20 research outputs found
RFI mitigation: cyclostationary criterion
Radio astronomical observations are increasingly corrupted by radio frequency interferences. Thus, real- time ltering algorithms are becoming essential. One approach is to use a speci c time property of the Telecoms signals : the cyclostationarity. This property can be exploited for detection purpose or ltering purpose. In par- ticular, new generations of radio telescopes will be based on antenna arrays providing the possibility of applying spatial ltering techniques. In this paper, we compare the performance between classical approaches based on power statistics and cyclic approaches. This comparison is done through simulations on synthetic data and through simulations on real data acquired with the new generation low frequency array radio telescope, LOFAR
Rfi Mitigation Implementation For Pulsar Radioastronomy
International audienceThe observation of known pulsars (pulsar timing) or the search for new pulsars can be limited by radio frequency interference (RFI) generated by Telecommunications activity. In this paper we propose several RFI mitigation techniques to cope with impulsive and/or narrow band RFI. For pulsar timing, we have implemented, a pulse blanker and a cyclostationary blanker,both in real time. Exemple with real data are shown. For pulsar search, we propose a new approach which combines a hardware-efficient search method and some RFI mitigation capabilities. This method is based on a 2D FFT and Radon transform
RFI mitigation at Nanc¸ay Observatory: Impulsive Signal Processing
Radio astronomy has protected frequency bands for free observations. However, it is often necessary to observe outside of those sanctuaries. For example, it is the case for HI radio-sources with high red-shifts that are observed into radarallocated frequency bands. A radar pulse blanker based on statistical analysis has been implemented in a FPGA. Several tricks has made the implementation possible at a low hardware cost. Pulsar is another kind of impulsive signal which needs specific processing. In the proposed approach, the cyclostationarity is used to discriminate between radio-frequency interference (RFI) pulses and pulsar pulses
SETI Detection Strategies for Single Dish Radio Telescopes
Radio Searches for Extra Terrestrial Intelligence aim at detecting artificial
transmissions from extra terrestrial communicative civilizations. The lack of
prior knowledge concerning these potential transmissions increase the search
parameter space. Ground-based single dish radio telescopes offer high
sensitivity, but standard data products are limited to power spectral density
estimates. To overcome important classical energy detector limitations, two
detection strategies based on asynchronous ON and OFF astronomical target
observations are proposed. Statistical models are described to enable threshold
selection and detection performance assessment
Multi-Level Pre-Correlation RFI Flagging for Real-Time Implementation on UniBoard
Because of the denser active use of the spectrum, and because of radio
telescopes higher sensitivity, radio frequency interference (RFI) mitigation
has become a sensitive topic for current and future radio telescope designs.
Even if quite sophisticated approaches have been proposed in the recent years,
the majority of RFI mitigation operational procedures are based on
post-correlation corrupted data flagging. Moreover, given the huge amount of
data delivered by current and next generation radio telescopes, all these RFI
detection procedures have to be at least automatic and, if possible, real-time.
In this paper, the implementation of a real-time pre-correlation RFI
detection and flagging procedure into generic high-performance computing
platforms based on Field Programmable Gate Arrays (FPGA) is described,
simulated and tested. One of these boards, UniBoard, developed under a Joint
Research Activity in the RadioNet FP7 European programme is based on eight
FPGAs interconnected by a high speed transceiver mesh. It provides up to ~4
TMACs with Altera Stratix IV FPGA and 160 Gbps data rate for the input data
stream.
Considering the high in-out data rate in the pre-correlation stages, only
real-time and go-through detectors (i.e. no iterative processing) can be
implemented. In this paper, a real-time and adaptive detection scheme is
described.
An ongoing case study has been set up with the Electronic Multi-Beam Radio
Astronomy Concept (EMBRACE) radio telescope facility at Nan\c{c}ay Observatory.
The objective is to evaluate the performances of this concept in term of
hardware complexity, detection efficiency and additional RFI metadata rate
cost. The UniBoard implementation scheme is described.Comment: 16 pages, 13 figure
Blind detection of giant pulses: GPU implementation
International audienceRadio astronomical pulsar observations require specific instrumentation and dedicated signal processing to cope with the dispersion caused by the interstellar medium. Moreover, the quality of observations can be limited by radio frequency interference (RFI) generated by Telecommunications activity. This article presents the innovative pulsar instrumentation based on graphical processing units (GPU) which has been designed at the Nançay Radio Astronomical Observatory. In addition, for giant pulsar search, we propose a new approach which combines a hardware-efficient search method and some RFI mitigation capabilities. Although this approach is less sensitive than the classical approach, its advantage is that no a priori information on the pulsar parameters is required. The validation of a GPU implementation is under way
Traitement en temps réel des interférences radioélectriques sur une carte numérique de nouvelle génération : UNIBOARD
National audienceLes observations radioastronomiques sont de plus en plus perturbées par les signaux de télécommunications. Ce papier traite de la détection et de la suppression en temps réel des interférences radioélectriques causés par ces perturbations. D'une part, nous présentons l'architecture de la carte numérique UNIBOARD. Cette dernière est particulièrement dédiée au traitement intensif et en temps réel du signal radioastronomique. D'autre part, deux détecteurs d'interférences en cours d'implantation sur cette carte seront décrits. Le premier est un détecteur d'impulsions radar fondé sur des mesures robustes de la puissance. Le deuxième est un détecteur cyclostationnaire qui recherche des signatures statistiques spécifiques aux signaux de Télécommunications. Pour finir, nous analyserons différentes manières de gérer les échantillons qui ont été détectés comme pollués par les dits détecteurs
Efficient spectrum-handoff schemes for cognitive radio networks
Radio spectrum access is important for terrestrial wireless networks, commercial earth observations and terrestrial radio astronomy observations. The services offered by terrestrial wireless networks, commercial earth observations and terrestrial radio astronomy observations have evolved due to technological advances. They are expected to meet increasing users' demands which will require more spectrum. The increasing demand for high throughput by users necessitates allocating additional spectrum to terrestrial wireless networks. Terrestrial radio astronomy observations s require additional bandwidth to observe more spectral windows. Commercial earth observation requires more spectrum for enhanced transmission of earth observation data. The evolution of terrestrial wireless networks, commercial earth observations and terrestrial radio astronomy observations leads to the emergence of new interference scenarios. For instance, terrestrial wireless networks pose interference risks to mobile ground stations; while inter-satellite links can interfere with terrestrial radio astronomy observations. Terrestrial wireless networks, commercial earth observations and terrestrial radio astronomy observations also require mechanisms that will enhance the performance of their users. This thesis proposes a framework that prevents interference between terrestrial wireless networks, commercial earth observations and terrestrial radio astronomy observations when they co-exist; and enhance the performance of their users. The framework uses the cognitive radio; because it is capable of multi-context operation. In the thesis, two interference avoidance mechanisms are presented. The first mechanism prevents interference between terrestrial radio astronomy observations and inter-satellite links. The second mechanism prevent interference between terrestrial wireless networks and the commercial earth observation ground segment. The first interference reductionmechanism determines the inter-satellite link transmission duration. Analysis shows that interference-free inter-satellite links transmission is achievable during terrestrial radio astronomy observation switching for up to 50.7 seconds. The second mechanism enables the mobile ground station, with a trained neural network, to predict the terrestrial wireless network channel idle state. The prediction of the TWN channel idle state prevents interference between the terrestrial wireless network and the mobile ground station. Simulation shows that incorporating prediction in the mobile ground station enhances uplink throughput by 40.6% and reduces latency by 18.6%. In addition, the thesis also presents mechanisms to enhance the performance of the users in terrestrial wireless network, commercial earth observations and terrestrial radio astronomy observations. The thesis presents mechanisms that enhance user performance in homogeneous and heterogeneous terrestrial wireless networks. Mechanisms that enhance the performance of LTE-Advanced users with learning diversity are also presented. Furthermore, a future commercial earth observation network model that increases the accessible earth climatic data is presented. The performance of terrestrial radio astronomy observation users is enhanced by presenting mechanisms that improve angular resolution, power efficiency and reduce infrastructure costs