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This paper describes the design of a simple low cost GNSS sampler with integrated storage. The sampler is built from low cost, off-the-shelf components. The proposed design stores digital IF samples from two separate front ends and record the data to a SD card for post-mission processing. The GNSS sampler currently supports GPS and GLONASS signals, but could also be configured for Galileo reception...
Ionospheric scintillation monitoring is becoming an increasing research activity in order to devise countermeasures to the harmful effects ionospheric activity has on positioning services based on Global Navigation Satellite Systems (GNSS). The amount of amplitude fluctuations in GNSS signals due to scintillation is estimated by the �������� index. For this purpose, traditional closed loop architectures...
The aim of this paper is to trigger a conversation about the assessment, definition of metrics and testing procedures of software-defined GNSS receivers. While the evaluation of traditional (i.e., built on application–specific integrated circuit technology) GNSS receivers is now well–understood, and enjoys both a solid testing industry providing the required equipment and universally agreed figures...
An implementation of a robust vector phase-locked loop (VPLL) for joint tracking of carrier phase from the navigation satellites in the event of ionospheric scintillation is presented. This partitioned tracking method leads to an increased tolerance to ionospheric disturbances due to scintillation in the carrier phase tracking, providing a trade off between the pure VPLL and the classic scalar tracking...
In the context of global navigation satellite systems, this paper addresses the problem of refining the Doppler frequency estimation provided in the acquisition stage for highorder binary offset carrier (BOC) signals in post-correlation. The refinement of Doppler frequency must be done because the estimation obtained from the acquisition stage is not usually accurate enough to track the signal in...
The Galileo E1 Open Service signal broadcasts a navigation message containing 120 bits of information per page on the signal component E1B. This raw navigation message is ½ convolutional encoded with a Forward Error Correcting (FEC) Code. The encoded symbols are interleaved within a block interleaver size of 240 symbols and broadcast every second. The resulting data rate is 250 symbol/second. The...
In recent years, the problem of Position, Navigation and Timing (PNT) resiliency has received significant attention due to an increasing awareness on threats and the vulnerability of the current GNSS signals. Several proposed solutions make uses of cryptography to protect against spoofing. A limitation of cryptographic techniques is that they introduce a communication and processing computation overhead...
The proliferation of GNSS-based (Global Navigation Satellite Systems) services and applications providing ubiquitous, seamless and secure/reliable positioning is driving the use of high-performance devices. This implies the requirement of a higher computational capability in miniaturized size and low power consumption devices such as smartphones or Smart- City sensors. In this context, a possible...
Severe performance degradation of Global Navigation Satellite Systems (GNSS) is produced in urban scenarios, mainly due to dense multipath and non-line-of-sight (NLoS) conditions. Thus, the integration of GNSS with additional positioning systems, such as the location methods in Long Term Evolution (LTE) cellular systems, may cope with these challenging scenarios. This work proposes a generic evaluation...
Advanced Receiver Autonomous Integrity Monitoring (ARAIM) is a new Aircraft Based Augmentation System (ABAS) technique, firstly presented in the two reports of the GNSS Evolutionary Architecture Study (GEAS). The ARAIM technique offers the opportunity to enable GNSS receivers to serve as a primary means of navigation, worldwide, for precision approach down to LPV-200 operation, while at the same time...
Current GNSS (Global Navigation Satellite System) receivers include an internal quartz oscillator, such as TCXO (Temperature Compensated Crystal Oscillator) or similar, limited by its frequency stability and a poor accuracy, being one of the main sources of uncertainty in the navigation solution (also multipath and ionosphere effects are an important error sources.) Replacing the internal TCXO clock...
Structural interference signals can severely jeopardize the performance of GNSS receivers which may lead to serious consequences for scores of applications. This type of interference is designed to be very similar to the authentic GNSS signals; therefore, it is very difficult for a conventional receiver to discriminate them from genuine observations. This research focuses on the application of a carrier...
The modernized GNSS systems introduced the idea of BOC signals, which provide better tracking accuracy than BPSK signals at the cost of having side lobes in the autocorrelation function. In closed-loop processing, or tracking, the presence of side lobes can origin false locks, thus making the ranging estimate to be biased by several meters. The overall position, velocity and time solution can then...
We discuss the advantages of using a vector delay/frequency-locked loop (VDFLL) architecture for GNSS receivers operating in scenarios disturbed by radio-frequency interference. Narrowband (sinusoidal) and wideband (chirp) interference signals are considered in the analysis. The VDFLL is constituted by a bank of code and frequency discriminators feeding a central extended Kalman filter that estimates...
We propose a digital modulation scheme, based on the generalization of the chirp signal, that allows to improve the performance of Global Navigation Satellite System receivers in scenarios affected by channel additive white Gaussian noise, narrowband interference and multipath. Different signaling schemes, characterized by autocorrelation functions with small secondary peaks, can be obtained by adjusting...
This paper describes a new method for the synchronisation of multiple low-cost open source software-defined radios (SDR). This solution enables the use of low-cost SDRs in interesting navigation applications, such as hybrid positioning algorithms, interference localisation, and cooperative positioning among others. Time synchronisation is achieved thanks to a time pulse that can be generated either...
GNSS signals are vulnerable to various types of interference including jamming and spoofing attacks. Spoofing signals are designed to deceive target GNSS receivers without being detected by conventional receiver quality monitoring metrics. This paper focuses on detecting an overlapped spoofing attack where the correlation peaks of the authentic and spoofing signals interact during the attack. Several...
The detection and localisation of multiple GNSS jammers in densely populated areas seems to be already a need due to the availability and proliferation of very cheap and small GNSS jammers (together with the raise of the privacy awareness), and the increasing number of services and applications relying on the GNSS signals for its operation. Densely populated areas do not only introduce the possibility...
Global Navigation Satellite System (GNSS) is becoming pervasive technology, widely used in many fields, like aviation, railway, maritime and road navigation systems. As a consequence an increasing number of applications are being created and it has become necessary to protect the GNSS receiver from malicious attacks, in order to guarantee the reliability of the navigation solution. In this work, a...
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