Lidar Cross-Correlation via Histogram Bin Accumulation
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Solution Overview
Problem
Current lidar systems face challenges in efficiently calculating time of flight due to computational intensity and limited applicability of pulse position modulated waveforms, especially in the presence of target motion and sparse photodetection sequences, which leads to cross-correlation latency and ambiguity.
Innovation Solution
A method and system for calculating cross-correlation in a lidar system by transmitting and detecting laser pulses, forming time differences, and incrementing elements of a memory array based on these differences, allowing for efficient memory allocation and attenuation to reduce computational burden and improve processing speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional cross-correlation methods are used to determine time of flight, then range measurement can be obtained, but computational intensity increases and processing latency increases
Solution Approach 1:
The patent segments the cross-correlation computation into discrete histogram bins representing time-of-flight ranges. Instead of computing continuous cross-correlation, the method divides the time domain into discrete intervals and accumulates photon detections into appropriate bins, significantly reducing computational complexity while maintaining measurement precision.
Solution Approach 2:
The system performs preliminary actions by pre-defining histogram bins and their corresponding time ranges before photon detection begins. This allows real-time accumulation of photon data into pre-allocated memory structures, eliminating the need for post-detection computational processing and reducing latency.
2Reliability
If pulse position modulated waveforms are used to solve range ambiguity, then time of flight can be determined, but computational intensity increases and applicability is limited
Solution Approach 1:
The histogram-based cross-correlation method is self-service in that it automatically handles range determination through simple bin accumulation and peak detection. The system naturally resolves range ambiguity through the histogram structure without requiring complex waveform encoding or decoding algorithms, reducing computational burden while maintaining reliability.
3Reliability
If multiple laser pulses are transmitted to improve target detection, then detection reliability improves, but integration time increases
Solution Approach 1:
The patent implements continuous accumulation of photon detections into histogram bins as pulses are transmitted and returns are detected. This continuous integration process allows the system to maintain detection reliability through multiple pulses without discrete processing interruptions, efficiently utilizing integration time by continuously building the cross-correlation histogram.
4Ease of operation
If widely spaced pulses are used to avoid range ambiguity, then pulse association is straightforward, but integration time becomes excessive
Solution Approach 1:
The patent transitions from the time dimension alone to a two-dimensional histogram structure where one dimension represents time-of-flight and the other represents pulse number or integration stage. This dimensional transformation allows closely spaced pulses to be processed without ambiguity, as the histogram structure naturally associates returns with transmit pulses through the cross-correlation process while maintaining efficient integration time.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces cross-correlation latency and enhances processing efficiency, effectively handling arbitrary target motion and improving range estimation accuracy with reduced memory usage and computational complexity.
Implementation Method 1
determine the range to a target by measuring the time of flight of short laser pulses reflected off the target
Implementation Method 2
a photodetector that can record the arrival of reflected light. The photodetector is capable of timing the arrival of return pulses with an accuracy similar in scale to the laser pulse duration
Data Source
AI summary
A method for operating a laser detection and ranging system. In some embodiments, the method includes 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 the 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; and incrementing a first element of a first array, the first element of the first array having an index based on the first time difference.