Phd Thesis

L’ENAC, École Nationale de l’Aviation Civile, est la plus importante des Grandes Écoles ou universités aéronautiques en Europe. Elle forme à un spectre large de métiers : des ingénieurs ou des professionnels de haut niveau capables de concevoir et faire évoluer les systèmes aéronautiques et plus largement ceux du transport aérien ainsi que des pilotes de ligne, des contrôleurs aériens ou encore des techniciens aéronautiques.

Ses laboratoires de recherche sont à la pointe de l’innovation et travaillent activement en coopération avec des universités internationales de haut niveau pour un transport aérien toujours plus sûr, efficace et durable.

L’ENAC est un établissement public à caractère scientifique, culturel et professionnel - grand établissement (EPSCP-GE), sous tutelle de la DGAC (Direction Générale de l’Aviation Civile), Direction du Ministère de la Transition Écologique et Solidaire. L’ENAC comprend une direction générale localisée à Toulouse et 8 sites en France.
- Pour soutenir sa dynamique en faveur de la promotion de la diversité, l’ENAC facilite l’accueil et l’intégration des travailleurs en situation de handicap._

The proposed PhD thesis is in the field of Navigation using GNSS reflectometry as a passive radar to detect and to localize different targets.

The lack of emitted signal presents some advantages and some challenges. The main advantages are an a priori reduction of the system cost due to the lack of transmitter and to not create additional radio frequency interferences to the other systems (especially near and airport). The challenges are a low received signal power (due to the inherent low received power of a GNSS signal), the differentiation between Line-of-Sight (LOS) signals received directly by the GNSS from the satellites and the target scattered signals as well as with respect to multipath generated by other non-desired sources (buildings, trees, etc.).

The goal of this study is to develop passive radar techniques based on the processing of GNSS signals (MEO/LEO) for detecting/localizing targets close to a (reference) receiver. For a given receiver design and a given target (boat, plane, etc.), the detection/localization performance will be evaluated from simulations and real measurements. Moreover, the proposed technique performance will be compared to SAR (Synthetic-Aperture Radar) image techniques performance.

Additionally, this PhD thesis aims to estimate and to demonstrate the performance and limitation of GNSS Passive Radar system under at least two receivers’ assumption: a high-performance receiver equivalent to ground station deployment with a high number of antenna and no constraint on the computation effort, and a low performance receiver, equivalent to payload, with a limited array size.

The GNSS passive radar concept has been already demonstrated for UAV or boat detection in [1][2]. However, those techniques are usually based on a simple receiver with one antenna, and the use of only one signal / one satellite for the detection / localization of large targets.

In this PhD thesis, the main idea is to improve those techniques by introducing several improvements:

- To use all the current, or future, GNSS signals (MEO satellite and also LEO-PNT satellites) available in all GNSS frequency bands (L1, L2, E5, E6, S bands, etc.). The use of more than one type of signal will improve the information diversity of the measurements and will allow the detection/localization even if one type of signal is not available or is corrupted.
- Advanced array antennas will be used to obtain polarization diversity and Angle of Arrival (AoA) information at the receiver. The polarization diversity will allow to differentiate between the LOS and the reflected signal (object to detect/localize) since the reflection on the object should change the GNSS signal’s polarization. Moreover, the AoA will also allow to different between the LOS signal (high elevation) from the reflected signal (low elevations).
- State-of-the-art propagation models will also be used to facilitate the signal processing, and to help in the separation/identification of the reflection from a target, and the reflection from the local environment such as ground reflection (sea, floor, etc.), close hill, etc.

Moreover, advanced synchronization techniques must be used to acquire and track the target reflected signals. These reflected signals can have very low power, which is one of the main challenges of the passive radar. Therefore, long-coherent integration time techniques will also be used in this PhD.

The focus of the PhD thesis will be centered around the synchronization algorithms of the target reflected signals and in the position estimation (if the vector tracking algorithm includes the target position estimation). Angle of arrival estimation through antenna array will also be explored. However, the exploitation of the polarization diversity and propagation channel will remain at state-of-the-art level.
- Mast