RESUMEN
Visible light communication (VLC) is a promising technology that meets illumination and information transmission requirements in an indoor environment. Because light waves convey energy, a VLC link may exploit that fact for energy harvesting purposes. In this context, a single light emitting diode lamp located at a close distance over a tablet or laptop PC can potentially offer simultaneous lighting, Internet access, and battery recharging without cables. The present study introduces this threefold role of VLC systems by properly adapting some energy harvesting receiver architectures recently launched for usage in RF communications. The rate-energy trade-off for these architectures is revealed in order to maximize the efficiency of simultaneous energy and information reception, by elaborating on indicative numerical results. Furthermore, the performance in terms of the bit-error rate for pulse amplitude modulated signals is investigated. The results obtained offer some useful insights into the effective optical receiver implementation from the aspect of information theory.
RESUMEN
An experimental setup for characterizing the magnetic field of MRI RF coils was proposed and tested. The setup consisted of a specially configured 3D-printer, a network analyzer and a mid-performance desktop PC. The setup was tested on a single loop RF coil, part of a phased array for fetal imaging. Then, the setup was used for determining the magnetic field characteristics of a high-pass birdcage coil used for neonatal MR imaging with a vertical static field. The scattering parameter S21, converted into power ratio, was used for mapping the B1 magnetic field. The experimental measurements from the loop coil were close to the theoretical results (R=0.924). A high degree of homogeneity was measured for the neonatal birdcage RF coil. The development of MR RF coils is time consuming and resource intensive. The proposed experimental setup provides an alternative method for magnetic field characterization of RF coils used in MRI.
Asunto(s)
Feto/diagnóstico por imagen , Imagen por Resonancia Magnética , Impresión Tridimensional , Diseño de Equipo , Humanos , Campos Magnéticos , Fantasmas de Imagen , Ondas de RadioRESUMEN
We present an analytical framework for the performance evaluation of laser satellite uplinks over the major probabilistic impairments, i.e., atmospheric turbulence and beam wander. Specifically, we consider a ground-station-to-space laser uplink with a Gaussian beam wave model, and we focus on the particular regime assuming untracked beams where beam wandering takes place. In that regime, the modulated gamma-gamma distribution has been proposed as an effective irradiance model to characterize the combined effect of turbulence and beam wander. First we provide a closed-form expression of the probability density function and deduce the fundamental statistics of the new model. Then we evaluate the performance of the laser system assuming coherent detection for several modulation schemes. An appropriate set of numerical results is presented to verify the accuracy of the derived expressions.