This development provides a method for correcting symbol decision errors made by a receiving modem in a formatted modem transmission. Although originally developed specifically for modems which use trellis-coded modulation, this technology is not limited and may be applied to other modulation schemes. Decision errors are usually caused by excessive amounts of noise in a transmission channel. The Viterbi algorithm, an example of dynamic programming, was developed to reduce probability of decision errors by finding the most likely sequence, it is able to find the N most likely sequence in order, where N is some arbitrary value.
Commercial modems have error correction capabilities in some form or another.
Trellis coding gain without any bandwidth expansion. Receiving modems determine the most likely sequence that was transmitted by Viterbi decoding. Currently, most modems establish a connection at the highest possible data rate based on channel conditions. If conditions worsen, the modems automatically fall back to a lower rate. On the other hand, if the conditions improve they renegotiate at a higher rate.