worse and iGMAS tracking network is much lower.

With continuous increasing of the data scale of GNSS observations network, the computing pressure of data processing is growing. The undifferenced precise point positioning (PPP) model is one of the main strategies of GNSS network data processing. With the increasing of stations’ scale, the processing time of PPP pattern also increases linearly, the traditional serial processing pattern need to consume a large amount of computing time. As the PPP model is not related, this model has good characteristics of parallel processing between stations. This paper established a distributed parallel processing strategy based on the PPP model, which can not only improve the efficiency of data processing, but also enhance the efficiency of hardware performance. However, due to the high concurrency of data access and processing, the parallel programming is faced with great challenges which can cause immeasurable results. In this paper, by analyzing the flow characteristics of the PPP method, a parallel GNSS data process model at multi-core and multi node level was set up, and a lightweight parallel programming model was adopted to realize the parallel model. Through a large number of data tests and experiments, high efficiency of parallel processing of GNSS data based on the PPP model was achieved. The experiment shows that, under the environment of four multi-core nodes, the parallel processing is at least six times faster than the traditional serial processing.

Nowadays there are more than 30 GNSS satellites equipped with laser retro-reflectors. Orbits of these satellites can be independently validated with a high precision using range observations by satellite laser ranging (SLR). China has completed the Asia-Pacific area COMPASS Satellite Network, and is committed to the establishment of the international GNSS Monitoring and Assessment System (IGMAS). Orbit validation is one of the key factors in the development of IGMAS, so this paper validated almost all GNSS satellites carrying reflectors to see whether the IGMAS orbits is qualified, including all 24 of GLONASS, 4 of COMPASS, 4 of GALILEO based on the rapid orbits from BACC IGMAS Analysis center. According to IERS2010 convention, correction models such as station coordinates, laser propagation delay models were introduced to establish the measurement model. The validation of the BACC orbits shows a mean deviation around 5–10 cm for the GLONASS satellites, 10–15 cm for the COMPASS MEO/IGSO satellites, 2.65 m for the COMPASS GEO satellites, and 20–25 cm for the GALILEO satellites.

Station-satellite DCB may be absorbed into the ionospheric delay in uncombined PPP resolution because of the direct usage of the precise clock offset production based on the ionosphere-free combination estimation. BDS station-satellite DCB is separated in this paper with the ionospheric delay estimation of uncombined PPP, analysis in results and stability is also introduced. Slant ionospheric delay is inverted with ionosphere observation and separated DCB at last.

This paper mainly focuses on the combination of station coordinates and ERPs and the realization of TRF based on four technologies GPS, VLBI, SLR and DORIS, and discussed some key points including the combination model, datum definition methods and strategies to the validity of solutions in detail. By comparing our results with ITRF08, the difference in determining the center of mass is 2.4–7.7 mm, the uncertainly error is 1.25 mm; the consistently in scale is 1.10 ± 0.06 ppb; small difference still remains in rotation because of the uncertainly of solutions. As to ERP, the combined solution showed a little difference with C04 and the optimal solution in xpo and ypo, the WRMS compared to C04 is 0.077 and 0.055 mas separately, LOD and UT are fused with DORIS solutions, the combined solution of LOD generally keep a consistency with C04, the WRMS is 0.026 ms, but UT show a large difference and unconsistence with C04 and the optimal solution because it could only be determined by VLBI.

This paper develops a new cycle slip detection and repair method that is based on polynomial-fitting ionosphere-free combination and ionosphere total electron contents (TEC) rate (TECR), and uses dual-frequency GNSS data to present the mathematical model of the two method. It proves that the new algorithm can detect and repair the cycle slips with a very high level of success by the experiments with 1 Hz or even higher rate data, especially the method of TECR. In addition, the combination of the two methods can detect and repair their insensitive cycle slips effectively. Because the new method only use carrier phase, it can not only detect the cycle slips effectively, but also repair them reliably.

Since BeiDou satellite navigation system (BDS), which is independently developed and being implemented in China, successfully realizes the coverage in the Asia-Pacific region at the end of 2012, it has been widely used in the national economy and society, with that the whole system runs stably, and is in good condition. In order to verify the precision level of the positioning solution of the second generation BeiDou system (BD-2) in the condition of short baseline, based on the measured data, through the use of self-written baseline solving program, we get the short baseline calculating results under the condition of the static and dynamic experiments respectively based on BD-2 and GPS. Then through the comprehensive comparison of the above results, we analyze the accuracy and reliability of ultra-short baseline results based on BD-2. The experimental results show that, the reliability of the short baseline solution of BD-2 is rather equal compared with GPS. Under the static condition, the precision of ultra-short baseline solution of BDS is slightly worse than GPS; under the dynamic condition, that of BDS in E and N directions are rather equal to that of GPS, while in the U direction it is not as good as GPS.

Several analysis centers (AC) and a product integration and service center have been built by the international GNSS continuous Monitoring and Assessment System (iGMAS). Product integration and service center (ISC) is a reprocessing center of high-precision products, which is also the window of products distribution center. Product integration and service center analyzes the quality of product from each analysis center, and then reprocesses to generate the combined product. The consistency of combined products is very important to the users of navigation and positioning, which directly affects the service performance of combined products. At first, this paper introduces the progress in iGMAS product combination. Then, the consistency of basic combined products (orbits, Earth rotation parameters, station coordinates, and clocks) is analyzed in details. And the precise point positioning tests are implemented to verify the consistency of combined products. Finally, some suggestions are given according to the test results of the present stage. The results of PPP test show that the static PPP coordinate daily repeatability of combined orbit/clock is at millimeter level. The standard deviation of combined orbit/clock single epoch PPP difference is comparable with the best AC orbit/clock solutions. The results of static and dynamic PPP also prove that the consistency of combined orbit/clock considering the consistency correction is improved significantly.

With the availability of BeiDou Navigation Satellite System (BDS) triple-frequency observations, more strategies can be carried out to improve integer ambiguity resolution (IAR) performance for both short and long baseline RTK. In this paper, we first present the intrinsic natures of IAR for short and long baseline RTK. The double differenced mathematical models for short and long baseline are specified first. From the model perspective, the IAR performances of dual-frequency and triple-frequency are analyzed and compared. To improve the AR performance using triple-frequency observations, the integer least-squares (ILS) success-rate can be increased by first partial fixing the Extra Wide-lane (B2&B3) and then the Wide-lane (B1&B2, B1&B3) integer ambiguities in a geometry-based model because of their relatively long wavelengths. For short baselines, the IAR at each carrier can be resolved conditioned on the resolved WL integer ambiguities. For long baselines, two ionosphere-free combinations (B1&B2, B1&B3) can be formulated, and only the integer ambiguity vector on each carrier needs to be fixed with more redundant observations. It turns out that with triple-frequency observations, the performances of both short and long baseline RTK can be improved.

In order to improve the precision of BDS precise ephemeris, GPS/BDS one-step combined precise orbit determination based on double-differenced mode was testified in this contribution. And double-differenced data was not formed between GPS and BDS, which eliminates the effect of inter system bias (ISB) on the precision of BeiDou precise orbit. Not only GPS and BDS orbit parameters are estimated, earth rotation parameter (ERP) and station coordinates are also estimated. Data of 114 tracking stations from MGEX are processed. The analysis shows that: Compared with IGS final orbit, the precision of GPS orbit is 5 cm, the precision of Xp, Yp, length of day (LOD) is 0.06, 0.10 mas, 21.6 μs. Validating the BDS orbit using SLR observation shows that the radial precision of BDS IGSO and MEO satellites is better than 6 cm, while that of GEO satellite is about 0.37 m.

The Dual One Way Ranging (DOWR) technique with PRN-code, which can remove the effect of time-asynchronous and improve ranging precision, is widely used in Inter-Satellite-Ranging. The ranging value based on DOWR is delayed, thus cannot match the actual distance at the time the value got within a dynamic environment. In this paper, a synchronous ranging algorithm based on combined-process method using Frequency-difference, Time-difference and relative velocity is proposed, which can realize real-time measurement in high precision by the calibration of ranging value. A dynamic model based on DOWR is introduced first. then, a general analytic expression of distance measurement is constructed, which involves the frequency-difference, the time-difference and the velocity between two aerocraft in different receiving patterns. Thus, the distance measurement can be deduced to a certain time, and then, a current-time ranging value would be extrapolated with local pseudo-speed information. The experiments results of certain product demonstrate the effectiveness of the proposed algorithm, the precision of synchronous distance measurement is better than 0.1 m in a dynamic environment.

Conventional phase center calibration is carried out in anechoic chamber, when in the outfield, the calibration values may be not useful because of the phase errors arose by multipath. In the paper, we present a model of antenna receiving signal; the model is improved by adding antenna model and the characterizations of right hand circular polarization and left hand circular polarization. Based on the model, we analysis the impact of up-to-down ratio on phase errors. As an example, we use a choke antenna to assess the performance of the simulation results. When the phase center variations tolerance is 2 mm, in order to mitigate the impact of phase center variations on high precision GNSS by using calibration values, the up-to-down ratios must be all higher than 15 dB.

The core issue for high precision relative dynamic positioning application is how to fix integer carrier ambiguity fast and accurately. Traditional three carrier ambiguity resolution (TCAR) method find the suitable combination of carrier phase and pseudo-range observations using integer search traversal method, which make the lower success reliability for narrow-lane ambiguity resolution. In the analysis of the error characteristics of the combined observations, we introduce a new procedure to select the optimal combination of carrier phase and pseudo-range observations based on the minimum of total noise level, with real-time estimating accurately and mitigating even eliminating the impact of ionospheric delay, successfully fixed three linearly independent combinations of the integer ambiguity, then determine the basic integer ambiguities. Finally, the performance of the improved TCAR in short-baseline condition is showed by processing the observations collected by two BeiDou triple-frequency receivers, the results show that, this method fix the integer ambiguities of double differenced extra-wide lane and wide line from single epoch, total noise level was decreased almost 15 %, with several epochs smoothing, the success reliability of basic ambiguities achieve 95 %, which is improved at least 30 % compare with traditional TCAR method.

The optimization of the inter-satellite link assignment is an important technical issue, especially, for the case that the number of inter-satellite spot-beam antennas is less than assignable links. Based on Minimum Spanning Tree (MST) theory in graph theory, this paper proposes a link assignment algorithm for the hybrid navigation constellation using GEO, IGSO and MEO satellites. Using GEO satellites as the core transfer node, this algorithm assigns inter-satellite links with lower communication costs firstly, and then assigns links at least once for all visible satellites by applying the iterative assignment. As a consequence, the integrated optimization of the inter-satellite observing and communication performance can be achieved. The simulated results show that, compared to the mesh-link assignment algorithm used for the Iridium system, the proposed link assignment algorithm can be able to improve the precision of orbit determination and reduce whole-network average communication delay.

It is a tendency for Global Navigation Satellite System to finish Autonomous Distributed Orbit Determination with in-satellite link measurement. Based on analysis of Whole-Constellation Centralized EKF and Iterative Cascade EKF, a new Increased Measurement Covariance EKF is proposed. Three algorithms are compared in performance. The new algorithm shows its advantages in Autonomous Distributed Orbit Determination.

The real-time orbit determination for Low Earth Orbiters (LEOs) is generally based on dual-frequency tracking data from on-board GPS receivers, and positioning accuracies for LEOs currently vary from 0.5 to 1.0 m with sophisticated reduced dynamic orbit determination techniques. In this paper, different strategies are designed and applied to real-time orbit determination only using single-frequency pseudo-range and carrier phase measurements to analyze their corresponding performances. Then some simulative tests are carried out to process the GRACE-A space-borne GPS data in the different solar sunspot activities. The test results demonstrate that the position and velocity accuracy (3DRMS) are up to 0.9 m and 0.9 mm/s respectively using only single-frequency GPS pseudo-range data, and their accuracies could be improved to 0.55 m and 0.55 mm/s using single-frequency combination of pseudo-range and carrier phase measurements, which is close to the dual-frequency real-time orbit determination. Therefore a low-cost single frequency space-borne GPS receiver can be used in real-time orbit determination for LEO missions when appropriate strategies and methods would be selected.

Nowadays, satellites in low earth orbit (LEO) can benefit from Global Navigation Satellite System (GNSS), such as Global Positioning System (GPS) of United States, to estimate positions and velocities. As China’s BeiDou Navigation Satellite System (BDS) has been formally operational since the end of 2012, standalone Beidou and combined GPS + Beidou positioning techniques tend to be applied in the future space missions. However, no LEO satellites have been operated with Beidou receivers at present. Hence Beidou-based precise orbit determination (POD) technique is required to be tested and verified on ground at first stage. This study is to test the GPS + Beidou orbit determination software in ground testbed. GNSS data collected from iGMAS (International GNSS Monitoring and Assessment Service) and MGEX (Multi-GNSS Experiment) stations are processed in both static and kinematic PPP (Precise Point Positioning) modes. Decimetre level of positioning accuracy is achieved. The inter-system biases between GPS and Beidou are estimated and analysed. Results indicate that GPS + Beidou solutions are more precise than the standalone GPS solutions.

The principle of GNSS VRS (Virtual Reference Station) was discussed in the paper. The critical technologies of VRS, like virtual station error modeling with reference networks and generation of virtual observables, were studied. The feasibility of BDS VRS technology, as well as the current position performance with BDS VRS, was verified. It is shown that, with BDS VRS, the positioning accuracy inside the local reference networks can reach 1–2 cm, provided baselines of 10–20 km.

Development of space mini passive hydrogen maser has been carried out in Shanghai Astronomical Observatory. Research on key technologies such as miniatured cavity-bulb assembly, absorption pump, magnetic state selection assembly and magnetic shield has made progress, Parameters of microwave cavity, storage bulb and state selection have been optimized to ensure system performance. Weight of physical package is less than 10 kg and atomic signal is up to 3 dB. Integration with electronic package, optimization and engineering modification are the main work at present. Less than 15 kg of total weight and frequency stability better than 1 × 10

−12

τ

−1/2

(1s ≤ τ ≤ 10,000 s) is expected.

With the performance upgrade of aerospace applications, the frequency source have raised higher requirement on frequency-temperature stability of OCXO (oven-controlled crystal oscillator). Based on the temperature control theory of OCXO and the character of frequency fluctuation in different temperature, we use analog temperature compensation technology in the design of OCXO. Finally, we realize a miniaturization 10 MHz OCXO for aerospace applications. This OCXO test result shows, the frequency-temperature stability is better than ±5.0E-9 with temperature range −30 to 70 °C.

In navigation satellites constellation comprised of multi-satellite, introducing an atomic clock ensemble in space is beneficial for improvement of its measurement accuracy and ability of autonomous operation. This paper summarizes the methods adopted currently at home and abroad towards atomic clock ensemble management in ground or in space and then proposes an initial design scheme of ACES management on a single satellite or among different satellite clocks within constellation which is based on the designing conception of atomic clock ensemble in navigation satellite constellation. Considering generation and characterize measurement of clock ensemble signal, anomaly detection and processing of atomic clock, this paper gives analysis and recommendation as for the key technologies and factors affecting ACES management, which will provide technical basis in designing a continuous, reliable, stable, accurate ACES running system for BEIDOU global navigation satellite system project.

The time-synchronization has no ground time criterion in the model of autonomous time-synchronization, time precision keep on the navigation satellite itself. When can make GEO satellite as time norm, and use satellite-satellite chain to give other satellite. This paper design the navigation constellation of the new satellite-navigation-system, and configure the satellite clocks, simulate all kinds of constellation time-synchronization precision, educe the satellite clock configure scheme in the new navigation system. Due to the introduction of high-precision optical clocks, the overall time of the entire navigation constellations drift is smaller, the accuracy is much higher than the link between self-ordinary; and because the presence of high-precision clock, the time synchronization algorithm’s requirements are lower, general EKF can meet the requirements.

High-precision time and frequency signals play an important role in many areas such as modern communication, navigation, and baseline interferometry. Optical fiber based time and frequency networking not only has a higher precision which can meet the demand of new generation time and frequency standard but also constructs to the ground based time and frequency network as a complementary choice of satellite based methods. As a consequence, we propose a fiber based radio frequency dissemination scheme to multiple users with a tree-like topology. The noise compensation system acquiring the noise information by measuring multiple reflection signal is put in remote terminals, which allow users to access the frequency signal along the fiber without affecting others. With this scheme, a high precise frequency transfer experiment is demonstrated along a 60 km fiber link to multiple users. The frequency stability of 7.1 × 10

−14

@1 s and 6.8 × 10

−17

@10

4

s are obtained. Furthermore, the influence induced by adding or cancelling a new terminal is tested when other terminals are operating. The result shows that the stability of radio frequency networking scheme which is robust and flexible can fulfil most atomic clock that is currently used and would bring benefit to establish a national or even continental ultra-stable frequency dissemination network.

Passive gas-cell rubidium atomic clock has been widely used in Global Navigation Satellite System (GNSS). Further improvement on the frequency stability of rubidium atomic clocks has extreme significance for promoting the positioning and timing precision of GNSS. Distortion of the lamp spectral profile, caused by self-absorption, is a common concern for the design of a rubidium clock. However, few literature has systematically investigated the impact of lamp spectral profile on a Rb clock. In this work, the influence of lamp spectral profile on both short-term frequency stability and light shift of a rubidium clock was studied theoretically and experimentally. The results showed that serious distortion of the lamp spectral profile could lead to one times deterioration to short-term frequency stability, and change the zero light shift point by a few degrees centigrade. Thus, we demonstrated that optimization of the lamp profile may be an effective way to improve the performance of a Rb clock, which should be paid more attention when designing a high performance spaceborne Rb clock.

With the improvement and updating of GPS, GLONASS navigation system, and the gradual establishment of GALILEO and China’s BeiDou system (BDS) navigation system, Multi-system GNSS navigation systems have become the main research directions. In order to achieve the compatibility and interoperability among the GNSS systems, accurately determine the time difference between different systems is the key. Based on this, this paper adopted the GNSS observation data, which is the output of the multi-mode dual-band receiver, and the GNSS system’ navigation message to monitor the time difference between different GNSS navigation systems. Because the BIPM T bulletin has no BDS data, so the measured time difference data of GLONASS and GPS and the corresponding time difference data of BIPM T bulletin were used to be evaluated. In this paper, the maximum, minimum, mean, mean square error and the RMSE of BDS, GPS and GLONASS time difference data were accumulated. 310 days’ time difference data were used to evaluation the difference. The results show that the residual’ standard deviation between GLONASS, GPS time difference and the results of T bulletin is 4.28 ns, and the residual’ standard deviation between BDS and GPS, GLONASS system can reach 5 and 10 ns in optimal conditions.

Many studies have been carried out in the past for forecasting satellite clock bias utilizing models such as the grey model, linear model, quadratic polynomial model, etc., but the accuracy of these models has not met the requirements for real-time applications. One reason for the fact is that onboard atomic clocks can be easily affected by various factors such as environment and temperature and this leads to complex aspects like periodic and stochastic variations, which are not sufficiently described by conventional models. A hybrid prediction model is thus developed in this work in order to be used particularly in describing the stochastic variation behavior satisfactorily. The proposed hybrid prediction model for satellite clock bias combines the quadratic model plus harmonic model to overcome the linear and periodic effects, and Gaussian process regression (GPR), whose input is reconstructed by the delay coordinate embedding to access linear or nonlinear coupling characteristics. The simulation results have demonstrated that the prediction accuracy of the proposed model is better that of the IGS ultra-predicted (IGU-P) solutions at least on a daily basis.

In global navigation satellite system (GNSS) collaborative positioning, each user shares its processed data with the neighboring users and conducts joint data processing. The study of the performance for distributed GNSS collaborative positioning algorithms is essential for the actual applications. In this paper, the Distributed Least Squares (DLS), Distributed Extended Kalman Filter (DEKF) and Distributed Unscented Kalman Filter (DUKF) algorithms are introduced in detail. After that, the simulation tests are carried out to analyze the performance in the outdoor and partially blocked scenarios respectively. The results show that the performance of three distributed algorithms is all better than GNSS standalone Least Squares algorithm, especially in the partially blocked scenario, the performance improvements are significant. Compared with the other two algorithms, the DEKF algorithm is pretty good in terms of performance and computational complexity. Besides, considering that the computational complexity of users is limited, the results also provide useful information of how to select collaborative users for a better positioning accuracy in different scenarios.

GNSS signal can be widely used in outdoor environment. However, due to the barrier of walls, GNSS signal becomes too weak to be used in indoor environment. This paper analyzed the Wi-Fi based indoor positioning method, which is mostly widely researched, introduced a DTMB based indoor positioning method and confirmed its feasibility. By using the KNN algorithm and the DTMB signal’s location fingerprint, the indoor positioning system proposed by this paper can locate any unknown nodes inside the room. And also some tests were designed to measure the positioning accuracy. Test results showed that the accuracy of the DTMB based indoor positioning system is similar to the Wi-Fi based positioning system. The new DTMB based indoor positioning method can be a useful complement to the existing indoor positioning methods.

Navigation based on stellar refraction refers to a method that uses large visual field star sensor to detect several stars refracted and not refracted by earth atmosphere, and then finishes autonomous navigation based on star map recognition, with merits such as simple system structure, low cost and high navigation accuracy. However, in order to achieve full-time-running high accuracy, three key technologies, namely strong background star map acquisition, refracted star extraction under strong background and atmospheric model should be solved for such method. By constructing observation policy model and detection limit model under the strong background, this paper realizes high SNR (Signal to Noise Ratio) star map acquisition under strong background through anti-blooming function of detector, and carries out theoretical analysis and outfield test; realizes recognition of dim refracted star and high-accuracy centroid positioning of refracted star under strong background via specific star pick-up algorithm, and performs outfield test on it; studies high-accuracy atmospheric model optimization method and proposes an applicable stellar refraction atmospheric model based on atmospheric refractivity change and identical with stellar refraction rule. Finally, on the basis of key technological solution study, it constructs stellar refraction navigation simulation system based on stellar refraction navigation realization approach and analyzes the influences of key error sources on navigation accuracy through simulation, so as to obtain the result that the accuracy of full-time-running navigation based on stellar refraction is superior to 1.2 km.

With the characteristics of good observing, simple structure and high reliability and so on, The CNS/SINS Integrated Navigation Using Star Tracker applies to seafaring and large-scale airborne platform in aerosphere. However, the star tracker can track only one star every time and celestial positioning depends on the performance of horizon measurement. Moreover, the horizon measurement of strapdown inertial navigation system is digital and low accurate. This brings on a reduced performance of CNS/SINS integrated navigation. Therefore, a new CNS/SINS method is advanced. With several observations of single star tracker, the attitude determination is realized. Finally, the CNS/SINS integrated navigation system is established. Both the simulation and experimental results demonstrate that the performance of this integrated navigation system is excellent. In this way, the output divergence is restrained and the accurate of positioning and heading is improved. In a word, the CNS/SINS method applies to the long-distance and long-endurance airborne platform.

To satisfy the increasing requirement for accurate range measurement and high rate data transmission, a new simultaneous ranging and communication system based on X-ray communications (XCOM) is proposed. To achieve simultaneous range measurement and data communication, a specific signal structure is designed. The designed signal structure guarantees the simultaneous transmission of the ranging and communication information. By matching the local sequence number of the signal symbol with the sequence number propagating through the two-way range, the range can be calculated. In this paper, the basic principles of the proposed method is described and the related key techniques are analysed in detail. Besides, the performance of the proposed method is analysed both theoretically and numerically. The analysis covers the data rate, the acquisition probability, the ranging jitter, etc. Compared with the available methods, the proposed method improves the link efficiency and is helpful for system miniaturization and integration, which provides an option for future deep space explorations.

In recent years, the location based service has been gradually integrated into people’s daily life. Many fields such as the public security, emergency rescue, warehousing logistics, and IOT (The Internet of things) applications present extensive application demand on indoor location. This paper discusses the cross correlation interference in the TC-OFDM (time divided CDMA-OFDM superimposed signal system) receiver which is based on ground mobile radio network. In the TC-OFDM system, because of the complexity of the indoor environment, multiple access interference is terrible, which greatly affects the performance of the receiver for signal acquisition and tracking. This paper studies the characteristics of the multiple access interference in TC-OFDM system in indoor environment. The cross correlation value between the strong and weak signal can be estimated by putting the characteristic information of strong signal into the weak signal tracking channel. While this information can be extracted from the strong signal’s tracking channel. Therefore, strong signal’s effection on the weak signal’s autocorrelation function can be reduced. So that the tracking loop can get more accurate phase value for tracking. This method can improve the TC-OFDM receiver’s ability of inhibiting cross correlation by 10–13 dB, and effectively enhance the capacity for sustained and stable tracking of weak signal. In addition, in the snapshot replay mode of the weak signal which cannot be tracked continuously, this method helps to estimate the correlation peak more accurate.

This paper describes the integration of

Locata

, GNSS and INS technologies within a loosely-coupled triple integration algorithm. The conventional methods for multi-sensor integration can be classified as either centralised filtering or decentralised filtering. Centralised Kalman filtering (CKF) provides globally optimal state estimation by directly combining measurement data. However CKF system has some disadvantages such as a comparatively large computational burden and poor fault detection and isolation ability. Decentralised Kalman filtering (DKF) addresses such defects while aiming to achieve the same accuracy as a centralised filter. On the other hand global optimal filtering (GOF) can achieve a higher accuracy than the traditional CKF because it utilises more information resources than the CKF. In the information space, the information resources that can be used for estimation include the measurements, the local predictions, and the global predictions. In order to evaluate the system performance, a field experiment was conducted on a vehicle with different kinds of maneuvers, including circular motion and accelerated motion. The results indicate that: (1) GOF-based PPP-GNSS/

Locata

/INS integration system can provide better positioning accuracy compared with CFK and federated Kalman filtering; (2) covariance analysis shows that the GOF improves the system estimation covariance; and (3) a comparison of GOF with local filters confirms the superiority of a GOF-based triple integration system.

Pulsar navigation is a possible measurement of spacecraft navigation autonomous navigation, and profile folding and measure is one of the core technologies of it, whose performance determines the capability of the final navigation result. Current profile folding measures are commonly based on the presumption that the time of photon arrival can be transformed to the solar system barycentre and the presumption that folding profile is exactitude. However, on the real navigation scene, since the position and the velocity of the spacecraft are not exactly acquirable, folding profile would bring deformation and therefore cause the phase measure error. In order to solve this problem, this paper introduces the loop tracking to the pulsar navigation profile folding and measurement processing. By lock the difference between measure phase and predict phase, the period feedback can be realized to rise the accuracy of the pulsar phase measurement. The result shows that this method could improve the profile folding and phase measure result, and suits for dynamic pulsar navigation.

In this paper, K nearest neighbor algorithm is improved in fingerprint information matching in WiFi indoor positioning system. Because the original K nearest neighbor algorithm ignores the relationship between the neighboring points, it doesn’t improve matching accuracy, and its positioning accuracy is not better. There is no effective treatment group sample points, matching time is greatly increased. In this paper, we study a modified K nearest neighbor algorithm in the application of WiFi indoor positioning. Because K neighbor points are given different weights according to certain rules, the matching accuracy is improved before matching method. And because of using grouping pretreatment of the sample space, the time of position matching accuracy is reduced. Therefore the positioning precision is improved.

X-ray pulsar navigation (XPNAV) is an important technology for long time and high precious spacecraft autonomous navigation. XPNAV system can offer position, velocity and accurate time navigation information for spacecraft in near-earth orbit, geostationary orbit, elliptic orbit or interplanetary orbit. XPNAV has an extremely important military use and wide application prospect. In XPNAV system, pulse time-of-arrival (TOA) is a basic observation, and its estimation precious decides the precious of XPNAV’s timing and position determination, thus high precious pulse TOA estimation is an important technology in XPNAV system. To improve the pulse TOA estimation precious of XPNAV system, we proposed a pulse TOA estimation method based on correlation information. First, based on the time observation data of photons radiating for X-ray pulsar to the spacecraft, the pulse folding profile is obtained by epoch folding. Then, we constructed the new observation equation by analyzing the correlation result between the folding profile and normal profile. At last, eigen-decomposed the new observation equation we can obtain two mutually orthogonal feature vectors, so the pulse TOA can be estimated by the orthogonal property of the two vectors. Simulation results show the validity of the proposed methods, and can improve the TOA estimation precious compared with the traditional correlation method.

Facing the increasingly complex electromagnetic environment, it is an attempt to introduce DS/FH hybrid spread spectrum technology to the field of TT&C. For DS/FH receiver, despreading and dehopping proceed respectively. However if DS/FH navigation signal is dealt with in the same way, there is no difference between DS/FH navigation signal and the existing DS signal. The code tracking algorithm proposed in this paper makes full use of frequency hopping information so that the correlation peak becomes very sharp. Computer simulation shows that the code tracking accuracy of DS/FH navigation signal reaches at 0.0028 m (CNR = 40 dB Hz) and the maximum of the multipath error envelope is 0.062 m (MDR = −10 dB), far better than the performance of existing navigation signals.

In consideration of advancing the technology of X-ray pulsar-based navigation, a theoretical method for space-based building of navigation database is raised. This method uses locus integration of the Earth orbit to provide the analytical solution to measured parameters of navigation sources. Numerical analyses reveals that to meet the demands of navigation with hundreds of meters’ accuracy, the testing database containing four pulsars can be built within two years with a 0.25 m

2

detector. For an extended database, it is recommended that X-ray binaries are included. The space-based observation data of X-ray binaries shall be collected before judging whether they will serve as navigation sources

Six X-ray pulsars (PSR J0218+4232, PSR J0437-4715, PSR B0531-21, PSR J1939+2134, PSR J1024-0719 and PSR J0751+1807) are selected for the mission of deep-space autonomous navigation, and the relevant parameters (including position, proper motion, period and period derivative, etc.) are also listed. Based on the XMM-Newton X-ray timing data and the radio ephemeris for the young pulsar PSR B1509-58, we adopted both absolute timing and relative timing methods to fold its pulse profile in the 0.2–12 keV band. In addition, for the sake of both pulsar-based deep-space autonomous navigation and scientific research, we take the Crab pulsar as an example to fit its X-ray (0.2–30 keV band) spectrum, and obtain its power-law fitted spectrum. Then we estimate the navigation accuracy of the detectors with different effective areas. Finally, we discuss a preliminary probe design principle of X-ray detectors for the pulsar navigation, and give the rough estimations on the effective area and sensitivity.

Multi-robots are often better choices to complete search-and-rescue tasks in some large-scale disasters, such as earthquakes, mine accidents, forest fires, etc. However, effects such as shadowing and fading for GNSS signals limit the positioning ability which is most important for search-and-rescue robots. To improve positioning availability and reliability, the article proposes a GNSS Peer-to-Peer cooperation positioning system for multi-robots search-and-rescue. The peers share GNSS-only data among neighbors as aiding information under light block scenario, and share both GNSS and terrestrial ranging data under deep indoor scenario. A particle filtering algorithm, the Monte Carlo numerical approximation of Bayesian filtering, is proposed to estimate position of peers utilizing both the prior information coming from robot motion model and posterior information provided by pseudo-range and terrestrial range observations, and the algorithm flow chart is presented. As a result, the acquisition time could be reduced and sensitivity could be improved for peers under light block scenario, and position could be solved under deep indoor scenario with fewer than 4 visible satellites. Simulation results show that the positioning error of particle filtering is less than that of Non-Bayesian filtering, and the error is about 5 m for low-cost receivers.

With the urgent need for indoor and outdoor seamless navigation service, it is imperative to develop high precise positing technique suitable for various scenarios. In this paper, considering the widely deployment and well coverage of the wireless cellular communication system, a position approach is proposed based on time duplex division long term evolution advanced (TDD LTE-A) network. A novel complex frame structure for positing is proposed based on the current TDD LTE-A protocol. In GP (Guard Period) of the special sub-frame, i.e., the downlink-uplink switch period of TDD system, the navigation (NV) signal is added for positing. NV signals are transmitted simultaneously from different base station (BS) with orthogonal PN (Pseudo Noise) code. By measuring the distance to different BSs which are time synchronized in TDD system, user’s position can be fixed as in the GNSS system. In this paper, the theoretical performance of the proposed position scheme will be analyzed, and the impact to the current system will also be discussed. The results show that, by properly allocating the time length of NV signal based on the coverage of the cell, signal conflicts with the current LTE-A signal can be effectively avoided.

The pulsar database is the foundation of X-ray pulsar navigation. The pulsar optimizing method is the premise of the pulsar navigation database. In this paper, the three characteristic parameters of “NR coefficient”, “stability factor” and “quality factor” are put forward, which is to consider the influence of the pulsar pulse cycle, radiation flow, pulse width, pulse rate and background radiation. Then, it can realize to prioritization of pulsars, and construct the navigation database. This new method overcomes the lack of an objective evaluation of each pulsar defects in the normal method. And a preferred pulsar database, applying to X-ray pulsar navigation, is obtained.

As a kind of two-dimensional materials, graphene has many excellent characteristics, such as zero band-gap, high electron mobility, high thermal conductivity and high mechanical strength, which make it widely applied in the field of photoelectric detection. X-rays can be detected based on the electric field effect of graphene. When the detector working, electron-hole pairs are generated in the substrate by the incident X-rays. The drift of the electrons in the substrate will change output of the detector. Therefore, it is necessary to study the transportation of electrons in the graphene-based X-ray detector. The motion of electrons in the detector is simulated using finite element method, and the influence of the electrons’ motion to the detector output is analyzed. Dependence of the detector output on the incident position of X-rays is studied. Also, the influence of structure parameters to the performance of the detector is analyzed. Based on the results of this study, performance of the graphene-based X-ray detector can be optimized.

The navigation satellite navigation autonomous health management system based on cognitive technology is an advanced intelligent spatial information processing system. It takes the working mode and mechanism of the human brain as reference, has more complex information and environment sensing ability, adaptively learns according to the information and environment statistic change, and effectively improves “behavioral effect feedback” capabilities of many navigation satellites in the system and the independent operation management capabilities of navigation satellite systems. Therefore it is an important direction for the development of future navigation satellite systems. Aimed at the building requirements of global satellite navigation system constellation configuration and navigation satellite function and based on exploring the cognitive technical background of navigation satellite system, the basic concepts and content of the autonomous health management system of navigation satellite based on cognitive technology are proposed. Through analyzing the existing information flow of navigation satellite, the idea of applying cognitive technology in cognitive technology-based navigation satellite health management system and the key technologies will be discussed and solved, and development recommendations of the cognitive technology-based navigation satellite health management system are given.

Pulse time-of-arrival (TOA) estimation is the key procedure to construct the measurement in X-ray pulsar navigation. Traditional TOA estimation methods are designed assuming spacecraft to be at rest. However, spacecraft orbit motion introduces doppler effect and causes observed pulse period shift, which makes TOA estimation harder. This paper provides a method based on average cross correlation to solve the problem in orbit motion situation. Instead of direct doppler frequency estimation, this idea transplants the static cross correlation method based on epoch folding into dynamic situation by folding at the middle of the observation period to counteract the doppler effect. At certain doppler frequencies, the average cross correlation method is tested via Monte-Carlo simulation. Results show that the proposed method can output high-precision TOA estimation at small accumulated doppler phases.

X-ray can’t be directly observed at laboratory due to the absorption of atmosphere. Furthermore, observation at space consumes a great deal of financial and material resources and is highly risky. Therefore, simulation data of X-ray pulsar is of great importance, whereas the current simulation method can only generate X-ray signals of constant period at the Solar System Barycenter (SSB), without considering the slow varying property of pulsar period and the large scale space-time effects. This paper proposes a new simulation method for X-ray pulsar signal. First, the arrival phase of the next photon at the SSB is recursively calculated according to the phase of the previous photon. Next, seek the pulsar ephemeris to obtain the phase evolution model of the current time. Then, transform the arrival phase of the photon to its arrival time at the SSB using the obtained phase evolution model. Subsequently, utilizing the solar system ephemeris and orbital parameters of the spacecraft, the arrival time of the corresponding photon at the spacecraft can be acquired by an iterative algorithm. Simulation results show the validity of the proposed methods. The simulation data of the proposed method includes the slow varying property of pulsar period and the large scale space-time effects, also is very similar to the RXTE observation data. Thus the proposed method can be applied to the validation of all the algorithms needed in the practical navigation, such as profile integrating and large scale time transformation.

This paper presents a novel stereo image-based image aided inertial navigation algorithm for reducing position and orientation drifts during GNSS outages or in a poor GNSS environment. Usually, the image aided navigation based on the visual odometry uses the tracked features only from a pair of the consecutive image frames. The proposed method integrates the features tracked from all overlapping image frames towards accuracy improvement and drift reduction. The measurement equation system in this multi-frame visual odometry algorithm (MFVO) is derived from Simultaneous Localization and Mapping (SLAM) measurement equation system where the landmark position parameters in SLAM are algebraically eliminated by time-differencing the measurement at two consecutive epochs. However the resulted time-differenced measurements are time-correlated. Through a sequential de-correlation the Kalman filter measurement update can be performed sequentially and optimally. Monte Carlo simulations show that the MFVO and SLAM pose estimates are similar. Compared with SLAM, the proposed method uses less computation resources especially when the number of features in view is large. The results from a real dataset are also presented.

In a GNSS/INS integrated system, the GNSS outputs, such as position and velocity, are used to estimate the INS navigation errors and inertial sensor errors and the inertial solutions are used to bridge the GNSS outages for which a good quality IMU is needed. Since MEMS IMU outputs are corrupted by significant sensor errors, the navigation errors will accumulate quickly which degrade the navigation solution over a short time period in the presence of GNSS outages. The rotary INS technique has been proposed to reduce the MEMS-based INS navigation errors recently. A rotary INS is an inertial navigator in which the IMU is installed on a rotation platform. By modulating the significant inertial sensor errors through proper IMU rotations, the accumulation of navigation errors can be effectively mitigated without a need for external aiding. Based on the previous work on MEMS-based rotary INS, this paper proposed an integrated system of GNSS and rotary INS. Given the ability of a rotary INS to extend autonomous navigation, the integrated system can significantly improve the navigation performance to bridge GNSS outages under GNSS-challenging environments, such as vehicles travelling through tunnels. Based on a single-axis rotation table, road kinematic tests are conducted to evaluate the performance of the proposed system using two different MEMS IMUs (MTi-G from Xsens and NAV440 from Moog Crossbow). The results indicate that the IMU rotation can reduce the horizontal position errors by about 2 times for the system with MTi-G and about 3 times for the system with NAV440 during the period of GNSS outages.

This paper is concerned with the estimation of heading information of the Pedestrian Navigation System (PNS). The MEMS inertial sensors as well as a miniature GNSS receiver are used to establish a pedestrian navigation prototype based on the Pedestrian Dead Reckoning (PDR) approach. An Extended Kalman Filter (EKF) structure is used for the estimation of the system’s attitude error and the bias of the gyroscope. If there is no external acceleration, errors of pitch and roll as well as the biases of the two horizontal gyros are compensated using the aiding information from the accelerometer. When GNSS is available, its output is used for heading and heading-gyro bias estimation. Using the aiding information provided by both GNSS and accelerometer, the proposed method prevents the errors in the attitude from increasing rapidly. The proposed method for pedestrian navigation application has been well verified through real field experiments.

In this paper, we propose a systematic framework for the ground moving target autonomous positioning with a Unmanned Aerial Vehicle (UAV). The proposed framework consists of the ground moving target positioning design and algorithm. Therein the camera mounted on the UAV functions as a mission sensor targeted for the ground moving target positioning. In this paper, We design an algorithm for the vision based mission system by using the navigation information outputted by Attitude and Heading Reference System (AHRS) and GNSS/Strapdown Inertial Navigation System (SINS) integrated navigation system, including motion detection and compensation, target detection and tracking, as well as target positioning. The experiments of the ground moving target autonomous positioning have been carried out. The test results show that the system can provide the positioning information of ground moving target for UAV.

Commonly, X-ray Pulsar Navigation should observe three pulsars to determine the position of the detector. It leads to at least three detectors should be equipped. In this paper, an initial orbit determination algorithm using one detector to observe a single X-ray pulsar is presented in this paper. The algorithm combines the two-body motion equations and least squares iterative method to obtain initial orbits of spacecrafts, in which the phase comparison method of weighted FFT is used to process simulation signal of an X-ray pulsar. Then, the feasibility of the orbit determination algorithm and the phase comparison method are verified on Matlab environment. As expected, the results show that the orbit determination algorithm is feasible and has a good accuracy. As well, it can be widely used on earth and other planets’ orbits.

According to the challenges of storage and computation faced by massive, multi-source and heterogeneous GNSS data, the design objective of cloud GNSS is analyzed, then the architecture of cloud GNSS from infrastructure, data management, service management to application is designed, the deployment model including service management platform, Web server cluster and multiple Hadoop clusters is provided, and its’ characteristics such as strong expansibility, high reliability, loose coupling, are summarized. Cloud GNSS platform is built in the experiment, the storage model of massive GNSS data and the parallel computing model of GNSS network are built, distributed storage, parallel retrieval, sub-network division distributed computing and data publication are achieved. The result shows that the architecture proposed by the paper can be applied in the storage, processing and service publication of large-scale GNSS network.

The widespread deployment of Wi-Fi communication makes it easy to find Wi-Fi access points in the indoor environment, which enables us to use them for Wi-Fi fingerprint positioning. Although much research is devoted to this topic in the literature, the practical implementation of Wi-Fi based localization is hampered by the variations of the received signal strength (RSS) due to e.g. impediments in the channel, decreasing the positioning accuracy. In order to improve this accuracy, we integrate Pedestrian Dead Reckoning (PDR) with Wi-Fi fingerprinting: the movement distance and walking direction, obtained with the PDR algorithm, are combined with the K-Weighted Nearest Node (KWNN) algorithm to assist in selecting reference points (RPs) closer to the actual position. To illustrate and evaluate our algorithm, we collected the RSS values from 8 Wi-Fi access points inside a building to create a fingerprint database. Simulation results showed that, compared to the conventional KWNN algorithm, the positioning algorithm is improved with 17 %, corresponding to an average positioning error of 1.58 m for the proposed algorithm, while an accuracy of 1.91 m was obtained with the KWNN algorithm. The advantage of the proposed algorithm is that not only the existing Wi-Fi infrastructure and fingerprint database can be used without modification, but also that a standard mobile phone is sufficient to implement our algorithm.

PDR (Pedestrian Dead Reckoning) is a relative positioning method using step length and heading. However, the step length is varying while a pedestrian performs different motions. With estimated motion state, the adaptive step length model can be applied. Considering that human motion is a continuous procedure, in this paper, we propose a sequence-based motion recognition method which estimates the motion states from a sequence of data. In contrast with traditional classifiers, this paper deploys a HMM (Hidden Markov Model) to infer the state labels of sequence motion. And with the assist of motion recognition, a 3D indoor pedestrian localization is presented. Experimental results show that the classification accuracy of sequence-based motion recognition is improved comparing to that of using Naïve Bayes classifier on standalone motion states. Furthermore, the positioning accuracy of a pedestrian in indoor environments is promoted using proposed method in this paper. The mean positioning error is reduced from 0.78 to 0.30 m. The 50th and 95th percentile errors are also cut down in the test within a typical office building.

Conventionally, all of the sensors, except the IMUs, function as aiding sensors in the multisensor integrated kinematic positioning and navigation. In this way, the IMU measurements are only used in free inertial navigation calculation, not through measurement update in Kalman filter (KF) between two adjacent aiding measurement epochs. This paper strives for a novel structure of IMU/GNSS integration KF, which deploys a kinematic trajectory model as the core of the KF system model and utilizes all of the measurements, inclusive of the ones from IMUs, through measurement updates. This novel multisensor integration strategy takes advantage of modern computing technology and well advances the realization of Kaman filter for a better utilization of the IMU measurements, especially either with low-cost IMUs or in poor GNSS and/or GNSS denied environment. Moreover, one no longer needs to distinguish between the core sensors and the aiding sensors. The conceptual comparison with the conventional error-state and error measurement based inertial navigation integration shows its advantages. The results from real road tests along with discussions are also presented.

An Inertial navigation System (INS) is self-contained, immune to jamming/interference and in many other ways is ideally for pedestrian navigation applications especially in indoor environments. However, due to the sensor properties the quality of the navigation solution from a stand-alone INS will degrade rapidly, and must rely on some form of external correction/calibration/aiding to ensure system stability and reliability. In this contribution the authors use GPS when outdoors and WiFi when indoors to aid the INS in order to support seamless pedestrian navigation. To improve the performance of WiFi positioning, an enhanced fingerprinting method is proposed. A new fingerprinting database augmented by two types of map-based information is described. One is the topological relationship linking corridors, and the other is the orientation information of different corridors. Test results confirm that the navigation accuracy and stability is improved.

Most of the phone has been configured IMU currently, includes an acceleration sensor and an electronic compass. In this paper, using the pedestrian dead reckoning algorithm based accelerometer and electronic compass composition IMU to assist indoor positioning. Detection walking step length and state. Currently detect direction of motion requires the user wear or hand in IMU with a fixed posture. To address this issue, using the terminal gesture recognition algorithm in the third quarter. When pedestrian walking on the same direction, the angle walking forward and walking backward was the same. To address this issue, using pedestrian movement direction detection method based on the differential cross-correlation of the acceleration in the fourth quarter. Based on the above, the article conducted experiments in Section V and the result shows that the proposed method can effectively detect pedestrian movement forward and backward state, the average accuracy of the detection results is 85.67 %.

Traditional Strapdown Inertial Navigation Systems (SINS) simulator based on pure mathematical model cannot reflect the reality of complex dynamics of a carrier. In this paper, based on the actual flight data of an airborne navigation system, navigation algorithms of high-precision carrier phase differences Global Navigation Satellite System (GNSS) and medium-precision Inertial Measurement Unit (IMU) are used, and combined with the partial feedback principle of Kalman filter and cubic spline interpolation method, to generate smooth trajectory parameters. Then, the simulation of inertial sensors is achieved with the inversed SINS algorithm, and the new algorithm considers the impacts of attitude coning error and velocity sculling error compensation. Numerical verifications of airborne flight test have demonstrated that the inertial sensor simulator has high accuracy and good frequency characteristic, and can meet the high-accuracy SINS requirements for simulated inertial sensor data source and frequency complexity.

Due to the increased complexity of the application scenario, the conventional navigation and positioning system, which uses a single method, can’t meet the challenge of accuracy and reliability. Comparing with multi-sensor fusion, All Source Navigation and Positioning (ASPN) provides an all-in-one solution. It uses a uniform architecture to achieve data fusion of numerous sensors and data filtering with the ability of re-configuration. It tries to provide the maximum accuracy and reliability when some navigation and positioning methods, especially the GNSS, are not available. This paper mainly introduces the ASPN’s concept and its development status. It also analyses and predicts the critical technology of ASPN.

Due to the complicated and changeable environment for moving target. Tracking is difficult through single system to observate. And single motion model cannot describe the moving state for changeable state. On Bayesian estimation theorem, the mixed interacting multiple system and model filter algorithm for tracking is proposed (IMSM). Its performance is better than single dimension interacting filter. Finally simulation results show the effectiveness of the proposed algorithm.

GNSS has been applied widely. Yet because satellite signals are vulnerable and susceptible to blockage, the operability of GNSS in urban canyons are greatly hampered and GNSS even proves useless for indoor settings. This paper proposes system architecture for the integration of WLAN fingerprinting, visual positioning, baroceptor-derived altitude estimation and GNSS for seamless indoor/outdoor positioning for vehicles and pedestrians. This architecture augments GNSS through the integration of terminal-side/network-side positioning and position/measurement domain. After temporal and spatial synchronization, data from each sensor is filtered by sub filters and then processed by the main filter. The purpose of these operations is to provide accurate and continuous estimates of positions. Tests conducted in the new technology center of CAS show that the architecture proposed can achieve seamless indoor/outdoor positioning, with a better accuracy performance than any single-source method as the former still maintains accuracy and continuity when the later generates noticeable errors. Calculation shows that multi-source fusion has an accuracy level of better than 1 m (outdoor)/3 m (indoor), hence capable of meeting users’ demand for seamless indoor/outdoor positioning.

It is a very important way to realize the satellite data injection, control and autonomous navigation through inter satellite link to communicate and range. Quantum technology has special advantages in realizing the secure communication, and has been gradually tested and applied. The technology based on the high precision ranging theory of quantum interference has become more mature. The design and analysis is of strategic significance to our future generation of global navigation satellite system inter-satellite technology development.

As a strategic emerging and national defense industry, the satellite navigation system needs effective industrial policy to drive rapid development. The following four reasons can account for this view. Firstly, the development of satellite navigation system needs effective industrial policy guidance urgently to adapt the disorder even vicious competition in the beginning. Secondly, satellite navigation deserves the government protection and support as a comparative advantage industry. Thirdly, the government must adjust the market access mechanism of satellite navigation industry to achieve the optimal resources allocation and strongest competitiveness. Fourthly, the policy efforts of satellite navigation is far lower than the US, Russia or other developed countries with the disadvantages of low level, no system, too general and lack of policy tools. To perfect the Beidou satellite navigation system, the following principals should be considered: the government leading adapted with market economy system; the global view based on national conditions; the systematic design with overall propulsion; the intensive attention of theoretical research.