Performance Evaluation of A Modified Sum-Product Decoding Algorithm for LDPC Codes

We propose a modified hyperbolic tangent (tanh) function that is used in the sum-product algorithm (SPA). This is done in order to approximate the infinite argument of the tanh function, when decoding low-density parity-check (LDPC) codes. As shown by computer simulation results, the proposed modification has a significant impact on the error floor reduction of the code and to the coding gain improvement with respect to the SPA with no modification. Computer simulation results with approximations using both piecewise linear function and coarse quantization are also presented