Disclosed is a network node and a method performed by a network node in a wireless communication network for determining signal to noise ratio of a signal received at a receiver from a first mobile station, which signal may include both noise and interference. The method comprises obtaining a plurality of measured noise and interference power values, IN values, of signals received at the receiver in one or more frequency sub-bands, determining IN for a lowest X percentile of the measured IN values, and applying the determined IN for the lowest X percentile as a measure of the noise. The method further comprises obtaining a measured signal strength value for a signal received at the receiver from the first mobile station, and determining SNR for the signal from the first mobile station by applying the determined noise measure.