PAPR Reduction for OFDM Mobile Wireless Communications by Constant-Amplitude Signal Decomposition

This paper proposes a constant-amplitude (CA) modulation scheme for orthogonal frequency-division multiplexing (OFDM) over mobile wireless channels. To cope with the high peak-to-average power ratio (PAPR) of OFDM signals, the proposed scheme decomposes one OFDM signal into two CA signals, and then transmits these two signals at different timings. Since CA signals give off a considerable amount of out-of-band emission (OOBE), the decomposed CA signals are passed into a low-pass filter (LPF) of which outputs are sequentially transmitted from one antenna. On the receiver side, the received signals are fed into a frequency-domain equalizer and then, combining the two time-domain equalizer’s outputs that originate from those two CA signals can regenerate the original OFDM signal. Especially when the channel is time-invariant without phase noise, lower complexity recovery of the original OFDM signal is to combine and equalize the two received signals that correspond to those two CA signals. As a conventional CA OFDM approach, the constant envelope OFDM (CE-OFDM) scheme transforms the OFDM signal into a phase modulated signal and is compared with the proposed scheme by computer simulation. It is demonstrated that the proposed scheme with LPF is superior to CE-OFDM in terms of both bit error rate (BER) performance and OOBE characteristics. Computational complexity of the proposed scheme is almost the same as that of CE-OFDM without any unwrappers in the phase demodulator, but the former can require a less amount of complexity than that of the latter with an accurate unwrapper being implemented.