Showing papers in "Annual of Navigation in 2015"

Railway Track Irregularity Measuring by GNSS/INS Integration

Abstract: Railway track irregularity measuring is a task of fundamental importance to guarantee operating safety and arrange proper maintenance, particularly for the high-speed lines. Conventional measuring methods cannot satisfy the requirements of accuracy and time-efficiency simultaneously. A GNSS/INS integrated technique is proposed based on the fact that railway track irregularity detection is essentially an issue of relative surveying. Key technologies of the integration algorithm aiming at track irregularity measuring are proposed to improve the performance of the GNSS/INS system. Results show that the proposed method can fulfill 1 mm relative accuracy in identifying track irregularities in the kinematic surveying mode, which means this method can satisfy the accuracy requirement for a high-speed line and is ten times faster than the conventional method based on total station. Copyright © 2015 Institute of Navigation

The GPS Block IIR and IIR-M Broadcast L-band Antenna Panel: Its Pattern and Performance

Abstract: The Global Positioning System (GPS) Block II Replenishment (IIR) space vehicle (SV) has made up at least one-half of the GPS constellation since 2006. This consists of the 12 original ‘classic’ IIR SVs and the eight ‘modernized’ IIR-M SVs. As a stepping-stone toward the IIR-M modernization, Lockheed Martin developed and deployed an updated version of the satellite antenna panel for the L-band broadcast signal. This is the signal used by the worldwide GPS user population. This paper describes both antenna panel versions, their broadcast signal patterns, the performance observed in factory testing, and their on-orbit performance. This is the initial publication of these antenna panel patterns. Ground and on-orbit measurements of both versions of the antenna show that all specification requirements are exceeded. They also reflect the increased antenna gain for the new IIR antenna. The L1 signal shows an increase of 1 dB in received power at edge of Earth, and L2 shows an increase of 2 dB in received power. All users, both terrestrial and on-orbit, benefit from this enhanced power profile.

A Robust Shadow Matching Algorithm for GNSS Positioning

Abstract: Commercial GNSS devices tend to perform poorly in urban canyon environments. The dense and tall buildings block the signals from many of the satellites. In this work, we present a particle filter algorithm for a Shadow Matching framework to face this problem. Given a 3D city map and given the satellites' signal properties, the algorithm calculates in real-time invalid regions inside the Region Of Interest (ROI). This approach reduces the ROI to a fraction of its original size. We present a general framework for a Shadow Matching positioning algorithm based on a modified particle filter. Using simulation experiments we have shown that the suggested method can improve the accuracy of existing GNSS devices in urban regions. Moreover, the proposed algorithm can be efficiently extended to 3D positioning in high sampling rate, inherently applicable for UAVs and Drones. Copyright © 2015 Institute of Navigation.

Tracking and Relative Positioning with Mixed Signals of Opportunity

Abstract: In Global Positioning System (GPS)-challenged environments, broadcast and wireless communications signals are used as alternatives via fingerprinting or trilateration for positioning and navigation. In trilateration, the time of flight of recognizable patterns of a signal of opportunity (SOOP) is determined from the time of departure (TOD) from its source and the time of arrival at a user. However, most SOOPs are neither synchronous nor cooperative. There is a need to deal with the unknown TOD. In this paper, relative ranges are generated from radio signals by time difference with respect to an initial known point (thus removing TOD) to enable relative positioning from the known initial point. The paper also considers a critical aspect of maintaining continuous tracking of signals of opportunity in the presence of mobile fading. To demonstrate, we built mobile testbeds and conducted field tests, which are presented in this paper together with an analysis of the results.

Jamming Detection in GNSS Receivers: Performance Evaluation of Field Trials

Abstract: We evaluate the detection performance of several commercial interference detectors and of a detector that uses the automatic gain control (AGC) level as a test statistic. The evaluations are based ...

Online Motion Mode Recognition for Portable Navigation Using Low-Cost Sensors

Abstract: The main challenge in portable navigation is obtaining accurate positioning results in urban canyons and indoors where global navigation satellite system signals are degraded/unavailable. Inertial sensors can be used; however, their traditional positioning performance is unacceptable. Motion mode recognition of the user carrying the portable device is needed to enhance the positioning performance. This paper illustrates the use of pattern recognition to detect stationary (including standing, sitting, and placing device on still surface), walking, running, cycling, and vehicle (including car, bus, and train). The use of sensor fusion to remove bias errors from sensor signals to calculate variables descriptive of motion has been introduced in this paper. The features are extracted from such variables and combined into a feature vector fed into the classification stage. Extensive data collection was conducted to gather training and evaluation data; the performance results on the latter have shown the efficacy of the solution. Copyright © 2015 Institute of Navigation

Performance Evaluation of the Early CNAV Navigation Message

Abstract: 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.

Classification and Mathematical Expression of Different Interference Signals on a GPS Receiver

Abstract: Interference is one of the major concerns in using the global positioning system (GPS) for civilian and military applications. In this paper, a new classification of different interference signals is presented. This classification is based on the interference signal's bandwidth and the GPS correlator coherent integration time. The new classification simplifies the evaluation of the interference effect on the GPS receiver correlator output for different interference signals such as: continuous wave interference (CWI), narrowband interference (NBI), partial band interference (PBI), and broadband interference (BBI). Novel closed form analytical expressions for the GPS receiver correlator output power for CWI, NBI, PBI, and BBI are derived. The effect of the GPS correlator coherent integration time, the interference bandwidth, and the interference frequency error are also investigated under the impact of these types of interference. Copyright © 2015 Institute of Navigation.

GNSS Multipath Mitigation using Antenna Motion

Abstract: A method is developed for characterizing and compensating specular GNSS multipath by considering signal amplitude and phase variations in response to antenna motion. This method seeks to improve multipath rejection capabilities. A known antenna motion profile is combined with a batch filter to estimate the code phase, carrier phase, and amplitude of the direct signal, the relative code phase, carrier phase, carrier Doppler shift, and amplitude of each significant multipath component, and the directions of arrival of the direct and multipath components. Hardware signal simulator results indicate accurate estimation of all multipath features, and experimental test results demonstrate measurable improvements in estimates of carrier amplitude in all cases, of direct-path carrier-phase in many cases, and of direct-path code phase in some cases. Anomalous results have also been obtained, including specular multipath component estimates that occur in doublets and that may represent attempts by the batch filter to approximate diffuse multipath. Copyright © 2015 Institute of Navigation.

Design of a Passive Ranging System Using Existing Distance Measuring Equipment (DME) Signals & Transmitters

Abstract: The US Federal Aviation Administration (FAA) is developing alternative navigation concepts to maintain operational capacity and efficiency even with the loss of Global Positioning System (GPS). One concept being studied for alternative position navigation and timing (APNT) is a ground based passive ranging system. This system has few capacity constraints and can provide other benefits. The APNT passive ranging system would use existing FAA terrestrial infrastructure, particularly distance measuring equipment (DME) ground beacons. APNT project team has developed a DME Pseudolite (PL) concept that enables a passive ranging signal on DME that is compatible with existing DME operations. It can provide additional benefits for APNT and non-APNT users with its data transmission. This paper introduces the DME PL concept and assesses the potential performance of the system. The paper focuses on signal structure design for best data capacity. It formulates a methodology and modeling for the developing the design. Copyright © 2015 Institute of Navigation.

Performance Analysis of L2 and L5 CNAV Broadcast Ephemeris for Orbit Calculation

Abstract: Ephemeris error is a limiting factor in GPS position accuracy. The newly introduced GPS Civil Navigation (CNAV) broadcast message, an upgraded version of the legacy NAV message, is designed to provide users with more precise satellite orbit and timing parameters. A CNAV broadcast test was conducted in 2013 on the L2C and L5 bands. Since April 2014, pre-operational CNAV started to broadcast to civilian users. Baseband civil GPS signals on L1, L2, and L5 were recorded during the broadcast test and the pre-operational broadcast using wideband software radio front ends. The signals were acquired and tracked, with navigation messages decoded by the conventional Viterbi method and a computationally efficient matrix-based method. GPS ephemerides were extracted from the messages to compute satellite orbit solutions. This paper evaluates the orbit solution of both CNAV and Legacy NAV during the same time period to demonstrate the improvements in the CNAV ephemeris accuracy. Copyright © 2015 Institute of Navigation.

Implementation Strategies for a Software-Compensated FFT-based Generic Acquisition Architecture with Minimal FPGA Resources

Abstract: A generic 2048-point FFT acquisition architecture is proposed to address L1 civil signals from all four GNSS constellations. After emphasizing hardware design criteria and their resulting design limitations, software compensation approaches are compared. A detailed validation methodology, involving a successive 1000-step Monte-Carlo study, was defined to optimally configure the acquisition channel, with new metrics to establish formal signal detection. The integration thereof results in a novel, minimalistic, yet generic, acquisition channel implementation, as well as a thorough validation method. Execution time of one acquisition iteration is approximately 5 ms, in line with VHDL simulations and foreseen channel management overhead. Coarse/fine search increments and thresholds are based on extensive experimentation. A 41 dB-Hz acquisition sensitivity threshold was established to achieve >95 % detection rates for 1 ms integrations, while 15 ms non-coherent integrations are required for signal strengths down to 37 dB-Hz. These thresholds account for known implementation losses. Copyright © 2015 Institute of Navigation

Examination of EGNOS Safety-of-Live service in eastern Slovakia

Abstract: Abstract The first PBN approach procedures in Slovakia became operationally effective at Bratislava and Košice airports as of 5 February 2015. The article presents the results of EGNOS Safety-of-Life Service preliminary examination in eastern Slovakia, just before official introduction of these procedures. The practical examination includes static test and test flight made with Cessna plane taking off at the airport in Bidovce — LZBD (just 16 km from international airport in Košice) and passing a route along eastern border of Slovakia. In this region the performance of EGNOS could be unsatisfactory due to lack of RIMS stations to the east from there. The experiment was performed on October 13, 2014 in cooperation of the Air Force Academy in Deblin, the Department of Aviation of Technical University in Košice and University of Warmia and Mazury in Olsztyn.

A Single Distance Measuring Equipment (DME) Station-Based Positioning System for Alternative Position Navigation and Timing (APNT)

Abstract: A single station-based positioning system, known as Mosaic/DME, is introduced. This new system has been designed for the Alternative PNT (APNT) solution to air services as it acts as a backup navigation system in case of GNSS outage. The Mosaic/DME is a single station consisting of conventional DME and multiple pseudolites. The DME is operated using two-way round signals for range measurements, with pseudolites broadcasting one-way continuous signals for carrier phase measurements. The receiver in the aircraft receives both signals and calculates its own position after the ambiguity resolution process. In this paper, the feasibility of this system is studied via two topics: the performance of the navigation accuracy and ambiguity resolution using the weighted dilution of precision and Monte Carlo simulations. The results conclude that this system satisfies the required navigation accuracy of the APNT and yields a very fast and easy ambiguity resolution.

Effect of Sampling Rate Error on GNSS Velocity and Clock Drift Estimation

Abstract: A sampling frequency error in a GNSS receiver is shown to manifest as a scaling of a satellite's true Doppler shift, which cannot be properly accounted for by estimating a common clock drift across satellites, resulting in slowly varying biases in the receiver's velocity and clock drift estimates. For typical GNSS receivers whose oscillator frequency error is in the range of a few parts per million (ppm), the errors are negligible. However, for oscillators whose frequency error is several thousand ppm (e.g., for MEMS-based oscillators), or for applications with large Doppler shifts (e.g., space-borne receivers), the effect is highly detrimental. A method to compensate for the effect on the Doppler measurements without changing the receiver architecture is presented. Results with real static data and simulated low-Earth orbit data show that applying the compensation algorithm yields errors similar to those with a near-perfect oscillator. Copyright © 2015 Institute of Navigation.

Weak GPS Signal Acquisition Using Antenna Diversity

Abstract: GPS signal acquisition is challenging in attenuating and multipath fading environments. Standard methods, such as extending the coherent integration time to achieve more processing gain, are not always feasible for acquiring weak signals using unaided receivers. Spatial antenna diversity is used for indoor applications to mitigate the multipath fading effect in the acquisition process. Equal gain combining of two received signals is considered in a standalone processing strategy. The main novelty of this paper is to investigate improvement in acquisition time by utilizing antenna diversity for indoor scenarios. A detection threshold for which mean acquisition time is minimized is numerically shown to exist. The importance of acquisition time variance is discussed and diversity gain is evaluated. Theoretical analysis is compared with Monte Carlo simulations and real GPS data. Results show that antenna diversity improves detection probability, reduces false alarms and mean and variance of acquisition time in fading environments. Copyright © 2015 Institute of Navigation

Improvement of INS-Aided GPS Tracking Performance under Strong Ionospheric Scintillation

Abstract: Ionospheric anomalies are major error sources that affect the performance of the GPS (Global Positioning System). In particular, ionospheric scintillation may cause GPS satellite signal loss, and multiple losses can degrade the availability of positioning/navigation services such as GBAS (Ground-Based Augmentation Systems). In order to improve the tracking performance of GPS receivers under scintillation conditions, a tracking loop aided by INS (Inertial Navigation System) has been developed, and flight tests to evaluate it were conducted around the island of Ishigaki where ionosphere scintillation frequently occurs. Phase tracking performance evaluation was carried out off-line using a software-defined GPS receiver which processes stored IF (Intermediate Frequency) data. The use of INS enabled a longer integration time of GPS signals, which increased the signal-to-noise ratio (SNR). As a result, the INS-aided tracking loop achieved continuous phase tracking even under strong scintillation conditions. Copyright © 2015 Institute of Navigation.

Methodology of Creation the Simulation Basin based on the Projected Canal through the Vistula Spit

Abstract: Abstract The biggest problem in the process of implementation of the new sea areas project or aids to navigation systems is to check the assumptions without compromising security on real waters. Today, digital models are available for easy and inexpensive replacement of the research methods used so far. For this purpose the navigational and maneuvering simulators are perfect. Simulators as a research tools allow you to define a more realistic and accurate data for the study and evaluation sea areas. The purpose of the simulation is to identify and reduce the risk for seafarers during navigation on the waterways, canals and port areas. These include quantitative and qualitative assessment of the canals and fairways construction. The main requirement for a simulation system is to have a multi-task simulation software, which includes effective tools for repositioning and designing safe waterways and port infrastructure. The Institute of Navigation and Maritime Hydrography of the Polish Naval Academy since the eighties of the twentieth century is carried out projects in the field of navigational and hydrographic support of human activities at sea. This is possible thanks to the extensive set of simulation tools. Planning this tasks in a simulators software environment allow not only to design of virtual counterparts of real sea areas, but also to evaluate the quality of manufactured parts before their actual exposure to sea areas.

Quasi-tightly Coupled GNSS-INS Integration

Abstract: Quasi-tightly coupled integration of Global Navigation Satellite System (GNSS) and inertial navigation system (INS) data is a method of loosely coupled integration that has the salient characteristic of continued aiding with fewer than four satellites that a tightly coupled integration typically exhibits. This method is intended for the integration of an existing GNSS navigation engine into a GNSS-INS closed-loop configuration with little or no modification of the GNSS navigation engine. The method of integration uses the range measurement model matrix typically used to compute dilutions of precision to identify the observable subspace in the time-space frame generated by the available satellites and project the loosely coupled INS–GNSS position measurement into this subspace. The GNSS navigation engine can therefore be any linear estimator. This paper describes the quasi-tightly coupled method applied to a single point positioning least squares adjustment and to a Kalman filter for GNSS position estimation. Copyright © 2015 Institute of Navigation

The Use of Magnetic Field and Magnetometers in Supporting the Air Navigation

Abstract: Abstract At present, the Earth’s magnetic field (geomagnetic field) undergoes considerable variations. The use of towers measuring areal variations in magnetic intensity may provide additional support for aircraft navigation. This paper presents the idea of using magnetometers for supporting GNSS as well as for creating a landing system based on magnetic field variations.

CSC Code Discriminator: Theoretical Analysis of Performance

Abstract: This paper presents the theoretical development and analysis of a novel DLL discriminator robust to multipath errors, called the Combination of Squared Correlators (CSC). The CSC discriminator features a simple implementation based on four (complex) static correlators per channel, without falling into the wide family of patented architectures. In this paper, the theoretical analysis of the properties of the CSC architecture is developed in a well structured context: (i) definition of the discrimination rule; (ii) theoretical analysis in the absence of noise; (iii) theoretical noise tracking jitter analysis; and, (iv) multipath error envelope analysis. In all cases, the CSC results are compared to those of the Strobe discriminator, which is the natural benchmark. The promising performance of the CSC discriminator inserted in a complete software receiver is also proved in a heavy multipath scenario, expressly simulated to stress the code tracking loop robustness. Copyright © 2015 John Wiley & Sons, Ltd.

Maritime safety in terms of the availability for the AIS class B binary data transmission, based on static measurements, performed on the VTS Zatoka Gdańska

Abstract: Abstract The problem of the safety navigation considered only in terms of position error measurement, seems to be solved on a global scale. Thus, the operational characteristics of radio navigation systems such as availability are equally important. The integrated navigation system operate in a multi-sensor environment and it is important to determinate a temporal validity of data to make it usable in data fusion process. In the age of digital data processing, the requirements for continuity, availability, reliability and integrity information are already grown. This article analyses the problem of time stamp discrepancies of dynamic AIS class B position reports. For this purpose, the statistical summary of Latency Position Reports, derived from class B units has been presented. The navigation data recordings were conducted during 82 days of August, September and November 2014 from 20 vessels located in area of VTS ‘Zatoka Gdańska’. On the base of Latency Position Reports class B it is possible to designate the availability of AIS information system. For this purpose, the model of availability of AIS binary data transmission and research outcomes have been presented.

Phase-Phase and Phase-Code Methods Modification for Precise Detecting and Predicting the GPS Cycle Slip Error

Abstract: Abstract There are three well-established detecting methods for cycle slip error, which are: Doppler measurement method, Phase-Code differencing method, and Phase-Phase Differencing Method. The first method depends on the comparison between observables and the fact that Doppler measurements are immune to cycle slip error. This method is considered as the most precise method for cycle slip detecting, because it succeed in detecting and predicting the smallest cycle slip size (1 cycle) in case the local oscillator has low bias. The second method depends on the comparison between observables (phase and code) and the code measurements are immune to the cycle slip error. But this method can’t detect or predict cycle slip size smaller than 10 cycles, because the code measurements have high noise. The third method depends on the comparison between observables (phase 1 and phase 2) and the phases measurements that have low noise. But this method can’t detect or predict cycle slip size smaller than 5 cycles, because the ionospheric change might have a high variation. For enhancing the precision of the last two methods in detecting the smallest cycle slip which size reaches 1 cycle, a new algorithm was developed in this research to determine the change in the ionospheric values and the code bias from epoch to epoch. That is done by solving all observables equations by least square technique. This modification on these methods succeed in detecting and predicting cycle slips of size of 1 cycle.

Some Aspects of Development in Radar Technology in the Context of Accurate Positioning

Abstract: Abstract In the end of XX century we were witnesses of the revolution in a radio-navigation, which led to the present domination of GPS. Dozens of radio-navigation systems disappeared. However now in many papers more and more often we can read an opinion, that GNSS monopoly becomes dangerous. This results from the similar sensibility of all GNSS systems on the same disturbances consequential from the similar radiofrequency band and similarly low powers of the signal. There is a growing approval in the maritime world that GNSS will not provide a required resilience because of common vulnerabilities. An anticipated radio navigation system should be a combination of systems, providing redundancy and effective work when GNSS does not work properly. Lately a lot of authors commonly pointed-out a potential advantages of modified Loran (e-Loran), however surely still it will be only a potential option, particularly for the southern hemisphere, where this system has never existed. An issue of alternative systems becomes urgent, because of the growing concern about GNSS system operation. The solution should not demand high financial effort, well fit to the existing law and utilize a present technology. The paper presents a general outlook of potential development in a present radar devices considering their use as an element of a positioning system. In this context radar seems to be an attractive option, however its utilization as an alternative for GNSS should reach considerably higher technical performances. The accessible information prove that it is possible to reach a higher accuracy of the position obtained from the modified radar in the future, especially with the suitable navigational infrastructure on shore.

An Investigation via Simulation and Measurements to Assess Vehicle Impact on Personal Privacy Device Antenna Radiation Patterns

Abstract: This article presents a study of the radiation pattern of a personal privacy device (PPD) antenna on a fabricated vehicle and three commercial vehicles. Initially, electromagnetic modeling of the PPD antenna on the fabricated vehicle in three distinct antenna locations and two orientations per location was performed. Measurements were then conducted to gauge the accuracy of the simulations. Next, the same PPD antenna was placed in three locations and two orientations per location on three commercial vehicles to create 18 unique configurations. The maximum right hand circularly polarized gain vs. theta angle was analyzed. The results show that electromagnetic modeling of antennas mounted inside a vehicle differ significantly from measurements of the same scenario but acceptable agreement was achieved for exterior-mounted antennas on a vehicle. It also provides a vehicle efficiency value corresponding to the vehicle body frame's impact on a component-level PPD antenna radiation pattern over theta angles. Copyright © 2015 Institute of Navigation.