Exact and approximated expressions of the log-likelihood ratio for 16-QAM signals

Abstract

This paper discusses the exact and approximate calculation of the bit log-likelihood ratio (LLR) for a 16-QAM signal. In particular, we introduce a new modified max function, which allows for an effective implementation of the LLR formula. The results of the paper are applicable to 16-QAM soft-demapping in digital receivers that perform soft decision decoding or iterative decoding.