Channel optimized predistortion for self-heterodyne DCT-based OFDM systems

This paper presents a novel technique to compensate intermodulation distortion of a self-heterodyne direct conversion OFDM system in multipath propagation environments. A self-heterodyne direct conversion system has an advantage that simple receivers can he built that are completely immune to any phase noise or frequency offset. This system, however, has a disadvantage that the nonlinear detector at the receiver of the self-heterodyne direct conversion system gives rise to intermodulation distortion. In this study, channel estimation is performed using a training sequence and then the predistortion coefficients with regard to estimated channel parameters are derived to compensate the receiver nonlinearity. Transmit power allocation technique is employed to overcome multipath fading channels as well. Computer simulation demonstrates that the proposed approach improves BER performance of the self-heterodyne direct conversion system in a multipath fading channel. This scheme gives advantage to multi-carrier systems, such as OFDM, that are much more sensitive to frequency and phase error than single-carrier systems.