| 摘要 |
PURPOSE:To discriminate between an AIS signal and data and to detect securely the AIS signal at a high speed by counting ''0'' frame signals which are inserted alternately with ''1'' and ''0'' for every frame signal for a period of at least seven frames. CONSTITUTION:Normally, ''1'' and ''0'' are inserted alternately as frame signals into respective frames F of a PCM signal (a). Therefore, even all ''1'' data contains three ''0''s in the period T of at least seven frames. For this purpose, ''0''s in the signal (a) are detected by a detection part 10 and counted by a counter 11, whose counted contents are applied to a decision part 13 to decide on whether the signal (a) is an AIS signal or not. Even if an error of transmission inverts some ''0'' frame signal to ''1'', but three ''0''s are not all inverted, so the contents of the counter 11 are >=2 and the AIS signal all consists of ''1''s including frame signals, so the decision part 13 discriminates securely between data and the AIS signal. |
