The limitations and rigidness of current use of spectrum resources have fostered the design of new power multiplexing techniques to improve frequency efficiency and flexibility. These techniques are based on the simultaneous transmission of different services on the same channel with different power distribution. At the receiver side Log-likelihood ratio (LLR) probability density functions have been so far optimized for single layer systems, so the reception quality of multilayer signals with the existing LLR algorithms is degraded. This paper proposes a new LLR probability density function, including corrections for the multilayer influence, in order to improve reception performance. Simulation results are also included to test the performance improvement in terms of the receiving SNR threshold.