  We consider bit interleaved coded modulation (BICM) receiver performance
improvement based on the concept of generalized mutual information (GMI).
Increasing achievable rates of BICM receiver with GMI maximization by proper
scaling of the log likelihood ratio (LLR) is investigated. While it has been
shown in the literature that look-up table based LLR scaling functions matched
to each specific transmission scenario may provide close to optimal solutions,
this method is difficult to adapt to time-varying channel conditions. To solve
this problem, an online adaptive scaling factor searching algorithm is
developed. Uniform scaling factors are applied to LLRs from different bit
channels of each data frame by maximizing an approximate GMI that characterizes
the transmission conditions of current data frame. Numerical analysis on
effective achievable rates as well as link level simulation of realistic mobile
transmission scenarios indicate that the proposed method is simple yet
effective.
