Modem signal transmitter, modem signal transmitting method, modem signal receiver, modem signal receiving method, modem signal transmitting/receiving system and modem signal transmitting/receiving method

摘要

In a modem signal transmitting/receiving system which includes a modem signal transmitter and a modem signal receiver connected to each other via a transmission line, a modem signal transmitter is suitable to transmit by multiplexing an analog signal such as audio and a modem carrier with digital data. Analog signals and digital data can be multiplex-transmitted at a high rate by effectively using an analog signal line. The modem signal transmitter includes a modem transmitting unit, an analog/digital converting unit which converts an analog signal into a digital signal, a demodulating unit which demodulates the digital signal with a predetermined carrier frequency signal, a decimation processing filter which decimates the demodulated signal and a deciding unit which decides a coordinate on a two-dimensional plane for the output from the decimation processing filter and then inputs the decision result to the modem transmitting unit. The signal received from the transmission line is subjected to an interpolation process, modulated with a predetermined carrier frequency, converted to an analog signal and outputted to the analog signal line.