A method of processing data received over a channel includes receiving data representing probabilities associated with a plurality of variables and receiving a parity check matrix associated with a factor graph which includes variable nodes and check nodes connected by edges. After each exchange of messages between the variable nodes and check nodes, messages are calculated based on messages received at the variable nodes and permuted messages to be sent from the variable nodes in the next iteration are calculated by applying a permutation to the calculated messages. The permutation is of a set of permutations which map each codeword of the set of codewords onto a different codeword of the set of codewords. Soft values associated to variable nodes can be accumulated over two iterations of the message exchange processing.