Constellation expansion-based sidelobe suppression for cognitive radio systems

In the scenario of dynamic spectrum access application for orthogonal frequency division multiplexing (OFDM)-based cognitive radio systems, the out-of-band radiation of the OFDM signals must be strictly controlled to protect licensed users in the adjacent band. This study proposes a constellation expansion-based scheme for suppressing the sidelobes. The proposed approach can provide much faster decaying sidelobes by remapping the adjacent symbols in the original sequence with preferred mapping or alternative mapping chosen from a higher constellation set. Moreover, a simple clipping technique, which has little effect on the sidelobe suppression, is used for peak-to-average power ratio reduction of the proposed system. At the receiver, the specific associations in the mapping can be used to correct decision errors. Simulation results show that our proposed scheme can effectively reduce sidelobe power levels with only a slight bit error rate performance degradation.