A Generalized Piecewise Linear Companding Transform for PAPR Reduction in OFDM Systems

Companding is a well-known technique for the peak-to-average-power ratio (PAPR) reduction of orthogonal frequency division multiplexing (OFDM) signals. Piecewise linear companding (PLC) scheme, compared with other companding schemes, can effectively reduce PAPR with much lower complexity, while achieving improved bit-error-rate (BER) performance. However, when the PAPR target value for companded signals is relatively small, such as 4 dB for 16-QAM or 5 dB for 64-QAM, there is a clear error floor of PLC in high SNR region for high-order QAM modulation. Focusing on this problem, we first analyze the reason for the error floor of PLC. Based on the analysis, we propose a generalized PLC scheme to reduce the distortion in decompanded signals with the relaxation of the constraint on the conservation of the average signal power. Finally, we formulate the optimization problems to obtain the parameters of the companding function in the pursuit of a preferable tradeoff between the BER and power spectral density performance under the constraint on PAPR. Simulation results verify that the proposed generalized PLC can significantly improve the BER performance while maintaining the same PAPR performance as PLC.