A technique for Out-of-Band radiation reduction in OFDM-based cognitive radio

Out-of-Band (OOB) radiations in Orthogonal Frequency Division Multiplexing (OFDM) system leads to the wastage of the scarce spectral resources and may pose severe interference threats to the legacy user in dynamic spectrum sharing environment. In this paper, we propose a novel technique for reducing OOB radiations caused by the high sidelobes in OFDM system. The principle of this technique is to map groups of two input transmit symbols on to expanded constellation points such that subcarriers in each group are 180 degrees out of phase. As a result, the proposed technique reduces the OFDM sidelobes by more than 10 dB in average at the cost of a slight increase in bit error rate. An important advantage of the proposed technique is that it does not require additional FFTs.