Transmitter and receiver for an othogonally multiplexed QAM signal of a sampling rate N times that of PAM signals, comprising an N/2- point offset fourier transform processor

摘要

In a transmitter for digitally converting PAM signals, 2L in number, of a common slow sampling rate of 1/T hertzes to an orthogonally multiplexed QAM signal of a fast sampling rate of N/T hertzes, N/2-point input data into which the PAM signals are pre-processed with addition thereto of dummy signals, only (N/2-L) in number, are supplied to at least one N/2-point ODFT (offset discrete Fourier transform) processor (61), a pair of which (61, 62) must have been an N-point ODFT processor accompanied by switches controlled at a T/2-second period. After caused to pass through respective filter units of a bank (71), N/2-point output data are time-division multiplexed into the QAM signal. The filter units may either be complex band-pass or real low-pass filter units. A receiver comprises similar parts and carries out entirely reversed operation.