In the current framework of Galileo and thanks to the flexibility of the I/NAV message, introducing new pages in order to propose an optimization of the E1-B Galileo signal has been proposed [1]. This optimization process pursues two different objectives. The first objective aims to reduce the Time To First Fix (TTFF), achieved by shortening the time to retrieve the Clock and Ephemerides Data (CED). The second objective aims to improve the resilience and robustness of the CED, particularly under hostile environments. Under the backward compatibility precondition, new outer channel error correction solutions for Galileo I/NAV are proposed in this paper. Especially, a new family of codes called Lowest Density Maximum Distance Separable codes (LD-MDS) is proposed to be used in this paper, thus in GNSS context. This family of codes, along with an enhanced performance decoding method based on the use of a soft serial iterative decoding, provides an optimal solution in order to reduce the TTFF as well as to improve the robustness of the CED.

The design of a new GNSS signal is always a trade-off between improving performance and increasing complexity, or even between improving different performance criteria. Position accuracy, receiver sensitivity (acquisition, tracking or data demodulation thresholds) or the Time-To-First-Fix (TTFF) are examples of those GNSS receivers performance criteria. Within the framework of Galileo 2nd Generation (G2G), adding a new signal component dedicated to aid the acquisition process on E1 can help to improve performance of GNSS receivers with respect to these criteria as it was shown in [1]. In order to create this new component, various aspects such as the spreading modulation, the data navigation content, the channel coding or the Pseudo-Random Noise (PRN) codes must be studied. To this end, this paper firstly proposes the study of new spreading modulations, and secondly, we investigate on PRN codes that can be well suited to the proposed Acquisition-Aiding signal.

Global Navigation Satellite System (GNSS) are present in our daily lives. Moreover, new users are emerging with further operation needs involving a constant evolution of the current navigation systems. In the current framework of Galileo (GNSS European system) and especially within the Galileo E1 Open Service (OS), adding a new acquisition aiding signal could contribute to provide higher resilience at the acquisition phase, as well as to reduce the time to first fix (TTFF). Designing a new GNSS signal is always a trade-off between several performance figures of merit. The most relevant are the position accuracy, the sensitivity and the TTFF. However, if one considers that the signal acquisition phase is the goal to design, the sensitivity and the TTFF have a higher relevance. Considering that, in this thesis it is presented the joint design of a GNSS signal and the message structure to propose a new Galileo 2nd generation signal, which provides a higher sensitivity in the receiver and reduce the TTFF. Several aspects have been addressed in order to design a new signal component. Firstly, the spreading modulation definition must consider the radio frequency compatibility in order to cause acceptable level of interference inside the band. Moreover, the spreading modulation should provide good correlation properties and good resistance against the multipath in order to enhance the receiver sensitivity. Secondly, the choice of the new PRN code is also crucial in order to ease the acquisition phase. A simple model criterion based on a weighted cost function is used to evaluate the PRN codes performance. This weighted cost function takes into account different figures of merit such as the autocorrelation, the cross-correlation and the power spectral density. Thirdly, the design of the channel coding scheme is always connected with the structure of the message. A joint design between the message structure and the channel coding scheme can provide both, reducing the TTFF and an enhancement of the resilience of the decoded data. In this this, a new method to co-design the message structure and the channel coding scheme for the new G2G signal is proposed. This method provides the guideline to design a message structure whose the channel coding scheme is characterized by the full diversity, the Maximum Distance Separable (MDS) and the rate compatible properties. The channel coding is essential in order to enhance the data demodulation performance, especially in harsh environments. However, this process can be very sensitive to the correct computation of the decoder input. Significant improvements were obtained by considering soft inputs channel decoders, through the Log Likelihood Ratio LLRs computation. However, the complete knowledge of the channel state information (CSI) was usually considered, which it is infrequently in real scenarios. In this thesis, we provide new methods to compute LLR approximations, under the jamming and the fading channels, considering some statistical CSI. Finally, to transmit a new signal in the same carrier frequency and using the same High Power Amplifier (HPA) generates constraints in the multiplexing design, since a constant or quasi constant envelope is needed in order to decrease the non-linear distortions. Moreover, the multiplexing design should provide high power efficiency to not waste the transmitted satellite power. Considering the precedent, in this thesis, we evaluate different multiplexing methods, which search to integrate a new binary signal in the Galileo E1 band while enhancing the transmitted power efficiency.

The invention provides a new method of unequal error protection which is based on a particular parity matrix structure for LDPC-type codes - Figure 1.

Precise and reliable positioning is nowadays of paramount importance in several mass-market civil, industrial and transport applications, safety-critical receivers and a plethora of engineering fields. In general, Global Navigation Satellite Systems (GNSS) is the positioning technology of choice, but these systems were originally designed to operate under clear skies and its performance clearly degrades under non-nominal conditions. In general, the channel conditions and the main impairments at the receiver level are application dependent. Some harsh propagation conditions, and some relevant applications such as i) urban environments, where a clear impact for autonomous cars and vulnerable road users, the main impairments are multipath, Non-Line-of-Sight (NLOS), shadowing, and a possible lack of satellite visibility in deep urban canyons. ii) For space exploration applications, where a spacecraft is exiting the atmosphere, the main limitations are high receiver dynamics and very weak signal conditions. Such weak signal conditions are mainly due to the use of signals coming from satellites on the opposite side of the Earth (w.r.t. the standard GNSS use). In this talk, we consider the standalone GNSS robust navigation problem, and taking into account the GNSS system-level architecture (space segment, ground segment, user segment), we will talk about the following main signal design challenges: There exist different signals in space, ranging from the legacy GPS L1 C/A Gold codes and BPSK modulation to the Galileo AltBOC signals, each of them having different characteristics, which may have an impact on the achievable PVT performance. Besides the existing signals, and considering the non-nominal conditions of interest, some questions naturally arises: i) which is the best signal (waveform and coding) to improve the mitigation capabilities at the receiver level? ii) each type of impairment requires different signal characteristics or there exists an optimal solution for all of them?

The design of a new GNSS signal is always a trade-off between several figures of merit such as the position accuracy, the sensitivity or the Time To First Fix (TTFF). However, if the goal of the new signal design is to improve the acquisition process, the sensitivity and the TTFF have a higher relevance as figures of merit. Considering that, the main goal of this work is to present the joint design of a GNSS signal and the message structure to propose a new Galileo 2nd Generation (G2G) signal, which provides a higher sensitivity in the receiver and reduces the TTFF, in order to improve the acquisition process. Besides that, since this work has focused on the Galileo E1 Open Service (E1-OS), the signal must be compatible with those signals already presented in the same radio frequency spectrum. However, many of the concepts and methodologies can be easily extended to any GNSS signal. In order to present the join design of a GNSS signal and the message structure, several aspects such as the spreading modulation, the pseudorandom noise (PRN) codes, the channel coding or the signal multiplexing must be addressed.

This is a supplementary material associated with the article "Band-limited impulse response estimation performance" that can be found, in the online version, at doi: https://doi.org/10.1016/j.sigpro.2023.108998.

This is a supplementary material associated with the article "Untangling first and second order statistics contributions in multipath scenarios" that can be found, in the online version, at doi: https://doi.org/10.1016/j.sigpro.2022.108868.