On the selection of the best companding technique for PAPR reduction in OFDM systems

Orthogonal frequency division multiplexing (OFDM) is used in high data rate applications due to its ability to cope with frequency-selective channels. However, OFDM suffers from the high peak-to-average power ratio (PAPR) problem, which reduces the power amplifier (PA) efficiency or otherwise degrades bit error rate (BER) and increases out-of-band (OOB) radiation. In the literature, there are various PAPR reduction techniques. Among them companding techniques have small computational complexity, which make them attractive to be used in mobile stations (MS). Generally, companding techniques expand small signals while compressing large signals or compress large signals without affecting small signals. In this paper, different PAPR reduction companding transforms are compared. Results showed that companding transforms that compress large signals without affecting small signals (such as, Log companding and Tanh companding) are better than the others from a BER point of view. Results also showed that the Log companding transform is better than the Tanh transform, in terms of PAPR reduction gain and OOB radiation reduction. So the Log companding transform can be considered as the best practical companding transform among others.