Hi Christoph, generally, in Hard decision decoding, the received codeword is compared with the all possible codewords and the codeword which gives the minimum Hamming distance is selected. Instead, in Soft decision decoding, the received codeword is compared with the all possible codewords and the codeword which gives the minimum Euclidean distance is selected. Thus the soft decision decoding improves the decision making process by supplying additional reliability information (calculated Log-Likelihood Ratio). comm.LDPCDecoder works in this way.
BR /Marco