FDM demultiplexer using oversampled digital filters

Details FDM demultiplexer using oversampled digital filters FDM demultiplexer using oversampled digital filters

1988-02-12

1988-11-15

Olms, Douglas W.

Multiplex communications

Wide area network

Packet switching

H04J 400

Patent

active

047854472

ABSTRACT:
An N-channel FDM signal is converted into complex signals of baseband frequencies spaced at intervals equal to frequency .DELTA.f. The complex baseband signals are converted first into digital samples having a frequency N.DELTA.f and then into N parallel digital signals. A plurality of first FIR subfilters respectively perform filtering on each of the parallel digital signals at frequency .DELTA.f to produce a first series of filtered digital signals from each of the first FIR subfilters, and (m-1) groups of second FIR subfilters respectively perform filtering on each of the parallel digital signals at frequency .DELTA.f to produce a second series of filtered digital samples from each of the second FIR subfilters at timing displaced with respect to the first series by a/m.DELTA.f, where is an integer ranging from unity to (m-1) and m is an integer equal to or greater than 2. Outputs of the first FIR subfilters are combined with outputs of the second FIR subfilters to produce N summation outputs at frequency m.DELTA.f. An N-point Fast Fourier Transform processor performs fast Fourier transform on the N summation outputs at frequency m.DELTA.f to derive digital channels. Because of the oversampling at frequency m.DELTA.f, each of the digital channels has a frequency response which can be made flat over the bandwidth .DELTA.f.

REFERENCES:
patent: 3891803 (1975-06-01), Daguet et al.
patent: 4131764 (1978-12-01), Claasen et al.
patent: 4312062 (1982-01-01), Bellanger et al.
patent: 4412325 (1983-10-01), Molo
IEEE Transactions on Communications, vol. COM-22, No. 9, Sep. 1974 "TDM-FDM Transmultiplexer: Digital Polyphase and FFT" Maurice Bellanger, et al.

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