On the crest factor approximation of non-contiguous OFDM signal

Two issues - out of band emission due to nonlinear processing in power amplifier and high amplitude variation of any multicarrier signal - are mutually connected. The higher the amplitude variation, defined usually as crest factor (CF), the higher the out of band emission. Such a problem is of particular importance in the case of non-contiguous orthogonal frequency division multiplexing (NC-OFDM) case, where a narrow frequency fragment is intentionally left vacant. In that context it is important to guarantee low level of interference induced to this narrow band. It is then important to know accurate CF characteristics. In this paper the discussion on the CF bounds and approximations based on the level-crossing rate are presented. Mathematical derivations are followed by the computer simulation results.