On the formal identity of EVM and NPR measurement methods: Conditions for identity of error vector magnitude and noise power ratio

NPR (noise power ratio) and EVM (error vector magnitude) measurements are used to characterize linear or non-linear distortions and degradations in digital modulators, microwave or RF amplifiers and transmission links. These methods are also used in system simulations. Each of these methods results in an equivalent noise power that can be added to the thermal noise in the link budget in order to compute the BER (bit error rate). In this paper we examine the conditions necessary for these two measurements (or simulations) to give the same value for this equivalent noise. From this identity, it is possible to use either one or the other method with the goal to simplify simulation software or test benches particularly in the case of wide bandwidth measurements.