Modulator and demodulator for data transmission systems

Claim 1

A modulating and demodulating device (MODEM) for data transmission systems, comprising: delay equalizing means for receiving via a transmission path a trellis-coded test signal transmitted from an opposite MODEM and compensating for delay distortion on said transmission path of said test signal; first switching means which can take either a first state wherein said test signal is supplied not via said delay equalizing means or a second state wherein the output signal of said delay equalizing means is supplied; demodulating means for demodulating the output signals of said first switching means; decision means for assigning the output signals of said demodulating means to predetermined signal point coordinates; Viterbi decoding means for computing branch metrics representing the distance between each assigned point and each receive signal point from the output signals of said decision means and said demodulating means, and figuring out pass metrics of accumulated values based on the computed branch metrics; arithmetic processing means for selecting the maximum and the minimum of said pass metrics from said viterbi decoding means, and determining and outputting the difference between said selected maximum and minimum as a difference signal; second switching means for supplying said difference signal determined by said arithmetic processing means as a first difference signal when said first switching means is in said first state and as a second difference signal when said first switching means is in said second state; and control means for comparing said first and second difference signals supplied by said second switching means, and holding said first switching means in said first state when said first difference signal is greater than said second difference signal, or holding said first switching means in said second state when said second difference signal is greater than said first difference signal.