Reducing the out-of-band radiation of OFDM using an extended guard interval

We investigate the spectrum, out-of-band radiation (OBR) and the use of extended guard interval (EGI) to reduce the out-of-band radiation of an OFDM signal when passing through different nonlinear devices. Spectra of the OFDM signal with different EGI lengths after passing through nonlinear devices are obtained through computer simulations. Mathematical expressions for the power spectral density of a conventional OFDM signal and an OFDM signal with different EGI lengths are also presented. Theoretical and simulated results are compared. Although the EGI reduces the OBR, this reduction is not significant in some cases. The effect of EGI on the OBR of an OFDM signal differs for different nonlinear devices. The EGI is also not capable of reducing the OBR caused by excessive clipping of the OFDM signal. Finally, it is also found that the length of the EGI does not have a considerable effect on the amount of OBR reduced when passing through a nonlinear device.