Contribuições aos projetos de sistemas com codificação espácio-temporal e sequências para espalhamento espectral.

Abstract

This thesis presents a performance analysis of space-time encoded communication systems, considering errors due to fails o n channel estimation. Transmission schemes combining coding, space diversity and fading resistant constellations are proposed. A n application of algebraic geometric codes to design efficient spread spectrum sequences to frequency hopping systems is also proposed. The work begins w i t h a discussion on channel characteristics by defining effects introduced by transmission media and mobile environment. A f t e r that, concepts related to space-time coding and channel estimation algorithms are presented. Invariant flat fading models and perfect channel state information are considered i n the first part of analysis. I n this part the objective is designing transmission schemes that combines coding, diversity and fading resistant constellations. Results show that an integration of these techniques improves the performance of communication systems. The second part of analysis copes w i t h two channel models, a flat time-variant model and a frequency selective time-invariant model. I n this part the receiver include some classical algorithms for channel state estimation. Here, the objective of analysis is to verify the performance of coding schemes over more complex environments, nearer real situations. I t is shown that coding gains are strongly affected b y channel state and channel identification algorithm. The contribution of this thesis i n applying algebraic geometric codes is made by means the use of Hermitian curves codes i n order to generate new frequency hopping spread-spectrum sequences. I t is verified that obtained sequences exhibit advantages over sequences generated using classical Reed-Solomon codes.