A communication system is provided which implements a method for up-converting a baseband signal to a given number of frequency bands that together define a signal transmission channel. A sequential order is defined in which the frequency bands are to be used for up-converting the baseband signal, and up-converting the baseband signal to one frequency band after the other in the defined sequential order such that the spectral distance between two frequency bands is equal or higher for the frequency bands being direct neighbors in the defined sequential order than being direct neighbors in the spectral order.