A transmission system encodes blocks of source data with error correction codes and spreads encoded data for each source block over a range of time and frequencies. This has the effect of reducing the impact of flat fading. This is because if a portion of the encoded data corresponding to a block of source data is lost, as a result of flat fading during a time interval, other portions, transmitted at a different time, may not be affected. A receiving system may therefore recover the original block of source data based on the portions of the encoded data that were received, including error correction bits. The transmission and receiving systems may be orthogonal frequency division multiplexed (OFDM) communications systems.