Rodolphe Weber

4D reconstruction of the left ventricle during a single heart beat from ultrasound imaging

Abstract A new acquisition system using a continuously rotating 2D ultrasound probe is proposed to reconstruct the movement and deformation of the left cardiac ventricle (LV). During only one cardiac cycle, the system acquires successive conic sections of the LV. Then, after the LV contour detection on each image, which may be performed manually or using an active modelling technique, the set of sparse spatio-temporal data is used to build a harmonic LV model. The proposed reconstruction technique is based on mild assumptions about the spatial and temporal frequency characteristics of the LV considered as a periodic four-dimensional signal. The reconstruction results are clinically promising.

DSP-enabled radio astronomy: towards IIIZW35 reconquest

In radio astronomy, the radio spectrum is used to detect weak emission from celestial sources. By spectral averaging, observation noise is reduced and weak sources can be detected. However, more and more observations are polluted by man-made radio frequency interferences (RFI). The impact of these RFIs on power spectral measurement ranges from total saturation to subtle distortions of the data. To some extent, elimination of artefacts can be achieved by blanking polluted channels in real time. With this aim in view, a complete real-time digital system has been implemented on a set of FPGA and DSP. The current functionalities of the digital system have high dynamic range of 70 dB, bandwidth selection facilities ranging from 875 kHz to 14 MHz, high spectral resolution through a polyphase filter bank with up to 8192 channels with 49 152 coefficients and real-time time-frequency blanking with a robust threshold detector. This receiver has been used to reobserve the IIIWZ35 astronomical source which has been scrambled by a strong satellite RFI for several years.

Oblique projection beamforming for RFI mitigation in radio astronomy

Radio astronomical observations are increasingly corrupted by radio frequency interference (RFI). Phased antenna array radio telescopes allow the recovering of spatial information of RFI and cosmic sources. Using this information, spatial signal processing techniques can limit the impact of the incoming interferences. In this article, we present an RFI mitigation technique, based on an oblique projector.

Coarsely Quantized Spectral Estimation of Radio Astronomic Sources in Highly Corruptive Environments

This chapter is devoted to an application of non-Gaussian signal detection. In radio astronomy, given the huge flow of processed data, quantized correlators are widely used. Unfortunately, the occurrence of non-Gaussian interference can strongly alter the shape of the estimated spectra. In this chapter, the effect of a sine wave interference on a 1-bit correlator is first analysed. Then, a new interference detection criterion is proposed. It uses the real-time capabilities of quantized correlators and makes a statistical comparison between contaminated and non-contaminated quantized correlation functions. Thus, the final spectral estimation can be preserved by blanking the correlator in real-time. Simulations, using synthetic and actual data, are presented. This technique of real time detection can significantly improve the quality of spectral line observations.

RFI spatial processing at nancay observatory : Approaches and experiments

Because of the denser active use of the spectrum, and because of higher radio telescope sensitivities, radio frequency interference (RFI) mitigation has become a sensitive topic for current and future radio telescope designs. In this paper, we consider different interference mitigation options which take advantage of both time-frequency and spatial RFI signatures. After specific subspace decompositions, these RFI spatial signatures are estimated and applied to pre- or post-correlation data by means of spatial filtering techniques based on projectors. We provide some performance analysis through simulations and Cramer-Rao Lower Bound derivations. In addition, recent results on real data from the LOFAR and EMBRACE radio telescopes are presented.

Impact of array calibration on RFI mitigation

Phased array radio telescopes allow for the filtering of Radio Frequency Interference (RFI) in the spatial domain. Spatial filters are advantageous in radio astronomy when the separation between RFI and astronomical sources cannot be made in the time or frequency domains. Consequently, the mitigation of the RFI relies on the quality of its spatial signature vector (SSV) estimation. The latter depends on the array calibration information which is investigated in this work. More precisely, by using the Cramér-Rao Bound (CRB) tool, we evaluate the astronomical source power estimation error variance in presence of RFI for different array calibration scenarios corresponding to perfectly calibrated, direction-independent uncalibrated and direction-dependent uncalibrated array cases. In addition, we consider in this study the case where only the data covariance information is available and investigate the loss of performance due to the missing data with respect to different system parameters.

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 ...

RFI mitigation at Nançay 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.

Generalized Minimum Noise Subspace For Array Processing

Based on the minimum noise subspace (MNS) method previously introduced in the context of blind channel identification, generalized minimum noise subspace (GMNS) is proposed in this paper for array processing that generalizes MNS with respect to the availability of only a fixed number of parallel computing units. Different batch and adaptive algorithms are then introduced for fast and parallel computation of signal (principal) and noise (minor) subspaces. The computational complexity of GMNS and its related estimation accuracy are investigated by simulated experiments and a real-life experiment in radio astronomy. It is shown that GMNS represents an excellent tradeoff between the computational gain and the subspace estimation accuracy, as compared to several standard subspace methods.

RFI mitigation at Nancay 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.