Constant false alarm rate circuitry in adaptive target detection of radar systems

1. A method for performing cell-averaging constant false alarm rate detection, the method comprising:

computing a target value based on at least one power value associated with a cell under test in a two-dimensional region of a range-Doppler map;

computing a noise value based on a weighted average of power values associated with cells surrounding the cell under test in the two-dimensional region of the range-Doppler map;

computing a test value based on the target value and the noise value; and

declaring a target in the cell under test when the test value exceeds a predefined threshold value.

2. The method of claim 1 , further comprising:

receiving a Doppler Fast Fourier Transform of a predetermined cell in the range-Doppler map; and

computing the power value of the predetermined cell based on the complex magnitude of the Doppler Fast Fourier Transform.

3. The method of claim 1 , wherein computing a noise value further comprises:

with a storage circuit, storing predefined coefficients associated with the cells surrounding the cell under test in the two-dimensional region of the range-Doppler map.

4. The method of claim 3 , wherein the predefined coefficients taper at edges of the range-Doppler map.

5. The method of claim 3 , further comprising:

selecting an address in the storage circuit based on a position of a current cell in the cells surrounding the cell under test relative to the cell under test; and

retrieving a stored predefined coefficient of the current cell at the selected address.

6. The method of claim 5 , further comprising:

with an arithmetic circuit, receiving the stored predefined coefficient of the current cell and the power value of the current cell; and

computing at least a portion of the noise value based on the stored predefined coefficient of the current cell and the power value of the current cell.

7. A method for processing a two-dimensional range-Doppler map, comprising:

computing a power value based on at least one complex number for cells in the two-dimensional range-Doppler map, wherein the at least one complex number has a real and an imaginary portion and represents a Doppler Fast Fourier Transform that is associated with a radar signal received by an antenna;

selecting the computed power value for each cell in a subset of the cells in the two-dimensional range-Doppler map, wherein the subset includes a cell under test;

selecting a predetermined coefficient for each cell in the subset; and

performing a two-dimensional filtering based on the selected power values and the selected predetermined coefficients of the cells in the subset to concentrate the selected power values into a peak power value for the cell under test.

8. The method of claim 7 , wherein computing the power value based on the at least one complex number further comprises:

computing a magnitude square number for each of the at least one complex number; and

accumulating the computed magnitude square numbers.

9. The method of claim 7 , further comprising:

selecting the computed power value for each cell in another subset of the cells in the two-dimensional range-Doppler map;

selecting a predetermined coefficient for each cell in the other subset; and

computing a noise value based on the selected power values and the selected predetermined coefficients in the other subset.

10. The method of claim 9 , wherein computing the noise value further comprises:

computing a weighted average of the selected power values based on the selected predetermined coefficients.

11. The method of claim 9 , further comprising:

computing a test value based on the peak power value and the computed noise value; and

declaring a target in the cell under test when the test value exceeds a predefined threshold value.

12. Circuitry for performing cell-averaging constant false alarm rate detection for a cell under test in a range-Doppler map that shows target discrimination along a range and a Doppler axis, the circuitry comprising:

a first circuit that computes a numerator based on power values associated with cells in a first two-dimensional region of the range-Doppler map, wherein the first two-dimensional region of the range-Doppler map includes the cell under test;

a second circuit that computes a denominator based on power values associated with cells in a second two-dimensional region of the range-Doppler map and predefined coefficients, wherein the first two-dimensional region is a subset of the second two-dimensional region; and

a third circuit that computes a test value based on the numerator and the denominator and that declares a target in the cell under test when the test value exceeds a predefined threshold value.

13. The circuitry of claim 12 , wherein the first circuit further comprises:

a filter circuit that performs two-dimensional filtering based on the power values associated with the cells in the first two-dimensional region.

14. The circuitry of claim 13 , wherein the filter circuit further comprises:

a coefficient storage circuit that stores filter coefficients; and

a multiplier that receives the filter coefficients from the coefficient storage circuit and that computes a product based on the filter coefficients and the power values associated with the cells in the first two-dimensional region.

15. The circuitry of claim 12 , further comprising:

a fourth circuit that receives a Doppler Fast Fourier Transform of a cell in the range-Doppler map and that computes the power value associated with the cell based on the complex magnitude of the Doppler Fast Fourier Transform.

16. The circuitry of claim 12 , further comprising:

a storage circuit that stores the predefined coefficients and the power values associated with the cells in at least a subset of the second two-dimensional region of the range-Doppler map.

17. The circuitry of claim 16 , wherein the predefined coefficients vary with the values of the Doppler axis.

18. The circuitry of claim 16 , wherein the predefined coefficients vary depending on a position on the range-Doppler map relative to the cell under test.

19. The circuitry of claim 16 , wherein the predefined coefficients taper at edges of the range-Doppler map.

20. The circuitry of claim 16 , wherein the second circuit further comprises:

an arithmetic circuit that receives the stored predefined coefficients and the power values of the cells in the second two-dimensional region from the storage circuit and that computes the denominator based on a weighted average of the stored predefined coefficients and the power values.

21. The circuitry of claim 20 , wherein the second circuit further comprises:

a circuit that computes an address of one of the predefined coefficients in the storage circuit based on a position of a predefined cell in the second two-dimensional region relative to the cell under test.