A BPSK Model for Soft-Output Decoding of Binary Linear Block Codes

|It is shown that the bit LLR value in soft-output decoding of a binary linear block code with BPSK modulation can be closely modeled by a second BPSK modulation of reduced noise power. With this modeling, it is possible to provide bit error performance approximations to help in the evaluation of binary linear codes. This can also be used in the design of communications systems which require knowledge of the characteristics of the channel, such as combined source-channel coding. Simulation results are presented which show that the actual bit error performance of the code is very well approximated by this modeling, especially for low signal-to-noise ratios (SNR). Furthermore, arguments are presented which show that the approximation requires fewer samples than conventional simulation methods to obtain the same precision in the bit error probability value. This translates into fewer computations and therefore , less time is needed to obtain performance results.