Detection and ranging methods and systems
There is provided a system and a method for acquiring a detected light optical signal and generating an accumulated digital trace The method comprises providing a light source for illumination of a field of view, an optical detector, an analog-to-digital converter (ADC), emitting one pulse from the light source in the field of view, detecting a reflection signal of the pulse by the optical detector, acquiring j points for the detected reflection signal by the ADC, storing, in a buffer, the digital signal waveform of j points, introducing a phase shift of 2pi/P, repeating, P times, the steps of emitting, detecting, acquiring, storing and introducing, to store, in the buffer, an interleaved waveform of P×j points, accumulating M traces of interleaved P×j points for a total of N=M×P acquisition sets, N being a total number of pulses emitted, creating one combined trace of the reflected signal of j×P points by adding each point of the M traces Additionally, the combined trace can be compared to a detected reference reflection signal of the pulse to determine a distance traveled by the pulse.
1. A method for acquiring a detected light optical signal and generating an accumulated digital trace, the method comprising:
providing
a light source for illumination of a field of view;
an optical detector;
an analog-to-digital converter (ADC) with a sample rate of F Hz and B bits of resolution;
emitting one pulse from said light source in said field of view;
detecting a reflection signal of said pulse by the optical detector;
acquiring j points for said reflection signal by said ADC by acquiring one of said j points at each 1/F second thereby converting said reflection signal into a digital signal waveform of j points;
storing, in a buffer, said digital signal waveform of j points;
introducing a phase shift of 2π/divided by a factor P between said emitting light pulse and a beginning of said acquiring j points by the ADC;
repeating, P times, said steps of emitting, detecting, acquiring, storing and introducing, to store, in said buffer, an interleaved waveform of P×j points, said interleaved waveform being equivalent to a single acquisition with a temporal resolution of 1/(F×P) second;
accumulating M traces of interleaved P×j points for a total of N=M×P acquisition sets, N being a total number of pulses emitted;
using the N sets, creating one combined trace of the reflected signal by adding each point of the M traces, point per point, to generate one accumulated digital trace of j×P points, each point in the combined trace being an accumulation of M=N/P sets and an effective time resolution of the combined trace being 1/(F×P) second;
wherein a length of said buffer is at least j×P and a number of bits of each element in said buffer is B+log 2 M;
wherein said sample rate of said ADC is virtually increased thereby allowing a low cost ADC having a low sample rate F to be used.
2. The method as claimed in claim 1 , wherein j equals 1, thereby acquiring only one point per pulse.
3. The method as claimed in claim 1 , wherein at least one of P and M is adjusted as a function of j.
4. The method as claimed in claim 1 , further comprising convoluting a reference signal with said combined trace.
5. The method as claimed in claim 1 , further comprising
detecting a reference reflection signal of said pulse by a reference optical detector at said emission of said pulse thereby acquiring a reference zero value and a reference trace for said pulse;
comparing said reference trace for said pulse to said combined trace;
determining a distance traveled by said pulse based on said comparison.
6. The method as claimed in claim 1 , further comprising:
providing a timer;
triggering said timer to calculate a time elapsed between said emission of said pulse and said detection of said reflection signal;
determining a distance traveled by said pulse based on said time elapsed.
7. The method as claimed in claim 1 , wherein said introducing a phase shift comprises delaying a clock of the ADC by a fraction of a period.
8. The method as claimed in claim 1 , wherein said introducing a phase shift comprises delaying a driver of the light source.
9. The method as claimed in claim 1 , wherein said lighting light source comprises several optical sources being driven sequentially using at least one sensor, a frequency of acquisition is a frequency of the optical source multiplied by a number of said optical sources.
10. The method as claimed in claim 1 , further comprising:
determining a time at which said emitting occurred;
choosing a filter based on a frequency of a transition;
filtering the reflection signal using said filter to obtain a filtered reflection signal;
detecting at least one of rising and falling edges for said filtered reflection signal and locating at least one of a rising and a falling slope;
acquiring samples in said at least one of a rising and a falling slope to memorize a digital waveform of the slope;
calculating a linear regression on said digital waveform of the slope;
calculating an intercept point in said linear regression;
calculating a difference in time between said emitting and said intercept point to estimate a distance to an object causing said reflection signal.
11. The method as claimed in claim 10 , wherein said determining a time comprises sampling said signal from said source.
12. The method as claimed in claim 11 , wherein said determining a time comprises using an electrical synchronization signal.
13. The method as claimed in claim 11 , further comprising determining different weights in the calculation as a function of the level of the noise.
14. The method as claimed in claim 11 , further comprising:
providing a threshold; and
determining the presence of an object at a predetermined target distance using said threshold.
15. The method as claimed in claim 11 , further comprising diminishing a level of noise using at least one of an averaging and a filtering technique.
16. The method as claimed in claim 11 , further comprising using a shifting technique to acquire more points.
17. A powered lighting system for acquiring a detected light optical signal and generating an accumulated digital trace, the powered lighting system comprising:
at least one light source for illumination of a field of view and emitting a pulse in said field of view;
an illumination driver for driving said light source;
an optical detector for detecting a reflection signal of a reflection of said pulse;
an analog-to-digital converter (ADC) with a sample rate of F Hz and B bits of resolution for acquiring j points for said reflection signal by acquiring one of said j points at each 1/F second thereby converting said optical reflection signal into a digital signal waveform of j points;
a buffer for storing said digital signal waveform;
a processor for
controlling said illumination driver and said optical detector;
sending information for storage in said buffer, wherein a length of said buffer is at least j×a factor P and a number of bits of each element in said buffer is B+log 2 M;
introducing a phase shift of 2π/P between said emission of said light pulse and a beginning of said acquisition of said j points by the ADC;
causing to repeat, P times, said emitting, detecting, acquiring, storing and introducing, to obtain an interleaved waveform of P×j points, said interleaved waveform being equivalent to a single acquisition with a temporal resolution of 1/(F×P) second;
accumulating M traces of interleaved P×j points for a total of N=M×P acquisition sets, N being a total number of pulses emitted;
creating one combined trace of the reflected signal using the N sets, by adding each point of the M traces, point per point, to generate one accumulated digital trace of j×P points, each point in the combined trace being an accumulation of M=N/P sets and an effective time resolution of the combined trace being 1/(F×P) second;
wherein said sample rate of said ADC is virtually increased thereby allowing a low cost ADC having a low sample rate F to be used.
18. The system as claimed in claim 17 , wherein j equals 1, thereby acquiring only one point per pulse.
19. The system as claimed in claim 17 , wherein at least one of P and M is adjusted as a function of j.
20. The system as claimed in claim 17 , further comprising:
a memory for providing a reference signal;
said processor convoluting said reference signal with said combined trace.
21. The system as claimed in claim 17 , further comprising:
a reference detector for detecting a reference reflection signal of said pulse at said emission of said pulse thereby acquiring a reference zero value and a reference trace for said pulse;
said processor comparing said reference trace for said pulse to said combined trace and determining a distance traveled by said pulse based on said comparison.
22. The system as claimed in claim 17 , further comprising:
a timer;
said processor triggering said timer to calculate a time elapsed between said emission of said pulse and said detection of said reflection signal and determining a distance traveled by said pulse based on said time elapsed.
23. The system as claimed in claim 17 , wherein said introducing a phase shift comprises delaying a clock of the ADC by a fraction of a period.
24. The system as claimed in claim 17 , wherein said introducing a phase shift comprises delaying a driver of the light source.
25. The system as claimed in claim 17 , wherein said powered lighting system comprises several optical sources being driven sequentially using at least one sensor, a frequency of acquisition is a frequency of the optical source multiplied by a number of said optical sources.