A New Soft Decoding Method for Systematic LT Codes

In this paper, we propose a method to construct the modified Tanner graphs for systematic Luby transform (LT) codes. The modified Tanner graph is drawn in terms of bit nodes and check nodes, instead of encoding nodes and information nodes as in the conventional Tanner graphs for LT codes. By using this modified Tanner graph, we can use a more simplified soft iterative decoding algorithm, and also the decoding performance can be improved, compared to the conventional method. Most importantly, we can simply derive the corresponding parity check equation with the modified Tanner graph, and thus the iterative decoding process can be terminated easily. The average number of iterations can be largely reduced. Simulation results in this paper reveal that our proposed method can achieve better performance than the conventional iterative soft decoding with much less complexity.