Simultaneous Predistortion and Nonlinear Detection for Nonlinearly Distorted OFDM Signals

Orthogonal Frequency Division Multiplexing (OFDM) is vulnerable with respect to nonlinear distortions caused, for example, by a nonlinear high power amplifier. In the presence of nonlinear high power amplification, OFDM suffers from crosstalk between all subcarriers. Furthermore, the power density spectrum is significantly widened. In this paper, we simultaneously use a memoryless predistorter at the transmitter side and a nonlinear detector at the receiver side. The predistorter reduces the out-of-band power, whereas the nonlinear detector improves the bit error rate. Since maximum-likelihood detection is prohibitive, a novel reducedstate symbol detector derived from the maximum-likelihood detector is proposed. For a QPSK/OFDM system in the presence of a memoryless solid-state power amplifier it is shown that the predistorter is not only useful for spectral shaping, but also in order to reduce the computational complexity of the nonlinear detector and to provide more robustness concerning an incomplete knowledge of the characteristics of the nonlinearity at the receiver. The overall raw bit error performance is shown to be close to that of a linear QPSK/OFDM system.