Americo Brajal

Orthogonal multicarrier techniques applied to direct sequence spread spectrum CDMA systems

We design a new scheme for DS-CDMA applications. The basic principle consists in applying orthogonal multicarrier transmission to DS spread spectrum systems. Several algorithms for estimating the equalizer coefficients are investigated in order to reduce the interuser interference due to multipath propagation and cross-correlation between the code sequences. The resulting system achieves high robustness against channel impairments and outperforms the conventional single-carrier DS-CDMA system.<<ETX>>

Compensation of nonlinear distortions for orthogonal multicarrier schemes using predistortion

In the Digital Terrestrial Television Broadcasting European project, the orthogonal frequency division multiplexing (OFDM) technique is seen as a good candidate. In this paper, characterization of the effects of a nonlinear channel over the OFDM signal is performed for 16-QAM and 64-QAM signal constellations. As expected, the attained performance is poor when compared to a single carrier scheme. To improve the performance low-complexity predistortion techniques are applied. It is shown that a predistorted OFDM system achieves almost the same performance as a single carrier scheme without predistortion.