A PAPR Reduction Method for CPM-OFDM Systems using Initial Phase Randomization

Abstract

In this paper, CPM-OFDM systems which use CPM (Continuous Phase Modulation) as the first modulation scheme of OFDM (Orthogonal Frequency Division Multiplexing) are considered. As is the case for conventional OFDM systems, PAPR (Peak to Average Power Ratio) reduction is the most important task in CPM-OFDM systems. PAPR reduction by varying the initial phase of each sub-carrier with a fixed offset and a random offset are proposed. In the random offset method, the initial phase of each sub-carrier is not known at the receiver side, so we propose a demodulation algorithm using the phase continuity property of CPM and MLSD (Maximum Likelihood Sequence Detection). Simulation results show that the PAPR performance is improved if we use the random offset method. Also, we found that even though the initial phase is unknown at the receiver, the proposed algorithm can demodulate CPM-OFDM symbols as well as an algorithm where the initial phase is known.