Digital channelizer with arbitrary output sampling frequency

• US 6,356,569 B1
• Filed: 12/31/1997
• Issued: 03/12/2002
• Est. Priority Date: 12/31/1997
• Status: Expired due to Term

• Current Assignee: AT&T Corporation (AT&T, Inc.)
• Original Assignee: AT&T Corporation (AT&T, Inc.)
• Inventors: Sonalkar, Ranjan V., Helms, Howard David
• Primary Examiner(s): Kizou, Hassan
• Assistant Examiner(s): Elallam, Ahmed
• Application Number:
  US09/001,581
• Time in Patent Office: 1,532 Days
• Field of Search: 370/210, 370/343, 370/344, 370/480, 370/545, 375/229, 375/260, 375/354, 375/377, 708/313, 708/400, 708/405
• US Class Current: 370/545
• CPC Class Codes: H03H 17/0213 Frequency domain filters using Fourier transforms
• CPC Class Codes: H03H 17/0266 Filter banks
• CPC Class Codes: H04J 1/05 using digital techniques

Abstract

A digital channelizer employs a polyphase filter element in which a shift register is used to commutate time series data to a bank of polyphase filters at the inputs of an FFT module. The filter bank and FFT module are updated at a frequency that is independent of the rate that the data is fed into the buffer and filter/FFT cycle rates of less than the ratio of the input data rate to the number of input channels may be accommodated by the shift register commutation. The output of the FFT module is interpolation filtered by inserting interpolated points between adjacent data points in the channelized output stream to increase the output frequency by an integral multiple of the update rate of the polyphase filter/FFT update rate. By determining an integer, q, such that (R_o/R_i)(2N−q) is a non-zero integer l, where R_o is a desired output data rate, R_i is an input data rate and 2N is the number of output channels (M<N), updating the filter/FFT at a rate of R_i/(2N−q), and interpolation filtering by inserting l−1 interpolated data between each successive pair of channelized data, a desired output data rate can be matched with an input data rate.

Claims

1. A signal conditioning apparatus receiving primary data from a data source at a primary sample rate and outputting final data at a final sample rate, comprising:

a data buffer connected to receive data sequentially from said data source and output buffered data in sequential blocks;

a block filter, connected to receive said blocks, that generates block output data;

a connection between said data buffer and said block filter permitting input to said block filter of blocks with overlapping portions of selectable size, such that said operation may be performed at a selected rate independent of the size of said blocks and said primary sample rate; and

an interpolation filter connected to receive said block output data and configured to insert interpolated data into said block output data to generate said final data at said final sample rate.

2. A signal conditioning apparatus as in claim 1, further comprising:

a controller connected to control said interpolation filter,

said controller controlling said selectable size such that said final sample rate is an integral multiple of a product of said selected rate and a size of said blocks less said selectable size.

3. A signal conditioning apparatus as in claim 1, further comprising a controller connected to control a rate of insertion of said interpolated data by said interpolation filter such that said final sample rate is an integral multiple of a product of said selected rate and a size of said blocks less said selectable size.

4. A signal conditioning apparatus as in claim 1, wherein said buffer includes a shift register.

5. A signal conditioning apparatus as in claim 1, wherein said block filter is a computer programmed to calculate a spectra of a time series represented by said data blocks.

6. A method of controlling a signal conditioning apparatus receiving primary data from a data source at a primary sample rate and outputting final data at a final sample rate, the method comprising steps of:

buffering said primary data to form blocks of said primary data;

outputting said blocks of said primary data to a block filter at a block update rate;

performing a block filter operation on said blocks of primary data to form output blocks;

inserting interpolation data into said output blocks to form the final data having a final sample rate that is an integral multiple of said primary sample rate.

7. A method as in claim 6, wherein, in said step of outputting, said block update rate is such that each blocks of primary data contains at least one datum overlapping at least one datum in a successive block of primary data, whereby said block update rate is greater than a ratio of said primary sample rate and a size of said blocks of primary data.

8. A method as in claim 6, wherein said insertion rate is an integral multiple of said block update rate.

9. A method as in claim 6, wherein said step of performing the block filter operation includes calculating a fast Fourier transform of said blocks of primary data.

10. A method of separating the combined signals in a frequency division multiple access (FDMA) signal, comprising the steps of:

digitizing said FDMA signal at a primary sample rate to produce a primary data stream;

buffering said primary data stream to output said primary data stream in blocks at a block generation rate, each of said blocks being of size 2N, said block generation rate being equal to be a ratio of said primary sample rate and (2N−

q), where q is an integer;

digital-Fourier-transforming said blocks at said block generation rate to produce multiple channel signal streams;

inserting interpolated data in said multiple channel signal streams at a rate equal to an integral multiple of said block generation rate to produce final multiple channel signal streams.

11. A method of controlling a polyphase filter having 2N input channels and a shift-register buffer to supply data received from a data source at a rate of R_i to 2N inputs of a Fourier transform computer, said polyphase filter supplying channelized data to a data sink at a rate of R_o, comprising the steps of:

determining an integer, q, such that (R_o/R_i)(2N−

q) is a non-zero integer l;

commutatingly applying input data from said data source by shift-register buffering said input data laterally across B input channels of a Fourier transform computer;

Fourier transforming a result of said step of applying at a rate of R_i/(2N−

q) to generate channelized data; and

inserting l−

1 interpolated data between each successive pair of said channelized data.

12. A method as in claim 11, wherein q is the lowest non-zero integer such that (R_o/R_i)(2N−

q) is a non-zero integer l.

13. The method according to claim 11, wherein the step of inserting l−

1 interpolated data inserts l−

1 interpolated data between each successive pair of said channelized data so that R_o is an integral multiple of a ratio of R_i and (2N−

q).

14. A method of controlling a polyphase filter having 2N input channels and a shift-register buffer to supply data received from a data source at a rate of R_i, to 2N inputs of a Fourier transform computer, said polyphase filter supplying channelized data to a data sink at a rate of R_o, the method comprising steps of:

determining an integer value q such that (R_o/R_i)(2N−

q) is a non-zero integer l;

commutatingly applying input data from said data source by shift-register buffering said input data laterally across 2N input channels of the Fourier transform computer;

Fourier transforming a result of said step of applying at a rate of R_i/(2N−

q) to generate channelized data; and

inserting l−

1 interpolated data between each successive pair of said channelized data so that R_o is an integral multiple of a ratio of R_i and (2N−

q).

15. A method as in claim 14, wherein q is the lowest non-zero value such that (R₀/R₁)(2 N−

q) is a non-zero interger l.

16. A signal channelizer, comprising:

a data buffer receiving data sequentially from a data source at an input sampling frequency, the data buffer outputting buffered data in sequential blocks, the sequential blocks of buffered data having overlapping portions of selectable size;

a block filter receiving the sequential blocks of buffered data at a selectable rate that is independent of a size of the sequential blocks of buffered data and independent of the input sampling frequency, the block filter generating block output data; and

an interpolation filter inserting interpolated data into the block output data and generating an output having an output sampling frequency that is different from an input sampling frequency.

17. A signal channelizer as in claim 16, wherein said channelizer is a data channelizer.

18. A signal channelizer as in claim 17, wherein said channelizer is a frequency division multiple access signal channelizer.

19. A signal channelizer as in claim 16, wherein said data buffer is a shift register.

20. A signal channelizer as in claim 16, wherein the block filter includes

a Fourier transform processor generating the block output data, the block output data being a bandshifted sub-channel signal.

21. A signal channelizer as in claim 20, further comprising:

a controller connected to the interpolation filter and the block filter,

the controller controlling the data size so that the output sampling frequency is an integral multiple of a product of a selected rate and a size of the sequential data blocks less the selectable size of overlap.

22. A method of transforming a first signal having a first sample rate to a plurality of second signals each having a second sample rate, the method comprising steps of:

receiving said first signal;

separating a first data stream derived from said first signal into a plurality of second data streams at a first data rate, the second data streams including sequential blocks of data having overlapping portions of selectable size;

converting said plurality of second data streams from said first data rate to a second data rate, the second data rate being independent of a size of the sequential blocks of data and the first sample rate; and

inserting data in said plurality of second data streams to produce said plurality of second signals having said second sample rate, the second sample rate being different from said first sample rate.

23. A method as in claim 22, further comprising the step of:

filtering said plurality of second data streams with an interpolation filter to eliminate spectral copies.

24. A method as in claim 23, further comprising the step of:

digital-Fourier-transforming said plurality of second data streams.

25. A method as in claim 24, further comprising the step of:

polyphase filtering said plurality of second data streams.

26. A method as in claim 25, wherein said derivation of said first signal to said first data stream is digitizing said first signal at a first sample rate to produce said first data stream.