Modem apparatus, image communication apparatus and communication control method
View Patent ↗When a communication is started through a control channel in a half-duplex communication compliant with the Recommendation V.34, the modem apparatus of the present invention demodulates reception symbols subjected to quadrature amplitude modulation and thereby finds their coordinates on a signal space diagram. Then, the modem apparatus calculates a cross product of two vectors from the origin to the coordinates of two consecutive symbols and identifies a control signal from a polarity array configured by polarities of the calculation result arrayed over a span of a plurality of consecutive symbols.
1. A modem apparatus comprising:
a demodulator configured to demodulate a received symbol subjected to quadrature amplitude modulation;
a memory configured to store the demodulated symbol; and
a controller configured to detect coordinates of the demodulated symbols on a signal space diagram, to calculate a cross product of two vectors from the origin of the signal space diagram to the detected coordinates of two consecutive demodulated symbols, to obtain a polarity array of the calculation result over a plurality of consecutive demodulated symbols, and to determine a rotation direction of the demodulated symbol, based on the obtained polarity array,
the controller being further configured to determine that the received symbol is a Sh signal when positive polarity appears at least two times consecutively in the polarity array after a communication in compliance with Recommendation V.34 begins through a control channel.
2. An image communication apparatus equipped with a modem apparatus according to claim 1 .
3. A communication control method comprising:
demodulating a received symbol subjected to quadrature amplitude modulation;
detecting coordinates of the demodulated symbol on a signal space diagram;
calculating a cross product of two vectors from the origin of the signal space diagram to the detected coordinates of two consecutive demodulated symbols;
obtaining a polarity array of the calculation result over a plurality of consecutive demodulated symbols;
determining a rotation direction of the demodulated symbol, based on the obtained polarity array; and
determining that the received signal is a Sh signal when positive polarity appears at least two times consecutively in the polarity array when a communication in compliance with Recommendation V.34 begins through a control channel.
4. A modem apparatus operating according to Recommendation V.34 that receives one of a PPh signal and a Sh signal at the beginning of a communication on a control channel, the modem apparatus comprising:
a demodulator configured to demodulate a received symbol, the received symbol being modulated in quadrature amplitude modulation; and
a controller configured to detect a first rotation direction from a first demodulated symbol on a signal space diagram to a second demodulated symbol on the signal space diagram, and to detect a second rotation direction from the second demodulated symbol on the signal space diagram to a third demodulated symbol on the signal space diagram, the first demodulated symbol, the second demodulated symbol, and the third demodulated symbol being consecutively demodulated,
the controller being configured to determine receipt of the Sh signal when the first rotation direction and the second rotation direction are detected to be a same direction on the signal space diagram.
5. The modem apparatus according to claim 4 , wherein the same direction comprises a counterclockwise direction.
6. An image communication apparatus equipped with a modem apparatus according to claim 4 .
7. A communication control method for a communication in accordance with Recommendation V.34 that receives one of a PPh signal and a Sh signal at the beginning of a communication on a control channel, the communication control method comprising:
demodulating a received symbol, the received symbol being modulated in quadrature amplitude modulation;
detecting a first rotation direction from a first demodulated symbol on a signal space diagram to a second demodulated symbol on the signal space diagram;
detecting a second rotation direction from the second demodulated symbol on the signal space diagram to a third demodulated symbol on the signal space diagram, the first demodulated symbol, the second demodulated symbol, and the third demodulated symbol being consecutively demodulated; and
determining that the received signal is a Sh signal when the first rotation direction and the second rotation direction are detected to be a same direction on the signal space diagram.