Startup of V.34 communications

摘要

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 (S52). Then, the modem apparatus calculates a cross product of two vectors from the origin to the coordinates of two consecutive symbols (S53) 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 (S56). <IMAGE>