Abstract
The Viterbi decoding algorithm, which provides maximum
- likelihood decoding, is currently considered the most widely
used technique for the decoding of codes having a state description,
including the class of linear error-correcting convolutional
codes. Two classes of nonbinary convolutional codes are presented.
Distance preserving mapping convolutional codes and M-ary convolutional
codes are designed, respectively, from the distancepreserving
mappings technique and the implementation of the conventional
convolutional codes in Galois fields of order higher than
two. We also investigated the performance of these codes when
combined with a multiple frequency-shift keying (M-FSK) modulation
scheme to correct narrowband interference (NBI) in powerline
communications channel. Themodification of certain detectors
of the M-FSK demodulator to refine the selection and the detection
at the decoder is also presented. M-FSK detectors used in our
simulations are discussed, and their chosen values are justified. Interesting
and promising obtained results have shown a very strong
link between the designed codes and the selected detector for MFSK
modulation. An important improvement in gain for certain
values of the modified detectors was also observed. The paper also
shows that the newly designed codes outperform the conventional
convolutional codes in a NBI environment.