Methods and systems for measuring speckle translation with spatial filters
Two or more spatial filters are used in determining velocity based on speckle translation. A light source may be turned on, turned off, or both for a variable amount of time during operation. The velocity may then be determined with trend identification, correlation, recursive frequency estimation, or measurement bandwidth variation. A confidence level may also be calculated for the measured velocity, and the measured velocity reported or used only when the calculated confidence level meets or exceeds a given value.
1. A method for determining velocity, comprising:
receiving in-phase (I) and quadrature (Q) signals;
performing a recursive frequency estimation using the I and Q signals, wherein the recursive frequency estimation includes differentiating an equation for sum of squared errors, which includes at least one complex number that represents one of the I and Q signals; and
determining the velocity based on one or more results from the recursive frequency estimation.
2. The method of claim 1 , further comprising receiving a timing scheme that defines one or more illumination intervals and one or more non-illumination intervals, wherein the illumination intervals are periods when illumination provided by a light source is on and the non-illumination intervals are periods when the illumination provided by the light source is off.
3. The method of claim 1 , further comprising:
determining a confidence level for the velocity; and
estimating the velocity with interpolation when the confidence level falls below a given value.
4. The method of claim 1 , wherein the receiving includes receiving the I and Q signals from a spatial filter, the I and Q signals being outputs of the spatial filter.
5. A system for determining velocity, comprising:
two or more spatial filters, each of the spatial filters being configured to output in-phase (I) and quadrature (Q) signals; and
a measurement circuit configured to receive the I and Q signals output from the two or more spatial filters and configured to perform a recursive frequency estimation using the I and Q signals output from the two or more spatial filters, wherein the measurement circuit is configured to differentiate an equation for sum of squared errors, which includes at least one complex number that represents one of the I and Q signals, to perform the recursive frequency estimation.
6. The system of claim 5 , wherein the measurement circuit is further configured to determine the velocity using one or more results of the recursive frequency estimation.
7. The system of claim 5 , further comprising a controller configured to receive a timing scheme for each measurement time period and for each non-measurement time period.
8. A method for selecting a timing scheme for obtaining a plurality of velocity measurements, comprising:
determining whether a timing scheme has been selected, the timing scheme defining one or more illumination intervals and one or more non-illumination intervals, wherein the illumination intervals are periods when illumination provided by a light source is on and the non-illumination intervals are periods when the illumination provided by the light source is off;
if a timing scheme has not been selected, obtaining the plurality of velocity measurements with a default scheme; and
if a timing scheme has been selected, obtaining the plurality of velocity measurements with the selected scheme.
9. The method of claim 8 , further comprising determining whether a current timing scheme should be changed.