| 摘要 |
A digital transmission system for a selective call message communication network such as a paging network utilizes a quadrature amplitude modulation (QAM) transmitter (40) and receiver (42). The QAM transmitter (40) receives as a modulating input thereto, a message data encoded signal with a pilot carrier in a notch of the power spectrum of the signal. In order to generate the signal, the system generates a Hilbert transform of a wave-form representing message data to be transmitted. The Hilbert transform and message data waveform are combined to provide a positive frequency component and a negative frequency component. These frequency components are shifted apart and combined to provide a notch in which a DC component can be added to form a pilot carrier. A receiver of the system removes the pilot carrier from a received signal and shifts the positive and negative frequency components together to recover the message data.
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