Estudos sobre sistemas de comunicação com sonais não-ortogonais superpostos em frequência

Abstract

This work presents studies about communications systems where non- orthogonal signals with spectral overlapping, and carrier frequency separation less than the symbol rate, are used to transmit information. The research is focused on the definition of transmitter and receiver architecture, the modeling and mathematical analysis of the system including the channel, symbol detection strategies, and performance evaluation. A review of {m-QAM}² modulation is performed and a modification to the original {m-QAM}² system is suggested and discussed. The maximum-likelihood receiver to detect two m-QAM non-orthogonal signals, with spectral overlapping, and carrier frequency separation less than the symbol rate, is derived for an AWGN channel. A mathematical model and discussion about techniques of symbol detection are presented for the case where the m-QAM signal are band-limited. The two non-orthogonal band limited m-QAM model is extended to non- orthogonal m-PAM signals. New detection techniques applied to non-orthogonal m- PAM signals are proposed and discussed. The performance of new detectors are evaluated. The new proposed detection strategies are based on maximum-likelihood criterion and source separation concepts. Finally, the conclusions, the contributions, and new investigation perspectives are presented.