The number of satellites in Global Navigation Satellite System (GNSS) will be increased greatly for the launch of Galileo and Compass satellites. Receiver Autonomous Integrity Monitoring (RAIM) is expected to provide better guidance for aircraft approaching airports and landing, while the unaided GPS with RAIM provide hundreds meters in Horizontal Protection Level (HPL) nowadays. Firstly, different RAIM algorithms are analyzed in this paper and the algorithm free of weighting matrix is proposed to calculate protection levels. Secondly, the mathematical model for availability assessment is presented. Finally, the paper gives simulation results using dual frequency signals and GPS+Galileo constellations.The results show that the RAIM availability is no less than 99.5% in worldwide regions for LPV 200 and APV I, and GNSS with RAIM yields the Vertical Protection Level (VPL) under 25 meters for nominal operations.
As the measuring equipment of the navigation receivers, high precision pseudorange signal is generated by navigation signal simulator. Pseudorange error is mainly from modeling error in high dynamic scenarios, but it is mainly from phase quantization error of digital implementation process in high precision scenarios of evaluating receiver’s pseudorange accuracy. Is this paper, according to the implementation principle of carrier and code DDS, the causes of the phase quantization error is analyzed and the pseudorange error formula is derived and the simulation results are given. Analysis and simulation results show that phase critter originated by carry phase truncation effects measurement result of zero value and cannot be ignored. The conclusion can guide the design of navigation signal simulator.
Aiming at solving the real-time computation of the satellite orbit in GNSS(Global Navigation Satellite System) emulator with multiple constellations,the Newton and Hermite polynomial interpolation algorithms were analyzed and compared by computing efficiency and accuracy.The precision of the satellite position and velocity(PV) performed better by adding window in the Newton algorithm.The computation examples show that the real-time and high-precision computation of the satellite PV is achieved with position at the equation interval epoch known and velocity unknown.The results also show that the new method speeds up the computation seven times faster than the direct ephemeris calculation,and yeilds better performance in orbit precision than the 3-order Hermite Interpolation,for the position error is less than millimeter and the velocity error 1e-5 m/s.
To ensure the long-term stable and uninterrupted service of satellite navigation systems, the robustness and reliability of time–frequency systems are crucial. Integrity monitoring is an effective method to enhance the robustness and reliability of time–frequency systems. Time–frequency signals are fundamental for integrity monitoring, with their time differences and frequency biases serving as essential indicators. These indicators are influenced by the inherent characteristics of the time–frequency signals, as well as the links and equipment they traverse. Meanwhile, existing research primarily focuses on only monitoring the integrity of the time–frequency signals’ output by the atomic clock group, neglecting the integrity monitoring of the time–frequency signals generated and distributed by the time–frequency signal generation and distribution subsystem. This paper introduces a time–frequency signal integrity monitoring algorithm based on the temperature compensation frequency bias combination model. By analyzing the characteristics of time difference measurements, constructing the temperature compensation frequency bias combination model, and extracting and monitoring noise and frequency bias features from the time difference measurements, the algorithm achieves comprehensive time–frequency signal integrity monitoring. Experimental results demonstrate that the algorithm can effectively detect, identify, and alert users to time–frequency signal faults. Additionally, the model and the integrity monitoring parameters developed in this paper exhibit high adaptability, making them directly applicable to the integrity monitoring of time–frequency signals across various links. Compared with traditional monitoring algorithms, the algorithm proposed in this paper greatly improves the effectiveness, adaptability, and real-time performance of time–frequency signal integrity monitoring.
Differential code biases (DCBs) are important parameters that must be estimated accurately for precise positioning and Satellite Based Augmentation Systems (SBAS) ionospheric related parameter generation. In this paper, in order to solve the performance degradation problem of the traditional minimum STD searching algorithm in disturbed ionosphere status and in geomagnetic low latitudes, we propose a linear planar based minimum STD searching algorithm. Firstly, we demonstrate the linear planar trend of the local vertical TEC and introduce the linear planar model based minimum standard variance searching method. Secondly, we validate the correctness of our proposed method through theoretical analysis and propose bias detection to avoid large estimation bias. At last, we show the performance of our proposed method under different geomagnetic latitudes, different seasons and different ionosphere status. The experimental results show that for the traditional minimum STD searching algorithm based on constant model, latitude difference is the key factor affecting the performance of DCB estimation. The DCB estimation performance in geomagnetic mid latitudes is the best, followed by the high latitudes and the worst is for the low latitudes. While the algorithm proposed in this paper can effectively solve the performance degradation problem of DCB estimation in geomagnetic low latitudes by using the linear planar model which is with a higher degree of freedom to model the local ionosphere characteristics and design dJ to screen the epochs. Through the analysis of the DCB estimation results of a large number of stations, it can be found that the probability of large estimation deviation of the traditional method will increase obviously under the disturb ionosphere conditions, but the algorithm we proposed can effectively control the amplitude of the maximum deviation and alleviate the probability of large estimation deviation in disturb ionosphere status.
The recent rapid development of low Earth orbit (LEO) constellation-based navigation techniques has enhanced the ability of position, navigation, and timing (PNT) services in deep attenuation and interference environments. However, existing navigation modulations face the challenges of high acquisition complexity and do not improve measurement precision at the same signal strength. We propose a pulsed orthogonal time frequency space (Pulse-OTFS) signal, which naturally converts continuous signals into pulses through a special delay-Doppler domain pseudorandom noise (PRN) code sequence arrangement. The performance evaluation indicates that the proposed signal reduces at least 89.4% of the acquisition complexity. The delay measurement accuracy is about 8 dB better than that of the traditional binary phase shift keying (BPSK) signals with the same bandwidth. It also provides superior compatibility and anti-multipath performance. The advantages of fast acquisition and high-precision measurement are verified by processing the real signal in the developed software receiver. As Pulse-OTFS occupies only one time slot of a signal period, it can be easily integrated with OTFS-modulated communication signals and used as a navigation signal from broadband LEO satellites as an effective complement to the global navigation satellite system (GNSS).
In this paper,a real-time satellite clock anomaly monitoring algorithm is proposed,which is based on Kalman filter model of satellite clock offset.Principles of the new algorithm are discussed and the performance is verified using the IGS observation clock offset data.The results show that the new algorithm have a perfect performance of detecting the satellite clock anomaly in both single point phase jump and continuous phase jump.At the same time,it can also eliminate and replace the anomaly data,and the replaced error is negligible.In addition,the new algorithm possesses an obvious property of real-time detecting,which can be applied to real-time anomaly monitoring of satellite clock.
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