Global Navigation Satellite System Code Research Articles

Characterization and mitigation of urban GNSS multipath effects on smartphones

In urban environments, the code measurements of Global Navigation Satellite System (GNSS) on smartphones can be significantly degraded by presence of multipath and non-Line-Of-Sight (NLOS) effects. Extensive studies have been carried out on characterizing the quality of GNSS code measurements under different conditions, which can be used to refine the weighting model and fault detection method. However, our knowledge regarding the impacts of multipath effects on smartphones remains limited. This includes determining the dominant error source for urban GNSS on smartphones between multipath and NLOS errors, and characterizing the fault-free code measurements for pedestrians in urban canyons. To address these issues, we conducted extensive tests in a typical urban area in Hong Kong and analyzed characteristics of multipath effects. Analysis revealed that 92.5 % of code outliers stem from NLOS signals, which result in longer ranging measurements, making NLOS the dominant error source impacting GNSS performance. Further, we established that over 92 % of fault-free signals are from the opposite sky of a pedestrian, and we found that the sidewalk can be reliably determined by examining signal-to-noise ratio (SNR) measurements, eliminating the need of complex 3D building models. The identified sidewalk can be used to enhance GNSS performance in urban areas. An experiment in the urban canyon was performed in urban canyons. Results show that the accuracy can be improved from 15 m to 4.6 m when the correct sidewalk can be identified.

A Multi-Global Navigation Satellite System (GNSS) Time Transfer Method with Federated Kalman Filter (FKF)

Relative to single Global Navigation Satellite System (GNSS) measurements, i.e., the measurements from a single GNSS system, a single GNSS code, and a single GNSS receiver, multi-GNSS measurements for time transfer could improve reliability and provide better short-term stability. Previous studies applied equal weighting to different GNSS systems or different GNSS time transfer receivers, which, to some extent, revealed the improvement in the additional short-term stability from the combination of two or more kinds of GNSS measurements. In this study, the effects of the different weight allocation for multi-measurements of GNSS time transfer were analyzed, and a federated Kalman filter was designed and applied to fuse multi-GNSS measurements combined with the standard-deviation-allocated weight. Tests with real data showed that the proposed approach can reduce the noise level to well below about 250 ps for short averaging times.

Code phase tracking error based autonomous integrity monitoring for GNSS/INS ultra-tightly integrated system

The ultra-tight integration of GNSS (Global Navigation Satellite System) and INS (Inertial Navigation System) may suffer from faults in GNSS, INS and integration filter. Both the faults occurred at the current epoch and at previous epochs affect the position solution deviation of ultra-tight integration at the current epoch, and the effect is reflected in GNSS code phase tracking errors. In this paper, a new autonomous integrity monitoring algorithm is proposed for the federated GNSS/INS ultra-tight integrations in which the code phases of local GNSS signal replicas for GNSS signal tracking are completely derived from the integrated navigation solution. In the proposed algorithm, GNSS code phase tracking errors are employed to construct the test statistics for fault detection through a MHSS (Multiple Hypothesis Solution Separation) method improved from the classical MHSS used in ARAIM (Advanced Receiver Autonomous Integrity Monitoring). With the improved MHSS, the proposed algorithm can account for GNSS nominal biases, multiple GNSS faults and the faults in INS and integration filter. The protection levels under multiple hypothesis are also derived. A semi-physical simulation of the federated ultra-tight integration of GPS (Global Positioning System) and INS in airplane approaching case and a vehicle-based field test of the federated ultra-tight integration of GPS, Galileo and INS are conducted to validate the proposed algorithm. The experiments show that the designed fault detection can effectively detect the occurred faults and the derived protection levels can correctly bound the caused position solution error.

GNSS Code Multipath Time-Frequency Analysis Using Wavelet-Based Synchrosqueezing Transform in Urban Environments

Time–frequency (TF) analysis can be used as a useful tool to detect the global navigation satellite system (GNSS) code multipath (MP) and its frequency content. An accurate TF representation (TFR) is critical for highlighting the MP’s frequency signature and identifying its possible sources. The popular short-time Fourier transform (STFT) method has limitations in dealing with fast varying instantaneous frequencies, which are frequently observed in global navigation satellite system (GNSS) measurements due to MP. The wavelet-based synchrosqueezing transform (WSST) is a potential technique for providing a detailed high-resolution TFR. In this letter, we use WSST to perform TF analysis on both simulated and real-world data, demonstrating its utility in detecting code MP and its frequency content in urban environments. Based on the results, possible MP sources for the real datasets were identified. Furthermore, the proposed technique’s TF analysis results were validated using the ray-tracing method, demonstrating its effectiveness for MP detection.

GNSS Measurements Model in Ship Handling Simulators

Electronic chart display and information system (ECDIS) forms the basis of contemporary and future marine e-navigation, track control, and integrated navigation systems, and is a key navigational aid in maritime ship handling simulators. All the ECDIS information is referred to as positioning, navigation, and timing (PNT) data derived from the global navigation satellite system (GNSS) by default. GNSS data fidelity, its representation, and accurate model of error propagation to ship final position are becoming the key factors enabling ship handling simulators to be utilized in navigators' training and research analyses of vessels' maneuvering. This paper presents an advanced stochastic model of GNSS code pseudorange observations and position-fix calculation based on GPS example. It has been developed for simulated GPS shipborne receivers interconnected to the ECDISs in physical and virtual reality ship simulators.

Aircraft positioning using PPP method in GLONASS system

PurposeThe purpose of the study is focused on implementation of Global Navigation Satellite System (GLONASS) technique in civil aviation for recovery of aircraft position using Precise Point Positioning (PPP) method in kinematic mode.Design/methodology/approachThe aircraft coordinates of Cessna 172 plane in XYZ geocentric frame were obtained based on GLONASS code and phase observations for PPP method. The numerical computations were executed in post-processing mode in the RTKPOST module in RTKLIB program. The mathematical scheme of equation observation of PPP method was solved using Kalman filter in stochastic processing.FindingsIn paper, the average accuracy of aircraft position is about 0.308 m for X coordinate, 0.274 m for Y coordinate, 0.379 m for Z coordinate. In case of the mean radial spherical error (MRSE) parameter, the average value equals to 0.562 m. In paper, the accuracy of aircraft position in BLh geodesic frame were also showed and described.Research limitations/implicationsThe PPP method can be applied for determination the coordinates of receiver, receiver clock bias, Zenith Wet Delay (ZWD) parameter and ambiguity term for each satellite.Practical implicationsThe PPP method is a new technique for aircraft positioning in air navigation. The PPP method can be also used in receiver autonomous integrity monitoring (RAIM) module in aircraft-based augmentation system (ABAS) system in air transport. The typical accuracy for recovery the aircraft position is about cm ÷ dm level using the PPP method.Social implicationsThe paper is destined for people who work in area of geodesy, navigation, aviation and air transport.Originality/valueThe work presents the original research results of implementation the GLONASS satellite technique for recovery the aircraft position in civil aviation. Currently, the presented research PPP method is used in precise positioning of aircraft in air navigation based on global positioning system and GLONASS solutions.

Generalised Theory on the Effects of Sampling Frequency on GNSS Code Tracking

Synchronisation of the received Pseudorandom (PRN) code and its locally generated replica is fundamental when estimating user position in Global Navigation Satellite System (GNSS) receivers. It has been observed through experiments that user position accuracy decreases if sampling frequency is an integer multiple of the nominal code rate. This paper provides an accuracy analysis based on the number of samples and the residual code phase of each code chip. The outcomes reveal that the distribution of residual code phases in the code phase range [0, 1/ns), where ns is the number of samples per code chip, is the root cause of accuracy degradation, rather than the ratio between sampling frequency and nominal code rate. Doppler frequencies, coherent integration periods, front-end filter bandwidths and received Carrier to Noise ratios (C/N0) also influence receiver accuracy. Also provided are a sampling frequency selection guideline and new proposed estimates of the correlation output and the Delay Locked Loop (DLL) tracking error, which can be applied to precisely model GNSS receiver baseband signal processing.

Research on assessment method of intrasystem and intersystem of the global navigation satellite system

The global navigation satellite system (GNSS) has become an important space infrastructure. Following GPS and GLONASS, Europe and China have been building their own global navigation satellite system, respectively, GALILEO and Compass. In order to consolidate the leadership of GPS in the globe, United States is gradually upgrading the traditional GPS. Simultaneously, Russia is also intensively restoring full performance of GLONASS. With the advancement of international satellite navigation system, satellite navigation frequency resources are already in short supply, and the design and use of the navigation signals are more sophisticated and complex due to commercial, disaster relief and other reasons. Since there may be many navigation signals in the same basic bandwidth, the coexistence of multiple systems and the combined application make intersystem mutual interference become the focus research. Under this background, the satellite navigation system mutual interference evaluation system needs to be established urgently to meet and support the compatibility and interoperability of the GNSS system. In the paper, through the performance analysis of the GNSS signal acquisition, carrier tracking, data demodulation and code tracking, the equivalent carrier to noise ratio model based on spectrum isolation coefficient is established, and the theoretical system of the GNSS signal mutual interference is proposed according to the mechanism, and the mutual interference of GPS, GALILEO and Compass system is analyzed and assessed.

Memory‐based two‐dimensional‐parallel differential matched filter correlator for global navigation satellite system code acquisition

This study presents a code acquisition architecture for a global navigation satellite system (GNSS). The proposed scheme aim to reduce buffer resource required without reducing the number of code, frequency and satellite bins. Therefore the GNSS signal has no information loss. The code acquisition process in a GNSS attempts to find the code phase of a satellite signal, and it includes three procedures: coherent integration (CI), correlation and in CI. The proposed code acquisition architecture provides a lower operation count for correlation with reduced memory consumption. Firstly, the memory in CI and the shift register in the correlator are integrated by changing the operation sequence of CI and correlation. Thus, half of the memory in CI can be removed, and the shift register becomes the sharing buffer for both correlation and CI. Secondly, the addition count in the correlation is reduced by combining a parallel differential matched filter (PDMF) with a two-dimensional (2D) architecture to form a memory-based 2D-PDMF correlator. Finally, changing the sample sequence before integration reduces the memory of in CI. Compared with conventional code acquisition, the proposed design can reduce register consumption by 80% and addition count by 60% operation count for correlation and 50% memory consumption of incoherent integration.

Multi-objective approach in GNSS code discriminator design

In spread spectrum ranging system receivers such as the Global Navigation Satellite System (GNSS) receivers, a discriminator is used in the code tracking loop to provide an error signal for the tracking of incoming signals. Typically, the discriminator manipulates several correlator outputs to form the correction signal. A multi-objective approach is adopted here to design the coefficients associated with a multi-correlator-based discriminator to lead to a better performance tradeoff in large tracking range, acceptable multipath-induced bias, high sensitivity, free of ambiguity, and small variance. It is shown that the multiple-objective problem can be tackled via a quadratic/linear programming method, rendering the optimal coefficient vector for the implementation of the discriminator. In addition, as the discriminator design is often subject to conflicting requirements, it is shown that the proposed design approach is capable of establishing bounds on achievable performance. Examples with respect to BPSK (binary phase-shift keying) NRZ (nonreturn-to-zero), and BOC (binary-offset carrier) signals are given to illustrate the design approach.