DOUBLE SIDE BAND ORTHOGONAL PHASE CARRIER MODULATION SYSTEM

PURPOSE:To obtain a minimum error rate by measuring phase jitter and noise amount with equivalent base band at the reception side in a narrow band high speed data transmission, and changing the detection and identification area depending on the comparison of detected result in quantity. CONSTITUTION:A reception signal is inputted to a demodulation and detection circuit 1 201 and a demodulation detection circuit 2 202. The demodulation detection circuit 1 201 has an identification area having a margin in the phase rotating direction from the amplitude direction of a detection complex signal space and the demodulation and detection circuit 2 202 has an identification area having a margin in the amplitude direction from the phase rotation. An output data of the detection circuits 201, 202 is inputted respectively to error detection circuits 203, 204, where an error rate is calculated. An error rate output of the error detection circuits 203, 204 is inputted to a comparator circuit 205, which compares the level of the output of the error detection circuits 203, 204 and a control signal controlling a selection circuit 206 is outputted corresponding to the level. The selection circuit 206 uses the control signal of the comparator circuit 205, selects the output of the circuit giving less error rate from the detector circuits 201, 202 and outputs a data at the data terminal device.