RANGE INFORMATION DETECTION USING COHERENT PULSE SETS WITH SELECTED WAVEFORM CHARACTERISTICS
Method and apparatus for obtaining range information associated with a target using light detection and ranging (LiDAR). An emitter transmits a set of pulses of electromagnetic radiation to illuminate a target. The set of pulses includes a pair of emitted pulses with different waveform characteristics, such as slightly different phases. A detector receives a reflected set of pulses from the target. The received set of pulses includes a pair of received pulses with corresponding different waveform characteristics. The detector determines the range information by decoding the received pulses, such as by calculating an average of the phase differential in the received pulses. In this way, a single stage detector can be used without the need for separate I/Q (in-phase and quadrature) channels. Phase chirping can be used so that each successive pair of pulses has a different phase difference. Other waveform characteristics can be used including frequency, amplitude, shape, etc.
1 . A method, comprising:
emitting, from an emitter, a set of pulses of electromagnetic radiation to illuminate a target, the set of pulses comprising a first emitted pulse with a first waveform characteristic and a second emitted pulse with a second waveform characteristic different from and in non-quadrature relation with the first waveform characteristic;
receiving, by a detector, a reflected set of pulses from the target, the reflected set of pulses comprising a first received pulse corresponding to the first emitted pulse and a second received pulse corresponding to the second emitted pulse; and
combining the first received pulse with the second received pulse to determine range information associated with the target.
2 . The method of claim 1 , wherein the first and second waveform characteristics are each a phase of the respective first and second emitted pulses, wherein the second emitted pulse is out of phase with the first emitted pulse by a non-zero phase differential that is not a multiple of 90 degrees, and the range information is determined responsive to a detected phase differential between the first and second received pulses.
3 . The method of claim 2 , wherein the non-zero phase differential between the first and second emitted pulses has a magnitude of nominally between 5 degrees and 30 degrees.
4 . The method of claim 1 , wherein the range information is determined responsive to an average of respective phases of the first and second received pulses.
5 . The method of claim 1 , wherein the first and second waveform characteristics are each a frequency of the respective first and second emitted pulses so that the first emitted pulse is at a first frequency and the second emitted pulse is at a different, second frequency.
6 . The method of claim 1 , wherein the first and second waveform characteristics are each an amplitude of the respective first and second emitted pulses, and wherein the first emitted pulse has a first amplitude and the second emitted pulse has a different, second amplitude.
7 . The method of claim 1 , wherein a first modulation signal is applied to a first light source to generate the first emitted pulse, and wherein the first modulation signal is further applied to a delay circuit to generate a delayed modulation signal which is applied to a second light source to generate the second emitted pulse, the first and second light sources arranged in separate, parallel channels of an emitter.
8 . The method of claim 1 , wherein the combining step comprises evaluating a difference in at least a selected one of frequency, waveform shape, phase differential or amplitude between the first and second received pulses to determine the range information.
9 . The method of claim 1 , wherein the set of pulses is a first pulse set having the first and second emitted pulses, and wherein the method further comprises successively emitting each of a plurality of additional pulse sets each comprising at least corresponding first and second emitted pulses, each of the additional pulse sets having at least a selected one of a different average phase differential, a different average wavelength, a different average amplitude or a different overall total number of pulses therein.
10 . The method of claim 9 , wherein each of the first pulse set and the additional pulse sets occur over an associated pulse set time interval, wherein an intervening elapsed time interval is provided between each successive pair of the first pulse set and the additional pulse sets, and wherein each intervening elapsed time interval is multiple times greater in duration than the associated pulse set time intervals of the first pulse set and the additional pulse sets.
11 . The method of claim 1 , wherein the range information comprises an overall distance between the detector and the target.
12 . The method of claim 1 , further comprising using the range information to adjust a position of a moveable object.
13 . An apparatus comprising:
an emitter configured to emit a set of pulses of electromagnetic radiation to illuminate a target downrange from the emitter, the set of pulses comprising a first emitted pulse with a first waveform characteristic and a second emitted pulse with a second waveform characteristic different from and in non-quadrature relation with the first waveform characteristic;
a detector configured to receive a reflected set of pulses from the target, the reflected set of pulses comprising a first received pulse corresponding to the first emitted pulse and a second received pulse corresponding to the second emitted pulse, the detector further configured to combine the first and second received pulses to determine range information associated with the target.
14 . The apparatus of claim 13 , wherein the range information comprises an overall distance between the detector and the target.
15 . The apparatus of claim 13 , further comprising a controller circuit which controllably positions a moveable element responsive to the range information.
16 . The apparatus of claim 13 , wherein the first and second waveform characteristics are each a phase of the respective first and second emitted pulses, wherein the second emitted pulse is out of phase with the first emitted pulse by a non-zero phase differential that is not a multiple of 90 degrees, and the range information is determined responsive to a detected phase differential between the first and second received pulses.
17 . The apparatus of claim 16 , wherein the non-zero phase differential between the first and second emitted pulses has a magnitude of nominally between 5 degrees and 30 degrees.
18 . The apparatus of claim 13 , wherein the detector is configured to determine the range information by calculating an average of respective phases of the first and second received pulses.
19 . The apparatus of claim 13 , wherein the pulse set is a first pulse set, wherein the emitter is further configured to emit a pulse set cycle comprising the first pulse set as well as a succession of additional, spaced apart pulse sets each having at least a first pulse and a second pulse, and wherein each pulse set in the pulse set cycle has a different phase differential between the associated first and second pulses in the corresponding pulse set.
20 . The apparatus of claim 13 , further comprising a programmable processor with associated program instructions stored in a memory configured to carry out at least selected operations of the emitter and the detector.