François Marie

An Operational HF System for Single Site Localization

This paper presents an operational HF (3-30MHz) system designed for single site localization (SSL) of transmitters involved in trans horizon radio links. It associates the estimation of the directions of arrival of incident radio waves refracted by the ionosphere with a ray tracing software based on the PRIME model of the channel. The direction finding processing is implemented on an array of non identical sensors that presents a polarization sensitivity. A specific version of the MUSIC algorithm jointly estimates the angles of arrival (azimuth and elevation) of incident waves and their polarization. Statistics of the angles of arrival (mean values and standard deviation) are the input data of a ray tracing software based on the PRIME model of the ionosphere which computes the estimated position of the transmitter. Numerous radio links have been tested for long distances up to 2000 km. A very good agreement is observed between the exact and the estimated positions of the transmitters with a standard localization error being less than 10% of the distance to the receiving system.

New improvements in HF Ionospheric Communication and Direction Finding Systems

This chapter presents new HF (3–30 MHz) systems dedicated to ground to ground radio links with applications to ionospheric characterisation, channel modelling, radio communications, direction finding and single site localisation. The received signals result from the vectorial addition of the multipaths generated by the ionosphere. Considering the acquisitions at the outputs of an array of identical antennas (homogeneous array), a high level of spatial and temporal correlation can be observed. Therefore, it appears relevant to additionally discriminate the incoming modes by considering their polarisations. The purposes of the different systems which are described in the following sections are the use of a heterogeneous array. This polarisation-sensitive solution for array processing is principally characterized by the spatial distribution of non identical antennas. Consequently, the applications to digital communication involve a multi channel processing in the receiver as a SIMO (single input multiple output) structures. The correlation factors depend on the polarisation characteristics of the incident wave. Moreover, the heterogeneous array is still efficient with a reduced space diversity (set up in a limited place), the differences in the polarisation parameters balancing the weak values of the differential geometrical phases. In the following developments, the suggested techniques aim to take some better advantage of the ionospheric medium in several applications.

Evaluation of Ionospheric HF MIMO Channels: Two complementary circular polarizations reduce correlation.

An original multiple-input, multiple-output (MIMO) system for a transhorizon transmission through the ionospheric channel is presented. This project, involving decametric wavelengths, has to cope with the constraints of reasonable array dimensions at both ends of the radio link. Therefore, this work considers a diversity in transmitted polarizations as an alternative to the classical spatial diversity and, more specifically, the generation of complementary circular polarizations. The design of the corresponding system is described with a focus on antenna arrays, waveforms, and signal processing for channel sounding. This novel communication system has been tested on a 850-km long radio link to exhibit the degree of diversity provided by the ionospheric MIMO channel. The measurements indicate a significantly low level of correlation for the four-channel transfer functions linking the transmitting and receiving ends (in a frequency dispersive context). Moreover, the ergodic or outage capacities have been calculated over several hundreds of channel estimations: the gain in the capacity of a MIMO versus a single-input, single-output (SISO) architecture reaches the value of 1.82.

Multiple criterion selection of heterogeneous circular arrays of loop antennas

A heterogeneous array is made up of sensors which are different from one another. It has been demonstrated that this original structure induces a polarisation sensitivity of the array and consequently, an improvement of the angular resolution in HF direction finding applications. This paper investigates the particular case of circular arrays set up with vertical active loop antennas.

Vers les 20 kbit/s en transmission décamétrique ionosphérique : une application du traitement d'antenne sur des capteurs colocalisés

RésuméCet article décrit un système opérationnel de transmission numérique en gamme décamétrique (H.F.) visant à augmenter le débit binaire de façon significative par rapport à la norme actuelle (4800 bit/s). Pour cela, un traitement d’antenne est mis en œuvre sur un ensemble de capteurs colocalisés présentant une diversité de leurs réponses spatiales. La dépendance de la polarisation reçue vis-à-vis de la direction d’arrivée est exploitée pour assurer une décorrélation efficace des signaux reçus en absence de tout déphasage géométrique. Les techniques de traitement du signal en réception s’appliquent sur la sortie du filtre spatial; elles font appel, tant pour la synchronisation que pour le filtrage (algorithme lms) à des solutions classiques et éprouvées utilisant des séquences d’apprentissage. Une liaison expérimentale de portée égale à 250 km a été établie afin de tester l’influence du choix de la forme d’onde sur les performances en réception. Les résultats obtenus sont conformes à l’objectif fixé puisque le débit binaire atteint 20 kbit/s dans une bande de 6 kHz.AbstractThis paper presents an operational system of digital transmission within the h.f. frequency range, aiming at a significant increase of the data transfer rate compared with the current standard (4800 bit/s). Therefore, an array processing algorithm performs with a set of collocated sensors, the spatial responses of which are different one from each other. The dependence of the incoming polarization relatively to the direction of arrival induces a significant decorrelation of the received signals though no geometrical phase exists. Signal processing techniques run at the output of the spatial filter resorting for the synchronisation and the filtering (lms algorithm) to classical and well-tested techniques involving training sequences. An experimental radio link with a 250 km range has been set up to test the sensibility of the performances in reception regarding the choice of waveforms. The operational results reach the expected goal as the data transfer rate increases up to 20 kbit/s in a bandwidth of 6 kHz.