Fujitsu Corporation

Takeshi Yagi

Kenzo Kobayashi

Toshio Tamura

A subsignal transmitting system had working lines for respectively transmitting multiplexed signals each including a main signal, and had at least one protection line for transmitting one of the multiplexed signals when it is detected that the transmitting conditions of one of the working lines along which the signals are being transmitted are deteriorated. To realize the switching of the subsignal transmitting through the protection line, the system comprises a switching signal transmission line for transmitting, in the direction opposite to the transmission of the multiplexed signals, a switching signal indicating which one of the working lines is too deteriorated for transmission of the corresponding multiplexed signal, a transmitting side subsignal switching unit for outputting one of the input subsignals to one of the working lines respectively and for outputting, in response to the switching signal, one of the input subsignals to the protection line; and a receiving side subsignal switching unit, operatively connected to the subsignal output terminals, for outputting the subsignal through the protection line to, in response to the switching signal, the corresponding one of the subsignal output terminals, the remaining subsignals through the working lines being output to the remaining output terminals, respectively.

Subsignal transmitting system

A multi-level quadrature amplitude modulation and demodulation system includes a first exchange circuit for cyclicly exchanging input digital signals and for outputting exchanged signals to D/A converters. The D/A converters provide analog signals to a QAM modulator which produces a modulated signal. In the receiver side of the system, a QAM demodulator demodulates the modulated signal to produce analog signals which are converted to digital exchanged signals by A/D converters. The digital exchanged signals are exchanged in a manner which is the reverse of that of the first exchange circuit to provide output digital signals on output terminals which respectively correspond to the input terminals. By cyclicly exchanging the input signals in this manner, the transmission quality for each of the input signal channels is maintained equal.

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Otawara, Japan

Takeshi Yagi