ALBERT

Description:    The carrier phase tracking loop is the primary focus of the current work. In particular, two carrier phase tracking techniques are compared, the standard phase tracking loop, i.e., the phase lock loop (PLL), and the extended Kalman filter (EKF) tracking loop. In order to compare these two different techniques and taking into consideration the different models adopted in each, it is important to bring them to one common ground. In order to accomplish this, the equivalent PLL for a given EKF has to be determined in terms of steady-state response to both thermal noise and signal dynamics. A novel method for experimentally calculating the equivalent bandwidth of the EKF is presented and used to evaluate the performance of the equivalent PLL. Results are shown for both the L1 and L5 signals. Even though the two loops are designed to track equivalent dynamics and to have equivalent carrier phase standard deviations, the EKF outperforms the equivalent PLL in terms of both the transient response and sensitivity. Content Type Journal Article Pages 1-11 DOI 10.1007/s10291-011-0222-z Authors Dina Reda Salem, Position, Location and Navigation (PLAN) Group, Department of Geomatics Engineering, Schulich School of Engineering, University of Calgary, Calgary, AB, Canada Cillian O’Driscoll, Position, Location and Navigation (PLAN) Group, Department of Geomatics Engineering, Schulich School of Engineering, University of Calgary, Calgary, AB, Canada Gérard Lachapelle, Position, Location and Navigation (PLAN) Group, Department of Geomatics Engineering, Schulich School of Engineering, University of Calgary, Calgary, AB, Canada Journal GPS Solutions Online ISSN 1521-1886 Print ISSN 1080-5370

Description:    Stand-alone, unaided, single frequency, single epoch attitude determination is the most challenging case of GNSS compass processing. For land vehicle applications, the baseline approximately lies in the plane of the local geodetic horizon. This provides an important constraint that can be exploited to directly aid the ambiguity resolution process. We fully integrate the constraint into the observation equations, which are transformed orthogonally. Our method can acquire the high-quality float solution by means of a heading search strategy. The fixed solution is obtained by weighted constrained integer least squares for each possible heading. The correct solution is identified by three consecutive steps: Kolmogorov–Smirnov test, heading verification, and global minimizer of the fixed ambiguity objective function. The analysis focuses on single frequency, single epoch land vehicle attitude determination using low-end GPS receivers with very low precision of carrier phase and code measurements. The error analysis is given for choosing a proper baseline length in practical application. Experimental results demonstrate that this scheme can improve the ambiguity success rate for very short baseline. Content Type Journal Article Pages 1-10 DOI 10.1007/s10291-011-0234-8 Authors Wantong Chen, School of Electronic and Information Engineering, Beihang University, Beijing, 100191 People’s Republic of China Honglei Qin, School of Electronic and Information Engineering, Beihang University, Beijing, 100191 People’s Republic of China Journal GPS Solutions Online ISSN 1521-1886 Print ISSN 1080-5370

Description:    The performance of real - time single-frequency precise point positioning is demonstrated in terms of position accuracy. This precise point positioning technique relies on predicted satellite orbits, predicted global ionospheric maps, and in particular on real-time satellite clock estimates. Results are presented using solely measurements from a user receiver on the L1-frequency (C1 and L1), for almost 3 months of data. The empirical standard deviations of the position errors in North and East directions are about 0.15 m, and in Up direction about 0.30 m. The 95% errors are about 0.30 m in the horizontal directions, and 0.65 m in the vertical. In addition, single-frequency results of six receivers located around the world are presented. This research reveals the current ultimate real-time single-frequency positioning performance. To put these results into perspective, a case study is performed, using a moderately priced receiver with a simple patch antenna. Content Type Journal Article Pages 1-8 DOI 10.1007/s10291-011-0228-6 Authors Roel J. P. van Bree, Delft University of Technology, Delft, The Netherlands Christian C. J. M. Tiberius, Delft University of Technology, Delft, The Netherlands Journal GPS Solutions Online ISSN 1521-1886 Print ISSN 1080-5370

Description:    The Global Navigation Satellite System Reflectometry (GNSS-R) concept was conceived as a means to densify radar altimeter measurements of the sea surface. Until now, the GNSS-R concept relied on open access to GNSS transmitted codes. Recently, it has been proposed that the ranging capability of the technique for ocean altimetric applications can be improved by using all the signals transmitted in the bandwidth allocated to GNSS, which includes open access as well as encrypted signals. The main objective of this study is to provide experimental proof of this enhancement through a 2-day experiment on the Zeeland Bridge (The Netherlands). In the experiment, we used a custom built GNSS-R system, composed of high gain GPS antennas, calibration subsystem, and an FPGA-based signal processor which implemented the new concepts, an X-band radar altimeter and a local geodetic network. The results obtained indicate that the new approach produces a significant improvement in GNSS-R altimetric performance. Content Type Journal Article Pages 1-11 DOI 10.1007/s10291-011-0225-9 Authors Antonio Rius, Institut d’Estudis Espacials de Catalunya-CSIC, Campus UAB, Fac. Ciencias, Torre C5 parell 2, 08193 Bellaterra, Spain Oleguer Nogués-Correig, Institut d’Estudis Espacials de Catalunya-CSIC, Campus UAB, Fac. Ciencias, Torre C5 parell 2, 08193 Bellaterra, Spain Serni Ribó, Institut d’Estudis Espacials de Catalunya-CSIC, Campus UAB, Fac. Ciencias, Torre C5 parell 2, 08193 Bellaterra, Spain Estel Cardellach, Institut d’Estudis Espacials de Catalunya-CSIC, Campus UAB, Fac. Ciencias, Torre C5 parell 2, 08193 Bellaterra, Spain Santi Oliveras, Institut d’Estudis Espacials de Catalunya-CSIC, Campus UAB, Fac. Ciencias, Torre C5 parell 2, 08193 Bellaterra, Spain Enric Valencia, Institut d’Estudis Espacials de Catalunya-UPC, Campus Nord, Jordi Girona 1-3, 08034 Barcelona, Spain Hyuk Park, Institut d’Estudis Espacials de Catalunya-UPC, Campus Nord, Jordi Girona 1-3, 08034 Barcelona, Spain José Miguel Tarongí, Institut d’Estudis Espacials de Catalunya-UPC, Campus Nord, Jordi Girona 1-3, 08034 Barcelona, Spain Adriano Camps, Institut d’Estudis Espacials de Catalunya-UPC, Campus Nord, Jordi Girona 1-3, 08034 Barcelona, Spain Hans van der Marel, Institute of Earth Observation and Space Systems, Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS Delft, The Netherlands Roel van Bree, Institute of Earth Observation and Space Systems, Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS Delft, The Netherlands Bas Altena, Institute of Earth Observation and Space Systems, Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS Delft, The Netherlands Manuel Martín-Neira, European Space Research and Technology Centre, Keplerlaan 1, 2200 AG Noordwijk, The Netherlands Journal GPS Solutions Online ISSN 1521-1886 Print ISSN 1080-5370

Description:    A new algorithm for single receiver DCB estimation using GIM vertical TEC gridded values is proposed. It estimates receiver DCB and vertical residual ionospheric delays using the least squares approach with linear constraints. The performance of the proposed algorithm was assessed by comparing estimated receiver DCBs with those provided by the IGS. The same comparisons were done using two other algorithms for receiver DCB estimation. It is demonstrated that the proposed algorithm is capable of reproducing IGS DCB values at the level of 0.1–0.3 ns, which is better than the level of agreement observed for the other two algorithms. For our tests, we considered data from more than 100 IGS stations, daily, such that all major regions of the world were covered. Besides, both ionospherically quiet and disturbed days were considered. It provides some evidence that the aforementioned level of agreement with IGS receiver DCB values does not significantly dependent on geographical region and the state of the ionosphere. The algorithm is easy to implement and can be considered for online use. Content Type Journal Article Pages 1-10 DOI 10.1007/s10291-011-0230-z Authors Maxim Keshin, School of Civil Engineering and Geosciences, Newcastle University, Newcastle upon Tyne, NE1 7RU UK Journal GPS Solutions Online ISSN 1521-1886 Print ISSN 1080-5370

Description:    Global Positioning System (GPS) plays a central role in solving the location-based needs of wheelchair users and efficient route guidance. An essential process in wheelchair navigation is matching the position obtained from GPS or other sensors on a sidewalk network. This process of map matching in turn assists in making decisions under uncertainty. However, GPS-based wheelchair navigation systems have difficulties in tracking wheelchairs in urban areas due to poor satellite availability. To overcome this, a fuzzy logic-based algorithm is applied to effectively perform matching wheelchair movements on sidewalks. Fuzzy logic, based on fuzzy reasoning concepts, in many circumstances can take noisy and imprecise input to yield numerically accurate output. Experiments on a university campus validate it practicable. Content Type Journal Article Pages 1-10 DOI 10.1007/s10291-011-0229-5 Authors Ming Ren, University of Pittsburgh, Pittsburgh, PA, USA Hassan A. Karimi, University of Pittsburgh, Pittsburgh, PA, USA Journal GPS Solutions Online ISSN 1521-1886 Print ISSN 1080-5370

Description:    The network-based real-time kinematic (RTK) positioning has been widely used for high-accuracy applications. However, the precise point positioning (PPP) technique can also achieve centimeter to decimeter kinematic positioning accuracy without restriction of inter-station distances but is not as popular as network RTK for real-time engineering applications. Typically, PPP requires a long initialization time and continuous satellite signals to maintain the high accuracy. In case of phase breaks or loss of signals, re-initialization is usually required. An approach of instantaneous cycle slips fixing using undifferenced carrier phase measurements is proposed, which leads to instantaneous re-initialization for real-time PPP. In the proposed approach, various errors such as real-time orbit and clock errors, atmosphere delay and wind-up effects are first refined and isolated from integer cycle slips. The integer values of cycle slips can then be estimated and fixed with the LAMBDA technique by applying a cascade cycle slip resolution strategy. Numerical experiments with different user dynamics are carried out to allow a comprehensive evaluation of efficiency and robustness of the cycle slip fixing algorithm. The results show that the cycle slips can be fixed correctly in all cases considered and that data gaps of up to 300 s can be connected with high confidence. As a result, instantaneous re-initialization is achieved in the real-time PPP processing. Content Type Journal Article Pages 1-13 DOI 10.1007/s10291-011-0233-9 Authors Zhang Xiaohong, School of Geodesy and Geomatics, Wuhan University, 129 Luoyu Road, Wuhan, 430079 China Li Xingxing, School of Geodesy and Geomatics, Wuhan University, 129 Luoyu Road, Wuhan, 430079 China Journal GPS Solutions Online ISSN 1521-1886 Print ISSN 1080-5370

Description:    The analysis of tracking loops for global navigation satellite systems (GNSS) receivers is often confined to Monte Carlo approaches that can result in long simulation times and a limited number of simulation runs. A different approach based on Semi-Analytic principles is considered here. Matlab ® code implementing a Semi-Analytic framework for the fast simulation of GNSS digital tracking loops is presented. The code structure is detailed and two specific examples implementing a standard PLL and the Double Estimator for unambiguous binary offset carrier (BOC) tracking are provided. The code has been organized in a modular way, and can be easily modified for the simulation of different tracking loops. Content Type Journal Article Pages 1-5 DOI 10.1007/s10291-011-0221-0 Authors Daniele Borio, PLAN Group, Department of Geomatics Engineering, University of Calgary, Calgary, AB, Canada Pratibha B. Anantharamu, PLAN Group, Department of Geomatics Engineering, University of Calgary, Calgary, AB, Canada Gérard Lachapelle, PLAN Group, Department of Geomatics Engineering, University of Calgary, Calgary, AB, Canada Journal GPS Solutions Online ISSN 1521-1886 Print ISSN 1080-5370

Description:    A major challenge in using GPS guidance for aircraft final approach and landing is to reject interference that can jam reception of the GPS signals. Antenna arrays, which use space–time adaptive processing (STAP), significantly improve the signal to interference plus noise ratio, but at the possible expense of distorting the received signals, leading to timing biases that may degrade navigation performance. Rather than a sophisticated calibration approach to remove biases introduced by STAP, this paper demonstrates that a relatively compact calibration strategy can substantially reduce navigation biases, even under elevated interference conditions. Consequently, this paper develops an antenna bias calibration strategy for two classes of adaptive array algorithm and validates this method using both simulated and experimental data with operational hardware in the loop. A proof-of-concept system and an operational prototype are described, which implement the adaptive antenna algorithms and deterministic corrections. This investigation demonstrates that systems with adaptive antenna arrays can approach the accuracy and integrity requirements for automatic aircraft landing, and in particular for sea-based landing on board aircraft carriers, while simultaneously providing significant attenuation of interference. Evidence suggests that achieving these goals is possible with minimal restrictions on system hardware configuration—specifically, limitations on the permissible level of antenna anisotropy and the use of sufficient analog-to-digital converter resolution. Content Type Journal Article Pages 1-10 DOI 10.1007/s10291-011-0224-x Authors David S. De Lorenzo, GPS Research Laboratory, Department of Aeronautics and Astronautics, Stanford University, Durand Building, Room 452, Stanford, CA 94305-4035, USA Sherman C. Lo, GPS Research Laboratory, Department of Aeronautics and Astronautics, Stanford University, Durand Building, Room 452, Stanford, CA 94305-4035, USA Per K. Enge, GPS Research Laboratory, Department of Aeronautics and Astronautics, Stanford University, Durand Building, Room 452, Stanford, CA 94305-4035, USA Jason Rife, Automated Systems and Robotics Laboratory, Department of Mechanical Engineering, Tufts University, 024 Anderson Hall, Medford, MA 02115, USA Journal GPS Solutions Online ISSN 1521-1886 Print ISSN 1080-5370

Description:    The world of global navigation satellite systems has been enhanced with several new or improved signals in space aiming to optimize accuracy, reliability, navigation solution, and interoperability between different constellations. However, such developments bring various challenges to the receivers’ designers. For example, acquisition and tracking stages turn into more complex processes while handling the increasing bandwidth requires additional processing power. In this context, we study the code tracking of Galileo E5ab in a full band or of only one of its components, i.e., either E5a or E5b. More specifically, an architecture for tracking the E5 pilot channel as an AltBOC(15,10) or BPSK(10) modulation is introduced, and the performance of well-known discriminator types is analyzed using analytical derivations and simulations of linearity and stability regions, thermal noise tracking errors, multipath error envelopes and tracking thresholds. Different parameters, such as the front-end filter bandwidth, the early/late chip spacing, un-normalized and normalized discriminators, are taken into consideration. The results obtained are used to illustrate the main advantages and drawbacks of tracking the E5 signal as well as to help defining the main tracking loop parameters for an enhanced performance. Content Type Journal Article Pages 1-16 DOI 10.1007/s10291-011-0226-8 Authors Youssef Tawk, Institute of Microengineering (IMT) Electronics and Signal Processing Laboratory, Ecole Polytechnique Fédérale de Lausanne, Breguet 2, 2000 Neuchâtel, Switzerland Cyril Botteron, Institute of Microengineering (IMT) Electronics and Signal Processing Laboratory, Ecole Polytechnique Fédérale de Lausanne, Breguet 2, 2000 Neuchâtel, Switzerland Aleksandar Jovanovic, Institute of Microengineering (IMT) Electronics and Signal Processing Laboratory, Ecole Polytechnique Fédérale de Lausanne, Breguet 2, 2000 Neuchâtel, Switzerland Pierre-André Farine, Institute of Microengineering (IMT) Electronics and Signal Processing Laboratory, Ecole Polytechnique Fédérale de Lausanne, Breguet 2, 2000 Neuchâtel, Switzerland Journal GPS Solutions Online ISSN 1521-1886 Print ISSN 1080-5370