The growing demand of location, navigation and positioning services is boosting the development of new signals and modulations that will be adopted by new global navigation satellite systems (GNSS), such as the European Galileo, the Chinese Compass and the modernized GPS. A common feature of these new modulations is the presence of two channels, the data and pilot components, that separately carry the navigation message and the ranging information. Three different techniques, noncoherent combining, coherent combining with sign recovery and differentially coherent combining, are analyzed for the joint acquisition of data and pilot signals. For each acquisition strategy the probabilities of detection and false alarm are provided. In particular closed-form expressions for the probabilities of coherent channel combining and of the differentially coherent integration strategy are derived. To the best of our knowledge these expressions are new. Monte Carlo simulations are used to support theoretical analysis demonstrating the accuracy of the proposed models.

GNSS jammers are small portable devices able to broadcast disruptive interference and overpower the much weaker GNSS signals. In this paper, the effects of GNSS jammers on GPS and Galileo receivers are thoroughly analyzed and the use of an adaptive notch filter is suggested as an effective countermeasure to jamming. Signals generated by a commercial jammer are broadcast in a large anechoic chamber along with the GPS and Galileo signals generated by a hardware simulator. The analysis is conducted in terms of C/N₀ degradation and different jammer power levels are considered. The use of mitigation techniques, such as notch filtering, significantly improves the performance of GNSS receivers even in the presence of strong and fast-varying jamming signals. The presence of a pilot tone in the Galileo E1 signal enables pure PLL tracking and makes the processing of Galileo signals more robust to jamming.

A semi-assisted GNSS authentication concept is proposed, with two main advantages. Firstly, it can be implemented in a GNSS without modifications to the signal plan, provided that the GNSS can transmit an encrypted signal and an open signal with unpredictable and verifiable bits regularly. Secondly, it can work in a receiver for up to several days without any assistance or the possession of a private key, at the expense of some authentication latency. In this concept, parts of the encrypted signal to be transmitted in the future are re-encrypted, published, and downloaded in the receiver. Some seconds after transmission, the satellite openly broadcasts the decryption key, and the receiver performs the a-posteriori correlation with the encrypted signal. The concept is particularized for the Galileo system as Galileo ACAS (Assisted Commercial Authentication Service), based on OSNMA in E1B for the decryption keys and E6C for the encrypted signal. An end-to-end procedure for measurement authentication is proposed and tested, showing its viability.

The new signals employed by modern global navigation satellite system (GNSS) will be characterized by a data/pilot structure and by the presence of secondary codes. These innovations require special acquisition techniques for efficiently recovering all the transmitted power and dealing with the problem of sign transitions. In this paper three integration strategies, noncoherent, semi-coherent, and differentially coherent integrations, are analyzed for the joint acquisition of data and pilot signals over multiple primary code periods. Each strategy is statistically characterized and false alarm and detection probabilities are provided. To the best of our knowledge the characterization and comparison of these algorithms are new. Monte Carlo simulations and real data analysis demonstrate the accuracy of the proposed model.

Global Navigation Satellite Systems (GNSSs) are vulnerable to several threats including jamming and spoofing. Jamming is the deliberate transmission of powerful Radio-Frequency (RF) signals which can easily overpower the much weaker GNSS components disturbing and, in some cases, denying GNSS operations. In recent years an increasing number of cheap, though illegal, jammers have become commercially available. In this paper, the impact of these jammers on Global Positioning System (GPS) and Galileo L1/E1 signal reception is investigated. It is shown that the signals of each system are affected in similar ways and this is due to the wide-band nature of the jamming signals. Narrow-band receivers are less impacted by jamming since they are able to filter out a greater portion of the interfering signal. Interestingly, the presence of a pure pilot channel in the Galileo E1 modulation allows receivers to use a pure Phase Lock Loop (PLL) which in turn allows signal reception in the presence of stronger jamming signals with respect to the GPS L1 C/A case.