Correlation based optical ranging and proximity detector

• US 6,307,622 B1
• Filed: 02/17/1999
• Issued: 10/23/2001
• Est. Priority Date: 02/17/1999
• Status: Expired due to Term

• Current Assignee: Infineon Technologies AG
• Original Assignee: Infineon Technologies North America Corporation (Infineon Technologies AG)
• Inventors: Lewis, Robert Alden
• Primary Examiner(s): Buczinski, Stephen C.
• Application Number:
  US09/252,361
• Time in Patent Office: 979 Days
• Field of Search: 342/114, 342/115, 342/189, 342/195, 356/4.01, 356/5.01, 180/169
• US Class Current: 356/4.01
• CPC Class Codes: G01S 17/04 Systems determining the presence of a target
• CPC Class Codes: G01S 17/08 for measuring distance only indirect measurement G01S17/46; active triangulation systems G01S17/48
• CPC Class Codes: G01S 17/32 using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
• CPC Class Codes: G01S 17/87 Combinations of systems using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 17/931 of land vehicles

Abstract

A method and a system for detecting and ranging objects utilize summed and difference signals to determine whether a target is present at a predetermined distance from the system. The summed and difference signals represent corresponding points on two discriminator functions that are derived by summing and subtracting two autocorrelation functions. The two autocorrelation functions are identical functions, except that one has been shifted by a one-bit period. By analyzing the summed and difference signals, the system is able to detect objects that cross a boundary zone located at the predetermined distance from the system. In the preferred embodiment, an optical signal is transmitted by a transmitter of the system to detect a target. Preferably, the optical signal is modulated in accordance with a double concatenated eleventh order Barker-based code. The optical signal is received by an associated photodiode after being reflected by the target. The received signal is then cross-correlated to produce the two autocorrelation signals.

Claims

1. A system for detecting and ranging objects comprising:

sequence generating means for providing a binary code having an autocorrelation function with negative sidelobes;

transmitting means electrically coupled to said sequence generating means for emitting a transmission signal that is representative of said binary code;

reception means operatively associated with said transmitting means for receiving a return signal;

first correlating means connected to said reception means and said sequence generating means for comparing said return signal with a first correlation signal to produce a first autocorrelation signal, said first correlation signal being said binary code with a selected time delay;

second correlating means connected to said reception means and said sequence generating means for comparing said return signal with a second correlation signal to produce a second autocorrelation signal, said second correlation signal being said first correlation signal with a preselected delay period;

calculating means electrically coupled to said first and second correlating means for generating a sum signal and a difference signal, said sum signal being at least partially based on combining said first and second autocorrelation signals, said difference signal being at least partially based on a difference between said first and second autocorrelation signals; and

processing means for analyzing said sum and difference signals to determine whether said return signal is an echo of said transmission signal from a target.

2. The system of claim 1 wherein said binary code provided by said sequence generating means is based on an eleventh order Barker-based code, said preselected delay period being a one-bit delay.

3. The system of claim 2 wherein said binary code is a double concatenated eleventh order Barker-based code.

4. The system of claim 1 wherein said transmitting means includes an optical pulse emitter and wherein said transmission signal is composed of light energy.

5. The system of claim 4 wherein said optical pulse emitter is a semiconductor device.

6. The system of claim 4 wherein said reception means includes a photodiode to detect said return signal, said photodiode being configured to generate current in response to said return signal.

7. The system of claim 4 further comprising a state controller that is connected to said sequence generating means to invert said binary code for input to said transmitting means and said first and second correlating means, said inversion being selectively invoked by said state controller.

8. The system of claim 7 wherein said state controller is configured to direct said transmitting means to modulate said optical pulse emitter to emit a leader segment prior to transmitting said transmission signal, said leader segment having an average amplitude equal to a selected portion of the maximum amplitude of said transmission signal to establish a reference amplitude when an echo of said transmission signal is received by said reception means.

9. The system of claim 1 wherein said sequence generating means is operationally responsive to said processing means to adjust said selected time delay for said first correlation signal, said adjustment being made in response to movement of said target for tracking said target.

10. A method of detecting and ranging objects from a source location comprising steps of:

transmitting a transmission signal from a ranging detector at said source location, including modulating said transmission signal in accordance to a binary code having an autocorrelation function with negative sidelobes;

subsequent to said step of transmitting said transmission signal, receiving a return signal by said ranging detector at said source location;

cross-correlating said return signal with a first correlation signal and a second correlation signal to produce a first autocorrelation signal and a second autocorrelation signal, said first and second correlation signals being time-delayed versions of said binary code, said second correlation signal being further time-delayed than said first correlation signal by a preselected bit period;

combining said first and second autocorrelation signals in a manner at least partially based on a signal summing to derive a summed signal;

combining said first and second autocorrelation signals in a manner at least partially based on a signal differencing to derive a difference signal; and

processing said summed and difference signals by a processor of said ranging detector to determine presence of a target, said presence being defined by relative amplitudes of said summed and difference signals.

11. The method of claim 10 wherein said step of modulating said transmission signal is a step of modulating said transmission signal in accordance to a double concatenated eleventh order Barker-based code.

12. The method of claim 10 further comprising a step of transmitting a leader segment, prior to said step of transmitting said transmission signal, to establish an amplitude reference when said leader segment and said transmission signal are received by said ranging detector.

13. The method of claim 10 further comprising steps of:

repeating said steps of transmitting, receiving, cross-correlating, summing and differencing to derive next-summed and difference signals; and

comparing said next-summed and difference signals with said summed and difference signals to determine a relative direction of movement of said target with respect to said ranging detector.

14. The method of claim 13 further comprising a step of adjusting time delays of said first and second autocorrelation signals to track said target in response to said determination of said relative direction of movement of said target.

15. The method of claim 10 further comprising a step of transmitting a second transmission signal from said ranging detector, wherein said second transmission signal has been modulated in accordance with a second binary code, said second binary code being an inverted version of said binary code.

16. The method of claim 10 wherein said step of transmitting said transmission signal is a step of transmitting an optical transmission signal, and wherein said step of receiving said return signal is a step of receiving an optical return signal.

17. A system for detecting presence of objects at a vicinity from a source location comprising:

a code sequence generator configured to generate a binary code having an autocorrelation function with negative sidelobes;

a transmitter electrically coupled to said code sequence generator to emit an electromagnetic signal that is representative of said binary code;

a receiver operatively associated with said transmitter to receive a return electromagnetic signal;

a first correlator connected to said receiver and said code sequence generator designed to compare said return signals with a first correlation code to produce a first autocorrelation signal, said first correlation code being said binary code with a selected time delay, said selected time delay defining a predetermined proximity from said source location being monitored;

a second correlator connected to said receiver and said code sequence generator designed to compare said return signal with a second correlation code to produce a second autocorrelation signal, said second correlation code being said first correlation code with a one-bit period delay;

calculating means electrically coupled to said first and second correlators for summing and subtracting said first and second autocorrelation signals in order to output a sum signal and a difference signal; and

a processor connected to said calculating means to analyze said sum and difference signals, said processor configured to determine whether said return signal is an echo of said emitted electromagnetic signal from a target at said predetermined proximity by the analysis of said sum and difference signals.

18. The system of claim 17 wherein said transmitter is configured to emit said electromagnetic signal in an optical form, and wherein said receiver is configured to receive optical signals.

19. The system of claim 17 wherein said processor is connected to said fist and second correlators to adjust said selected time delay to modify said first and second correlation signals in order to track said target by varying said predetermined proximity being monitored.

20. The system of claim 17 wherein said binary code is a double concatenated eleventh order Barker-based code.