Analytical methods for the evaluation of the impact of the VCO phase noise and the modulator/demodulator IQ imbalance for a QAM modulation

This paper deals with the impact of both VCO phase noise and modulator/demodulator impairments on the BER performances. We propose here two analytical methods for the evaluation of their impacts. These methods are interesting when dealing with very low BER values, where classical simulations take time to be processed: for example, to achieve a BER of 10^-8, more than 10⁹ points would have to be calculated to reach a confident interval of 95%. The first method presented is based on the analytical formulation of a QAM modulation BER considering the impact of the impairments on the constellation. The second method only use the Signal to Noise ratio degradation linked to these imperfections. We will demonstrate the usefulness of both calculations and their limitations.