Reduced complexity adaptive filter

1. A FIR filter for use in an adaptive multi-channel filtering system, comprising:

a first memory for storing data;

a second memory for storing filter coefficients, said second memory storing only non-zero valued coefficients or coefficients that are above a predetermined magnitude threshold such that the overall number of coefficients processed is significantly reduced,

wherein each storage location of said second memory includes a first address field for storing an address identifying a channel associated with the stored coefficient and a second address field for identifying the location of corresponding data within said first memory for that particular channel; and

a processing unit for processing said data and said coefficients to form accumulated filter outputs.

2. A FIR filter as claimed in claim 1 , wherein said first memory includes a buffer for each channel, and said first address field is used to select a particular data buffer in said first address field.

3. A FIR filter as claimed in claim 2 , wherein buffers are circular buffers.

4. A FIR filter as claimed in claim 2 , further including an accumulator for each channel, and wherein said first address field is also used to select the particular accumulator associated with said first field.

5. A FIR filter as claimed in claim 1 , further comprising an address register for temporarily storing said first and second address fields output from said first memory, a modulo counter for cycling through addresses, and an adder for adding an address output by said modulo counter to and address stored in said second address field.

6. A FIR filter as claimed in claim 5 , wherein said processing unit is a convolution unit, said FIR filter further comprising a coefficient register for temporarily storing coefficients output from said second memory and a plurality of pipeline registers between said coefficient register and said convolution unit.

7. A FIR filter as claimed in claim 6 , wherein said convolution unit is connected to said accumulators.

8. A FIR filter as claimed in claim 6 , wherein a first portion of said address register storing said first address field is connected through a series of pipeline registers to said accumulators.

9. A network echo cancellation unit comprising a FIR filter as claimed in any one of claims 1 to 8 .

10. A method of processing coefficients in a FIR filter in an adaptive multi-channel filter system, comprising storing said coefficients in a coefficient memory along with associated address data identifying a corresponding channel and data address in a data memory, using said address data to select an appropriate channel and data address for the associated coefficient, wherein each storage location in said coefficient memory includes a coefficient field for storing a particular coefficient, a first address field for storing data identifying a channel, and a second address field for storing data identifying the storage location in said data memory of the data corresponding to said particular coefficient, and processing said coefficients and associated data in said data memory to form accumulated filter outputs.

11. A method as claimed in claim 10 , wherein a variable number of coefficients is used for each channel.

12. A method as claimed in claim 10 , further comprising using said first address field to select a circular buffer in said data memory.

13. A method as claimed in claim 12 , further comprising using said first address field to select an accumulator associated with the identified channel.

14. A method as claimed in claim 13 , wherein said processing comprises convolving each coefficient with the associated data in said data memory and inputting the convolved coefficient into the associated accumulator.

15. A method as claimed in claim 10 , further comprising adding said second address field to an output from a modulo offset counter to select a particular storage location in said data memory and maintain circular buffers in said data memory.

16. A method as claimed in claim 15 , wherein said address fields are addressed by an address counter.

17. A method as claimed in claim 10 , wherein said coefficients are stored without regard for order of the coefficients.