In previous works, new families of Pseudo-Random Noise (PRN) codes of length 1023 chips were proposed in order to ease the acquisition engine. These studies analyzed several metrics for code design in order to improve the acquisition but no analysis was conducted on the estimation performance, which in turn drives the final position, velocity and timing estimates. The main goal of this contribution is to assess if these new PRN codes designed to improve the acquisition engine lose in achievable time-delay estimation performance with respect to the standard GPS L1 C/A Gold codes. The analysis is performed by resorting to a new compact closed-form Cramér-Rao bound expression for time-delay estimation which only depends on the signal samples. In addition, the corresponding time-delay maximum likelihood estimate is also provided to assess the minimum signal-to-noise ratio that allows to be in optimal receiver operation.

Error correcting schemes are fundamental in the new generation of data navigation signals. Thanks to those, the system has the capability to correct possible data navigation errors, which potentially induces delays in first fix of the receiver. In the GNSS receivers, those error correcting schemes use the Log Likelihood Ratio (LLR) as the input of the decoding algorithm. Until now, the LLR was always computed under the Gaussian assumption and considering perfect Complete State Information (CSI), which does not hold in most of the real scenarios. Then, in this paper we proposed several methods to compute the LLR, considering a set of realitic scenarios and considering that perfect CSI is not available at the receiver. We test the proposed LLRs for several new generation GNSS signals.

New generation of GNSS systems seeks to provide new features in order to create or to improve their currents services. Between those possible features; the increase of the data rate is necessary in order to to provide services such as authentication, precise positioning or reduce the Time-To-First-Fix (TTFF). On the other hand, the data availability in harsh environment suggest the need of error correcting technologies. Then, based on previous works over the Code-Shift Keying (CSK) modulation and in Root Protograph LDPC code to reduce the TTFF, in this paper, it is presented the optimization of Root Protograph LDPC codes for the CSK modulation in a Bit-Interleaved Coded Modulation context and the optimization of Root Protograph LDPC codes for the CSK modulation in Bit-Interleaved Coded Modulation Iterative Decoding context. Both optimization where base on the Protograph EXIT chat algorithm, providing promising results.

In this article, we provide the method to construct two error correcting structures for GNSS systems, which are capable to provide Maximum Distance Separable (MDS), full diversity and rate-compatible properties. Thanks to those properties, the GNSS receiver is capable to reduce the Time-To-First-Fix (TTFF) and to enhance the robustness of the data demodulation under low Carrier to Noise ratio environments, urban environments and pulsed jamming environments. The proposed error correcting structures are then simulated and compared with the GPS L1C subframe 2 error correcting scheme under the precedent transmission environments. Simulations show an outstanding improvement of the error correction capabilities (which reduce the TTFF in harsh environments) mainly caused by the rate-compatible and the full diversity properties. Moreover, thanks to the MDS property a high reduction of the TTFF under good environments is appreciated.

Reducing the Time To First Fix (TTFF) and improving the resilience of future Galileo signals are two important characteristics, especially when considering urban environments. To reach these goals, we studied two new advanced techniques based on the co-design of the message structure and the channel coding scheme. The first technique proposes a reduction of time needed to retrieve the data by reinforcing the parity check matrix structure constraints. The second technique provides an enhancement of the retrieved data error rate in parallel to a reduction of the time needed to retrieve the data thanks to a new co-design requirement based on a family of codes inspired from the rate-compatible root LDPC codes. The results obtained are promising, since the time to retrieve the data (and thus the TTFF) is significantly reduced, while keeping a good level of demodulation performance.

In the recent times, the interest of reducing the time to retrieve the Clock and Ephemerides Data (CED) has provided an open subject of study to design the structure of the message along with the channel coding scheme of the GNSS signals. As a direct consequence, a new methodology to co-design the navigation message and the channel coding scheme structure is proposed in this paper. This new co-design enables both to reduce the time to retrieve the CED and enhanced error correction capabilities under degraded channel conditions. In order to accomplish such as requirements, codes, which provide both maximum distance separable and full diversity properties under the non-ergodic channel assumption, are designed.

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.