In this article, we discuss the important role of time-frequency (TF) signal representations in enhancing global navigation satellite system (GNSS) receiver performance. Both linear transforms and quadratic TF distributions (QTFDs) are considered. We review recent advances of antijam techniques that exploit the distinction in the TF signatures between the desired and undesired signals, enabling effective jammer excision with minimum distortion to the navigation signals. The characterization of jammers by their instantaneous frequencies (IFs) lends itself to sparse structures in the TF domain and, as such, invites compressive sensing (CS) and sparse reconstruction to aid in joint-variable domain jamming localization and suppression. Furthermore, the integration of the spatial domain with the TFDs, through the use of multiantenna receivers, permits the applications of space-time processing for effective jamming mitigation. The article also describes the fundamental role of TFDs in monitoring the performance of new GNSSs, including satellite clocks and ionospheric scintillation data. Real GNSS data collected in the presence of jamming are used to demonstrate the effectiveness of TF-based antijam approaches.

Several new global navigation satellite system modulations adopt a binary offset carrier (BOC) subcarrier to shape the signal spectrum, increase the frequency separation and improve the tracking performance. BOC modulated signals are, however, characterised by ambiguous multi‐peaked correlation functions and several techniques have been proposed in the literature to solve the problem of locking into secondary peaks. In this study, a novel unambiguous BOC tracking technique, the double phase estimator (DPE), is designed to account for the effect of signal bandlimiting. The DPE is an effective alternative to the double estimator (DE) tracking technique where the subcarrier lock loop is replaced by a subcarrier phase lock loop. In the presence of signal bandlimiting, the DPE is able to generate local signal replicas matched in a better manner to the input components, outperforming the DE. The performance of the DPE is thoroughly characterised and the processing of real wideband BOC signals is used to demonstrate the effectiveness of the algorithm proposed. In addition to this, the DPE requires a lower computational load than the DE and thus should be adopted for the processing of wideband BOC signals.

Robust signal processing techniques are effective mitigation approaches that can enable Global Navigation Satellite System (GNSS) receiver operations even in the presence of strong interference. We extend robust GNSS signal processing to the case where interference admits a sparse representation in a transform domain (TD). More specifically, an orthonormal transformation is used to project the received GNSS samples into an appropriate TD. Robust signal processing strategies are then applied. The robust transform domain (RTD) cross‐ambiguity function (CAF) is obtained by applying a zero‐memory nonlinearity (ZMNL) to the TD samples, which, in turn, are used for the evaluation of the CAF. Different nonlinearities are analyzed and different implementations for the evaluation of the RTD CAF are proposed. The RTD approach is characterized from a theoretical point of view, with the usage of Monte Carlo simulations and through the processing of GNSS signals generated with a hardware simulator.

This paper presents in detail an outer‐coding proposal for long GNSS messages disseminated by multiple satellites. The proposal minimizes the message reception time, or Time To Retrieve Data (TTRD), over a page erasure channel in most types of environments and visibility conditions. A message M consisting of k pages is encoded into a set C consisting of n pages, such that when any subset C′ of C of k pages is correctly received, the message can be decoded. The scheme vertically encodes each page symbol in a separate high‐parity Reed‐Solomon code and allocates different parts of it to different satellites. The scheme has been designed for the Galileo High Accuracy Service (HAS), but it can be used for longer messages and other constellations. The performance results show TTRDs on the order of few seconds, at a very low decoding complexity for the receiver.

Satellite-based navigation is prevalent in both commercial applications and critical infrastructures, providing precise position and time referencing. As a consequence, interference to such systems can have repercussions on a plethora of fields. Additionally, Privacy Preserving Devices (PPD)—jamming devices—are relatively inexpensive and easy to obtain, potentially denying the service in a wide geographical area. Current jamming mitigation technology is based on interference cancellation approaches, requiring the detection and estimation of the interference waveform. Recently, the Robust Interference Mitigation (RIM) framework was proposed, which leverages results in robust statistics by treating the jamming signal as an outlier. It has the advantage of rejecting jamming signals without detecting or estimating its waveform. In this paper, we extend the framework to situations where the jammer is sparse in some transformed domain other than the time domain. Additionally, we analyse the use of Huber’s non-linearity within RIM and derive its loss of efficiency. We compare its performance to state-of-the-art techniques and to other RIM solutions, with both synthetic and real signals, showing remarkable results.