No abstract

Este trabalho apresenta uma visão geral do modo de transmissão OFDM do padrão IEEE 802.16. O controle de acesso ao meio (MAC) e da camada física (PHY) são descritos em detalhes. Especialmente a estrutura do frame na camada (PHY). Além disso, as diferentes configurações da camada PHY com diferentes níveis de robustez são analisadas. Em seguida a simulação de um frame de dados com ADS (Advanced Design System) com todas as especificações da camada PHY são incluídas: Randomização, FEC, modulação adaptativa e IFFT/FFT. Um canal com multipercursos Rayleigh fading é implementada também. Finalmente são analisadas as curvas de espectro em freqüência e tempo, e a constelação no transmissor e receptor Downlink e Uplink, respectivamente.

AGRADECIMENTOS ABSTRACTThis work aimed at studying the synthesis and characterization of core-shell nanoparticles of polystyrene and polymethylmethacrylate obtained in a two-stage emulsifier-free emulsion polymerization and photopolymerization. The influence of different operational conditions based on kinetic factors was experimentally evaluated. In the first stage (seed preparation) the process temperature, initiator and monomer concentrations and the effect of surface-modifier agents (acids, salts, comonomers and crosslinker) were investigated; similarly in the second stage, the concentration and feeding regime of monomer were evaluated with respect to the shell formation. Experimental results showed that both, crosslinker and co-monomer are the best alternative to achieve a stable seed with small diameter; hence, with this core, uniform coating is obtained in the second stage and core-shell morphology is reached. In order to evaluate the efficiency of the preparation of core-shell particles, two experimental systems (conventional and photochemical reactor) were studied.Different characterization techniques indicated that in most of the cases studied particles with the desired core-shell morphology were formed. The use of spectroscopic techniques NIR and Raman were tested for the real-time monitoring of the process using adequate calibration models developed to correlate the average size of the growing core particle with the spectra. In the same way, thermodynamic factors were used to predict the expected final morphology of the particles.Experimental and predicted results were compared and discussed in terms of the key aspects involved in the control of the particle morphology.