659 research outputs found
GNSS signal acquisition in the presence of sign transitions
The next generation of Global Navigation Satellite Systems (GNSS), such as Galileo [1] and GPS modernization [2], will use signals with equal code and bit periods, which will introduce a potential sign transition in each segment of the signal processed in the acquisition block. If FFT is used to perform the correlations a sign transition occurring within the integration time may cause a splitting of the main peak of the Cross Ambiguity Function (CAF) into two smaller lobes along the Doppler shift axis [3]. In this paper a method to overcome the possible impairments due to the lobe splitting is proposed and validated by simulatio
Unambiguous Acquisition for Galileo E1 OS Signal Based on Delay-And-Multiply
Galileo E1 Open Service (OS) signal is transmitted with the modulation of Composite Binary Offset Carrier (CBOC). CBOC has a main drawback that is the autocorrelation function has multiple side-peaks, which will lead to ambiguous acquisition. The high rate of data bit and secondary code makes it very difficult to increase coherent integration time. This paper will propose a new scheme based on the delay-and-multiply concept. And also this scheme combines the data channel and pilot channel. Finally, the theoretical results will be given to prove that the new scheme will accomplish unambiguous acquisition and also eliminate the influence of bit transition
GNSS signal acquisition in the presence of sign transitions
The next generation of Global Navigation Satellite
Systems (GNSS), such as Galileo [1] and GPS
modernization [2], will use signals with equal code
and bit periods, which will introduce a potential
sign transition in each segment of the signal
processed in the acquisition block. If FFT is used to
perform the correlations a sign transition occurring
within the integration time may cause a splitting of
the main peak of the Cross Ambiguity Function
(CAF) into two smaller lobes along the Doppler
shift axis [3]. In this paper a method to overcome
the possible impairments due to the lobe splitting is
proposed and validated by simulation
Seguimiento de la señal de Galileo E1 OS para UAVs
Este proyecto está relacionado con el seguimiento de la señal E1 OS de Galileo. El objetivo es llevar a cabo el procesado en banda base de señales de Galileo usando Matlab, por lo que el alcance del proyecto está dentro del procesado digital de señales de radiofrecuencia. La implementaciĂłn se basa en un toolbox existente desarrollado en el departamenteo de DTU Space para GPS, que ha sido adaptado para aceptar la señal de Galileo. Además de esto, se han recogido datos usando un receptor software y el toolbox ha sido probado. Asimismo, se ha llevado a cabo un estudio de multipath usando una estrategia multicorrelador. La tesis está dividida en cuatro bloques principales. El primero introduce la señal de Galileo, asĂ como algo de teorĂa sobre receptores software como background para la implementaciĂłn, que se describe justo despuĂ©s. Posteriormente, se muestra el setup para la recogida de datos junto con algunos resultados y la discusiĂłn de los mismos. Finalmente, se analiza el multipath en un capĂtulo separado, que consiste en una pequeña secciĂłn de teorĂa, las modificaciones en la implementaciĂłn y la seccion de resultados
A new peer-to-peer aided acquisition approach exploiting C/N0 aiding
The aim of this paper is to present an acquisition strategy for Global Navigation Satellite System (GNSS) signals exploiting aiding information provided by GNSS receivers in a Peer-to-Peer (P2P) positioning system. This work sheds light on the benefits of sharing information regarding the received satellite signal power: the Carrier-to-Noise density ratio (C/N0) estimated by aiding peers relatively close to each other, is used to optimize signal acquisition capability in terms of detection performance as well as Mean Acquisition Time (MAT). The proposed approach has been validated and assessed using real data collected with an experimental setup in light indoor conditions and by means of simulations. The performance obtained has also been compared with an Assisted-GNSS (A-GNSS) like acquisition strategy, showing the benefits of the availability of C/N0 aiding information in terms of MAT. ©2010 IEEE
Design of pilot channel tracking loop Systems for high sensitivity Galileo receivers
Global Navigation Satellite Systems (GNSS) have been in the center stage of the recent technological upheaval that has been initiated by the rise of smartphones in the last decade. This is clearly reflected in the development of many applications based on GNSS technology as well as the emergence of multi-constellation GNSS with the launch of the first Galileo satellites at the end of the year 2011. GNSS does not only guarantee global positioning, navigation and timing services but also extends to applications in banking, agriculture, mapping, surveying, archaeology, seismology, commerce, ionosphere scintillation monitoring, remote sensing (soil moisture, ocean salinity, type of surface), wind speed monitoring, ocean surface monitoring, altimetry and many others. In the last decade, Location Based Services (LBS) have increased significant market demand where GNSS has been coupled with technologies based on terrestrial communication links in order to meet strict positioning accuracy requirements. In these conditions, relying on GNSS technology alone, raises a few challenges for signal synchronization even before positioning attempts and are mainly due to a considerable signal attenuation as it propagates through construction material and into indoor environments. Ionosphere scintillation induces a similar challenge where in addition to amplitude fading, the carrier phase and frequency suffer from indeterministic fluctuations.
This research activity is devoted to explore and design the elements constituting pilot channel scalar tracking loop systems, specifically tailored to Galileo signals. It is expected that running such systems with extended integration intervals offers robust synchronization of the incoming signal which is heavily affected by external indeterministic fluctuations. In some conditions, it is desired to follow these fluctuations as in ionosphere scintillation monitoring while in other instances it is mainly desired to filter them out as noise to guarantee positioning capabilities. This is the objective of this research study which applies for both indoor environments and ionosphere scintillation affected signals. Towards this endeavor, a comprehensive theoretical study of the carrier and code tracking loops elements is undertaken, and particular attention is directed to the following aspects:
• carrier frequency and phase discriminators and the relative optimum integration time
• Galileo specific code discriminators and code tracking architecture especially tailored to Composite Binary Offset Carrier (CBOC) modulated signals.
• optimum loop filters designed in the digital domain for different types of phase input signals
• local signal generation using a numerically controlled oscillator and loop filter estimates
• front-end filter bandlimiting effects on the tracking performance.
This design is further tested with simulated Galileo signals with and without ionosphere scintillation as well as raw Galileo signals in an equatorial region during March 2013. Tracking performance comparison is carried out between the customized Galileo receiver developed in this research activity and an ionosphere scintillation dedicated professional GNSS receiver, the Septentrio PolaRxS PRO R receiver
Development and Analysis of Advanced Techniques for GNSS Receivers
With the rapid development of digital techniques, the concept of software-defined radio (SDR) emerged which accelerates the first appearance of of the real-time GNSS software receiver at the beginning of this century, in the frame of a software receiver, this thesis mainly explores the possible improvement in parameters estimate such as frequency estimate, code delay estimate and phase estimate.
In the first stage, acquisition process is focused, the theoretical mathematical expression of the cross-ambiguity function (CAF) is exploited to analyze the grid and improve the accuracy of the frequency estimate. Based on the simple equation derived from this mathematical expression of the CAF, a family of novel algorithms are proposed to refine the Doppler frequency estimate. In an ideal scenario where there is no noise and other nuisances, the frequency estimation error can be theoretically reduced to zero. On the other hand, in the presence of noise, the new algorithm almost reaches the Cramer-Rao Lower Bound (CRLB) which is derived as benchmark. For comparison, a least-square (LS) method is proposed. It is shown that the proposed solution achieves the same performance of LS, but requires a dramatically reduced computational burden. An averaging method is proposed to mitigate the influence of noise, especially when signal-to-noise ratio (SNR) is low. Finally, the influence of the grid resolution in the search space is analyzed in both time and frequency domains.
In the next step, a new FLL discriminator based on energy is proposed to adapt to the changes brought by the new introduced signal modulation. This new discriminator can determine the frequency error only using the minimum period of data, it can also extend the pull-in range to nearly six times larger as the traditional arctangent discriminator. The whole derivation of the
method is presented. From the comparison with traditional ATAN and another similar discriminator that is also based on energy, it is shown that the new proposed discriminator can inherit the merits of these two references, avoiding their drawbacks at the same time. Owing to the property of the new discriminator, in case of composite GNSS signals such as Galileo E1 Open Service (OS) signal, coherent combination of data and pilot channels can be adopted to improve the frequency estimate by exploiting the full transmitted power.
In order to incorporate all the available information, the structure of a tracking loop with Extended Kalman Filter (EKF) is analyzed and implemented. The structure of an EKF-based software receiver is proposed including the special modules dedicated to the initialization and maintenance of the tracking loop. The EKF-based tracking architecture has been compared with a traditional one based on an FLL/PLL+DLL architecture, and the benefit of the EKF within the tracking stage has been evaluated in terms of final positioning accuracy. Further tests have been carried out to compare the Position-Velocity-Time (PVT) solution of this receiver with the one provided by two commercial receivers: a mass-market GPS module (Ublox LEA-5T) and a professional one (Septentrio PolaRx2e@). The results show that the accuracy in PVT of the software receiver can be remarkably improved if the tracking is designed with a proper EKF architecture and the performance we can achieve is even better than the one obtained by the mass market receiver, even when a simple one-shot least-squares approach is adopted for the computation of the navigation solution. Furthermore in depth, KF-based tracking loop is analyzed, a control model is derived to link the KF system and the traditional one which can provide an insight into the advantages of KF system.
Finally, conclusions and main recommendations are presented
Performance of precise marine positioning using future modernised global satellite positioning systems and a novel partial ambiguity resolution technique
The International Maritime Organisation (IMO) established a set of positioning requirements for
future Global Navigation Satellite System (GNSS) constellations in IMO resolution A.915. It is
important to be able to determine if these requirements can be met, and what shore infrastructure
would be required. This thesis describes the collection of data in a marine environment and the
analysis of these data with regards to the requirements.
The data collection exercise was held at the beginning of May 2008 and saw THV Alert
navigate into Harwich Harbour whilst Global Positioning System (GPS) observation data were
recorded from onboard the vessel and from shore-based reference stations. Additional data were
obtained from nearby Ordnance Survey reference stations, and two total stations were used to
track the vessel’s passage to provide a truth model. Several modernised GPS satellites were
tracked. The data were processed under different scenarios, using software developed at UCL,
and the positioning performance was analysed in the context of the IMO requirements. Potential
performance improvements from modernised GPS and Galileo were then discussed.
Providing integrity through single-epoch real-time kinematic positioning, required to meet
the strictest IMO requirements, is particularly difficult. The identification of phase observation
outliers is not possible before the integer ambiguities are resolved, but an undetected outlier
could prevent successful ambiguity resolution. It will not always be necessary to fix all the
ambiguities to achieve the required positioning precision, particularly with a multi-GNSS constellation.
This thesis introduces a new algorithm for partial ambiguity resolution in the presence
of measurement bias. Although computationally intensive, this algorithm significantly improves
the ambiguity resolution success rate, increasing the maximum baseline length over which the
highest requirements are met with dual-frequency GPS from 1 km to 66 km
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