Bit Error Rate Locked Loops Using Log-likelihood Decoders

An automatic feedback control system that maintains an average bit error rate (BER) on decoded code words is proposed for log-likelihood ratio (LLR)error correction code (ECC) decoders. The input to the controller is the LLR output of the decoder, while the controller output is the decoder iteration parameter. The loop error signal is constructed by computing the difference between the scaled decoder LLR of codeword estimates and an ideal LLR value derived from a target BER. The discrete time transfer function of a proposed proportional-integral (PI) loop filter with integrator feedback using ideal linear analysis is presented, followed by loop simulation results using the decoder.