| 摘要 |
<p>A modem comprising error control encoder means (16) which adds redundancy according to a predetermined procedure to a transmission bit sequence from bit processing means (10) on the transmitting side (1) and encodes them; data sequence-to-coordinate conversion means (18) which converts a bit sequence from said error control encoder means (16) into a signal point coordinate on a complex plane; coordinate rotating means (20) that rotates said converted signal point coordinate based on frame phase data from said frame phase generating means (12); coordinate rotating means (34) which rotates the reception point coordinate reversely to that of the coordinate rotating means (20) on the transmitting side based on the frame phase data of frame phase generating means (28) of the receiving side; second judging means (38) that judges the signal point of the maximum likelihood and corrects error in the reception point coordinate by utilizing the redundancy added by the error control encoder means (16) of the transmitting side; and judging means (40) which judges the presence or absence of an out-of-frame synchronism condition based on a distance between a judging point by said second judging means (38) and a demodulation reception point on the complex plane; wherein out-of-frame synchronism is quickly detected. In the modem, furthermore, values for evaluation are set for the transition series of the signals, the transition series of received signals of the maximum likelihood is selected based on the evaluation values renewed for each reception of signal on the receiving side, error control signal is decoded to correct error at a demodulated signal point, and error is corrected in the data transmission.</p> |
