Theoretical analysis of intermodulation distortion in OFDM signals in the presence of nonlinear RF high power amplifiers

This paper addresses different signal representation philosophies for the behavioral analysis of the nonlinear power amplifier (PA), in the context of modeling the passage of a multicarrier OFDM signal through a real PHEMT solid state power amplifier (SSPA) with and without linearisation. Three classes are identified, denoted direct time domain, mixed time and frequency domain, and statistical. A comparative analysis in respect of complexity, accuracy, availability of the modeled real signal for further behavioral analysis and constellation diagram analysis, and computational time is presented. The 'accuracy' is of the modulation fidelity (MF) degradation, measured as an error vector magnitude (EVM) deterioration. The degree of linearisation is measured in terms of percentage linearisation (PL) with respect to the unlinearised PA. The results, apart from being new in respect of the comparative analysis and are also new in that for the first time they present the impairment amelioration obtained through the introduction of different degrees of linearisation in OFDM based systems, and show this to be not of significant benefit.