Performance limitations in an OFDM system due to non-linearities

The third order intermodulation products in OFDM systems caused by nonlinear analog circuits are presented. These impairments result in inter-bin interference (IBI) which causes errors in the constellation diagram of each subcarrier. Changes in amplitude and phase of the subcarriers by IBI combined with communication system noise can cause increased bit error rate (BER) in the demodulation process of some modulation types, particular for higher order types where one symbol consist of more bits. Because the Fourier Transform is a fundamental operation in processing subcarriers in OFDM systems we have analyzed the inter-bin interference by means of FFT, IFFT and some statistical methods to clarify the statistical behavior of the errors. We have try to fit the statistics of the amplitude and phase errors of each subcarrier with a known probability density function and investigated the influence of peak-to-average ratio (PAR) on IBI.