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A novel multicarrier CDMA transmission scheme for cognitive radios with sidelobe suppression
Author(s) -
Rajabzadeh Morteza,
Khoshbin Hossein
Publication year - 2013
Publication title -
international journal of communication systems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.344
H-Index - 49
eISSN - 1099-1131
pISSN - 1074-5351
DOI - 10.1002/dac.2326
Subject(s) - computer science , code division multiple access , cognitive radio , telecommunications link , cyclic prefix , synchronous cdma , spectral efficiency , eigendecomposition of a matrix , transmission (telecommunications) , bandwidth (computing) , algorithm , orthogonal frequency division multiplexing , electronic engineering , eigenvalues and eigenvectors , telecommunications , multiuser detection , wireless , physics , channel (broadcasting) , engineering , quantum mechanics
SUMMARY Noncontiguous multicarrier code division multiple access (MC‐CDMA) is an effective multiple access method for cognitive radio systems that can deploy the noncontiguous vacant parts of a certain spectrum shared with the users of a primary system. However, the large spectral sidelobes of the Fourier transform based implementation of the MC‐CDMA interfere with the adjacent primary transmission. In this paper, a novel complex signature sequence set is proposed for synchronous downlink MC‐CDMA based cognitive radio networks to suppress the sidelobes. To do so, the minimization of the sidelobes power is developed as an eigen‐optimization problem that is optimally solved by using the eigenvalue decomposition method. The optimal complex signature sequences are chosen as the eigenvectors attained by the eigenvalue decomposition of a symmetric matrix that is dependent of the spectral characteristics of the primary users. Simulation results show that by a slight decrease in the maximum number of active users compared with full load, the sidelobes can be considerably suppressed. The effect of cyclic prefix length, the bandwidth of the primary system and the number of active users on the sidelobe suppression performance is analyzed through numerical simulations. Copyright © 2012 John Wiley & Sons, Ltd.