We present a modified belief propagation (BP) algorithm for decoding low density parity check codes having graphs with short cycles. The modified algorithm in log domain is superior in terms of numerical stability, precision, computational complexity and ease of implementation when compared to the algorithm in the probability domain. Simulation results show improvement in decoding performance for the modified BP compared to the original algorithm. The modified approach is also generalized for graphs with isolated cycles of arbitrary length by considering the statistical dependency among messages passed in such cycles.
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