Marco Pini

Exploiting GNSS signal structure to enhance observability

There are a number of different error sources, such as multipath and thermal noise, which corrupt satellite navigation waveforms from their theoretical structure. However, even under ideal conditions the broadcast signals have some degree of deformation as a result of the practical individual hardware implementation. For the most demanding users of satellite navigation, such as aircraft navigation and landing systems, it is important to characterize the nominal signal structure in order to detect minimal variations resulting from hardware-based errors. Thus far such precorrelation Global Navigation Satellite System (GNSS) signal quality monitoring has been performed through high gain antennas, which allow for raising the GNSS spectrum above the thermal noise floor and observing the structure of the signal directly at the front end output. This paper describes a new approach to achieve such observability based on signal processing techniques, such as dithering and averaging, which leverage the repetitive nature of the GNSS signal. The paper presents how these techniques can drastically improve the signal-to-noise ratio (SNR) in postprocessing, allowing for the direct analysis of GNSS signals using traditional front end designs and conventional antennas. Results are predicted using the appropriate theory and validated using data collected from the Global Positioning System (GPS).

Multiple DLL architecture for multipath recovery in navigation receivers

Since the selective availability was turned off, one of the major error sources in GNSS user positioning is represented by the deleterious superimposition of the same signa-in-space due to obstruction and ground reflections (multipath). Such an error component is the most critical in case of urban (or indoor) navigation due to the high density of possible scatterers around the receiver. In this paper, a multiple delay lock loop (DLL) architecture for navigation receivers, which is derived from the philosophy of the RAKE receiver for communication, is proposed. In this sense, it is quite different from common multipath rejection techniques already proposed, where the multipath is not tracked. Simulation results of the innovative scheme highlight the increased performance with respect to common multipath rejection techniques.

Performance Assessment of the TurboDLL for Satellite Navigation Receivers

In this paper a detailed evaluation of the performance of the architecture named Turbo Delay Lock Loop (TurboDLL) is presented. Such an architecture has been introduced by the authors in [1], as an innovative solution for improving the performance of satellite navigation receivers in multipath affected scenarios. The relevant innovation resides in the fact that the architecture aims at tracking each multipath component and, after a transient time, use them to wipe the multipath components off the input signal. The iterative procedure allows for a major improvement in the error induced in the code-based pseudorange measurement. The architecture uses a preliminary estimation of the propagation channel in terms of number of not negligible reflections, and of their relative amplitude. In this paper the robustness of the TurboDLL architecture with respect to imperfect channel estimation is demonstrated.

A fully software GNSS-R receiver for soil dielectric constant monitoring

GNSS Reflectometry is an emerging technique used for the remote sensing of soil surfaces. In this contribution an application of dielectric constant retrieval is presented. Both direct and reflected GPS signals were collected by a fully software receiver mounted on-board an aircraft. The reflected signal was processed with an open loop approach, obtaining Delay Doppler Maps (DDMs) and corresponding Delay Waveforms. Signal to Noise Ratios (SNRs) time series were estimated from (non coherently) integrated Delay Waveforms. To take into account variations of system parameters from nominal values, a calibration was performed considering signals reflected from a water lake. Finally, the retrieval process able to estimate dielectric constant of soil surface from evaluated SNR was applied and the results showed good correlation with fields flooding state.

Estimation of Satellite-User Ranges Through GNSS Code Phase Measurements

A Global Navigation Satellite System (GNSS) receiver is able to compute the user position through a trilateration procedure, which includes the measure of the distance between the receiver and a set of satellites. Two different approaches are tipically used and implemented in commercial receivers. The former relies on code tracking, the latter leverages carrier phase measurements performed during carrier tracking.

First Results on Acquisition and Tracking of the GIOVE-A Signal-in-Space

This paper presents the first results obtained processing the Signal-In-Space broadcast by the Galileo In — Orbit Validation Element A (GIOVE-A) satellite, the first experimental Galileo satellite. The paper analyzes both the acquisition and tracking phase of a Galileo software receiver able to process raw samples of the signal collected by means of a commercial front end. Starting from the description of the system set up used to collect the data set the paper introduces the Partial Correlation approach adopted in the acquisition phase and describes the tracking structures used to synchronize the local and the incoming codes. Techniques tailored to the new structure of the Galileo signal have been employed. In fact, the GIOVE-A signal uses novel modulation schemes and it is made of longer spreading codes that required modification to both the acquisition and tracking algorithms usually implemented within a GPS receiver.