[Show abstract][Hide abstract] ABSTRACT: The radio frequency compatibility between Galileo and Compass has become a matter of great concern for the system providers and user community. This paper mainly deals with the intersystem interference between Galileo and Compass systems and displays some important analysis results. First, a comprehensive methodology for the radio frequency compatibility assessment is described, considering the geometry-dependent and time-varying terms such as space constellation, signal modulation, emission power level, space loss, satellite antenna gain, and user receiver characteristic. Second, real simulations were carried out to assess the interference effects where Galileo and Compass signals were sharing the same band. Simulation results show that Compass introduces intersystem interference to Galileo, but the interference effects are lower than those of Compass interfered to Galileo signals. In addition, the radio frequency compatibility in Asia-Pacific region was analysed. It was found that the maximum interference suffered by Galileo from Compass was below 0.25dB under existing rules of coordination at International Telecommunication Union (ITU). In other words, Compass can provide a sound basis for compatibility with Galileo.
Preview · Article · Oct 2011 · Defence science journal
[Show abstract][Hide abstract] ABSTRACT: The concept of full autonomous navigation for Autonomous Underwater Vehicles (AUVs) is motivated by the needs of small AUVs, such as those described in [1-3]. Traditional navigation technologies, such as acoustic positioning system and Global Positioning System (GPS), are usually difficult to use for miniature AUVs characterized by complicated working environments, strictly volume constraints and low cost, which to some extent limited the application field of small AUVs. This work proposes a model-embedded integration of two aiding information sources to enhance the performance of full autonomous navigation system based on inertial navigation system (INS). A new methodology is derived to embed the vehicle model (VM) and ambient flow field model into EKF filter and use the pseudo-sensors information to improve navigation precision. By integrating the vehicle model and flow field model into the extended Kalman filter (EKF), the EKF state vector is carefully selected to exploit the dynamic characteristics of the vehicle to the maximum extend.. Navigation aided by model-embedded has the potential to achieve higher positioning accuracy and reduce the amount of real-time navigation calculation, and it may enable other navigation objectives, such as navigation of small AUVs relative to a larger AUV. The Matlab/Simulink simulation tool was used to produce the motion trajectory and the simulation results demonstrate the effectiveness and universality of the proposed approach. It greatly improves the positioning accuracy by utilizing object's kinetic properties to maximal extent, and the calculation for embedded object modelling is also simplified as a part of the EKF algorithm.
[Show abstract][Hide abstract] ABSTRACT: The spectral separation coefficient (SSC) is used as a major parameter for the assessment of GNSS radio frequency compatibility. As the computation load to calculate the SSC is extremely intensive, one way to simplify the SSC calculation is to replace the factor "signal power spectral density" by "code chip power spectral density". However, this approach will introduce greater error in certain situation. This paper analyses the influence of the signal's power spectral density (PSD), length of spreading code, code chip rate and data rate of navigation signals on SSC. It suggests and proves a criterion that the simplified SSC calculation can be applied safely when signal's code length is greater than or equal to the ratio of code chip rate to data rate. The simplified calculation criterion proposed in this paper allows fast calculation of SSC so that compatibility amongst different GNSS signals can be assessed quickly and accurately without introducing notable calculation error.
[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.
No preview · Article · Jun 2010 · Journal of Navigation
[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: 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.
No preview · Article · Mar 2010 · IEICE Electronics Express
[Show abstract][Hide abstract] ABSTRACT: For the design of a hybrid GNSS/INS or other multisensors navigation system, a very challenging topic is the timing issue. Unknown time synchronization errors among IMU, GNSS receiver and other sensors lead to significant data source errors and degrade alignment or navigation performance. Traditional methods to resolve this problem is based on hardware, software or the combination of both, each of which is unable to achieve the simultaneous optimization of cost and performance. In this paper, a flexible, low-cost time synchronization system (FLTS) is proposed to eliminate time synchronization errors and supply satisfied precision with much lower complexity and cost. Some key issues on Field Programmable Gate Array (FPGA) hardware design and programming of FLTS are detailed discussed. To achieve millisecond synchronization precision, the IPPS (Pulse Per Second) signal from GPS receiver is used as time reference to add timestamps for the output data of INS and other auxiliary navigation sensors. With low cost hardware and flexible configuration, our FLTS wins features of grand usage and expansibility, and can meet the time synchronization needs not only of GNSS/INS integration, but also other multi-sensors navigation systems.
[Show abstract][Hide abstract] ABSTRACT: With great demand of navigation products in social life, loosely coupled GPS/INS has been successfully developed in daily life. Although tightly coupled GPS/INS is a robust solution with superior position accuracy to loose coupling, GPS receiver navigation performance are being challenged under signal-attenuated environments since attenuation degrades the ability of GPS to acquire and track signals largely. Hence, it is a trend to improve the robust of GPS signal tracking so as to augment the availability and continuity of GPS receiver in GPS/INS integration. Currently, it is popular to integrate a GPS receiver with a low-cost micro-electro-mechanical system (MEMS) IMU in the navigation product markets. The high points of MEMS, low cost, immediate start-up time and low power consumption, wholly meet the requirements for commercial applications, especially for land vehicle navigation. However, the size depresses MEMS-technology inertial products allowing for a relatively large space occupied by a triad of gyros and accelerometers. Therefore, it is necessary and vital to minimize the size of MEMS IMU so as to be integrated with GPS on a single chip and further develop the compact MEMS IMU/GPS products. This paper puts emphasis on the performance evaluation of MEMS IMU/GPS tight coupling with IMU-aided tracking loop in signal-attenuated environments, such as under foliage areas and in urban canyon areas. Both tracking capability of the aided receiver and navigation accuracy of the integrated system are studied in this research. On the one hand, a detailed analysis of the aiding tracking effects is involved, and then the required bandwidth suitable to guarantee the tracking condition under low signal-to-noise ratio environment is determined. On the other hand, the integration method of a sub-optimum IMU configuration with a heading gyro and two level accelerometers is investigated. Then the compact IMU/GPS system and aiding navigation performance are presented and analyzed on tight coupling solution level.
[Show abstract][Hide abstract] ABSTRACT: As quickly growing of global navigation satellite system community, there is increasing interest in new signals for military and civilian uses. New signals must provide more robustness, higher performance, and greater capacity than already-existing signals and compliant with the radio frequency compatibility rule with existing and planned signals. This paper presents a class of particularly attractive modulations called modified Binary Coded Symbol modulations, and demonstrates their essential characteristics and performance for GNSS. Firstly, the principle of the modified Binary Coded Symbol modulation is described and the general mathematical model of the modulations is introduced. The modified Binary Coded Symbol modulations present important characteristics for GNSS and provide superior performance with regards to noise, interference and multipath when compared to other BCS modulations. Finally, the application of modified Binary Coded Symbol modulations in Compass BIC signal design is investigated. The results show that the proposed modulation can provide potential opportunities for GNSS modernization and construction.
[Show abstract][Hide abstract] ABSTRACT: When the receivers of GPS, GLONASS, COMPASS and other such systems are equipped with multiple antennas, they can give attitude information. Based on the difference carrier phase equations established in local level frame (LLF), a new algorithm is presented to resolve aircraft attitude determination problems in real-time. Presuming that the cycle integer ambiguity is known, the measurement equations have attitude analytical resolutions using single difference (SD) equations of two navigation satellites in-view. Similar with SD process, the double difference (DD) measurements are established and analysed. In addition, the SD and DD algorithms are capable of reducing the integer search space into some discrete point space and then the ambiguity function method (AFM) resolves the ambiguity function within the point solutions space. Therefore the procedures have very low computation, thus saving time. The hardware architecture has been realised using multiple GPS/GLONASS OEMs. 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.
[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.
[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.
[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.
[Show abstract][Hide abstract] ABSTRACT: The present land navigation system is composed mainly of IMU (Inertial Measurements Units) and some other auxiliary sensors. Although IMU can give all-round behavior representations using angle velocity and acceleration, it is inevitable that the measurement error, angle in particular, increases with time rapidly. Based on an overall consideration, magnetic compass, especially for its low cost, small size and low power loss, is generally selected as an important auxiliary sensor and popular with integrated system to eliminate the angle error. When magnetic compass is configured in land integrated navigation system, it can give heading information as an auxiliary attitude reference sensor. The precision of magnetic compass serves an important role in the performance of integrated system. Since magnetic compass measurements are vulnerable to magnetism disturbances from surrounding iron magnetic materials, the calculated heading is distorted as well. In actual application, the heading distortion may reach up to ten degrees. Correspondingly, the performance of integrated system can surely meet with degradation. Therefore, magnetic compass measurements error compensation is necessary and vital before giving the reference attitude. In this paper, three aspects are highlighted. Firstly, magnetic measurements error tests under different magnetic disturbances are developed, and then heading distortion calculated from the magnetic measurements is analyzed. Secondly, according to the characteristics of the measurements, an error model based on ellipse hypothesis is proposed. Considering low calculations and high stability, direct least square fitting is applied in ellipse curve fitting. Finally, magnetic compass is equipped on vehicle to conduct the land experiment, and GPS attitude determining system with high precision is selected as an attitude reference system. The experimental results have demonstrated that the magnetic compensation algorithm is effective and convenient in land navigation system.
[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.
[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.