Time reversal gaussian approximation filter
OwnerRaphael L. Levieninventor
Life of this patent
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Abstract
A time reversal filter uses exponential decay infinite impulse response filters to achieve an approximation to a true Gaussian low pass filter. In one embodiment, a time reversal Gaussian approximation filter performs the forward and backward passes of a time reversal filter in essentially one pass using a segmented signal approach. The input signal is divided into segments, each segment is filtered first in the forward direction, then in the reverse direction, and the segments thus filtered are reassembled to form the output signal. In addition, the overlap in the reverse direction from each filtered segment extending backward into the prior filtered segment is preserved in memory and added to the output of reassembled segments.
Claims25
In a time reversal filter including an input terminal for receiving an input signal, a first filter coupled to said input terminal, a first time reversal memory coupled to said first filter, a second filter coupled to said first time reversal memory, a second time reversal memory coupled to said second filter and an output terminal coupled to said second time reversal memory, the improvement comprising:
- wherein said first and second filters are infinite impulse response filters, and wherein said first and second filters are both a cascade of two exponential decay filters in series.
A method for time reversal filtering an input signal, to form a time reverse filtered output signal, said method comprising:
- dividing said input signal into a plurality of segments;
- selecting a first segment of said plurality of segments in the time forward direction;
- time reverse filtering said first segment in the time reverse direction to form a first time reversed filtered segment;
- selecting a second segment following said first segment of said plurality of segments in the time forward direction;
- time reverse filtering said second segment in the time reverse direction to form a second time reversed filtered segment;
- and
- combining said first time reversed filtered segment and said second time reversed filtered segment in the time forward direction to form said time reverse filtered output signal.
A method for time forward and time reversal filtering an input signal, to form a time forward filtered and time reverse filtered output signal, said method comprising:
- dividing said input signal into at least first and second segments, said second segment following said first segment in the time forward direction;
- filtering each said first and second segments in the time forward direction to form respective third and fourth segments;
- time reversing said third and fourth segments to form respective fifth and sixth segments;
- filtering said fifth and sixth segments in the time reverse direction to form respective seventh and eighth segments;
- time reversing said seventh and eighth segments to form respective ninth and tenth segments;
- and
- combining said ninth and tenth segments, wherein said tenth segment follows said ninth segment in the time forward direction to form said time forward filtered and time reverse filtered output signal.
An apparatus for time reversal filtering an input signal, to form a time reverse filtered output signal, said apparatus comprising:
- means for dividing said input signal into a plurality of segments;
- means for selecting a first segment of said plurality of segments in the time forward direction;
- means for time reverse filtering said first segment in the time reverse direction to form a first time reversed filtered segment;
- means for selecting a second segment following said first segment of said plurality of segments in the time forward direction;
- means for time reverse filtering said second segment in the time reverse direction to form a second time reversed filtered segment;
- and
- means for combining said first time reversed filtered segment and said second time reversed filtered segment in the time forward direction to form said time reverse filtered output signal.
An apparatus for time forward and time reversal filtering an input signal, to form a time forward filtered and time reverse filtered output signal, said apparatus comprising:
- means for dividing said input signal into at least first and second segments, said second segment following said first segment in the time forward direction;
- means for filtering each said first and second segments in the time forward direction to form respective third and fourth segments;
- means for time reversing said third and fourth segments to form respective fifth and sixth segments;
- means for filtering said fifth and sixth segments in the time reverse direction to form respective seventh and eighth segments;
- means for time reversing said seventh and eighth segments to form respective ninth and tenth segments;
- and
- means for combining said ninth and tenth segments, wherein said tenth segment follows said ninth segment in the time forward direction to form said time forward filtered and time reverse filtered output signal.
A composite filter comprising:
- an input terminal for receiving an input signal;
- an output terminal;
- a plurality of time reversal filters having respective input and output terminals, each of said plurality of time reversal filters providing a substantially similar signal delay between respective input and output terminals thereof;
- means for coupling the respective input terminals of said plurality of time reversal filters to said input terminal;
- and
- means for coupling the respective output terminals of said plurality of time reversal filters to said output terminal.
Dependencies are inferred from the claim text.