Peak-to-average power ratio reduction of OFDM signals using broadband pulse shaping

Abstract

Orthogonal frequency division multiplexing (OFDM) techniques allow the transmission of high data rates over broadband radio channels subject to multipath fading without the need for powerful channel equalization. However, they are very sensitive to nonlinear effects due to the high peak-to-average power ratio (PAPR) owned by the transmitted signal. This paper proposes an efficient technique for reducing the PAPR of OFDM signals. The proposed technique is very effective and flexible. The method avoids the use of extra inverse fast Fourier transformations (IFFT) as was done in some previously published techniques but instead is based on a proper selection of the time waveforms of the different subcarriers of the OFDM modulation scheme. Thus, its implementation complexity is much lower in comparison to the previous published methods. A closed form relation between the maximum PAPR and the used pulse shaping waveform is derived. The obtained results show that with broadband pulse shaping, the PAPR of OFDM modulated signals can be made very close to that of single carrier signals. The improved statistics of the PAPR in the transmitted signal is demonstrated through numerical results for some sets of time waveforms. The significant improvement in PAPR given by the present technique permits us to reduce the complexity and cost of the transmitter significantly. In that, pulse shaping can be used not only to shape the spectrum of the transmitted signal but also to reduce its PAPR.