Multi-satellite cycle-slip detection and exclusion using the noise subspace of residual dynamics

Real-time detection of cycle-slips on undifferenced carrier-phase measurements is an important task to properly exclude wrong phase trackers from precise positioning algorithms. The detection is especially challenging in high-dynamic mobile scenarios, where traditional approaches (as those based on single-channel polynomial fitting) may easily lead to false positives. Using a multi-channel formulation of the problem, the proposed technique takes benefit of the available data redundancy (high number of tracked satellites) in order to ameliorate the false positives. This robustness is accomplished by adaptively estimating the orthogonal subspace spanned by the polynomial time-varying residuals obtained from all available channels (treated as a vector process), and using that subspace to form efficient channel combinations with cancelled satellite-receiver dynamics. The main advantage of the multi-channel approach is that wrong measurements can be discarded without needing any positioning estimate nor phase-ambiguity solver, thus improving the accuracy, reliability and integrity of positioning. The performance improvement is shown by means of theoretical analysis and computer simulations.Peer ReviewedPostprint (published version

Failure Detection of a Pseudolite-Based Reference System Using Residual Monitoring

The 746th TS uses a flight reference system referred to as the Central Inertial and GPS Test Facility (CIGTF) Reference System (CRS). Currently the CRS is the modern standard flight reference system for navigation testing, but high accuracy is dependent on the availability of GPS. A pseudolite system is currently being developed to augment the CRS and supply the capability to maintain high accuracy navigation under normal and jamming conditions. Pseudolite measurements typically contain cycle slips and other errors (such as multipath, tropospheric error, measurement noise) that can affect reliability. Past work relied on the receiver-reported signal-to-noise (SNR) value to determine whether or not a cycle slip occurred. However it has been shown that even when the SNR is relatively high, a cycle clip can occur. To reduce the error in the pseudolite measurements, the pseudolite system was integrated with an inertial navigation sys- tem (INS). The integrated system detects failures through residual monitoring using a likelihood function. Integrating the inertial sensor provides a means for a filter to maintain the reliability of the pseudolite data which, in turn, increases the integrity of the resulting navigation solution. An experiment was conducted using six pseudolites and a ground vehicle equipped with a pseudolite receiver, and both a commercial-grade and tactical-grade inertial systems. The inertial data was combined with both real and simulated data to evaluate cycle slip detection performance. Results from this experiment have shown cycle slips in the carrier phase measurements were detected and corrected using both commercial-grade and tactical- grade INS, but that performance, in terms of probability of detection and time to detect, was improved with the higher quality inertial data

Multi-frequency and multi-GNSS PPP phase bias estimation and ambiguity resolution

Multi-frequency and multi-GNSS measurements from modernized satellites are properly integrated for PPP with ambiguity resolution to achieve the state-of-the-art fast and accurate positioning, which provides an important contribution to GNSS precise positioning and applications. The multi-frequency and multi-GNSS PPP phase bias estimation and ambiguity resolution, which is accomplished by a unified model based on the uncombined PPP, are thoroughly evaluated with special focus on Galileo and BDS

GPS-aerotriangulation : in observation space

PhD ThesisThe research completed on UPS-aerial triangulation has been focused on combining of UPS and photogrammetric data in the way using GPS derived antenna coordinates, so called as "combination in position space". Thus, these antenna coordinates are used, or replaced with the normal control points on the ground, as control points which have been moved into the air. It was noticed that it is necessary to use crossing strips and introduce drift parameters into the analytical aerial triangulation estimation to compensate the shifts which are seen in these coordinates, probably caused by cycle slips in the UPS data. UPS offered a good opportunity to supplement, or completely replace, the ground control required by aerial triangulation procedures by determining the positions of an antenna onboard the aircraft, at each moment of exposure, quickly, cheaply and accurately but with crossing strips, drift parameters and stand-by GPS data, postprocessed GPS data as UPS derived antenna coordinates. This thesis offers a new method which is based on a combination of GPS dual frequency phase observations and photogrammetric measurements in a bundle estimation process, so called as "combination in observation space". Thus the new method leads to the solution of the redundancy problem facing the GPS users if the ambiguities and the point coordinates (or coordinate differences) together with the other parameters are to be solved for simultaneously. It also removes the need for cioss strips to compensate for shifts in the antenna coordinates and provides a good basis for the determination of integer ambiguities and cycle slips thereby saving a lot of effort and time. To explain this concept, the thesis reviews the UPS double differencing processes based upon phase observations and analytical aerial triangulation estimation method with emphasis being laid upon estimation using bundles. Alongside these, error sources that are likely to affect the UPS and bundle measurements are discussed and the new combination method is explained. The ability of the combined system to solve for the perspective center coordinates and the attitude of the camera onboard the aircraft, the coordinates of object points and integer ambiguities and to determine cycle slips in the way it propagates several random errors were the focus of the simulated tests carried out. The tests revealed the high potential of the combined system in relation to this. Although the system may be regarded as a reasonably sensitive method to solve for these parameters simultaneously as there are some cases where some of these parameters, especially integer ambiguities, cannot be solved for correctly or cycle slips cannot be detected. This is thought not to be a disadvantage of the method itself, but is rather due to weak geornetly or insufficient observations with the small sample used. The main conclusion from this work is that a combination of GPS and photogramrnetiy is indeed possible in observation space. The advantage in that cycle slips and integer ambiguities can be solved for (i.e. photogrammetry is contributing to GPS - not just the other way around as in the usual case) and additional photogrammetric data (in the form of cross strips) is not needed. The method has been to be successful even in the presence of severe multipath (up to 5 cm).Turkish governmen

Survey on Signal Processing for GNSS under Ionospheric Scintillation: Detection, Monitoring, and Mitigation

Ionospheric scintillation is the physical phenomena affecting radio waves coming from the space through the ionosphere. Such disturbance is caused by ionospheric electron density irregularities and is a major threat in Global Navigation Satellite Systems (GNSS). From a signal processing perspective, scintillation is one of the most challenging propagation scenarios, particularly affecting high-precision GNSS receivers and safety critical applications where accuracy, availability, continuity and integrity are mandatory. Under scintillation, GNSS signals are affected by amplitude and phase variations, which mainly compromise the synchronization stage of the receiver. To counteract these effects, one must resort to advanced signal processing techniques such as adaptive/robust methods, machine learning or parameter estimation. This contribution reviews the signal processing landscape in GNSS receivers, with emphasis on different detection, monitoring and mitigation problems. New results using real data are provided to support the discussion. To conclude, future perspectives of interest to the GNSS community are discussed

Multi-frequency and multi-GNSS PPP phase bias estimation and ambiguity resolution

Multi-frequency and multi-GNSS measurements from modernized satellites are properly integrated for PPP with ambiguity resolution to achieve the state-of-the-art fast and accurate positioning, which provides an important contribution to GNSS precise positioning and applications. The multi-frequency and multi-GNSS PPP phase bias estimation and ambiguity resolution, which is accomplished by a unified model based on the uncombined PPP, are thoroughly evaluated with special focus on Galileo and BDS