Multiplex communications – Wide area network – Packet switching
Patent
1979-04-10
1980-12-23
Stewart, David L.
Multiplex communications
Wide area network
Packet switching
370 84, H04J 105
Patent
active
042414431
ABSTRACT:
An apparatus for reducing a sampling frequency which derives information with the bandwidth f.sub.B /N (N is an integer) having a sampling frequency of 2f.sub.B /N from an input FDM signal with a bandwidth up to f.sub.B having the sampling frequency 2f.sub.B has been found. The present apparatus comprises a pair of partial frequency reduction systems and a switch for alternately selecting the outputs of said partial frequency reduction systems to provide the output signal. Each of said partial frequency reduction systems comprises a DFT means for performing the discrete Fourier transform for every G sampling points (G is the multiple of N) to said input signal, a multiplication means for multiplying the predetermined frequency characteristics with the output of said DFT means, linear conversion means for linear conversion of the output of said multiplication means and for providing G/N number of data, and means for performing the inverse discrete Fourier transform to the output of said linear conversion means. The present invention reduces sampling frequency by performing a smaller number of multiplications than a prior art, thus, the structure of an apparatus can be simple.
REFERENCES:
patent: 3605019 (1971-09-01), Cutter
patent: 3912870 (1975-10-01), Roy
patent: 4001510 (1977-01-01), Reed
patent: 4021616 (1977-05-01), Betts
patent: 4131766 (1978-12-01), Narasimha
IEEE Transactions on Communications; vol. Com-22, No. 9; Sep. 1974; "TDM-FDM Transmultiplexer . . . " by Bellanger.
IEEE Transactions on Communication Technology; vol. com-19; No. 1; Feb. 1971; "SSB/FDM Utilizing TDM Digital Filters" by Kurta.
Sakaki Hiroshi
Shintani Sotokichi
Kokusai Denshin Denwa Co. Ltd.
Stewart David L.
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