Title: Digital filter bank

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1. A digital filter for use in a voice multiplexing system for modulating a series of data samples representing a number of voice channels in time division multiplexed format into a series of data samples representing said voice channels in frequency division multiplexed format comprising:

complex low pass filter means connected to receive said series of time division multiplexed data samples for converting said samples to an analytic signal for each of said voice channels,

Fourier transform processor means connected to receive each of said analytic signals for transforming said analytic signals into a frequency division multiplexed signal having frequency components corresponding to different ones of said voice channels and

weighting means connected to receive said frequency multiplexed signal for weighting said frequency components with weighting coefficients having predetermined passband characteristics.

2. A digital filter as in claim 1 wherein said low pass filter means include delay means connected to sequentially receive said series of data samples for each voice channel for delaying said samples, storage means for storing predetermined complex filter coefficients having real and imaginary components, multiplier means for sequentially multiplying said received samples by said complex filter coefficients, and adder means for adding the multiplied samples thereby forming a real and an imaginary component of said analytic signal for each of said voice channels.

3. A digital filter as in claim 2 wherein said weighting means include delay means for delaying said frequency components, storage means for storing predetermined weighting coefficients for weighting said frequency components with corresponding passband characteristics, multiplier means for sequentially multiplying said frequency components by said weighting coefficients, and adder means for adding the multiplied components thereby forming said frequency components with said predetermined passband characteristics.

4. A digital filter as in claim 3 wherein said weighting coefficients are real.

5. A digital filter as in claim 3 wherein said weighting coefficients are complex.

6. A digital filter as in claim 1 wherein said processor means includes a fast Fourier transform processor.

7. A digital filter as in claim 1 wherein said processor means includes a Winograd Fourier transform processor.

8. A digital filter as in claim 1 wherein said processor means includes first input means for connecting said data samples representing said number of voice channels to said processor means and second input means for connecting a corresponding number of zero valued data samples to said processor means for simultaneously processing the first and second inputs.

9. A digital filter as in claim 8 wherein said processor means include a pipeline processor.

10. A digital filter as in claim 8 wherein said processor means include a parallel processor.

11. A digital filter for use in a voice multiplexing system for demodulating a series of frequency division multiplexed data samples representing a number of voice channels in a frequency spectra, comprising:

complex weighting network means connected to receive said data samples representing said voice channels where each of said voice channels has a predetermined bandwidth and a center frequency at an odd multiple of one-half of said bandwidth for weighting said samples with predetermined weighting coefficients,

Fourier transform processor means connected to receive the weighted samples for transforming said samples into a time division multiplex signal, and

complex low pass filter means connected to receive said transformed signal for converting said transformed signal to a series of data samples representing each of said voice channels in time division multiplexed format.

12. A digital filter as in claim 11 wherein said weighting network includes delay means for sequentially delaying said series of data samples, storage means for storing predetermined weighting coefficients, first multiplier means for sequentially multiplying some of the delayed samples by some of said weighting coefficients, second multiplier means for sequentially multiplying others of said delayed samples by others of said weighting coefficients, and adder means for adding said multiplied samples thereby forming weighted samples.

13. A digital filter as in claim 11 wherein said complex lowpass filter means include first delay means for delaying the real component of said transformed signal, second delay means for delaying the imaginary component of said transformed signal, storage means for storing predetermined complex filter coefficients for each channel, multiplier means for multiplying said delayed and imaginary components by corresponding ones of said filter coefficients, adder means for adding the multiplied real and imaginary components thereby forming said time division multiplexed signal representing said number of voice channels.

14. A digital filter for use in a voice multiplexing system for modulating a series of data samples representing a number of voice channels in time division multiplex format into a series of data samples representing said voice channels in a frequency division multiplexed format comprising:

Fourier transform processor means connected to receive said series of time division multiplexed samples representing said voice channels where each of said voice channels has a predetermined bandwidth for transforming said samples into a frequency division multiplexed signal having predetermined frequency components corresponding to different ones of said voice channels, and

complex weighting means connected to receive said frequency multiplexed signal corresponding to said voice channels where the center frequency of each voice channel in the frequency multiplexed signal is at an odd multiple of one-half of said bandwidth for weighting said frequency components with weighting coefficients having predetermined passband characteristics.

15. A digital filter as in claim 14 wherein said weighting means include complex lowpass filter means connected to receive said data samples for converting said samples to an analytic signal for each of said voice channels.

16. A digital filter for use in a voice multiplexing system for modulating and demodulating a number of voice channels comprising:

multiplexer means for multiplexing said number of voice channels into a first series of data samples in time division multiplexed format,

complex low pass filter means connected to receive said first series of data samples for converting said samples to an analytic signal for each of said voice channels,

Fourier transform processor means connected to receive each of the analytic signals for transforming said analytic signals into a frequency division multiplexed signal having frequency components corresponding to different ones of said voice channels,

weighting means connected to receive said frequency division multiplexed signal for weighting said frequency components with weighting coefficients having predetermined passband characteristics,

first converter means for converting the weighted frequency components into an analog signal having frequency components with predetermined passband characteristics,

second converter means for converting an analog signal into a second series of data samples,

said weighting means including means for receiving said second series of data samples in frequency division multiplexed format for weighting said second samples with predetermined weighting coefficients,

said Fourier transform processor means including means connected to receive said weighted samples for transforming said samples into a time division multiplexed signal,

said complex low pass filter means including means connected to receive said transformed signal for converting said transformed signal to said first series of data samples representing each of said voice channels in time division multiplexed format, and

demultiplexer means for demultiplexing said first series of data samples into an analog signal for each of said voice channels.

17. A digital filter for use in a voice multiplexing system for modulating a first series of data samples representing a number of voice channels in time division multiplexed format into a second series of data samples in frequency division multiplexed format and for demodulating said second series of data samples into said first series of data samples in time division multiplexed format comprising:

Fourier transform processor means connected to receive said first series of samples representing said voice channels where each of said voice channels has a predetermined bandwidth for transforming said samples into a frequency division multiplex signal having frequency components corresponding to different ones of said voice channels,

complex weighting means connected to receive said frequency multiplex signal corresponding to said voice channels where the center frequency of each voice channel in said frequency division multiplex signal is at an odd multiple of one-half of said bandwidth for weighting said frequency components with weighting coefficients having predetermined passband characteristics thereby forming said second series of samples, said weighting means connected to receive said second series of data samples representing said voice channels where each of said voice channels has a predetermined bandwidth and a center frequency at an odd multiple of one-half of said bandwidth for weighting said samples with said coefficients, and

said processor means connected to receive said weighted samples for transforming said samples into a time division multiplexed signal representing each of said voice channels thereby forming said first series of samples.

18. A digital filter as in claim 17 wherein said weighting coefficients are real and wherein said processor means includes a number of inputs corresponding to said number of voice channels, storage means for storing predetermined periodic complex coefficients and multiplier means for sequentially multiplying said transformed series of samples and said weighted series of data samples by said periodic complex coefficients.

19. A digital filter for use in a voice multiplexing system for demodulating a series of frequency division multiplexed data samples representing a number of voice channels in a frequency spectra, comprising:

complex weighting means connected to receive said series of data samples representing said voice channels where each of said voice channels has a predetermined bandwidth and a center frequency at an odd multiple of one-half of said bandwidth for weighting said samples with predetermined weighting coefficients, and

Fourier transform processor means connected to receive the weighted samples for transforming said weighted samples into a time division multiplex signal representing said number of voice channels.

20. In a digital filter for use in a voice multiplexing system having a first series of data samples representing a number of voice channels in time division multiplexed format and a second series of data samples representing said number of voice channels in frequency division multiplexed format, the method comprising the steps of:

converting said first samples for each of said voice channels to an analytic signal,

processing said analytic signal into a frequency division multiplexed signal having predetermined frequency components corresponding to different ones of said voice channels,

weighting said frequency components with predetermined weighting coefficients having passband characteristics thereby forming a frequency division multiplexed signal having proper passband characteristics for each voice channel,

weighting said second data samples with said predetermined weighting coefficients,

transforming said weighted samples into a time division multiplexed analytic signal, and

converting said transformed signal to a series of data samples representing each of said voice channels in time division multiplexed format.
Other info:

Inventors: Narasimha, Madihally J. (Mountain View, CA, US)

Application Number: 814303
Filing Date: 1977-07-11
Publication_date: 1978-12-26
Assignee: Granger Associates (Menlo Park, CA)
Primary Class(es): 370/484 708/404, 708/406
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: Flehr, Hohbach, Test, Albritton & Herbert