Search

Fifth generation (5G) mobile communication systems have been deployed in the millimeter wave (mmWave) band. Since electromagnetic (EM) waves in this band exhibit high propagation loss and antennas are highly directive, the performance of wireless communications is largely degraded in a non-line-of-sight (NLOS) area, resulting in a limited coverage area. To improve the performance and increase the coverage area, a metamaterial-based electromagnetic scattering sheet (EMSS) with broad scattering characteristics is proposed in this paper. We also introduce fast design and optimization methods using equivalent circuits of metamaterials, antenna array theory, and the genetic algorithm (GA). The diffusion coefficient is used as a fitness value to evaluate the scattering characteristics of the EMSS generated by GA. The broad scattering characteristics of the designed EMSS are experimentally confirmed. We clarified that the optimized EMSS has a higher diffusion coefficient than a metal plate of the same size. Finally, we demonstrated improved wireless communication performance in an NLOS area by diffusing the incoming EM fields using our designed EMSS.

Recently, ultra high definition television (UHDTV) services have become popular using satellites and the Internet. However, there are expansive volumes of high definition television (HDTV) and standard definition television (SDTV) contents held by broadcasting companies and in storage devices. Herein we propose two color space conversion (also known as gamut mapping) methods from BT.709 (used for current HDTV broadcast) to BT.2020 (used for UHDTV broadcast) that restore or estimate lost color information. One of our methods anisotropically diffuses the BT.709 chromaticities with regard to the direction of the original chromaticities in the BT.2020 color space, generating chromaticities out of BT.709 gamut. The other learns an end-to-end conversion method from a BT.709 image to a BT.2020 image and restores lost color information using convolutional neural network (CNN). Using these methods along with BT.709 images, we obtain BT.2020 images with chromaticities from the BT.709 color gamut.