A Novel Companding Technique For The Reduction Of Peak-to-Average Power Ratio Of OFDM Signals

Orthogonal Frequency Division Multiplexing(OFDM) has attracted extensive attention for its high spectrum efficiency and its great performance under frequency selective channels. But a main draw back is its high Peak to Average Power Ratio(PAPR). There are many techniques for reducing the PAPR of an OFDM signal, including but not limited to pre-distortion techniques, probabilistic techniques and coding techniques. As one kind of the pre-distortion techniques, companding techniques can efficiently reduce signal’s PAPR. The famous Exponential Companding(EC) can limit PAPR to below 4.77 d B. However the large non-linear distortion EC introduced degrades the system BER performance greatly.The main contribution of this paper is first proposing a new performance index, the normalized cross correlation coefficient of the signals before and after companding,. Theoretical analyses and simulations have showed its validity. Second a new family of companding function, the Triangular Companding(TC), has been proposed. As a companding technique, TC is simple, effective and independent of the subcarriers’ number and modulation scheme. Meanwhile the nonlinear distortion introduced by TC is relatively low. By adjusting a parameter, trade-off between PAPR reduction and BER performance can be made. Theoretical analyses and simulation results have showed that TC can limit signal’s PAPR to between 3.01 d B and 7.78 d B and the SNR degradation at the same BER level between original OFDM and TC companded signals is between a few hundredths to a few tenths which implies the special processing equipments at the receiver are not necessary. Compared with another widely used PAPR reduction technique, clipping, TC achieves the same level of PAPR reduction at a smaller cost of BER degradation. As a side note, an analytical expression of a important parameter of EC is derived in this paper.