[Show abstract][Hide abstract] ABSTRACT: The intersystem interference between Galileo and Compass, known as a radio frequency compatibility problem, has become a matter of great concern for the system providers and user communities. This paper firstly describes two fundamentally different methods to assess the Global Navigation Satellite System (GNSS) intersystem interference, by using different interference coefficients that are calculated for each combination of signals: the spectral separation coefficient (SSC) and code tracking spectral sensitivity coefficient (CT_SSC). And then a complete methodology combining the SSC and CT_SSC is presented. Real simulations are carried out to assess the interference effects where Galileo and Compass signals are sharing the same band (E1/B1 and E6/B3 bands) at every time and place on the Earth. Simulation results show that the effects of intersystem interference are significantly different by using these two methodologies. It is also shown that the Compass system leads to intersystem interference on Galileo but that the maximal values are lower than Galileo interference to Compass. The design and implementation of any new signal has to be conducted carefully in order for there to be radio frequency compatibility.
[Show abstract][Hide abstract] ABSTRACT: New signal modulation design for next-generation of global navigation satellite systems (GNSS) must offer improved performance and the opportunity for spectrum compatible with existing and planned signals. This paper proposes a class of particularly attractive modulations called Minimum Shift Keying - Binary Coded Symbol (MSK-BCS) modulations, and demonstrates their essential characteristics and performance for GNSS. The principle of MSK modulation is first described. Then, based on the BCS modulations technique, the general mathematical model of MSK-BCS modulations is described. The MSK-BCS modulations present important characteristics for GNSS and provide superior performance with regards to noise, interference and multipath when compared to other BCS modulations. MSK-BCS modulations can provide potential opportunities for GNSS modernization and construction, such as Galileo, Compass, and so on.
[Show abstract][Hide abstract] ABSTRACT: This paper presents a method of AROF (Ambiguity Resolution On The Fly) with extended Kalman filter (EKF) to resolve ambiguities for pseudolite-based indoor navigation system. The carrier phase measurements of pseudolites can obtain high positioning precision. In many pseudolite systems which recently have been proposed and tested, pseudolites are usually used to offer positioning and navigation applications in indoor or blocked environments. However, like indoor environment, the carrier phase measurements of pseudolite are not entirely same as GPS. A major difference is carrier phase integer ambiguity resolution. The traditional way of ambiguity resolution (AR) for GPS is static or kinematic initialization. But the static initialization is not suitable for pseudolites. Using pseudolites for static initialization, the equations are correlated with each other at observation epochs and the ambiguities can't be calculated from the equations. As a result, the integer ambiguity resolution is using the initial position of receiver as a known parameter. This paper proposes a method of ambiguity resolution on the fly (AROF) with EKF, which doesn't need to know the staring vector of receiver and achieve the kinematic initialization of carrier phase measurement in pseudolite-based indoor navigation system. As same as GPS measurement equations, Dual-Differential observation model is given based on indoor-pseudolite positioning system, which is non-linear and dynamic model. In general, the standard Kalman filter can't deal with this nonlinear situation, since the covariance equations are based on the linearized system and not the true nonlinear system. So, the best approach to this problem is to use the Extended Kalman Filter (EKF). As a result of this approach, the measurement equations of the Kalman filter become linear, and the computational requirements are significantly reduced, making it possible to estimate ambiguity in real time. Extensive testing of the filter with s- - ynthetic data proved it to be satisfactory. Test cases included the presence of large initial errors as well as high noise levels. In all cases the filter was able to get ambiguities.
[Show abstract][Hide abstract] ABSTRACT: The basic principle of attitude determination by multi-antenna GPS technology is discussed and the algorithm model is established. According to the problems in the applications, the RAIM algorithm is used in the GPS attitude determination. The performance of this system is improved in this paper. The test result and the accuracy analysis have demonstrated that the new method used in attitude determination is effective.
Mechatronics and Automation, 2009. ICMA 2009. International Conference on; 09/2009
[Show abstract][Hide abstract] ABSTRACT: This paper puts emphasis on the following three main areas. First, it highlights the measurement error forms of magnetic compass and analyzes soft magnetic interference and hard magnetic interference which influence the precision of magnetic compass. Second, the paper proposes a rapid error compensation method based on ellipse hypothesis which uses direct least square to estimate the parameters of an ellipse quickly. Third, in this paper land experiment is conducted in order to evaluate the effect of compensation method. The result of experiment verifies that the method is efficient and can be utilized in underwater vehicle's navigation. According to the statistic analysis of compensated heading error, the ranging improves 63 percent on straight route and 82 percent on curve route referring to a higher accuracy GPS attitude determining system.
Mechatronics and Automation, 2009. ICMA 2009. International Conference on; 09/2009
[Show abstract][Hide abstract] ABSTRACT: To satisfy inertial navigation demands for space flight, high performance space-oriented strapdown inertial navigation system (SINS) algorithms are developed in the paper. The new algorithms are derived from a two-speed updating approach, which are far fit for the integration in digital computer than conventional methods and improve the robustness of space inertial navigation system (INS) in high dynamic environments. The performance is validated through high-fidelity simulations, and inertial measurements data for simulating are generated based on true trajectories of space vehicles and inertial sensor (gyro and accelerometer) error models. Moreover, the effects of inertial sensorspsila measurement errors on the precision of the new spaceflight SINS algorithms are evaluated.
Systems and Control in Aerospace and Astronautics, 2008. ISSCAA 2008. 2nd International Symposium on; 01/2009
[Show abstract][Hide abstract] ABSTRACT: A new solution for time synchronization using GPS receiver signals as reference is proposed. In the GPS/INS applications, unknown time errors between IMU (Inertial Measurement Unit) measurements and GPS time have a significant influence on the data fusion performance of hybrid filter. However, each of exiting methods for time synchronization bears such-and-such shortcomings, for example high cost, complex or just dedicated to special situation etc. In order to improve the accuracy of time synchronization, we utilize 1PPS (Pulse Per Second) signal from GPS receiver as a synchronization reference, and tag time stamp on the serial data package from IMU. This scheme is implemented with a Field Programmable Gate Array (FPGA) device in Verilog programming language. Results of simulation and experiment show that with a simpler hardware design compared to exiting methods, the proposed solution of time synchronizer can reach the time synchronization accuracy on 1 millisecond level.
[Show abstract][Hide abstract] ABSTRACT: Signal quantization levels can have significant impact on the performance of a GPS receiver, especially in the present of the interference. In this paper, signal quantization model for estimating interference suppression of the correlator output and evaluating the performance of GPS receiver is presented. With the proposed model, performance of the receiver in acquisition process is demonstrated by showing the quantization effects on SNR degradation and detection. Test results show the limits of the low-SNR acquisition of the receiver and the better performance GPS receiver will achieve with a proper set quantization method.
Image and Signal Processing, 2008. CISP '08. Congress on; 06/2008
[Show abstract][Hide abstract] ABSTRACT: To design a future GNSS constellation which can not only provides perfect navigation performance but also achieves compatibility and interoperability with other GNSS constellations, a systematic approach based on GNSS compatibility and interoperability is proposed. Firstly, in order to choose the optimal constellation parameters, three criteria which include the constellation positioning performance, geometry repeatability and stability are taken into account and evaluated. Secondly, four optimal compatible GNSS constellations are presented based on compatibility. Finally, two optimal compatible and interoperable GNSS constellations are presented through analyzing the constellation positioning performance and global satellites visibility. The systematic approach and the analysis results can provide the beneficial reference for future GNSS constellation design.
[Show abstract][Hide abstract] ABSTRACT: When the receivers of GPS, GLONASS and other such systems are equipped with multiple antennas, they can also give attitude information. In this research, two works are highlighted. Firstly, based on the single differencing (SD) carrier phase equations established in local level frame (LLF), a new algorithm is presented to resolve vehicle attitude determination problems in real-time. Secondly, presumed that the cycle integer ambiguity is known, the measurement equations have attitude analytical resolutions by simultaneous single difference equations of two navigation satellites in-view. In addition, the algorithm is capable of reducing the search integer space into countable 2D discrete points and the ambiguity function method (AFM) resolves the adaptive function within the analytical solutions space. Therefore the procedures have very low computation and time is saved greatly. The hardware platform has been realized using multiple NovAtel GPS/GLONASS OEM boards. The proposed algorithm for analytical resolution attitude determination is validated using many static and dynamic ground tests. The experimental results have demonstrated that the proposed approach is effective and can satisfy the requirement of real-time application in cases of GPS and combined GPS and GLONASS.