L. Bertel

HF radio direction finding operating on a heterogeneous array: Principles and experimental validation

[1]xa0Array processing usually operates on identical sensors. In this paper an investigation is made to apply the direction finding algorithm MUSIC to an antenna array with nonidentical elements (heterogeneous array). This original solution is polarization-sensitive though it resorts to only one sensor at each point of the spatial sampling. As a major consequence of its structure, the computation of the MUSIC algorithm is based on an expression of the steering vector that integrates the spatial response of each sensor. This concept is then validated in the special context of HF radio direction finding, for which a deterministic model of the polarization at the exit of the ionospheric channel is derived. A multichannel radio receiving system has been developed and experimented using transmitters located more than 1000 km from the receiving site.

Investigations into the feasibility of multiple input multiple output techniques within the HF band: Preliminary results

[1]xa0The concept of multiple input multiple output (MIMO) has become a productive area of research in the field of wireless communications with the aim of delivering increased data throughput. However, to date, MIMO research has focused primarily on short-range communications within the VHF, UHF, and SHF bands, and very little research has been conducted toward exploiting MIMO techniques for long-range communications within the HF band. Between September 2007 and September 2008, several experimental campaigns were conducted to investigate the feasibility of applying MIMO techniques within the HF band. The results of measurements over a 255 km path from Durham to Leicester within the United Kingdom are presented in this paper with particular emphasis on the use of heterogeneous antenna arrays at the transmitter and receiver.

Early results of experiments to investigate the feasibility of employing MIMO techniques in the HF band

Over the last few years, the concept of multiple input multiple output (MIMO) has become a popular area of research in the field of wireless communications with the aim of delivering increased data rates. However, to date, MIMO research has focussed primarily on communications within the VHF, UHF and SHF bands (and above). Very little experimental or modelling research has been conducted in the area of exploiting MIMO techniques within the HF radio band. This paper describes some of the preliminary experimental work that has been carried out in order to investigate the feasibility of implementing MIMO techniques within the HF band.

A new VLF/LF atmospheric noise model

[1]xa0Atmospheric noise, originating essentially from lightning discharges, is the main disturbance of VLF/LF telecommunications. This paper characterizes atmospheric noise in the 10–80 kHz range and proposes a new model: very accurate low-frequency noise model (VALERIE). This model uses a new approach, which combines noise measurements with lightning data. The noise statistics were obtained from several years of measurements taken by the Delegation Generale de lArmement (DGA)/Centre Technique des Systemes Naval (CTSN) (Toulon, France) and the Space and Naval Warfare Systems (SPAWAR) (San Diego, California). Lightning data were provided by recent satellite observations made by NASA. A comparison of VALERIE predictions with measurements by cross validation showed an increase in accuracy compared to the current International Telecommunication Union (Geneva) model and a decreased average deviation. The model has been validated for the Atlantic area but may be extended as new measurements are collected.

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.

Possible use of the LOCAPI ionospheric prediction software to digital communications

Abstract The LOCAPI ionospheric propagation software, developed by the University of Rennes 1, uses the multiquasi-parabolic expression for the electron density profile. Its inputs are : date, frequency, transmitting and receiving locations. An original fast and accurate algorithm determines the output parameters : MUF, occultation LUF, elevation angles, group delays, pathlosses for an important range of possible O and X propagation modes. The accuracy of the simulated results permits the use of LOCAPI software to determine the slope of the group time delay as a function of frequency of HF radio links, for each propagation mode, and to evaluate the coherent bandwidth for a digital communication channel. In addition, improved results can be obtained if the polarization and antennas effects are taken into account.

A 3D ray tracing procedure to study ionospheric tilts

Abstract Tilts associated with ionospheric horizontal gradients are one of the causes of bearing errors in HF links. Our purpose is to describe a fast, three dimensional, ray tracing procedure using geometrical optics. A three dimensional model was built, based on the spatially variable parameters of the ionospheric layers obtained from forecast procedures, associated with an MQP profile, which may be considered as realistic. The refractive index and the vertical and horizontal gradients are taken into account. In this paper, a software permitting to estimate the mean bearing deviations estimation is described.

New diversity combination algorithms for DVB-T COFDM mobile reception

New combination methods for the reception of DVB-T signals in mobile receiver configuration are proposed. These methods are tested for different real reception problem cases. The experimental mobile system is presented, including demodulation tools, and several new combination techniques. These techniques are based on MRC algorithm improving by an original criterion, called CSIl,k. Finally, better results are obtained compared to MRC algorithm with an adaptive algorithm using these new combination techniques using CSIl,k criterion.

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.