Julien Renard

Learn More
— Cognitive radios are devices capable of sensing a large range of frequencies in order to detect the presence of primary networks and reuse their bands when they are not occupied. Due to the large spectrum to be sensed and the high power signal dynamics, low-cost implementations of the analog front-ends leads to imperfections. Two of them are studied in(More)
Recent years have shown a growing interest in the concept of Cognitive Radios (CRs), able to access portions of the electromagnetic spectrum in an opportunistic operating way. Such systems require efficient detectors able to work in low Signal-to-Noise Ratio (SNR) environments, with little or no information about the signals they are trying to detect.(More)
This paper studies the impact of the spatial sign function on the cyclic features of communication signals and thereby on the performance of cyclic-feature detectors. It extends the existing results obtained for Gaussian signals and provides new insights into the interactions between the cyclic features of a cyclostationary signal sent through a spatial(More)
—The emergence of cognitive radios and their opportunistic use of the radio spectrum calls for efficient spectrum sensing algorithms, able to reliably detect signals in very low Signal-to-Noise Ratio (SNR) environments with unknown or changing statistical distributions. Cyclic-feature detectors, which make use of the cyclostationary signature of(More)
We present a microphotoluminescence study of single GaN/AlN quantum dots embedded in single nanowires. At low excitation power, single exciton lines with full width at half-maximum as narrow as 1 meV are observed. The study of the excitation power dependence of the emission allows us to identify the biexciton transitions with binding energies ranging from(More)
This paper presents a sequential likelihood ratio test (SLRT) detector for spectrum sensing scenarios in cognitive radios (CRs). Similar to other CR detectors, we exploit the structure of the sample covariance matrix of the received signal to achieve detection with minimal information regarding the signal. Unlike the majority of covariance-based CR(More)
This paper studies the performance of the scaled largest eigenvalue (SLE) detector used for the detection of stationary time-series. We focus on a single-antenna setup and a blind detection scenario (neither the signal covariance, nor the noise variance are known). The SLE detector has received much attention in the context of cognitive radios (CR) due to(More)
We demonstrate a novel near-field absorption spectrometer with 100 nm spatial resolution based on an ultrabroadband Ti:sapphire oscillator coupled to an aperture NSOM, enabling the measurement of nanoscale absorption spectra. The instrument is particularly suited for structural phase-selective imaging of organic materials at the nanoscale. We demonstrate(More)
  • 1