A new stopping criterion for fast low-density parity-check decoders

Nonbiliary low-density parity-check (LDPC) codes can lead to excellent error performance while the codewords are of short or moderate length. However, the high decoding complexity of nonbiliary LDPC codes inevitably depreciates their practical values. The computational bottleneck arises from the check node processing in the iterative message passing (MP) algorithms which terminate when either all parity checks are satisfied or the maximum iteration number is reached. We have observed that for undecodable blocks, the MP algorithms always run up to the maximum iteration limit and therefore cannot generate the correct codeword. Thus, it would be better to terminate the algorithms early so as to save the unnecessary computational time and reduce the extra power consumption when undecodable blocks are experienced. In this paper, we propose a new T-tolerance stopping criterion for LDPC decoders by exploiting the fact that the total a posteriori probability (APP) should increase as the iteration number grows. Simulation results demonstrate that our proposed new T-tolerance criterion can greatly reduce the average iteration number (complexity) while restricting the decoding performance degradation within 0.1 dB in low bit-energy-to-noise ratio scenarios.