In this paper, a novel non-contiguous non-systematic coded unique word (UW)-OFDM system is proposed to opportunistically transmit data on the spectrum holes available in a cognitive radio network. In such a system, the spectral sidelobes of the active subcarriers interfere with the adjacent spectral band used by the primary system. In the proposed scheme, the code generator matrix of the UW-OFDM is designed to suppress the sidelobes. So, there is no need to add any extra processing to the transmitter for suppressing sidelobes. The derived code generator matrix is optimum in the sense of being matched to the best linear unbiased estimator and to the linear minimum mean square error data estimators. The achieved sidelobe suppression is a function of the number of transmitted data symbols. Simulation results show that by a slight decrease in the number of transmitted data symbols, the sidelobes power can be suppressed to zero.

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