Improved Viterbi-decoding performance in the presence of permanent frequency disturbances in power-line environment

Since 1967, Viterbi decoder is considered to be the maximum-likelihood decoding algorithm for convolutional codes and codes with state machine representation. Distance-preserving mapping codes designed from the mapping of convolutional codes outputs to permutation sequences make use of constructions that help choosing the best mapping and improving the performance of Viterbi decoding by improving the distances metrics in the trellis diagram of the code. Combining these new designed codes with M-FSK modulation is to combat permanent frequency disturbances in power-line communications channel. The choice of the M-FSK detector also plays a role in the improvement of the decoding process at the demodulator. Viterbi's ratio Threshold test (VRTT) is modified to avoid the erasure detection, as we are not interested in such errors in our channel and to be considered as a soft decision detection for the envelope detector.