Legacy Navigation Research Articles

Evaluation and Comparison of Power Spectral Density for GPS Signals using UTC and NMC Parameters

GPS Signals (L1 C/A, L2 & L5) are widely used for accurate location determination and appropriate navigation with the support of GPS Receivers data. This paper provides generation of GPS Legacy Navigation data, evaluation of Power Spectral Density (PSD) of L1 C/A, L2 & L5 signals using frame structure, obtained the autocorrelation of GPS C/A (Coarse Acquisition) – Code & Precision Code and PSD of complex Baseband GPS Signal. With the help of the received signal, create a Navigational System Based GPS (NSBG). Various parameters like a clock, “Universal-Time-Coordinated”-(UTC), ionosphere, and – “Navigation-Message-Correction”-(NMC) are necessary to test the receiver side. The proposed work is obtain the evaluation of Power Spectral Density (PSD) for complex Baseband GPS Signals like L1 C/A, L2 & L5 using frame structure and the autocorrelation of GPS C/A (Coarse Acquisition) – Code & Precision Code.

Performance Evaluation of the CNAV Broadcast Ephemeris

The new Global Positioning System (GPS) Civil Navigation Message (CNAV) has been transmitted by Block IIR-M and Block IIF satellites since April 2014, both on the L2C and L5 signals. Compared to the Legacy Navigation Message (LNAV), the CNAV message provides six additional parameters (two orbit parameters and four Inter-Signal Correction (ISC) parameters) for prospective civil users. Using the precise products of the International Global Navigation Satellite System Service (IGS), we evaluate the precision of satellite orbit, clock and ISCs of the CNAV. Additionally, the contribution of the six new parameters to GPS Single Point Positioning (SPP) is analysed using data from 22 selected Multi-Global Navigation Satellite System Experiment (MGEX) stations from a 30-day period. The results indicate that the CNAV/LNAV Signal-In-Space Range Error (SISRE) and orbit-only SISRE from January 2016 to March 2018 is of 0·5 m and 0·3 m respectively, which is improved in comparison with the results from an earlier period. The ISC precision of L1 Coarse/Acquisition (C/A) is better than 0·1 ns, and those of L2C and L5Q5 are about 0·4 ns. Remarkably, ISC correction has little effect on the single-frequency SPP for GPS users using civil signals (for example, L1C, L2C), whereas dual-frequency SPP with the consideration of ISCs results have an accuracy improvement of 18·6%, which is comparable with positioning accuracy based on an ionosphere-free combination of the L1P (Y) and L2P (Y) signals.

Estimation of GPS LNAV based on IGS products for real-time PPP

Precise satellite orbit and clock corrections are essential to precise point positioning (PPP). The standard GPS legacy navigation (LNAV) message disseminated by the satellite is one of the most widely used sources for deriving orbit and clock corrections in real-time using efficient analytical user algorithms. However, the quality of the satellite orbit and clock corrections computed with the standard LNAV is not adequate for real-time PPP mainly due to the low update rate. In this study, we proposed an improved LNAV which is estimated based on the IGS ultra-rapid (IGU) orbit and real-time service (RTS) clock products. Two advantages characterize this improved LNAV message. The first one is that scalable update rates can be used for disseminating satellite orbit and clock corrections. Users can decide to receive and decode the improved LNAV message at the desired update rate considering the availability of correction streams, communication bandwidth, and targeted accuracy. With sufficiently high update rates, the improved LNAV can be applied for high-precision applications such as real-time PPP. The second advantage is that the legacy user algorithms can be maintained for computing real-time satellite orbit and clock corrections. Since the improved LNAV has the same parameter representation as the standard LNAV, no changes are required at the user algorithms. To validate the proposed method, the quality of real-time orbit and clock corrections computed with the improved LNAV, IGU products, Centro Nacional de Estudios Espaciales (CNES) real-time products, and the standard LNAV is compared, while the IGS final products are used as the reference. The numerical results indicate that the improved LNAV can achieve comparable orbit accuracy as CNES real-time products, while the clock accuracy highly depends on the update rate. A globally distributed network of 40 IGS stations is used to assess the kinematic PPP performance. Using the improved LNAV with update intervals of 5 min, an average positioning accuracy of 0.122, 0.100, and 0.242 m at 95% confidence level can be obtained in the east, north, and up directions, respectively. Even when the update intervals extend to 2 h, the positioning accuracy is still about 1.2 times better than that of using IGU products. The proposed method provides a scalable and flexible way to improve the standard LNAV for real-time PPP users.

A joint tracking method for NSCC based on WLS algorithm

Navigation signal based on compound carrier (NSCC), has the flexible multi-carrier scheme and various scheme parameters configuration, which enables it to possess significant efficiency of navigation augmentation in terms of spectral efficiency, tracking accuracy, multipath mitigation capability and anti-jamming reduction compared with legacy navigation signals. Meanwhile, the typical scheme characteristics can provide auxiliary information for signal synchronism algorithm design. This paper, based on the characteristics of NSCC, proposed a kind of joint tracking method utilizing Weighted Least Square (WLS) algorithm. In this method, the LS algorithm is employed to jointly estimate each sub-carrier frequency shift with the frequency-Doppler linear relationship, by utilizing the known sub-carrier frequency. Besides, the weighting matrix is set adaptively according to the sub-carrier power to ensure the estimation accuracy. Both the theory analysis and simulation results illustrate that the tracking accuracy and sensitivity of this method outperforms the single-carrier algorithm with lower SNR.

SAINT: Self-Adaptive Interactive Navigation Tool for Cloud-Based Vehicular Traffic Optimization

This paper proposes a self-adaptive interactive navigation tool (SAINT), which is tailored for cloud-based vehicular traffic optimization in road networks. The legacy navigation systems make vehicles navigate toward their destination less effectively with individually optimal navigation paths rather than network-wide optimal navigation paths, particularly during rush hours. To the best of our knowledge, SAINT is the first attempt to investigate a self-adaptive interactive navigation approach through the interaction between vehicles and vehicular cloud. The vehicles report their navigation experiences and travel paths to the vehicular cloud so that the vehicular cloud can know real-time road traffic conditions and vehicle trajectories for better navigation guidance for other vehicles. With these traffic conditions and vehicle trajectories, the vehicular cloud uses a mathematical model to calculate road segment congestion estimation for global traffic optimization. This model provides each vehicle with a navigation path that has minimum traffic congestion in the target road network. Using the simulation with a realistic road network, it is shown that our SAINT outperforms the legacy navigation scheme, which is based on Dijkstra's algorithm with a real-time road traffic snapshot. On a road map of Manhattan in New York City, our SAINT can significantly reduce the travel delay during rush hours by 19%.

Performance Evaluation of the Early CNAV Navigation Message

Following an initial test campaign in June 2013, the GPS Directorate has initiated a pre-operational routine generation and transmission of the Civil Navigation Message CNAV starting on 28 April 2014. The new message is broadcast by Block IIR-M satellites on the L2C signal as well as the L2C and L5 signals of the Block IIF satellites. The improved resolution and larger number of parameters in the new CNAV ephemeris message offers a notably reduced ephemeris fitting error and largely avoids the discontinuities of consecutive ephemeris messages from the same upload. CNAV data of the Block IIR-M and IIF satellites have been collected since the start of transmission using a small set of globally distributed receivers offering an almost continuous coverage. Based on comparison with precise ephemerides of the International GNSS Service (IGS), a Signal-in-Space Range Error (SISRE) of about 1.1 m is obtained for the CNAV message whereas it is 0.6 m for the legacy navigation message (LNAV). This degraded performance is related to less frequent CNAV updates resulting in prediction times of up to four days. For a three week period with a daily CNAV update rate almost the same SISRE is obtained as for LNAV. Complementary to the SISRE analysis, the new Inter-Signal Corrections (ISCs) have been monitored, which enable users to correctly account for differential code biases (DCBs) when using other signals than the L1/L2 P(Y)-code observations in real-time positioning applications. The broadcast ISC values agree with DCBs derived in the frame of the IGS Multi-GNSS Experiment and DCBs from the Center for Orbit Determination in Europe on the 0.1 – 2 ns level depending on the ISC type. While users of the the civil L1C/A and L2C signals have, so far, experienced a notably degraded positioning, the ISCs now enable a single point positioning accuracy that is fully competitive with that of semi-codeless P(Y)-code receivers.

Performance Evaluation of the Early CNAV Navigation Message

Following an initial test campaign in June 2013, the GPS Directorate has initiated a pre-operational routine generation and transmission of the Civil Navigation Message CNAV starting on 28 April 2014. The new message is broadcast by Block IIR-M satellites on the L2C signal as well as the L2C and L5 signals of the Block IIF satellites. The improved resolution and larger number of parameters in the new CNAV ephemeris message offers a notably reduced ephemeris fitting error and largely avoids the discontinuities of consecutive ephemeris messages from the same upload. CNAV data of the Block IIR-M and IIF satellites have been collected since the start of transmission using a small set of globally distributed receivers offering an almost continuous coverage. Based on comparison with precise ephemerides of the International GNSS Service (IGS), a Signal-in-Space Range Error (SISRE) of about 1.1 m is obtained for the CNAV message whereas it is 0.6 m for the legacy navigation message (LNAV). This degraded performance is related to less frequent CNAV updates resulting in prediction times of up to four days. For a three week period with a daily CNAV update rate almost the same SISRE is obtained as for LNAV. Complementary to the SISRE analysis, the new Inter-Signal Corrections (ISCs) have been monitored, which enable users to correctly account for differential code biases (DCBs) when using other signals than the L1/L2 P(Y)-code observations in real-time positioning applications. The broadcast ISC values agree with DCBs derived in the frame of the IGS Multi-GNSS Experiment and DCBs from the Center for Orbit Determination in Europe on the 0.1 – 2 ns level depending on the ISC type. While users of the the civil L1C/A and L2C signals have, so far, experienced a notably degraded positioning, the ISCs now enable a single point positioning accuracy that is fully competitive with that of semi-codeless P(Y)-code receivers.

Broadcast versus precise ephemerides: a multi-GNSS perspective

A consistent analysis of signal-in-space ranging errors (SISREs) is presented for all current satellite navigation systems, considering both global average values and worst-user-location statistics. The analysis is based on 1 year of broadcast ephemeris messages of the Global Positioning System (GPS), GLONASS, Galileo, BeiDou and QZSS collected with a near-global receiver network. Position and clock values derived from the navigation data are compared against precise orbit and clock products provided by the International GNSS Service and its multi-GNSS experiment. Satellite laser ranging measurements are used for a complementary and independent assessment of the orbit-only SISRE contribution. The need for proper consideration of antenna offsets is highlighted and block-/constellation-specific radial antenna offset values for the center-of-mass correction of broadcast orbits are derived. Likewise, the need for application of differential code biases in the comparison of broadcast and precise clock products is emphasized. For GPS, the analysis of the legacy navigation message is complemented by a discussion of the CNAV message performance based on the first CNAV test campaign in June 2013. Global average SISRE values for the individual constellations amount to 0.7 ± 0.02 m (GPS), 1.5 ± 0.1 m (BeiDou), 1.6 ± 0.3 m (Galileo), 1.9 ± 0.1 m (GLONASS), and 0.6 ± 0.2 m (QZSS) over a 12-month period in 2013/2014.

The Development of GPS Navigation Systems in Civil Aircraft

The industry of civil aviation is developing in a fast manner to occupy the increasing needs for a fast, safe and comfortable transportation. To achieve these needs, some effective programs, plans, and systems designs are required. The current reliable aircraft navigation and landing systems have relatively a low level of accuracy especially in aircraft landing stage. The best landing category could be achieved requires a runway visual range up to 50 meters and automatic landing system is not in operation yet all over the world. Aircraft navigates using Radar, Radio and Satellite navigation systems. The Federal Aviation Administration (FAA) plans to replace legacy navigation systems with satellite based navigation technology. Currently, the Global Positioning System (GPS) and its augmentations is the main satellite navigation system used all over the world for air navigation applications. The development of aircraft navigation has been performed with the enhancement of GPS augmentation systems. In this paper, aircraft navigation systems and techniques will be presented in this paper to evaluate the integrity and reliability of each system, and to make a comparison among these systems according to accuracy, integrity and availability.