Out-of-band power reduction in OFDM systems using double-length symbols

In this paper we investigate a method for reducing out-of-band power emissions in orthogonal frequency division multiplexing (OFDM) systems. This proposal is based on the usage of an OFDM signal obtained from an inverse discrete Fourier transform (IDFT) calculation with double length, compared to conventional OFDM systems. Since an OFDM signal is composed by the concatenation of individual OFDM symbols, continuity is implicitly obtained in half of all the union points of the whole transmission. A cyclic prefix and cyclic suffix strategy is also presented, to accommodate the obtained signal without affecting the original bandwidth or the sampling rate of the communication, but considering different channel states. Obtained results show a reduction in the out-of-band power emission. Since the output signal can be digitally obtained, the proposed approach is suitable for applications such as software defined radio (SDR) and cognitive radio (CR).