For a large number of subchannels,the arrays of sinusoidal generators and coherent demodulators required in a parallel system become unreasonably expensive and complex.The receiver needs precise phasing of the demodulating carriers and sampling times.Weinstein and Ebert applied the discrete Fourier transform (DFT)to parallel data transmission system as part of the modulation and demodulation process. For a large number of subchannels, the arrays of sinusoidal generators and coherent demodulators required in a parallel system become unreasonably expensive and complex. The receiver needs precise phasing of the demodulating carriers and sampling times. Weinstein and Ebert applied the discrete Fourier transform (DFT) to parallel data transmission system as part of the modulation and demodulation process