Reducing the Peak to Average Power Ratio of LDS-OFDM signals

Low Density Signature-Orthogonal Frequency Division Multiplexing (LDS-OFDM) has been introduced recently as an efficient multiple access technique. High Peak to Average Power Ratio (PAPR) is an important obstacle to multicarrier communication systems. This paper concentrates on the PAPR investigation and its reduction for LDS-OFDM signals. Specifically, we will investigate the impact of subcarrier allocation schemes and the phases of the signatures on the PAPR of LDS-OFDM signals. Firstly, the PAPR of LDS-OFDM with conventional signatures is investigated. Then we propose two methods for PAPR reduction; Newman phases and DFT pre-coding. The former method is simple and doesn´t imply changes in the system structure while the DFT pre-coding implies a modification in the system. Simulation results show that using Newman phases considerably reduces the PAPR of LDS-OFDM. Further PAPR reduction is achieved using DFT pre-coded LDS-OFDM on the cost of higher complexity.