Noise power ratio calculation based on the power spectra measurement

Power amplifiers and mixers are important components in digital radio communications systems, however, they are naturally nonlinear. Nonlinearity generates unwanted spectral components in digitally modulated signals which causes in-channel distortion of useful signal and adjacent channels interference. The basic spectral domain in-channel and in-band measures of nonlinear distortion are noise power ratio (NPR) and adjacent (alternate) channel (leakage) power ratio (ACPR or ACLR). This paper presents a method of NPR calculation of a nonlinear system driven by a near-Gaussian modulated signal. The calculation is based on the output signal power spectral density (PSD) measurement and in-channel nonlinear distortion estimation. The presented method reduces equipment costs compared to the traditional analog test method or the vector signal generator test method, while the duration of measurement and measurement uncertainty is preserved. The accuracy of proposed method is verified by a practical measurement.