Title: Digital SSB-FDM communication system derived from a complex band-pass digital filter bank and by a filter breakdown process

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Claims: What is claimed is:

1. A single side-band frequency division multiplexed communication system for input sample sequences of real samples derived with a first sampling frequency f.sub.s from baseband channel signals, respectively, of a plurality of baseband channels, N in number, said baseband channels including a predetermined number of dummy baseband channels, said predetermined number being less than N, each of said baseband signals having a bandwidth equal to or less than f.sub.s /2, said communication system comprising:

first means for subjecting said sample sequences of real samples to offset discrete Fourier transformation to convert said sample sequences into a first set of complex sample sequences, N in number;

second means for digitally band-pass filtering said first set of complex sample sequences into a first set of real single side-band frequency division multiplexed sequence of samples corresponding to said real samples of said input same sequences and sampled at a second sampling frequency equal to Nf.sub.s ;

third means for converting said first set of real single side-band frequency division multiplexed sequence into a plurality of constituent sample sequences of real samples, N in number;

fourth means for converting said real samples of said plurality of constituent sample sequences into a second set of complex sample sequences, N in number, by digitally band-pass filtering said real samples of said constituent sample sequences, said second set of complex sample sequences corresponding to said samples of said single side-band frequency division multiplexed sequence and being sampled at said first sampling frequency; and

fifth means for subjecting the second set of complex sample sequences to offset discrete Fourier transformation to convert said second set of complex sample sequences into reproductions of said input sample sequences of real samples.

2. A modulator for modulating input sample sequences of real samples derived with a first sampling frequency f.sub.s from baseband channel signals, respectively, of a plurality of baseband channels, N in number, into a real single side-band frequency division multiplexed sequence of samples corresponding to said real samples and sampled at a second sampling frequency equal to Nf.sub.s, said baseband channels including a predetermined number of dummy baseband channels, said predetermined number being less than N, each of said baseband signals having a bandwidth equal to or less than f.sub.s /2, said modulator comprising:

Fourier transfer means for subjecting said sample sequences of real samples to offset discrete Fourier transformation to convert said sample sequences of real samples into a first set complex sample sequences, N in number;

complex band-pass digital filter means for digitally filtering said first set of complex sample sequences into filter output signals, said digital filter means performing a filter breakdown process and comprising a complex filter operable at said second sampling frequency;

digital processing means for digitally converting said filter output signals into a time division multiplexed signal having said second sampling frequency and having real components only; and

means for converting said real components of said time division multiplexed signal into said single side-band frequency division multiplexed sequence of samples.

3. A demodulator for demodulating a single side-band frequency division multiplexed sequence of real samples into a plurality of output sample sequences of real samples derived with a first sampling frequency f.sub.s from baseband channel signals, respectively, of a plurality of baseband channels, N in number, the real samples of said single side-band frequency division multiplexed sequence corresponding to the real samples of said output sample sequences and being sampled at a second sampling frequency equal to Nf.sub.s, said baseband channels including a predetermined number of dummy baseband channels, said predetermined number being less than N, each of said baseband signals having a bandwidth equal to or less than f.sub.s /2, said demodulator comprising:

complex band-pass digital filter means for converting said real samples of said frequency division multiplexed sequence into a set of complex sample sequences, N in number, by digitally band-pass filtering said real samples of said frequency division multiplexed sequence, said set of complex sample sequences corresponding to the samples of said frequency division multiplexed sequence and sampled at said first sampling frequency; and

Fourier transfer means for subjecting said complex sample sequences to offset discrete Fourier transformation to convert said complex sample sequences into said output sample sequences of real numbers.

4. The system of claim 1 further including spectrum reverser means for reversing the frequency spectrum of selected ones of said input sample sequences prior to applying said input sample sequences to said first means.

5. The system of claim 1 further including spectrum reverser means for reversing the frequency spectrum of selected ones of said sample sequences developed by said fifth means.

6. The modulator of claim 2 wherein said digital filter means comprises:

a plurality of slow complex filter means, each of said slow complex filter means for shifting the frequency of a different one of said sample sequences of real samples; and

means for sequentially coupling each of said frequency shifted sample sequences generated by said slow complex filter means to a common output terminal.

7. The system of claim 2 further including spectrum reverser means for reversing the frequency spectrum of selected ones of said sample sequences of real samples before they are applied to said Fourier transfer means.

8. The system of claim 2 wherein said Fourier transfer means comprises an inverse discrete Fourier transformation (IDFT) processor and a post processor coupled to said processor for offsetting the outputs of said IDFT processor.

9. The system of claim 3 wherein said Fourier transfer comprises a preprocessor and an inverse discrete Fourier transformation (IDFT) means coupled to said preprocessor, said preprocessor comprising multiplier means for coupling offsetting inputs to said IDFT means.

10. The system of claim 1 wherein said first means generates said first set of complex sample sequences from said real samples only.

Other info:

Inventors: Maruta, Rikio (Tokyo, JP)

Application Number: 770426
Filing Date: 1977-02-22
Publication_date: 1978-08-15
Assignee: Nippon Electric Co., Ltd. (Tokyo, JP)
Primary Class(es): 380/28 375/270, 375/321, 380/39, 708/405
Other Classes:
US Patent Ref:

3605019	Sep, 1971	Cutter	179/15.
3891803	Jun, 1975	Daguet	179/15.
3971922	Jul, 1976	Bellanger	179/15.

Other Refs:
Primary Examiner: Claffy, Kathleen H.
Assistant Examiner: Popek, Joseph A.
Attorney: Ostrolenk, Faber, Gerb & Soffen