Logo do repositório

Percorrer por autor "Rodrigues, Luis"

A mostrar 1 - 3 de 3
  • DLL architecture for OFDM based VLC transceivers in FPGA
    Publication . Duarte, Luis; Rodrigues, Luis; Alves, Luis N.; Ribeiro, Carlos; Figueiredo, Mónica
    This paper addresses the problem of achieving high bandwidth in a DLL design for OFDM based VLC broadcast systems. It describes the implementation of efficient Data Link Layer (DLL) and Forward Error Correction (FEC) modules in a Xilinx FPGA. The proposed DLL aims at furnishing the adequate means to fragment and route both high data-rate (HDR) and moderate data-rate (MDR) service requests while maintaining a continuous transmission flow. The FEC modules aims at providing sufficient error correction capabilities with reasonable computation overheads. Another goal was to develop these modules under a globally asynchronous locally synchronous paradigm, ensuring high modularity and performance.
    2016-07Comunicação em conferência Acesso restrito Ver mais
  • Optimized Analog Multi-Band Carrierless Amplitude and Phase Modulation for Visible Light Communication-Based Internet of Things Systems
    Publication . Rodrigues, Luis; Figueiredo, Mónica; Alves, Luis Nero
    This paper presents a multi-user Visible Light Communication (VLC)-based Internet of Things (IoT) system using multi band-Carrierless Amplitude and Phase (m-CAP) modulation for IoT applications. The proposed system uses a digital m-CAP modulator embedded in a ceiling LED light fixture and analog receivers, aiming at low-cost, low-power, and small-sized IoT devices. The performance was evaluated in terms of the filtering stage design and the usage of guard bands. Different pairs of emitter and receiver filters were considered. While Bessel and Butterworth analog filters were tested in the analog receiver, the digital m-CAP modulator pulse shaping filter considered raised cosine filters, as well as digital matched filters for the analog Bessel and Butterworth filters. Regarding the guard bands, two approaches were considered: either by using the raised cosine roll-off factor (bandwidth compression) or by suppressing the even bands. The Bit Error Rate (BER) performance was obtained by simulation. The usage of the Bessel filter in the receiver, along with a digital matched filter, proved to be the best solution, achieving a BER lower than 10−3 for an Eb/No of 6 dB, using a third-order filter. Furthermore, guard bands should be used in order to mitigate inter-band interference in order to have improved performance when multiple users intend to simultaneously communicate.
    2021-04-05Artigo científico Acesso aberto Ver mais
  • Thermal analysis of high power LEDs using different PCB materials
    Publication . Kyatam, Shusmitha; Camacho, Pedro; Rodrigues, Luis; Alves, Luis Nero; Mendes, Joana Catarina; Figueiredo, Monica Carvalho
    Visible Light Communication is an emerging technology in Optical Wireless Communication where the Light Emitting Diodes (LEDs) are utilized for transmission of data. The luminance of the LEDs increases with the forward current; however, for high current levels the heat generated by nonradiative recombination of carriers increases the LED junction temperature, decreasing the efficiency and the lifetime of the devices. Therefore, the design of high power LED driver circuits needs to take into account the unavoidable local heating produced by high power components. In this paper, we performed thermal analysis of an LED driver mounted on Printed Circuit Boards (PCBs) using Thermal Risk Management (TRM) software and studied the heat dissipated by various components on PCBs composed of different dielectric materials such as FR4 and Diamond. Based on TRM simulations, the replacement of FR4 with diamond caused the junction temperature to decrease from 64°C to 45.2°C for a forward current level of 350 mA. The replacement of FR4 with diamond thus effectively improves the thermal management of LEDs and corresponding driver circuits.
    2017-09Comunicação em conferência Acesso restrito Ver mais