| 摘要 |
A receiver unit in a radio communication system in which a transmitter unit outputs transmission data, modulated in accordance with a multilevel QAM method and containing a leakage carrier by addition of a DC offset signal to either one of the quadrature components forming the transmission data, to the receiver unit through a transmission line, including: means for receiving the transmission data; means for branching a signal received at the transmission data receiving means into first and second signal components forming the multilevel QAM data, each including the leakage carrier having a phase difference of pi /2 radian; first channel means for demodulating the first branched signal component and including a first synchronous detection circuit and a first discriminator; second channel means for demodulating the second branched signal component and including a second synchronous detection circuit and a second discriminator; and means for recovering the carrier including a control circuit, for cancelling a noise component contained in the output signal from either one of the first and second synchronous detection circuits and for providing only a DC component representing a phase difference between a leakage carrier and a reference carrier, and a phase-locked loop (PLL) circuit, for controlling the phase difference to zero and for providing phase-locked leakage carriers to the reference carriers, having a phase difference of pi /2 radian, to the first and second synchronous detection circuits.
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