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Constant False Alarm Rate

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  1. 1. Constant False Alarm Rate (CFAR) Presented By: Umair Saeed
  3. 3. What is CFAR?• Constant false alarm rate (CFAR) detection refers to a common form of adaptive algorithm used in radar systems to detect target returns against a background of noise, clutter and interference.
  4. 4. What is CFAR?• Constant false alarm rate (CFAR) is a property of threshold or gain control devices that maintain an approximately constant rate of false target detections when the noise, and/or clutter levels, and/or ECM (electronic countermeasures) into the detector are variable.
  5. 5. Why Do We Use CFAR?• CFAR techniques are used in reception and signal processing to avoid increased false alarm rates in the presence of jamming, clutter residue, or other interference sources.
  6. 6. CFAR• The basic feature of CFAR is that the false alarm probability remains approximately constant in clutter by a threshold, riding a definite value above clutter. Targets with an echo power exceeding the threshold level can still be detected.
  7. 7. Efficient CFAR Requirements• Efficient implementation regarding required processing power and production costs.• Low CFAR-loss.• Accurate fitting of the CFAR threshold to the clutter scenario.• The CFAR threshold must pass point targets and extended targets.• Closely spaced targets must not mask each other.
  8. 8. CAGO-CFAR
  9. 9. CAGO-CFAR• The CAGO-CFAR (Cell Averaging Greatest Of-) comprises essentially a shift register consisting of two sub-registers, each containing L storage cells. Between the sub-registers, the so-called cell under test (CUT) is located. Each sub- register has its own adding circuit.(MAX) is use for adding purpose.
  10. 10. CAGO-CFAR continue…• Using a multiplicative factor α for linear processing or an additive factor β for processing with a LOG-amplifier, the threshold value (TV) is calculated. Finally, the amplitude of the signal under test (SUT) is compared with the threshold value to decide whether the SUT belongs to a target or not.
  11. 11. Advantages of CAGO-CFAR• Require little processing power.• Having low CFAR loss.
  12. 12. Disadvantages of CAGO-CFAR• Ineffective thresholding.• Closely spaced targets can mask each other.• MAX-process, the CAGO threshold cannot immediately follow an abrupt rise or fall in clutter level.
  13. 13. OS-CFAR
  14. 14. OS-CFAR• The OS-CFAR (Ordered Statistic) comprises a shift register containing “A” storage cells, plus the CUT.• A sorting algorithm arranges the amplitudes of the storage cells in order of decreasing magnitude.• In a rank-selection process, the “r-th” largest amplitude is chosen as a representative of the clutter.• The TV is calculated using a multiplicative α or additive factor β as described for the CAGO-CFAR above. Target detection is accomplished by comparing the SUT with the TV.
  15. 15. Advantage of OS-CFAR• In contrast to the CAGO-CFAR, the OS-CFAR has the advantage of effective threshold formation. Disadvantage of OS-CFAR• The major disadvantage of the OS-CFAR is the high processing power required for performing the sorting algorithm.
  16. 16. CASH-CFAR
  17. 17. CASH-CFAR• The CASH-CFAR (Cell Averaging Statistic Hofele) comprises essentially a shift register configured by “A” sub-registers, each having its own adder and containing L storage cells.• By means of a special maximum-minimum process a clutter-representative sum-value Sr, will be selected from the “A” sum-values S1 to SA.• The threshold value is then calculated using a multiplicative (α/L) and/or additive (β/L) factor.• Special maximum-minimum circuit block interference.
  18. 18. Advantages of CASH-CFAR• CASH-CFAR avoids mutual masking of targets.• In clutter level with almost no time displacement.• CASHCFAR requires much less processing power than the OS-CFAR with its rank- selection method.
  19. 19. MAMIS-CFAR
  20. 20. MAMIS-CFAR• The MAMIS-CFAR (Maximum Minimum Statistic) is essentially the same as the CASHCFAR,• except that the special maximum-minimum circuit M replaces the adders of the• CASH-CFAR. The characteristics of the MAMIS- CFAR are quite similar to those of the• CASH-CFAR. For the CFAR-handling of block interference and of point- and extended targets.
  21. 21. THANKS