System and method for calculating a binary cross-correlation

1. A method for operating a laser detection and ranging system, the method comprising:

transmitting a plurality of laser pulses, each at a respective one of a plurality of pulse transmission times;

detecting a plurality of return pulses, each at a respective one of a plurality of return pulse times;

forming a first time difference, the first time difference being a difference between a first return pulse time of the plurality of return pulse times and a first pulse transmission time of the plurality of pulse transmission times;

forming a first element of a cross-correlation array based on the first time difference;

incrementing the first element of the cross-correlation array by n to form a second element of the cross-correlation array, where n is an integer based on a second time difference between a second pulse transmission time and a second return pulse time;

forming a first index to the first element of the cross-correlation array based on the first time difference;

forming a second index to the second element of the cross-correlation array based on the second time difference; and

estimating a range to a target based on the cross-correlation, the first index and the second index.

2. The method of claim 1 , wherein the first element of the cross-correlation array has a size of n memory words.

3. The method of claim 1 , further comprising calculating a plurality of time differences including the first time difference and the second time difference, the calculating of the plurality of time differences comprising calculating all time differences between a first subset of the pulse transmission times and a first subset of the return pulse times.

4. The method of claim 3 , further comprising calculating all time differences between a second subset of the pulse transmission times and a second subset of the return pulse times, wherein:

a pulse transmission time of the second subset of the pulse transmission times is greater than a pulse transmission time of the first subset of the pulse transmission times, and

a pulse transmission time of the second subset of the return pulse times is greater than a pulse transmission time of the first subset of the return pulse times.

5. The method of claim 1 , wherein:

the transmitting of the plurality of laser pulses comprises transmitting a first burst of laser pulses of the plurality of laser pulses, waiting during an inter-burst interval, and transmitting a second burst of laser pulses of the plurality of laser pulses;

each of the pulse transmission times of the first subset of the pulse transmission times is a pulse transmission time of a pulse of the first burst; and

each of the pulse transmission times of the second subset of the pulse transmission times is a pulse transmission time of a pulse of the second burst.

6. The method of claim 1 , further comprising allocating a region of memory for the cross-correlation array, the region of memory having a size based on the difference between:

the difference between an earliest return pulse time of the plurality of return pulse times and a latest pulse transmission time of the plurality of pulse transmission times; and

the difference between a latest return pulse time of the plurality of return pulse times and an earliest pulse transmission time of the plurality of pulse transmission times.

7. The method of claim 1 , further comprising:

estimating a range to a target, and

allocating a region of memory for the cross-correlation array, the region of memory having a size based on an uncertainty in the estimated range to the target.

8. The method of claim 7 , further comprising multiplying each element of the cross-correlation array by an attenuation factor, the attenuation factor being a positive number less than 1.

9. A laser detection and ranging system, comprising:

a laser transmitter;

a receiver; and

a processing circuit,

the processing circuit being configured to:

transmit, through the transmitter, a plurality of laser pulses, each at a respective one of a plurality of pulse transmission times;

detect, using the receiver, a plurality of return pulses, each at a respective one of a plurality of return pulse times;

form a first time difference, the first time difference being a difference between a first return pulse time of the plurality of return pulse times and a first pulse transmission time of the plurality of pulse transmission times;

form a first element of a cross-correlation array based on the first time difference;

increment the first element of the cross-correlation array by n to form a second element of the cross-correlation array, where n is an integer based on a second time difference between a second pulse transmission time and a second return pulse time;

form a first index to the first element of the cross-correlation array based on the first time difference;

form a second index to the second element of the cross-correlation array based on the second time difference; and

estimate a range to a target based on the cross-correlation, the first index and the second index.

10. The system of claim 9 , wherein the first element of the first array has a size of n memory words, and the index of the second element of the first array equals n times the second time difference plus the offset.

11. The system of claim 9 , wherein the processing circuit is further configured to calculate a plurality of time differences including the first time difference, the calculating of the plurality of time differences comprising calculating all time differences between a first subset of the pulse transmission times and a first subset of the return pulse times.

12. The system of claim 11 , wherein the processing circuit is further configured to calculate all time differences between a second subset of the pulse transmission times and a second subset of the return pulse times, wherein:

a pulse transmission time of the second subset of the pulse transmission times is greater than a pulse transmission time of the first subset of the pulse transmission times, and

a pulse transmission time of the second subset of the return pulse times is greater than a pulse transmission time of the first subset of the return pulse times.

13. The system of claim 12 , wherein:

the transmitting of the plurality of laser pulses comprises transmitting a first burst of laser pulses of the plurality of laser pulses, waiting during an inter-burst interval, and transmitting a second burst of laser pulses of the plurality of laser pulses;

each of the pulse transmission times of the first subset of the pulse transmission times is a pulse transmission time of a pulse of the first burst; and

each of the pulse transmission times of the second subset of the pulse transmission times is a pulse transmission time of a pulse of the second burst.

14. The system of claim 9 , wherein the processing circuit is further configured to allocate a region of memory for the first array, the region of memory having a size based on the difference between:

the difference between an earliest return pulse time of the plurality of return pulse times and a latest pulse transmission time of the plurality of pulse transmission times; and

the difference between a latest return pulse time of the plurality of return pulse times and an earliest pulse transmission time of the plurality of pulse transmission times.

15. The system of claim 9 , wherein the processing circuit is further configured to:

estimate a range to a target, and

allocate a region of memory for the first array, the region of memory having a size based on an uncertainty in the estimated range to the target.

16. The system of claim 15 , wherein the processing circuit is further configured to multiply each element of the first array by an attenuation factor, the attenuation factor being a positive number less than 1.