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Orthogonal frequency-division multiplexing (OFDM) systems exhibit significant out-of-band radiation caused by high sidelobes of the modulated subcarriers. Existing techniques for reducing this undesirable effect have several drawbacks as they waste the scarce spectral resources or expand the signal in time domain. In this paper, we propose a new technique which overcomes these problems. A few so-called cancellation carriers are inserted on the left and right hand side of the used OFDM spectrum. These special subcarriers are not employed for data transmission, but carry complex weighting factors which are determined such that the sidelobes of transmission signal and cancellation carriers cancel each other. Simulation results show that with the proposed method a significant sidelobe suppression is achieved with only a small loss in bit error rate performance. This loss is due to the fact that a certain amount of the transmission power has to be spent on the cancellation carriers and is not available for data transmission.