Reduction of OFDM Peak to Mean Envelope Power Ratio Using Ghost Carriers.

The main disadvantage of OFDM is its high Peak to Mean Envelope Power Ratio (PMEPR), which can result in significant signal distortion in presence of nonlinear amplifiers. A major part of the proposed PMEPR reduction schemes is carry out on base band signals. In order to implement a digital modulator, an oversampled version of the continuous signal which would be generated by the analog modulator is required. This oversampling function is equivalent to add blocks of null symbols in the frequency domain. Referring to the pioneer work of [2], these blocks of null symbols will be called "Ghost Carriers". In this paper, we combine a Constraint Second Order Cone Program (C-SOCP) formulation with Ghost Carriers to reduce even more the PMEPR. As the Ghost Carriers (GC) are Out-Of-Band (OOB) carriers, the amount of OOB power should respects the spectrum mask specified in the standard. We show in this paper that with constraints on the increase of the mean power, the OOB power respects the spectrum mask. Therefore the proposed peak reduction scheme is formulated as a convex optimization problem with constraints on the increase of the mean power. The results are presented for the 802.11a standard.