In this paper, we present two pre-processing based techniques in unitary transform-domain for narrow-band interference rejection in CDMA communication systems. In our techniques, by using Karhaunen-Loeve Transform (KLT) and Discrete Fourier Transform (DFT), at the transmitter, eigenvectors occupied by NBI are determined; then the energy of the transmitted signal is set to zero into the direction of those determined vectors. Hence, any information is not deleted by NBI through channel. As a result after applying these transforms, a major part of the processing would be shifted to the transmitter, and thus complexity of receiver is reduced. Our simulation results show that the proposed methods improve the performance of the CDMA communication systems in the presence of narrow-band interference.
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