GNSS Multipath Estimation and Mitigation Using a Rotating Antenna

Cyril Botteron, Joaquin Cabeza de Pablo, Pierre-André Farine, Miguel Angel Ribot Sanfelix
2017
Conference paper

Abstract

We describe the experimental framework that we have developed to study the use of synthetic aperture in GNSS receivers to estimate and mitigate multipath interference. By combining the signal received by a single moving antenna during different time instants along a known trajectory, it is possible to per-form spatial filtering on the received signal. Our framework is divided in two parts. First, we modified a software GNSS receiver to implement beamforming and direction of arrival (DoA) algorithms, which have been adapted to work with synthetic aperture, instead of with a fixed antenna array. Second, we built a rotating arm supporting an antenna in order to implement circular trajectories of 0.5 to 1 m radius, and adjustable rotating speeds of up to 1.5 rev/s. Finally, we present an analysis of the performance of the algorithms implemented using real data obtained with our rotating antenna.

Official source

https://infoscience.epfl.ch/record/228836?ln=en

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Estimation Bounds for GNSS Synthetic Aperture Techniques

Cyril Botteron, Joaquin Cabeza de Pablo, Pierre-André Farine, Miguel Angel Ribot Sanfelix

This paper characterizes the estimation performance of synthetic aperture (SA) techniques in the context of moving GNSS receivers. Under the assumption of a stationary channel, SA techniques transform a single antenna into a virtual array. We first introduce a model for the GNSS signal received by a single moving antenna. Leveraging this model, SA processing enables direction-of-arrival (DOA) and beamforming on a single antenna. The model does not make use of the narrowband assumption, which makes it suitable for relatively large trajectories. In addition, it includes the effects of the polarization mismatch between the received signal and the receiving antenna. Then, the proposed model is used to derive the Cram´er-Rao lower bound (CRB) for the joint estimation of the received signal amplitudes, synchronization and DOA parameters. We compute the CRB for two different antenna motions, with results depending on the antenna trajectory as well as on the scenario geometry. Results highlight how SA processing profits from spatial and polarization diversities, pointing out its potential for DOA estimation and beamforming applications in moving GNSS platforms, such as unmanned air vehicles or smartphones.

2017

The present thesis deals with the design of a planar antenna array for the communication between a civil aircraft (Dassault's Falcon) and an Inmarsat satellite. The final goal is to provide high speed Internet access in X/Ku-Band (8-12GHz / 12-18GHz), and possibly even in K/Ka- Band (18-27GHz / 17-40GHz). The study starts with the Ku-Band only, then evolves towards the transmission band and finishes with their Ka-Band counterparts. The main constraint of the thesis is that the final result should be a low profile antenna that will be easy to integrate below the fuselage of an aircraft. At the same time, the antenna has to provide a beam steering mechanism in order to track the position of the targetted satellite while the aircraft is moving. The usual way to achieve it is to implement some dedicated electronic chips below each radiating element of array. Dassault Aviation has its own alternate and more mechanical oriented solutions. Since the communication system is intended for top-notch business jets produced in small series, cost is not here a decisive criterion. This thesis assumes the existence of the beam-steering system and concentrates on a proof of concept and careful design of the antenna elements that will constitute the final array. They have to satisfy tight constraints in terms of size, return loss, mutual coupling with neighbors, efficiency, radiation pattern and dual circular polarization quality. Printed multilayer antennas have been retained as the best candidates, and themain parts of the thesis have been dedicated to their study. The thesis concludes with the presentation of an apparently completely unrelated and independant topic, namely the simulation of nanoscale 2D planar structures based on Graphene. The rationale for this last chapter is to provide a prospective study of the use of Graphene to create a variable capacitance. This component is always needed in the beamforming network of reconfigurable and scanning arrays. Our laboratory is developing a deep knowledge of the electromagnetic properties of Graphene-based devices and these varicaps could lead to very interesting applications in high frequencies, once the Graphene technology has definitely progressed. Thanks to electrostatics Green's functions, a variable capacitor based on Graphene has been simulated, and a Quantumeffect -the Quantum capacitance of Graphene- has been successfully tackled from a numerical point of view.

EPFL2016

The invention concerns a device for automatically and rapidly locating (10) a person or an object at sea in poor meteorological conditions, comprising a radio wave transmitting device (20) provided on the person or the object and a reception device (30), provided in a boat, and designed to receive directly said waves and to process them without any other intermediary than the radio link (40) established between them. The transmitting device (20) comprises a transmitter (21) supplied by a power source (23), and delivering a radio signal to an antenna (22). Said transmitter is activated by an actuating member (24). The reception device (30) consists of a receiver (31) for the signal transmitted by the transmitter (21) and picked up by an antenna array (32) co-operating with an antenna switch (33). The antenna array (33) is connected to the receiver (31) whereof an output is connected to said unit processing (34) the received signal. A display unit (37), connected to said processing unit (34) via a user interface (35), enables the display of the information delivered by said unit (34). An audio warning (36) is connected to the activation of the transmission device (20).

2004

EPFL2016