Cyclostationary noise in radio-frequency communication systems

Because of the periodically time-varying nature of some circuit blocks of a communication system, such as the mixers, the noise which is generated and processed by the system has periodically time-varying statistics. An accurate evaluation of the system output noise is not straightforward as in the case where all the circuit blocks are linear-time-invariant and the noise that they generate is time-independent. We qualitatively examine here, conditions under which we can treat the noise at the output of every circuit block of a practical communication system as if it were time-invariant, in order to simplify the noise analysis without introducing significant inaccuracy in the noise characterization of the overall communication system.