Digital ssb-fdm communication system derived from a complex band-pass

Abstract

An SSB-FDM modulator derived from a complex band-pass digital filter bank and by a filter breakdown process comprises a discrete Fourier transform (DFT) processor capable of giving phase offsets to complex output signals thereof. In a broader sense, DFT includes inverse DFT (IDFT). The processor is called an offset discrete Fourier transform (ODFT) processor and supplied with real baseband sample sequences. The phase offset complex output signals are frequency-selected by a complex band-pass digital filter unit operable at a sampling frequency for the baseband sample sequences into a real SSB-FDM signal. An SSB-FDM demodulator likewise derived comprises a complex band-pass digital filter unit for frequency-selecting a real SSB-FDM signal into complex sample sequences of the respective baseband channels. The complex sample sequences are ODFT'ed into real baseband sample sequences. For simplified processing of signals transmitted between the modulator and demodulator, use is made of at least one dummy baseband channel. The phase offsets may be provided in the modulator by a post-processor following a conventional DFT processor and in the demodulator by a pre-processor prior to conventional DFT. If desired, frequency spectra of the sample sequences of predetermined one or ones of the baseband channels may be reversed in the modulator prior to digital filtering and in the demodulator after the ODFT.