Method and device for enhancing accuracy in ultrasonic range measurement

1. A method for short range detection using ultrasonic sensing, comprising:

shaping a pulse signal to produce a pulse shaped signal;

transmitting the pulse shaped signal, the pulse shaped signal reflecting off a finger to produce a reflected signal;

receiving the reflected signal;

identifying a relative phase of the reflected signal with respect to a previously received reflected signal;

tracking a location and a movement of the finger from an arrival time of the reflected signal and the relative phase;

saving most recent echoes to a history, and selectively discarding echoes less recently saved in the history based on a similarity measure between echoes in the history; and

providing touchless control to a user interface control in accordance with the location and the movement of the finger,

wherein the shaping uses a combination of amplitude modulation, frequency modulation, and phase modulation.

2. The method of claim 1 , further comprising converting the location and the movement to a coordinate or control action to associate with the user interface control.

3. The method for claim 1 , wherein the step of identifying further comprises:

identifying an arrival time from a correlation between a first reflected signal and a second reflected signal;

identifying a phase delay from the correlation for establishing a relative displacement of the finger; and

controlling the user interface control in accordance with the arrival time and the relative displacement.

4. The method of claim 1 , wherein the step of discarding echoes comprises selectively pruning the history based on one among an L2 norm based, spectral distortion based, log-likelihood based, or mean-squared error based metric.

5. The method of claim 1 , comprising

creating a sparse history of echoes based on a difference rate between echoes; and

updating an index table to the echoes in the history according to the sparse history,

wherein the sparse history weights echoes more heavily in the near-time than in the far-time.

6. The method of claim 5 , comprising

scanning through the history to identify an index for the echoes where an echo difference (ePR(i)−ePR(i−n)) is significantly greater than a noise difference (n(i)−n(i−n)),

where the index is large and that the echo difference for current and past ambient conditions are below a predetermined minimum threshold.

7. A method for enhancing range detection accuracy suitable for use in ultrasonic touchless sensing applications, comprising

transmitting an ultrasonic signal intended to reflect off a finger and produce an echo;

receiving the echo and saving most recent echoes to a history;

selectively discarding echoes less recently saved in the history to produce a sparse history;

identifying a relative phase of the echo with respect to a previously received echo in the sparse history;

comparing the echoes in the history for similarity and selectively pruning echoes in the history with high similarity;

replacing the pruned echoes with echoes having low similarity;

tracking a location and a movement of the finger from an arrival time of the echo and the relative phase; and

providing touchless control to a user interface control in accordance with the location and the movement of the finger.

8. The method of claim 7 , comprising

generating an index table for the echoes in the history such that the history then identifies echoes with time indexes and corresponding distance measures.

9. The method of claim 7 , comprising

comparing a present echo to the echoes in the history to calculate an updated set of differences; and

removing echoes in the history that do not contribute a noticeable difference based on the updated set of differences for pruning the echoes in the history.

10. The method of claim 9 , comprising subtracting off an echo if a current ambient components is distorting the echo.

11. The method of claim 7 , where the history table indirectly stores information associated with previous ambient components.

12. The method of claim 7 , comprising subtracting from an echo return that includes a primary response (PR) component, a direct path (DP) component, an ambient component (A), and a noise (N) component a Primary Response (PR) component of a previous echo saved in the history.

13. The method of claim 12 , comprising adaptively removing echo components received from a non-moving object in proximity of the finger to increase a signal to noise ratio of the echo for tracking the finger when the finger is moving.