Performance degradation of OFDM signals passing through nonlinear circuits

This paper presents a theoretical analysis of performance degradation in an orthogonal frequency division multiplexing (OFDM) system when the signal is passed through a nonlinear circuit such as high power amplifier (HPA) which is modeled as a fifth order memory-less nonlinear polynomial model (5^th order MLNPM). Theoretical analysis shows that the detected data symbol at the receiver consists of attenuated version of the original transmitted data symbol, third and fifth order intermodulation (IM) components. Analytical expressions for intermodulation noise term are derived using combinatorial methods. By use of the derived expressions, a closed form output signal to noise ratio, degradation factor (DF) and probability of error can be evaluated theoretically. For verifying the accuracy of our analysis a comparison between the theoretical and simulated results for one actual HPA are also presented.