A method for mapping cells onto symbols is provided. The cells include two or more cells processed by pre-coding in groups, the symbols include N symbols in a time-sequence, and each symbol includes M carriers in a frequency-order. The method comprises: mapping each cell to a carrier of a symbol; and frequency interleaving the carriers of each symbol. The mapping and the frequency interleaving are performed such that, following the frequency interleaving, the cells of a group of pre-coded cells are each mapped to carriers having the same carrier frequency or to carriers having carrier frequencies differing by no more than a threshold.