Guangfu Sun

A modified sidereal filtering for mitigating the code measurement multipath effects of BeiDou GEO satellites

Multipath delay is one of major error sources which limit global navigation satellite systems positioning accuracy. Due to the orbit characteristics, multipath effects are more evident on the code range observables of BeiDou Navigation Satellite System (BDS) geostationary earth orbit (GEO) satellites. We employed zero-phase filter to extract the low-frequency components of multipath series with the definite cutoff frequency and pass-band gain, and introduced a modified sidereal filtering for mitigating the multipath effects on code measurements of GEO satellites. The applications of this modified sidereal filtering show that the corrections for the standard deviation of code observables residuals on BDS B1, B2, and B3 frequency have reached more than 30, 22, and 14%, respectively. After resolving the GEO satellites code measurement multipath effects, the precisions of code-only single-point positioning were also improved.

Multipath detection based on single orthogonal dual linear polarized GNSS antenna

Based on the polarization difference between the multipath and the line-of-sight (LOS) signal, a method for multipath detection using a single antenna is proposed. The antenna has two channels to receive two orthogonal linear polarized components of the multipath and LOS signal, respectively. A hypothetical model of the antenna is employed such that the antenna patterns of the channels are assumed identical regarding amplitude and phase and are independent of azimuth. The antenna gain in the direction below the local horizon is assumed to be larger than in the direction toward LOS signals. Parallel cross-cancellation is used to remove the LOS signal from the received signals based on the magnitude and phase difference between the two orthogonal components. Then the residual signals are processed by a conventional digital processor of global navigation satellite system. The multipath can be detected by parallel cross-cancellation in the receiver in real time. The proposed method makes use of the polarization and spatial information of the multipath and LOS signal, and can detect short-delay multipath.

Impact of reference element selection on performance of power inversion adaptive arrays

Antenna arrays with adaptive algorithms are widely used to provide anti-jamming abilities for Global Navigation Satellite System (GNSS) receivers, among which Power-Inversion (PI) algorithm is attractive for suppression of jammers before de-spreading of signals and simplicity for implementation. Most of previous works either selected the reference element arbitrarily or naturally selected the center element of the array geometry as reference. In this paper, we studied the effect of reference element selection on the performance of the adaptive array receivers. The results show that although the selection of reference element has negligible effects on interference cancellation, it does affect the array gain in the direction of desired signal as well as the array output signal-to-interference-plus-noise ratio (SINR). When the optimal reference element is selected, it will give more than 30% improvement in terms of available angular region under no SNR loss condition over arbitrary reference element selection.

Adaptive wavelet denoising unscented Kalman filter for BeiDou signal carrier tracking under ionospheric scintillation conditions

Abstract. Ionospheric scintillation can cause BeiDou system (BDS) signal amplitude fading and phase variation as the radio frequency (RF) signals pass through the ionosphere. With the accidental, sudden, and regional characteristics of ionospheric scintillation, it is difficult to effectively mitigate the impacts of ionospheric scintillation from a system perspective. To overcome this problem, this work addresses the mitigation of scintillation for the BDS signal. We propose an adaptive wavelet denoising unscented Kalman filter (WDUKF)-based carrier tracking algorithm to mitigate the adverse impacts of ionospheric scintillation. First, as WD can better characterize the nonstationary of signal, the non-Gaussian noise caused by scintillation can be filtered by designing a sliding window-based online WD filter. Second, taking the denoised integrations as an input, we employ the phase lock indicator (PLI)-based adaptive UKF carrier phase estimator to reduce the linearization approximate error of conventional KF-based algorithms. Through adjusting the measurement vector of UKF with different scintillation scenarios adaptively, the divergence problem of UKF can be mitigated. Simulation and real data experimental results demonstrate the validity of the proposed method, especially in the case of 36 dB-Hz in moderate scintillation, the phase jitter and probability of loss-of-lock decrease about 6 deg (40%) and 71%, respectively.

High Accuracy and Real-Time Pseudorange Generation for GNSS Navigation Signal Simulator Based on Hermit Interpolation

Focusing on the issue that the traditional high accuracy pseudo range generation is hard to satisfy the real-time request, a high accuracy real-time pseudo range generation method based on Hermit interpolation was proposed after the performance comparison of different interpolation algorithm. Then, its theoretical accuracy is analyzed and the main influence factors on the pseudo range generation accuracy are simulated. The results indicate that the real-time performance can reach 10 milliseconds on the condition of 1 millimeter accuracy, which can fully satisfy the real-time request of GNSS navigation signal simulator.

The application of zero phase filter on BDS geostationary satellite code multipath mitigation

Multipath delay is one of major error sources which limit global navigation satellite system (GNSS) positioning accuracy. Duo to the orbit characteristics, multipath effects on the code observables of geostationary earth orbit (GEO) satellites are more evident and can be tracked continuously over long time scales. We introduce a data processing technique, based on residual analysis, zero-phase filter and sidereal filtering, for mitigating the multipath effects on code rang measurement of GEO satellites, and investigate the characteristics of multipath series both in time and frequency domain. Since the multipath series have different frequency components, zero-phase filter is employed to decompose the low frequency components of multipath series with no phase shifting and distortion, and then the extracted multipath terms are applied as reference to correct the multipath effects on code observables of the subsequent day. A real data experiment shows that 33~64% improvement can be achieved in standard deviation of code measurement residuals, and the standard deviations of east, north and up components of single point positioning (SPP) accuracy are approximately reduced by 0.3m, 0.5m and 0.6m.

A Quick A-BDS Location Method Based on Characteristics of GEO Satellite and Ridge Estimate

The calculation of traditional A-GPS time-free positioning method will be very complex without the approximate position. But hybrid constellation was adopted by BeiDou Navigation Satellite System (BDS). And the GEO satellite of BDS has high speed of NAV data rate. So a fast positioning method for BDS receiver based on characteristics of GEO satellite and ridge estimate was proposed in this paper. First, an approximate position was got by using ridge estimate with GEO constellation. The ridge estimation can solve problem of coefficient matrix ill-conditioned. Then the signal transmission time of MEO/IGSO satellite was restored with the approximate position. A simulation environment was built by using BDS broadcast ephemeris information. The white noise with 6 m standard deviation was added to pseudoranges. The success rate of the quick location method is big than 99.65 % in China surrounding area. And about 80 % of China surrounding area can 100 % guarantee to restore a complete satellite signal emission time and obtain an accurate position.

NLOS Signal Detection Based on Single Orthogonal Dual-Polarized GNSS Antenna

Nowadays users have a high demand for the accuracy of position and velocity, but errors caused by non-line-of-sight (NLOS) signals cannot be removed effectively. Since the GNSS signal is right-hand circular polarized (RHCP), the axial ratio of the strong NLOS signal is larger than that of the Line-of-Sight (LOS) signal. Based on the difference of the axial ratio, a method for NLOS signal detection using single orthogonal dual-polarized antenna is proposed. The antenna has two channels to receive two orthogonal linear polarized components of the incoming signals. Parallel cross-cancellation is used to remove the LOS signal while maintaining most of the NLOS signals from the receiving signals. The residual NLOS signals are then detected by conventional GNSS digital processor in real time without any prior knowledge of their characteristics. The proposed method makes use of the polarization and spatial information and can detect long delay NLOS signal by miniature and inexpensive receiver GNSS. The effectiveness of the proposed method is confirmed by simulation data.

An Improved Geometry-free Three Carrier Ambiguity Resolution Method for the BeiDou Navigation Satellite System

BeiDou satellites transmit triple-frequency signals, which bring substantial benefits to carrier phase Ambiguity Resolution (AR). The traditional geometry-free model Three-Carrier Ambiguity Resolution (TCAR) method looks for a suitable combination of carrier phase and code-range observables by searching and comparing in the integer range, which limits the AR success probability. By analysing the error characteristics of the BeiDou triple-frequency observables, we introduce a new procedure to select the optimal combination of carrier phase and code observables to resolve the resolution of Extra-Wide-Lane (EWL) and Wide-Lane (WL) ambiguity. We also investigate a geometry-free and ionosphere-eliminated method for AR of the Medium-Lane (ML) and Narrow-Lane (NL) observables. In order to evaluate the performance of the improved TCAR method, real BeiDou triple-frequency observation data for different baseline cases were collected and processed epoch-by-epoch. The results show that the improved geometry-free TCAR method increases the single epoch AR success probability by up to 90% for short baseline and 80% for long baseline. The A perfect (100%) AR success probability can also be effortlessly achieved by averaging the float ambiguities over just tens of epochs.

A Hybrid Navigation Constellation Inter-satellite Link Assignment Algorithm for the Integrated Optimization of the Inter-satellite Observing and Communication Performance

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.