PRISM :: Browsing by Author "Petovello, Mark"

Browsing by Author "Petovello, Mark"

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Open Access
3D Building Model-Assisted Snapshot GNSS Positioning Method
(2017) Kumar, Rakesh; Petovello, Mark; Petovello, Mark; Lachapelle, Gérard; O'Keefe, Kyle; Fapojuwo, Abraham
Global Navigation Satellite Systems (GNSS) have proven to be a viable and reliable solution in interference-free environments and in presence of Line-of-Sight (LOS) signals only. However, in urban canyons, multipath signals directly affect the pseudorange measurements resulting in degraded positioning performance of traditional GNSS receivers. Moreover, traditional GNSS receivers cannot distinguish between non-LOS (NLOS) and LOS signals, resulting in even worse performance if the receiver tracks NLOS-only signal. Hence, NLOS and multipath signals remains a dominant source of error in satellite-based navigation. Most of the existing research has focused on identifying and rejecting NLOS measurements. However, little research has used NLOS signals constructively. In this regard, this research uses snapshots of GNSS data in order to estimate position, utilizing all NLOS signals constructively with the help of a 3D Building Model (3DBM). Using a 3DBM and a ray-tracing algorithm, the number of reception paths and the corresponding path delays of reflected signals is predicted across a grid of candidate positions. These predictions are then used to compute least-squares fit to the GNSS receiver’s correlator outputs and the position with smallest residuals is selected as the position estimate. This approach is termed Signal Delay Matching (SDM) and yields a solution that is nearly unaffected by traditional GNSS error sources, and has capability of providing a position solution using a single satellite only. The use of snapshots of data mean the receiver need not perform tracking operations, thus making it easier to implement and power efficient. The feasibility and performance of the algorithm was tested using data collected in downtown Calgary, Canada, where buildings reach heights of over 200 m. Contrary to traditional approaches, results for the proposed method show that positioning error decreases as sky-visibility decreases. For sky-visibility below 20%, the median error was found to be just over 3 m. Compared to two pseudorange-based receivers, the proposed method yields RMS errors improvements of 22% to 48% in the horizontal plane.
Open Access
A Standalone Approach for High-Sensitivity GNSS Receivers
(2014-09-29) Ren, Tiantong; Petovello, Mark
Global Navigation Satellite Systems (GNSS) such as the Global Positioning System (GPS) can provide users with accurate navigation and timing services worldwide. Recently, processing weak GNSS signals has been receiving growing attention because of the increased demand for navigation in signal challenged environments, e.g., indoors, under dense foliage canopies, in urban canyons, etc. High-sensitivity GNSS receivers are preferred for the improved acquisition and tracking capabilities under degraded signal environments. The current mainstream high-sensitivity GNSS receiver design utilizes assisted-GNSS to maximize performance. However, the assistance source is not always available and the cost of additional communication channels is often a requisite concern. In light of this, the standalone performance of high-sensitivity GNSS receivers is addressed in this thesis. In order to achieve bit wipe-off and extend coherent integration time, a newly proposed standalone high-sensitivity GNSS receiver uses Maximum-Likelihood (ML) bit synchronization and ML bit decoding algorithms to estimate the location of bit boundaries and the bit values from GNSS signals. A systematic performance analysis of ML bit synchronization and ML bit decoding is achieved. The theoretical performance models of ML bit synchronization and ML bit decoding are developed based on statistical theory. In order to further improve the performance of ML bit decoding, the benefits of using the advanced tracking algorithms in standalone mode to improve ML bit decoding are analyzed using a software GNSS receiver. Those advanced tracking algorithms include: vector tracking, ultra-tightly coupled architecture and open-loop tracking. Finally the estimated data bit values are used to extend coherent integration via the ML-based bit wipe-off, and the accuracy and reliability of the whole system are assessed in the navigation domain. The results of the vehicular field tests in dense foliage and urban canyon environments show the advanced tracking algorithms can improve the successful decoding rate (SDR) of bit values about 2% to 30% depending on signal power. Meanwhile, by extending coherent integration time from 20 ms to 100 ms using ML-based bit wipe-off in the standalone approach, the position and velocity accuracy has been shown to be improved about 50% in the vehicular field tests. In this thesis, two innovative strategies are proposed to mitigate the high bit error rate (BER) problem in ML-based bit wipe-off, and an innovative signal power based multipath mitigating algorithm is proposed. Finally, in order to improve the performance of ML bit synchronization, an innovative collective bit synchronization approach for weak GNSS signals using multiple satellites is proposed. The benefits of using collective bit synchronization to improve the detection rate of bit boundary positions are analyzed using a software GNSS receiver.
Open Access
Carrier Phase Prediction of Weak Signals for High-Accuracy Navigation
(2015-11-16) Wang, Boxiong; Petovello, Mark
In this thesis, carrier phase prediction method was investigated for improving real time kinematic (RTK) positioning when signals experience temporary loss of lock. The prediction method is developed and tested using GPS vector-based and GPS/IMU ultra-tight software receivers to generate predicted phase measurements. The main error sources and characteristics of the predicted phase are analyzed and tested using simulated data. Effort is then focused on evaluating the RTK positioning accuracy applying the predicted measurements. Positioning with and without using the prediction method is compared for the GPS vector-based receiver, and ultra-tightly coupled GPS/IMU receiver, and for an RTK/IMU loosely coupled system. Tests were carried out including simulated and foliage attenuation data. The tests’ outputs were analyzed in measurement and position domain separately, and it was verified that using predicted carrier phase measurements without an IMU do not provide significant benefits, but including the IMU provides considerable benefits.
Open Access
Combined Acquisition and Tracking Methods for GPS L1 C/A and L1C Signals
(Hindawi Publishing Corporation, 2010-09-18) Macchi-Gernot, Florence; Petovello, Mark; Lachapelle, Gérard
Open Access
Comparing Multicarrier Ambiguity Resolution Methods for Geometry-Based GPS and Galileo Relative Positioning and Their Application to Low Earth Orbiting Satellite Attitude Determination
(Hindawi Publishing Corporation, 2009-03-08) O'Keefe, Kyle; Petovello, Mark; Cao, Wei; Lachapelle, Gérard; Guyader, Eric
This paper presents an evaluation of several GNSS multicarrier ambiguity (MCAR) resolution techniques for the purpose of attitude determination of low earth orbiting satellites (LEOs). It is based on the outcomes of the study performed by the University of Calgary and financed by the European 6th Framework Programme for Research and Development as part of the research project PROGENY. The existing MCAR literature is reviewed and eight possible variations of the general MCAR processing scheme are identified based on two possible options for the mathematical model of the float solution, two options for the estimation technique used for the float solution, and finally two possible options for the ambiguity resolution process. The two most promising methods, geometry-based filtered cascading and geometry-based filtered LAMBDA, are analysed in detail for two simulated users modelled after polar orbiting LEOs through an extensive covariance simulation. Both the proposed Galileo constellation and Galileo used in conjunction with the GPS constellation are tested and results are presented in terms of probabilities of correct ambiguity resolution and float and fixed solution baseline accuracies. The LAMBDA algorithm is shown to outperform the cascading method, particularly in the single-frequency dual-GNSS system case. Secondly, more frequencies and multiple GNSS always offer improvement, but the single-frequency dual-system case is found to have similar performance to the dual-frequency single-system case.
Open Access
Development and testing of an l1 combined gps-galileo software receiver
(2010) Macchi, Florence; Lachapelle, Gérard; Petovello, Mark
Open Access
Development of a Multi-Frequency Adaptive Kalman Filter Based Tracking Loop for an Ionospheric Scintillation Monitoring Receiver
(2016-01-22) Ashwitha, Ashwitha; Lachapelle, Gérard; Lin, Tao; Petovello, Mark; Nowicki, Edwin
This thesis develops a combined GPS L1, L2C and L5 KF based tracking loop by exploiting the dispersive nature of the ionosphere and signal structure of the GPS signals. This results in a robust tracking loop suitable for a scintillation monitoring receiver. It also incorporates an adaptive algorithm that has adaptive bandwidth depending on scintillation level. Performance of combined KF based tracking algorithm compared with that of single frequency KF based tracking algorithm for both adaptive and non-adaptive cases are analysed and compared. A semi-analytic model is used to analyze the effect of scintillation on the tracking loop to perform faster and provide a reliable platform for analyzing the scintillation effects on the receiver performance. Results obtained from simulation data and real data show better performance for the adaptive multifrequency KF based tracking loop than that of the single frequency KF based tracking loop and the non-adaptive KF tracking loop.
Open Access
DGPS and UWB Aided Vector-Based GNSS Receiver for Weak Signal Environments
(2013-01-30) Chan, Billy; Petovello, Mark
Vector-based GNSS (VBGNSS) receivers attempt to bridge the gap between Assisted GNSS (AGNSS) and High Sensitivity GNSS (HSGNSS); AGNSS use satellite orbit and network time information to predict the incoming satellite frequency during signal acquisition while HSGNSS enables the tracking of GNSS signals with strong attenuation. Similar to AGNSS, VBGNSS receivers make use of both satellite and receiver navigation information (position, velocity, and clock) to better estimate the incoming signal frequency and code-phase to improve the tracking sensitivity of weak GNSS signals. The performance of VBGNSS receivers is proportional to the navigation solution accuracy; this research focuses on improving the performance of VBGNSS receivers using Ultra-Wideband (UWB) ranging and Differential GPS (DGPS) corrections. From the results presented herein, it was found that UWB ranging can improve the tracking sensitivity, position availability, and accuracy of a VBGNSS receiver; likewise DGPS can improve VBGNSS receiver performance in certain operating environments.
Open Access
Effect of GNSS Receiver Signal Tracking Parameters on Earthquake Monitoring Performance
(2016) Clare, Adam; Lachapelle, Gérard; Lin, Tao; Petovello, Mark; Wong, Ron
This research focuses on the performance of GNSS receiver carrier phase tracking loops for earthquake monitoring systems. An earthquake was simulated using a hardware simulator; position, velocity and acceleration displacements were obtained to recreate the dynamics of the 2011 Tohoku earthquake, Japan. Using a software defined receiver, various tracking bandwidths and integration times were tested. Using the phase lock indicator and carrier-to-noise ratio as metrics, an adaptive carrier tracking loop was successfully designed and tested to maximize performance for this application. Four different simulations were done to assess the performance of the adaptive carrier tracking loop. Two simulations with carrier-to-noise ratios greater and less than 35 dB-Hz were done using the original dynamics of the 2011 Tohoku earthquake. The other two simulations tested were the dynamics of the same earthquake scaled by a factor of 10, with carrier-to-noise ratios greater and less than 35 dB-Hz.
Open Access
Enhancing Student Learning Through the Eyes of Teaching Award Winners
(2013-05-15) Petovello, Mark; Ferber, Reed; Gabruck, Mila; Teng, Loretta (Moderator)
Open Access
High-Sensitivity GNSS Doppler and Velocity Estimation for Indoor Navigation
(2013-01-25) He, Zhe; Lachapelle, Gérard; Petovello, Mark
Doppler measurements in global navigation satellite system (GNSS) receivers are useful for various purposes since they not only convey velocity and attitude information, but also directly relate with carrier phase measurements. When it comes to poor signal conditions, conventional high sensitivity GNSS receivers usually extend integration time in order to maintain track of weak GNSS signals. However, due to low signal-to-noise ratio (SNR) and multipath effects, the navigation accuracy is still degraded in this case. Thus maintaining track of Doppler frequency with acceptable accuracy in challenged indoor environments is important and will be beneficial for both standalone and integrated solutions. This thesis investigates how to obtain more reliable and robust Doppler frequency and velocity estimates with GNSS signals for indoor navigation. Doppler errors due to indoor multipath and user dynamics are first investigated. Experimental results show that these errors are further affected by some multipath statistics such as averaged multipath angle of arrivals (AOAs). A directional signal/multipath model is thus developed to characterize such errors. To mitigate the adverse effects brought by multipath signals, a direct vector receiver with GLONASS capability is therefore proposed and developed. It is shown that when the user has partial visibility of line-of-sight (LOS) satellite signals, both the velocity and Doppler estimation accuracy is improved as compared to conventional high sensitivity receivers. Geometry dependent factors are defined and used to quantify such improvements. Finally, the benefits of using such Doppler measurements for consistent navigation are evaluated in two real indoor environments. Doppler measurements from both direct vector receiver and conventional high sensitivity receiver are tightly integrated with a PDR algorithm. Results show that in large open space indoor environments, the former integration strategy significantly improves the navigation accuracy. For office like indoor environments, improvements of the former integration strategy are not very apparent, but still outperform the conventional integration strategy. All these indicate that the quality of Doppler estimated by direct vector receiver is as good as or better than the conventional one for the indoor environments considered herein.
Open Access
Improving carrier phase reacquisition time using advanced receiver architectures
(2010) Xie, Peng; Petovello, Mark
A frequency lock loop (FLL) and a phase lock loop (PLL) are used to track the carrier in a GNSS receiver. In order to meet the most stringent positioning and navigation requirements, several receiver architectures have been proposed for global navigation satellite system (GNSS) including stand-alone receivers or GNSS receivers integrated with inertial navigation systems (INS). Basically, there are four receiver architectures, namely, standard receivers, estimator-based receivers, vector-based receivers, and ultratight receivers. The objective of this work is to reduce the camer phase reacquisition time usmg advanced receiver architectures. This paper looks at how different receiver architectures can be used or modified to more rapidly reacquire carrier phase tracking, thus providing more measurements that can be used for high-accuracy positioning applications. This contrasts with other work which has focused more on reacquiring range capability. Specifically, a piece-wise control method and a phase prediction architecture are proposed. The piece-wise method takes advantage of different parameters in the control system to produce different transition performance within the tracking loop. With this in mind, the approach divides the reacquisition process into separate periods each with different control system parameters in order to achieve a faster transition process. In the phase prediction architecture, carrier phase measurements are predicted for satellites that have lost lock by integrating the estimated Doppler computed from the navigation solution. Predicted phase quality is evaluated in both empirical and theoretical ways. All algorithms are tested usmg real data collected under mild to moderate operational conditions.
Open Access
Improving High Sensitivity GNSS Receiver Performance in Multipath Environments for Vehicular Applications
(2013-09-24) XIE, PENG; Petovello, Mark
Generally, standalone GNSS receiver architectures cannot provide a position accuracy suitable for use in vehicular applications in urban canyon scenarios. Specifically, GNSS signals are affected by the surrounding objects, such as high buildings, trees, etc., which will introduce multipath errors. Multipath arises from the reception of reflected or diffracted signals in addition to the line-of-sight (LOS) signal, and is one of the most detrimental error sources in GNSS positioning applications. By using a block processing high sensitivity receiver scheme with more correlators and/or longer coherent integration time, this thesis aims to obtain better positioning performance in the urban canyon areas. It was reported that signal correlation peaks (e.g., LOS correlation peaks, multipath correlation peaks) may be separated in the Doppler domain by a long coherent integration time. Generally, the dominant peak is utilized in high sensitivity receivers, however, this approach is not always optimal in multipath environments since it is not assured that the dominant peak is the LOS peak. In this regard, a LOS peak identification scheme is proposed in this work, which yields better positioning performance compared to the dominant peak scheme. Multipath distributions in the urban canyon area are characterized in this work. In particular, the Doppler frequency and code phase delay under different conditions are assessed as a function of vehicle speed and signal power. Results of this characterization is use to configure the receiver to better remove the multipath signals. More specifically, the multipath distribution will eventually affect the search strategy (i.e., search space size, coherent integration time) utilized in the high sensitivity receiver. Multipath directional-dependence phenomenon (i.e., the variation resulting from the direction of travel of the user) is observed during this process; and the multipath maximum Doppler offset and minimum Doppler offset are derived and verified by the real data, and finally used to detect errors in the receiver’s navigation solution. It is shown that most of the multipath peaks are removed in the receiver after using the proposed algorithm; consequently, pseudorange and Doppler accuracies are improved substantially. Also, different search space sizes and coherent integration times are compared in this work and an empirically-optimal search strategy is developed. Three data sets collected in the urban canyon areas are used to assess the proposed high sensitivity receiver strategy, it is shown that the position accuracies are better than 20 m.
Open Access
INTEGRATION OF UWB RANGING AND GPS FOR IMPROVED RELATIVE VEHICLE POSITIONING AND AMBIGUITY RESOLUTION
(2012-12-20) Jiang, Yuhang; Petovello, Mark; O'Keefe, Kyle
In this thesis, a system for GPS positioning augmented with Ultra-Wideband (UWB) ranges for vehicle relative positioning applied in Vehicle-to-Infrastructure (V2I) navigation is developed and tested. It is assumed that UWB ranging information and carrier-phase differential GPS (DGPS) corrections are only available via a limited-range communication link between the vehicle and the infrastructure points. The navigation solution is implemented in an extended Kalman filter where differential GPS pseudorange, Doppler and carrier phase measurements are used in conjunction with UWB ranges measured between the vehicle and infrastructure points purposefully chosen on the road. Results indicate that the GPS and UWB integrated positioning system can improve the float solution and ambiguity resolution compared to the GPS-only case. When a single UWB radio is located roughly 300 m north of a fictitious intersection in 25 out of 40 cases the RMS position errors improved before the vehicle approaching the intersection. The inclusion of UWB ranges also improves in the time to fix ambiguities by 4.1% (0.4 seconds), 9.4% (0.9 seconds), 16.8% (2.4 seconds), 16.9% (3.2 seconds) and 15% (4.0 seconds) when the additional UWB measurements are available for 25 m, 50 m, 100 m, 200 m, and 300 m, respectively.
Open Access
Interference Management in Heterogeneous Cellular Networks
(2016) Xiaobin, Yang; Fapojuwo, Abraham; Messier, Geoffrey; Sesay, Abu-Bakarr; Petovello, Mark; Witold, Krzymien
Heterogeneous cellular networks (HetNets), comprising one or more tiers of small base stations (BSs) overlaid on the tier of well-planned macro BSs, have been commonly recognized as a cost-effective solution to cater to explosive demands on mobile data traffic. However, HetNets also bring some unique challenges such as unplanned deployment of small BSs and increased complexity of interference management. Interference in HetNets becomes one of the major obstacles to capacity improvement and coverage enhancement. In this thesis, analytical approaches are developed to investigate interference statistics and the performance of 2-tier HetNets including coverage probability and spectral efficiency in mathematical expression, and some insights are revealed on the relationships of interference statistics and network performance with system parameters such as frequency reuse factor, transmission probability, and the signal-to-interference ratio (SIR) gap from Shannon capacity. Specifically, the interference and performance impact of Rician fading and lognormal shadowing are analytically investigated, first based on the Poisson point process (PPP) model where the locations of BSs in each tier are modeled as a PPP. Second, a hybrid model of HetNets is established which considers both location regularity of macro BSs and topological randomness of small BSs, where the coverage probability and the spectral efficiency are derived under different propagation conditions and the significance of macro BS deployment planning is revealed. Third, based on the aforementioned analyses, a well-known interference management technique of fractional frequency reuse (FFR) applied in the tier of macro BSs is studied in detail, and its optimal parameter settings in terms of spectral efficiency and suitable environments are identified. Finally, a particular interest is attached to multiple antenna technologies including classical beamforming and transmit diversity, which are studied with consideration of the impact of intra-tier and inter-tier interference in HetNets.
Open Access
Intermittent GNSS Signal Tracking for Improved Receiver Power Performance
(2015-12-07) Bellad, Vijaykumar; Petovello, Mark; Lachapelle, Gérard; Petovello, Mark; Lachapelle, Gérard; El-Sheimy, Naser; O'Keefe, Kyle; Nielsen, Jorgen; Gunawardena, Sanjeev
Power consumption is critical in battery-operated devices using GNSS receivers. Modern day receivers track satellite signals from multiple constellations to achieve a better position performance making power conservation critical. Receivers in battery-operated devices employ intermittent signal tracking (or cyclic tracking) to conserve power. This research investigates various aspects of intermittent tracking and analyze the positioning and tracking performance with different duty cycles and solution update intervals in stationary and kinematic cases. Although power conservation is important it is preferable to achieve position accuracy equivalent to that of a continuously tracking receiver when operating in intermittent tracking mode, known as “feasibility” in this research. However, pseudorange accuracy and in turn position accuracy depend on the ability of signal tracking loops to converge during the receiver active period. Predicting code phase and Doppler values over the receiver sleep period can help to achieve this. The first part of this research identifies code phase and Doppler parameters as the factors influencing intermittent tracking operation, proposes a vector-based approach to improve their estimates at the end of sleep periods and provides a theoretical framework to determine the feasibility of intermittent tracking. The signal parameter errors at the end of sleep periods, length of the receiver active periods and the tracking loop transient response determine the feasibility. The amount of power saving can be as high as 60% to 70% in typical open sky kinematic cases with a longer solution update interval of 5 s. The second part of the research investigates intermittent tracking in weak signal environments. Doppler uncertainty during the receiver sleep period is identified as the limiting factor when longer coherent integration is used and a method is proposed to overcome this challenge. The last part of the research explores the use of inertial sensor aiding for improving intermittent tracking performance. A MEMS IMU (representative of very low power modern day IMUs) is used to assist tracking and improve power performance through GPS/INS integration. The inertial aiding does not improve the code phase estimation accuracy during the sleep period significantly; however improved Doppler estimation makes shorter duty cycles feasible.
Open Access
Investigation of gps observations for indoor gps/ins integration
(2011) Aminian, Behnam; Lachapelle, Gérard; Petovello, Mark
Open Access
Multi-Constellation GNSS for Absolute and Relative Navigation in Highly Elliptical Orbits
(2017) Kahr, Erin Jennifer; O'Keefe, Kyle; Montenbruck, Oliver; Petovello, Mark; Lachapelle, Gérard; Skone, Susan; Knudsen, David; Axelrad, Penina
The goal of this research project was to determine to what order of magnitude relative positions of formation flying spacecraft in highly elliptical orbits (HEO) can be measured using Global Navigation Satellite Systems. The orbit of the European Space Agency’s upcoming PROBA-3 mission, with a roughly 600 km perigee and 60500 km apogee, was chosen as the test case throughout the research project. The key result was that, provided there were sufficient measurements, relative positioning could be accomplished throughout the HEO orbit to the sub-metre level in the absence of maneuvers, and to the sub-10 m level when a tight formation flying phase bracketed by maneuvers was simulated during the apogee arc. In the case of maneuvers or of too few measurements, the additional uncertainty prevents sufficiently rigorous blunder detection from being carried out, and the filter becomes extremely susceptible to outliers. In addition to answering the original research question, it was concluded that the regional navigation systems offer a significant advantage for above the constellation users, because the slower relative motion translates into longer arcs of uninterrupted measurement data. Using live signals collected from a low Earth orbiting CubeSat, Satellite Based Augmentation System (SBAS) tracking over the Earth’s limb was demonstrated, and it was proven for the first time that SBAS ranging is a viable source of positioning information for users in highly elliptical or other above the constellation Earth orbits. Finally, it was determined in the preliminary visibility studies that the entire positioning problem is extremely sensitive to the receiver’s ability to acquire and track weak GNSS signals. Hardware-in-the-loop simulation and receiver design work on a software research receiver confirmed that the power in the GNSS side lobes hovers slightly below the acquisition and tracking threshold of a standard receiver, but that these signals can be acquired and tracked making use existing weak signal algorithms, dramatically improving both absolute and relative positioning accuracies.
Open Access
Multichannel dual frequency glonass softwear receiver in combination with GPS L1 C/A
(2009) Abbasiannik, Saloomeh; Petovello, Mark
Open Access
Real-Time Ambiguity-fixed Precise Point Positioning Using Global and Regional Reference Networks
(2016-02-03) Li, Yihe; Gao, Yang; El-Sheimy, Naser; Petovello, Mark; Ghannouchi, Fadhel; Zhang, Kefei
Ambiguity resolution with PPP is able to reduce the long convergence time. However, real-time PPP suffers from slow ambiguity-fixing due to the real-time orbits and clocks with lower quality. The research in this thesis aims at addressing several challenging issues of PPP ambiguity resolution in real-time situations. The determination of real-time orbits and clocks has first been investigated in this thesis. The real-time orbits have been generated based on the estimated initial parameters with previous data, while the real-time satellite clocks and Fractional Cycle Biases (FCBs) have been estimated from a network of GNSS data. Then a software package has been developed to generate the real-time orbits and clocks as well as FCBs for assessing the performance of PPP ambiguity resolution and positioning. The Solar Radiation Pressure (SRP) parameters have been identified as the key factor driving orbit prediction accuracies as a function of arc length. Based on the minimization of SRP parameter variation, the optimal arc length has been determined for precise orbit prediction, with which the high-accuracy satellite clocks can be estimated. In addition, PPP ambiguity resolution performance has been quantitatively evaluated using the real-time orbits and estimated clocks with different arc lengths. A cascaded method of satellite FCB estimation has been developed to improve real-time PPP ambiguity resolution. The satellite clocks have been first estimated to compensate part of real-time orbit errors. Then the Narrow-Lane (NL) FCBs have been subsequently estimated as one directional-independent term and three direction-dependent terms, rather than a directional-independent term as did in the past. The improvements of the resulting ambiguity fix rates and positioning accuracy have been demonstrated. A new method for regional augmented PPP by using atmospheric corrections and their stochastic model derived from regional reference networks has been developed. The interpolated atmospheric corrections have been then applied by users as the pseudo-observations with the estimated stochastic model to properly describe their uncertainties. Some future work has been provided in the end to consider satellite FCB estimation and PPP ambiguity resolution, validation of Cascaded Orbit Error Separation (COES) method with multi-constellation data, and improvement of the integer ambiguity resolution in real-time PPP.