A soft-bit de-mapping device and method of generating soft bits for decoding quantizes a log-likelihood ratio (LLR) value for a received value using functions bits and channel parameter bits to generate the soft bits. The function bits are generated by quantizing an LLR function for the received value, which includes modifying an original curve of the LLR function to a modified curve such that a segment of the original curve with the lowest slope is protected in the modified curve for a fixed equal quantization step-size. The channel parameter bits are generated by quantizing a channel parameter for the received value to generate channel.