Lidar system and method of operation

1. A method for environment mapping, comprising:

generating a substantially continuous laser output representative of a periodic output signal that encodes a code sequence;

throughout a time period, continuously transmitting the substantially continuous laser output into an environment;

during the time period, at an optical sensor, receiving a return signal comprising a reflection, from an object within the environment, of the substantially continuous laser output;

determining a sample indicative of a contiguous time window of the return signal, wherein a duration of the contiguous time window is greater than a period of the periodic output signal;

generating a filtered sample, comprising filtering the sample based on the code sequence;

based on the filtered sample:

determining an extremum of the filtered sample; and

determining a delay time associated with the extremum; and

based on the delay time, determining a relative location of the object.

2. The method of claim 1 , wherein filtering the sample based on the code sequence comprises applying, to the sample, a matched filter for the periodic output signal.

3. The method of claim 2 , wherein applying the matched filter comprises determining at least one of: a circular convolution of the sample with a time-reversed version of the periodic output signal; or a circular convolution of the periodic output signal with a time-reversed version of the sample.

4. The method of claim 1 , wherein determining the delay time comprises:

determining an interpolated sub-sample comprising the extremum; and

determining the delay time based on the interpolated sub-sample.

5. The method of claim 4 , wherein determining the interpolated sub-sample comprises performing a continuous curve interpolation.

6. The method of claim 1 , wherein the return signal further comprises a second reflection, from a second object within the environment, of the substantially continuous laser output, the method further comprising:

based on the filtered sample, determining a second delay time associated with the second object; and

based on the second delay time, determining a relative location of the second object.

7. The method of claim 6 , further comprising, before determining the second delay time, determining a first peak region associated with the extremum; wherein determining the second delay time comprises:

determining a second extremum of the filtered sample, wherein the second extremum is not within the first peak region, wherein a magnitude of the extremum is greater than a magnitude of the second extremum; and

determining the second delay time based on the second extremum.

8. The method of claim 1 , further comprising:

at the optical sensor, after receiving the return signal, receiving a second return signal comprising a second reflection, from a second object within the environment, of the substantially continuous laser output;

determining a second sample indicative of a second contiguous time window of the second return signal;

generating a second filtered sample, comprising filtering the second sample based on the code sequence;

based on the second filtered sample, determining a second delay time associated with a second extremum of the filtered sample; and

based on the second delay time, determining a relative location of the second object.

9. The method of claim 1 , further comprising:

generating a second substantially continuous laser output encoding a second periodic output signal;

throughout the time period, continuously transmitting the second substantially continuous laser output into the environment;

generating a second filtered sample, comprising filtering the sample based on the second code sequence, wherein the return signal further comprises a second reflection, from a second object within the environment, of the second substantially continuous laser output;

based on the second filtered sample:

determining a second extremum of the second filtered sample; and

determining a second delay time associated with the second extremum; and

based on the second delay time, determining a relative location of the second object.

10. The method of claim 1 , wherein generating the substantially continuous laser output comprises modulating a substantially continuous-wave carrier signal based on a code sequence encoded using a phase-shift keying.

11. The method of claim 1 , further comprising, before generating the substantially continuous laser output, determining the code sequence such that a cross-correlation between the periodic output signal and other optical signals received at the optical sensor is less than a threshold value.

12. The method of claim 11 , further comprising, before determining the code sequence:

selecting a candidate code sequence;

generating a candidate laser output representative of a candidate output signal that encodes the candidate code sequence;

transmitting the candidate laser output;

at the optical sensor, receiving a test signal; and

based on the test signal, determining that a test cross-correlation between the candidate output signal and the other optical signals is greater than the threshold value;

wherein the code sequence is determined in response to determining that the test cross-correlation is greater than the threshold value.

13. The method of claim 1 , further comprising:

before the time period:

based on a first set of desired performance metrics, determining a first sequence length, wherein the first set of desired performance metrics comprises at least one of: accuracy, range, resolution, and latency; and

determining the code sequence based on the first sequence length, wherein a length of the code sequence is equal to the first sequence length;

based on the return signal, determining a second sequence length;

determining a second code sequence based on the second sequence length, wherein a length of the second code sequence is equal to the second sequence length;

generating a second substantially continuous laser output representative of a second periodic output signal that encodes the second code sequence;

throughout a second time period following the time period, continuously transmitting the second substantially continuous laser output into the environment;

during the second time period, at the optical sensor, receiving a second return signal comprising a second reflection, from the object, of the second substantially continuous laser output;

determining a second sample indicative of a second contiguous time window of the second return signal;

generating a second filtered sample, comprising filtering the second sample based on the second code sequence;

based on the second filtered sample:

determining a second extremum of the second filtered sample; and

determining a second delay time associated with the second extremum; and

based on the second delay time, determining an updated relative location of the object.

14. A method for environment mapping, comprising:

generating a first substantially continuous optical output representative of a first periodic output signal;

generating a second substantially continuous optical output representative of a second periodic output signal;

throughout a time period, continuously transmitting the first and second substantially continuous optical outputs into an environment;

during the time period, at an optical sensor, receiving a return signal, the return signal comprising:

a first reflection, from a first object within the environment, of the first substantially continuous optical output; and

a second reflection, from a second object within the environment, of the second substantially continuous optical output;

determining a sample by selecting a contiguous time window of the return signal;

generating a first filtered sample, comprising filtering the sample based on the first code sequence;

determining a first delay time associated with the first filtered sample;

based on the first delay time, determining a relative location of the first object;

generating a second filtered sample, comprising filtering the sample based on the second code sequence;

determining a second delay time associated with the second filtered sample; and

based on the second delay time, determining a relative location of the second object.

15. The method of claim 14 , further comprising, before the time period, determining the first and second code sequences such that a cross-correlation between the first and second periodic output signals is substantially zero.

16. The method of claim 15 , further comprising, before the time period, determining a sequence length, wherein the lengths of the first and second code sequences are each equal to the sequence length.

17. The method of claim 14 , further comprising, before the time period, determining a set of code sequences, each code sequence of the set associated with a respective periodic output signal that encodes the code sequence, wherein:

determining the set of code sequences comprises performing a stochastic optimization such that, for each pair of code sequences of the set, a respective cross-correlation between the respective periodic output sequences associated with the code sequences of the pair is less than a threshold value; and

the set of code sequences comprises the first and second code sequences.

18. The method of claim 14 , wherein:

the first periodic optical output is transmitted into the environment by a first laser; and

the second periodic optical output is transmitted into the environment by a second laser.

19. The method of claim 14 , wherein the optical sensor comprises a photodiode, wherein the return signal is received at the photodiode.

20. The method of claim 19 , wherein the first and second reflections are received at the photodiode concurrently.

21. The method of claim 1 , wherein the code sequence comprises a binary sequence of 0 bits and 1 bits, wherein generating the substantially continuous laser output comprises generating a high intensity output for each 1 bit and generating a substantially zero intensity output for each 0 bit.