The performance of bds relative positioning usage with real observation data

Precise relative positioning has numerous applications in collision avoidance, and lane-keeping/lane-changing maneuvers. For such applications, we need sensors that can precisely estimate the relative position. GPS carrier phase measurements can provide high accuracy if unknown cycle ambiguities (integers) are resolved correctly from among an integer search space of potential candidates. However, resolving these integers becomes challenging in urban areas where tall buildings and tree canopy can lead to poor satellite visibility and degraded measurement quality. To aid with integer fixing, multiple UWBs can be utilized, which provide noisy inter-ranging measurements at a high sampling frequency. We propose a precise relative positioning framework for a two-car setup via tight coupling of GPS carrier-phase and inter-ranging measurements from multiple UWBs. With these range measurements, we form an a priori estimate of the relative position that adaptively constrains the position search space, and subsequently reduces the induced integer search space. Adaptively constraining the integer search space improves integer fixing rate, enabling precise relative positioning. We demonstrate our algorithm’s performance on a real-world dataset collected with two cars in Stanford University. Our algorithm achieves improved accuracy over baseline methods, even in challenging urban settings.

Though widely used to generate the global navigation satellite system (GNSS) ultra-rapid orbit products for real-time applications, the batch least-squares (LSQ) adjustment and precise orbit determination (POD) prediction is limited for satellites undergoing maneuvers. To generate the truly real-time orbit products, we introduce the square root information filter (SRIF) real-time POD strategy, in which a real-time satellite maneuver handling algorithm that adapts the stochastic model for irregular satellite behaviors is implemented. The performance of the SRIF POD strategy is first evaluated with 1-month of data from multi-GNSS experiment (MGEX) network and BDS experimental tracking stations (BETS). Compared with the MGEX final products provided by GFZ (GBM), the SRIF solutions show higher precision than the ultra-rapid solutions. The averaged 3D RMS of the orbit differences between the SRIF solutions and the GBM final product is about 29.1 cm and 22.5 cm for the BDS IGSO and MEO satellites. The BDS orbits generated by SRIF are continuous over all the time, while the ultra-rapid orbits exhibit obvious jumps and discontinuity at the orbit update time. Validation by satellite laser ranging (SLR) shows that for GEO satellites, the SRIF solutions have better stability and continuity, whereas the GBM final products exhibit obvious accuracy degradation around the day boundary. To evaluate the performance of maneuver handling, the proposed method is further tested on 10 maneuver cases of BDS GEO and IGSO satellites. The start and end time of all maneuver events in different cases are precisely detected, which are consistent with the officially announced ones. Using the proposed strategy, the filter avoids divergence and outputs continuous orbit solutions during the maneuver periods and restores the normal POD within about 7.5 h after the maneuver is finished.

Combining GPS and TWSTFT considerably increases the robustness of the accurate time transfer result due to the complete independence between these two spatial techniques. In this paper we present the last improvements of a time and frequency transfer method based on a least-square analysis of GPS code and carrier phase measurements in common view, constrained by TWSTFT data. The combined method developed here provides a time transfer solution which benefits from the high short-term stability and high resolution of the GPS data and the high accuracy of the TWSTFT data. It allows to solve the large day boundary discontinuities that exist in some clock solutions obtained with geodetic time transfer, but some discontinuities appear occasionally in the CV+TW solution, due to the noise and diurnal perturbation in the TWSTFT data.

In this study, the carrier acceleration-ramp-step test was applied to GPS carrier phase measurements, and the results were compared and analyzed. In the carrier acceleration-ramp-step test, the acceleration, ramp, and measurements are estimated using 10 consecutive carrier phase measurements for satellites observed at the same time based on the least square method. As for the characteristic of this test, if failure occurs in the measurement, the value jumps significantly compared to the previous result; but it judges that failure has occurred in all the satellites although failure has occurred in one satellite. Therefore, in this study, a method that eliminates a satellite with failure was suggested, and thresholds of the carrier acceleration, ramp, and step were suggested. The evaluation of the failure detection performance of carrier phase measurement using the suggested thresholds showed that failure could be detected when the carrier phase measurement changed abruptly by more than about 0.1 cycles.

As airborne gravimetry matures as a technology, the major challenge remaining is to improve the accuracy and resolution of the measured gravity field. Errors in DGPS derived accelerations used for motion compensation are one of the main limitations. The standard method of determining aircraft acceleration is time differentiation of DGPS positions. In an effort to improve the quality of aircraft accelerations, an alternative method of deriving accelerations from DGPS is evaluated. The method, which was first presented by Jekeli (1994), estimates acceleration directly from GPS carrier phase measurements. It is revisited, with modification, and results in the gravity domain are presented for the first time.The carrier phase method is modified to utilize a least squares solution with a covariance model, to include all satellites available for a flight line.Using data from a strapdown airborne gravimetry campaign, gravity disturbance are estimated for the same input data with both the standard and modified carrier phase approaches. The results are compared and the effect of the carrier phase derived accelerations is shown.To assess the accuracy, results are compared to an upward continued reference field. The modified carrier method is shown to improve the estimated gravity disturbances, especially under turbulent flying conditions and during times of higher atmospheric activity. The results are discussed with respect to the requirements of exploration geophysics.

This paper proposed heave estimation using time-differenced GPS carrier phase measurement and compensated barometer measurement with applying error model. The carrier phase measurement makes a precise of the altitude more than code measurement because carrier phase based pseudo range has mm error. But integer ambiguity resolution problem must be solved when carrier phase measurement is used. Time-Differenced(TD) carrier phase measurements can be used to find a relative altitude using single GPS without an integer ambiguity resolution since a time-invariant. Integer ambiguity is removed by TD operation. Barometer error model estimated using Gauss-Morkov process. Output is result of kalman filter using barometer and carrier phase measurement. Performance of implemented system was evaluated through the experiments at various scenarios including static test in rural and urban areas.

ABSTRACT: This paper proposes a new cycle-slip correction method that enables instantaneous correction (i.e., using only the current epoch's GPS carrier-phase measurements) at the data quality control stage. The method was originally developed for real-time applications that require consistent high-precision positioning results with the carrier-phase measurements at a 10 Hz data rate. The approach includes (1) two parameters for generating and filtering cycle-slip candidates, and (2) a validation procedure that authenticates correct cycle-slip candidates. Compared with conventional approaches using carrier phases and pseudoranges, the approach does not require a smoothing or filtering process to reduce observation noise. Therefore, it is possible to implement the approach in real-time applications without undue complexity. Simulation tests were conducted to confirm the performance of the approach under worst-case scenarios. Test results for a variety of situations, including static and kinematic modes, short-baseline and long-baseline situations, and low and high data rates, are presented.

For its synergistic relationship, the integrated GPS/INS system has been adopted in many navigation systems. In this paper, a complete GPS/INS integration technique utilizing GPS carrier phase measurements is proposed. A measurement model of double-differenced GPS carrier phase measurements is newly derived in order to be used with the INS error model. Also, an algorithm is suggested to resolve the integer ambiguities of GPS carrier phase measurements by employing MS information. From simulation results, performance of the suggested technique is verified.

Robust and precise baseline determination of distributed spacecraft in LEO

Precision relative navigation is an essential aspect of spacecraft formation flying missions, both from an operational and a scientific point of view. When using GPS as a relative distance sensor, dual-frequency receivers are required for high accuracy at large inter-satellite separations. This allows for a correction of the relative ionospheric path delay and enables double difference integer ambiguity resolution. Although kinematic relative positioning techniques demonstrate promising results for hardware-in-the-loop simulations, they were found to lack an adequate robustness in real-world applications. To overcome this limitation, an extended Kalman Filter modeling the relative spacecraft dynamics has been developed. The filter processes single difference GPS pseudorange and carrier phase observations to estimate the relative position and velocity along with empirical accelerations and carrier phase ambiguities. In parallel, double difference carrier phase ambiguities are resolved on both frequencies using the least square ambiguity decorrelation adjustment (LAMBDA) method in order to fully exploit the inherent measurement accuracy. The combination of reduced dynamic filtering with the LAMBDA method results in smooth relative position estimates as well as fast and reliable ambiguity resolution. The proposed method has been validated with data from the gravity recovery and climate experiment (GRACE) mission. For an 11-day data arc, the resulting solution matches the GRACE K-Band Ranging System measurements with an accuracy of 1 mm, whereby 83% of the double difference ambiguities are resolved.

More recently, GPS carrier phase measurement using geodetic receivers is widely conducted for accurate time and frequency comparisons. Time transfer experiments were conducted using the Ashtech Z12T receivers whose internal frequency is provided by an external 20 MHz clock and an external 1 pps (pulse per second) of a reference clock. The results of time comparison has shown that the stability of time transfer using carrier phase is better than that of GPS common-view time transfer using GPS C/A or P3. The self-developed processing software was used to the cycle slip detection and ambiguity resolution determination. The objective of this paper is to compare the GPS P3 and GPS L3 time transfer. The GPS P3 and L3 data have been obtained using an Ashtech Z12T at NTSC and an Ashtech ZIIX3 at NICT. The main results and analysis are given in Section 3 and Section 4. For a long baseline comparison, the RMS of L3 is better than that of P3. The stability of frequency of L3 is better than that of P3 for short term tau>6d, however, for tau< 6d the stability of L3 and P3 is almost at the same level

This paper presents a random forest-based machine learning algorithm to automatically detect satellite oscillator anomaly by using dual- or triple-frequency GPS carrier phase measurements. The algorithm can distinguish satellite oscillator anomaly from other GPS carrier phase disturbances including ionospheric scintillation and the receiver oscillator anomaly. Carrier phase power spectral density and carrier phase ratios between carriers are extracted from measurements and applied as input features to the random forest algorithm. The method is trained using data collected at 7 GNSS monitoring stations located at Alaska, Ascension Island, Greenland, Hong Kong, Peru, Puerto Rico, and Singapore. The overall detection accuracies of 98.4% and 99.0% are achieved for dual- and triple-frequency signals, respectively. The method outperforms other machine learning algorithms. The preliminary detection results demonstrate that the proposed method can be employed on a global satellite oscillator anomaly monitoring system.

In GNSS real-time high-precision monitoring, the multipath spatial correlation is weak, it is difficult to eliminate the multipath error by double difference, and the traditional method based on the sidereal filtering in the coordinate domain to mitigate multipath error of MEO satellite will no longer be applicable. Aiming at the above problem, this paper storage single difference observation residuals after ambiguity resolved in real-time baseline resolution, where storage residual information for 1d in GPS, BDS GEO, IGSO, and BDS MEO satellite for 7d. When the residual information database initialization is complete, each satellite multipath error sequence model will be established from the residual database by using the low-pass filter method, then mitigating multipath error of the corresponding satellite carrier phase observations in real time. The measured data show that, based on the mitigating multipath of observation domain, the real-time monitoring accuracy of the 3D position can be improved by about 50% after mitigating multipath error in real-time.

Triple-frequency observations will introduce an inter-frequency clock bias (IFCB) between the new frequency and the original dual-frequency observations. It has been verified that satellite IFCB can reach dozens of centimeters and several centimeters for GPS Block IIF satellite and BDS satellite, respectively. The existence of satellite IFCB will significantly affect undifferenced triple-frequency data processing. Based on 4-year data collected from 80 globally distributed stations, the long-term characteristics of IFCB coefficients obtained by using harmonic analysis have been studied. The results demonstrate that the coefficients of IFCB periodic model cannot be well fitted only by using sun elevation angle. Also, coefficients have obvious periodic characteristics and their periods differ among different satellites. Thus, a new linear-plus-periodic model is proposed to fit the long-term coefficients. Then, IFCB empirical correction models for 12 GPS Block IIF satellites and BDS GEO and IGSO satellites are built. In order to validate the correction model, IFCB standard deviation (STD), triple-frequency precise point positioning (PPP) and undifferenced extra-wide-lane (EWL) ambiguity resolution are employed. The results based on more than 4-year observations show that, with correction model applied, the average IFCB STD decreases by about 65.5% and 45.5% for GPS and BDS satellites, respectively. Compared to triple-frequency PPP without IFCB correction, triple-frequency PPP results with IFCB correction show that Up, North and East components accuracy are improved by 12.3%, 16.0% and 13.2%, respectively. Besides, IFCB correction will greatly improve the consistence of EWL fractional cycle bias among different stations and improve the success rate of EWL ambiguity resolution.

Time transfer using GPS carrier phase measurements based on dual-frequency multi-channel common-view techniques is presented. By using the ionosphere-free combination of the carrier phase and performing the single-difference, we can obtain the relationship between two hydrogen-maser clocks. Moreover, combining the sub-nanosecond results of the multi-channel common-view based on dual-frequency code observations with the single-difference calculations, we resolve the ambiguity of the single-difference equation for time transfer. The short-baseline tests with common hydrogen-maser clock show that our methodology has a frequency stability of a few parts in 10/sup 16/ for averaging times of one day.