A preamble detector has a correlator outputting for every sample position of the preamble part of an incoming sampled signal stream a score and associated class value; and a multiple cluster unit receiving the class and score output values from the correlator, wherein a first cluster receives output values from the correlator and the following clusters are coupled in series such that each cluster receives output values from the correlator and a preceding cluster and wherein the output values of the correlator and a cluster are processed such that an n-th cluster of the multiple cluster unit, with n>1, accumulates the highest score values of n score values with matching class values.