Stepwise adaptive finite impulse response filter for spread spectrum radio

• US 6,438,156 B1
• Filed: 02/11/1999
• Issued: 08/20/2002
• Est. Priority Date: 02/11/1999
• Status: Expired due to Term

• Current Assignee: ADTRAN Incorporated (ADTRAN Holdings, Inc.)
• Original Assignee: ADTRAN Incorporated (ADTRAN Holdings, Inc.)
• Inventors: Ghobrial, Ayman K., Blackwell, Steven R.
• Primary Examiner(s): Le, Amanda T.
• Application Number:
  US09/248,664
• Time in Patent Office: 1,286 Days
• Field of Search: 375/130, 375/140, 375/147, 375/148, 375/229, 375/232, 375/233, 375/350, 708/319, 708/322, 708/323
• US Class Current: 375/148
• CPC Class Codes: H04L 2025/03375 Passband transmission
• CPC Class Codes: H04L 2025/03477 not time-recursive
• CPC Class Codes: H04L 2025/03617 Time recursive algorithms H04L2025/03643 takes precedence
• CPC Class Codes: H04L 25/03038 with a non-recursive structure H04L25/03031 takes precedence

Abstract

A distortion compensation filtering mechanism for a direct spread-spectrum radio receiver comprises an iteratively adaptive FIR filter installed in the received signal processing path of the radio just upstream of the despreading function. The filter may be implemented as a relatively small numbered tap filter, having its precursor tap fixed at a maximum value. The remaining filter tap values are individually adaptively adjusted by the radio'"'"'s control processor, which executes a tap adjustment routine to iteratively increment or decrement each variable tap value of the FIR filter to an ‘optimized’ value, that effectively minimizes the total (I and Q) power in the error in the data decisions performed by data signal analyzer.

Claims

1. For use with a direct spread-spectrum radio receiver, in which a demodulated spread signal received by way of a radio transmission channel from another direct spreading radio is processed in accordance with a despreading, pseudo-random chip sequence produced by a pseudo random noise generator to produce despread signals, said despread signals being processed by a data signal analyzer to recover transmitted data, a method for compensating for signal degradation effects imparted by said radio channel and internal distortion of said another direct spreading radio and said radio receiver, said method comprising the steps of:

(a) filtering said demodulated spread signal by means of an iteratively adaptive multitap finite impulse response (FIR) filter, installed in said receiver upstream of a signal processing location of said direct spread-spectrum radio at which said demodulated spread signal is processed in accordance with said despreading, pseudo-random chip sequence to produce said despread signals; and

(b) iteratively adjusting respective tap values of said multitap FIR filter to optimized values that effectively minimize the power in the error in data values produced by said data signal analyzer by setting the value of a selected tap of said multitap FIR filter to a fixed value, and iteratively adjusting tap values of remaining taps of said filter from initial settings to said optimized values, by iteratively adjusting the tap value of each of said remaining taps on. an individual tap basis, from an initial setting to an optimized value for that tap.

2. A method according to claim 1, wherein said fixed value of said selected tap is a maximum value, and each of said initial tap value settings is zero.

3. A method according to claim 1, wherein step (b) comprises, for each iterative adjustment of the value of a respective tap, calculating power in the error in data produced by said data signal analyzer and, in response to a reduction in the value of calculated error power from a previous value of calculated error power, performing a further iterative adjustment of said value of said respective tap.

4. A method according to claim 1, wherein step (b) comprises, for each iterative adjustment of the value of a respective tap, calculating power in the error in data produced by said data signal analyzer and, in response to no reduction in the value of calculated error power from a previous value of calculated error power, establishing said optimized value of said respective tap.

5. A filtering mechanism for a direct spread-spectrum radio receiver, in which a demodulated spread signal received by way of a radio transmission channel from another direct spreading radio is processed in accordance with a despreading, pseudo-random chip sequence produced by a pseudo random noise generator to produce despread signals, said despread signals being processed by a data signal analyzer to recover transmitted data, said filtering mechanism comprising:

an iteratively adaptive multitap finite impulse response (FIR) filter, installed in said receiver upstream of a signal processing location of said direct spread-spectrum radio at which said demodulated spread signal is processed in accordance with said despreading, pseudo-random chip sequence to produce said despread signals; and

a control processor coupled to said data signal analyzer, and being operative to iteratively adjust respective tap values of said multitap FIR filter to optimized values that effectively minimize the power in the error in data values produced by said data signal analyzer, by setting the value of a selected tap of said multitap FIR filter to a fixed value, and iteratively adjusting tap values of remaining taps of said filter from initial settings to said optimized values, by interatively adjusting the tap value of each of said remaining taps on an individual tap basis, from an initial setting to an optimized value for that tap.

6. A filtering mechanism according to claim 5, wherein said fixed value of said selected tap is a maximum value, and each of said initial tap value settings is zero.

7. A filtering mechanism according to claim 5, wherein, for each iterative adjustment of the value of a respective tap, said control processor is operative to calculate power in the error in data produced by said data signal analyzer and, in response to a reduction in the value of calculated error power from a previous value of calculated error power, to further iteratively adjust said value of said respective tap.

8. A filtering mechanism according to claim 5, wherein, for each iterative adjustment of the value of a respective tap, said control processor is operative to calculate power in the error in data produced by said data signal analyzer and, in response to no reduction in the value of calculated error power from a previous value of calculated error power, establishing said optimized value of said respective tap.

9. A method of controlling the operation of a direct spread-spectrum radio receiver, in which a demodulated spread signal received by way of a radio transmission channel from another direct spreading radio is despread in accordance with a despreading, pseudo-random chip sequence to produce despread signals, said despread signals being processed by a data signal analyzer to recover transmitted data, said method comprising the steps of:

(a) compensating for signal degradation effects imparted by said radio channel and internal distortion of said another direct spreading radio and said radio receiver by filtering said demodulated spread signal through an iteratively adaptive multitap finite impulse response (FIR) filter installed in said receiver upstream of a signal processing location of said direct spread-spectrum radio at which said demodulated spread signal is despread; and

(b) iteratively adjusting respective tap values of said multitap FIR filter to minimize error in data values produced by said data signal analyzer by iteratively adjusting respective tap values of said multitap FIR filter to optimized values that effectively minimize the power in the error in data values produced by said data signal analyzer, by setting the value of a selected tap of said multitap FIR filter to a fixed value, and iteratively adjusting tap values of remaining taps of said filter from initial settings to said optimized values.

10. A method according to claim 9, wherein said fixed value of said selected tap is a maximum value, and each of said initial tap value settings is zero.

11. A method according to claim 9, wherein step (b) comprises iteratively adjusting the tap value of each of said remaining taps on an individual tap basis, from an initial setting to an optimized value for that tap.

12. A method according to claim 11, wherein step (b) comprises, for each iterative adjustment of the value of a respective tap, calculating power in the error in data produced by said data signal analyzer and, in response to a reduction in the value of calculated error power from a previous value of calculated error power, performing a further iterative adjustment of said value of said respective tap.

13. A method according to claim 11, wherein step (b) comprises, for each iterative adjustment of the value of a respective tap, calculating power in the error in data produced by said data signal analyzer and, in response to no reduction in the value of calculated error power from a previous value of calculated error power, establishing said optimized value of said respective tap.