Dominique Lemur

Development and test of a trans-horizon communication system based on a MIMO architecture

A multiple-input multiple-output (MIMO) system for trans-horizon radio communications within the high-frequency (HF) band (3 to 30 MHz) is presented. The diversity of transmitted polarizations is proposed as an alternative to spatial diversity in order to limit the aperture of antenna arrays at both ends of the radio link. In a theoretical step providing the estimation of capacity gain for different MIMO architectures, a 2 × 2 MIMO solution transmitting two complementary circular polarizations is identified as a balanced trade-off between performance increase and complexity. The design of the corresponding system is described with a focus on antenna arrays and the kind of signal processing that should be implemented. This novel communication system has been tested on a 280-km-long radio link. The first results underline a data transfer rate reaching a value of 24.09 kbps (in a 4.2-kHz bandwidth) that significantly exceeds the current standards for HF modems.

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.

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.

Design and test of a HF MIMO system of transmission set up with compact antenna arrays

This paper proposes a MIMO 2×2 solution to increase the capacity of HF radio links through the ionospheric channel. A diversity in the transmitted polarizations replaces the classical space diversity and authorizes a compact set up in a context of decametric wavelengths. After a theoretical step of capacity estimation, an HF 2×2 MIMO system has been designed and tested on a 300 km long radio link. The data transfer rate reaches up to 24.09 kbps (in a 4.2 kHz bandwidth) with a good quality of service.

A MIMO solution based on polarization diversity for ionospheric radio links

This paper proposes a MIMO 2×2 solution to increase the capacity of HF radio links through the ionospheric channel. A diversity in the transmitted polarizations replaces the classical space diversity and authorizes a practical set up in a context of decametric wavelengths. Simulations, based on a realistic model of the ionosphere, underline a significant increase in the channel capacity if compared to a SISO system.

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.

A SIMO System of Digital Transmission Through the Ionospheric Channel

This paper presents a SIMO system of trans horizon transmission through the ionospheric channel in the HF band (3- 30 MHz). The technical challenge is to increase significantly the data transfer rate if compared with standard modems (typically 4.8 kbits/s in a 3 kHz bandwidth). A multi channel receiving system is connected to an original array of collocated antennas : this device appears as polarization sensitive and, consequently, makes the separation of the incident multi paths efficient though there is no spatial diversity. A blind spatio temporal equalization, based on the Constant Modulus Algorithm (CMA), balances the distortions of the spectrum in an extended bandwidth of 9 kHz. An experimental radio link has been tested with a range of 1300 km. The corresponding results underline the improvement of the bit transfer rate which attains 30 kbits/s in a 9 kHz bandwidth resorting to a 16 QAM waveform.

Array processing based on the polarization diversity: the example of an ionospheric radio link

The aim of this paper is to present a high data rate transmission system through the ionospheric channel in the HF band (3-30 MHz). The applications expected in this study are image transmission and real-time videoconferencing. Very high rates are required compared to the standard modems (4.8 kbits/s). Therefore, an array processing performs in the multi channel receiving system. Its main originality stands in the development of a compact device of collocated antennas, the spatial responses of which are different one from each other. Besides, synchronization (Zero Crossing Detector) and spatio temporal equalization (L.M.S. algorithm) as well resort to classical and well-tested techniques involving training sequences. An experimental radio link has been under test with a range of 800 km. The corresponding results underlines the improvement of the bit transfer rate which reaches 20 kbits/s (QAM 16 in a 6 kHz bandwidth) or 30 kbits/s (QAM 16 in a 9 kHz bandwidth). Several transmitted images are presented and appear quite consistent with the original.

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.