A novel multicarrier CDMA transmission scheme for cognitive radios with sidelobe suppression

Abstract

Noncontiguous multicarrier code division multiple access (MC-CDMA) is an effective multiple access<br><br>method for cognitive radio systems that can deploy the noncontiguous vacant parts of a certain spectrum<br><br>shared with the users of a primary system. However, the large spectral sidelobes of the Fourier transform<br><br>based implementation of the MC-CDMA interfere with the adjacent primary transmission. In this paper, a<br><br>novel complex signature sequence set is proposed for synchronous downlink MC-CDMA based cognitive<br><br>radio networks to suppress the sidelobes. To do so, the minimization of the sidelobes power is developed as<br><br>an eigen-optimization problem that is optimally solved by using the eigenvalue decomposition method. The<br><br>optimal complex signature sequences are chosen as the eigenvectors attained by the eigenvalue decomposition<br><br>of a symmetric matrix that is dependent of the spectral characteristics of the primary users. Simulation<br><br>results show that by a slight decrease in the maximum number of active users compared with full load,<br><br>the sidelobes can be considerably suppressed. The effect of cyclic prefix length, the bandwidth of the primary<br><br>system and the number of active users on the sidelobe suppression performance is analyzed through<br><br>numerical simulations.