This paper describes two new developed detection processes for a modem over the public
switched telephone network. The modem is a synchronous serial system using a 16-point
QAM signal with a detector. The detector is preceded by an adaptive filter that is adjusted
to make the sampled impulse response of the channel and filter minimum phase. The idea
of these two new detectors is to transmit a known retraining data every specified interval
and make use of these known data to improve the conventional nonlinear equalizer and
near maximum likelihood detector.
Results of computer simulation tests are presented comparing tolerance to additive white
Gaussian noise with retraining and with out retraining. The detectors with retraining
achieve a better noise performance than conventional detectors. Furthermore the amount
of retraining data is varied to find the best compromise between efficiency of data
transmission and performance improvement