Noise Subtracting Filter Study.
Final rept. 28 Jan 71-27 Jan 72,
STANFORD UNIV CALIF STANFORD ELECTRONICS LABS
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A new approach is presented to the problem of suppressing broadband additive interference corrupting a received signal. The noise cancelling procedure developed for the suppression of such interference is intended for problem situations where a second independent input related to the interfering process but not to the signal itself can be easily obtained. This input is called the reference and is used, after suitable filtering, to cancel the interference in the main or primary input. This filtering process is adaptive and is based on the Least Mean Square algorithm of Widrow and Hoff. The algorithm is applied here so as to minimize the output power of the system on the basis of measurements at the system terminals. The adaptive algorithm requires no a priori knowledge about the properties of the system inputs, but a certain amount of qualitative a priori knowledge is required for the proper design of the built in system parameters. In as much as the required signal itself is not filtered, it remains undistorted by the noise cancelling process. Some aspects of the implementation and practical application of adaptive filters are briefly discussed. The successful application of the noise cancelling concept, using a real-time hybrid adaptive signal processor, in two distinctly different practical situations is described. Modified author abstract