Signal elements are mapped to a limited range of identifiers by emulating a "virtual" space of identifiers larger than the real limited space of identifiers. The larger virtual identifier space is implemented by an intermediate memory, which provides storage of identifiers assigned from the real space of identifiers. For each signal element to be mapped to an identifier, the intermediate memory is addressed by a hash value calculated from at least part of the signal element, thus allowing access to an identifier. The larger virtual space gives a better distribution of signal elements to the identifiers; and reduces the probability of different signal elements being mapped to the same identifier ("clashing"). For an efficient reduction of the clashing probability, identifiers with a low probability of being active are assigned to the intermediate memory to represent new signal elements.