| 摘要 |
PURPOSE:To use multilevel quadrate amplitude moduration (QAM) waves in common and to reduce the cost of the titled system by dividing the signal point arrangement surface of the multilevel QAM waves, supervising the existence probability of signal points in respective divided areas and sending an asynchro nous alarm. CONSTITUTION:In case of 64 QAM waves, EX-OR of data D1 between Ich and Qch is found out by an EX-OR circuit 102 to divide the 1st and 3rd quardrants and the 2nd and 4th quardrants of the signal point arrangement surface. Namely, the circuit 102 outputs '0' e.g. when the signal points exist in the 1st and 3rd quardrants and '1' in case of the 2nd and 4th quardrants. On the other hand, an EX-OR circuit 101 divides the 1st-4th quardrants into a slashed area and a blank area. Namely, the circuit 101 outputs '0' e.g. when the signal points exist in the slashed area and '1' in case of the blank part. Since the ratio of appearance of '0' to '1' outputted from an EX-OR circuit 103 is about 60:40, a DC voltage approaching '0' is obtained. The DC voltage is detected, and whether the voltage is less than a prescribed range, e.g. 45% the voltage of '1', is judged to use the voltage for an asynchronous alarm. |
