Geiger-mode LiDAR Non-uniform Sampling for SNR
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Solution Overview
Problem
Existing LiDAR systems, particularly those using Geiger-mode avalanche photodiodes (GmAPD), face challenges in maintaining a high signal-to-noise ratio (SNR) across their entire scan range due to noise degradation with distance, leading to undesirable latency and performance issues in automotive applications requiring large fields of view and high resolution.
Innovation Solution
The LiDAR system employs a non-uniform sampling approach by progressively adjusting the gate delay across detection frames, allowing longer-range areas to be sampled more times than shorter-range areas within an image frame, thereby maintaining a uniform SNR throughout the detection region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If uniform sampling is applied across the detection region, then shorter-range areas are sampled adequately, but longer-range areas suffer from noise degradation and reduced signal-to-noise ratio
Solution Approach 1:
The patent applies non-uniform sampling where different regions of the detection space receive different numbers of samples. Specifically, longer-range detection zones are allocated more samples than shorter-range zones, creating a locally optimized sampling strategy that adapts to the signal-to-noise ratio characteristics at different distances.
Solution Approach 2:
The patent changes the sampling parameter (number of detections per zone) based on the detection range. By adjusting the gate delay across multiple image frames, the system dynamically modifies which spatial zones are sampled in each frame, thereby changing the sampling distribution parameter to match the noise characteristics at different ranges.
2Measurement precision
If multiple detection frames are used to improve signal-to-noise ratio through statistical methods, then noise is reduced, but latency increases
Solution Approach 1:
The patent performs preliminary non-uniform sampling across multiple image frames before final object detection. By pre-distributing samples non-uniformly across detection zones during the imaging phase, the system prepares the data in advance so that subsequent object detection can be performed with reduced latency while maintaining high signal-to-noise ratio.
Solution Approach 2:
The patent implements dynamic gating where the gate delay is varied across different image frames to achieve non-uniform sampling. This dynamic adjustment of the gating parameter allows the system to flexibly allocate sampling resources across different detection zones and time frames, optimizing both signal-to-noise ratio and latency characteristics.
3Measurement precision
If Geiger-mode avalanche photodiodes are used to detect single photons, then sensitivity is improved, but noise degradation with distance worsens
Solution Approach 1:
The patent employs periodic imaging frames with varying gate delays to sample different detection zones. By cycling through multiple frames with different gating configurations, the system periodically revisits each detection zone with optimized sampling parameters, thereby maintaining high sensitivity while mitigating distance-related noise degradation through statistical aggregation.
Solution Approach 2:
The patent creates multiple copies of the detection process across different image frames, each with different gate delay settings. By taking multiple measurements (copies) of the same detection zone under different gating conditions and combining them statistically, the system enhances the effective signal-to-noise ratio while maintaining the single-photon detection capability of the Geiger-mode photodiodes.
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 enhances the detection of objects across the entire scan range with improved noise performance, reducing latency and image blur, and enabling high-confidence object detection in varying environmental conditions.
Implementation Method 1
A GmAPD is a special type of avalanche photodiode (APD), referred to as a single-photon detector (SPAD), that has such high sensitivity that it can detect the receipt of a single photon of light. When biased above this voltage, the absorption of a single photon gives rise to the generation of a single charge-carrier pair that induces the SPAD to spontaneously generate an avalanche current that is macroscopically detectable.
Implementation Method 2
LiDAR is based on laser range finding technology, in which the position of an object in a detection region is determined by transmitting a pulse of light toward the detection region and determining the time at which a reflection of the light pulse off of the object is detected. The position of the object is estimated by the time-of-flight (TOF) of the optical pulse to and from the object.
Data Source
AI summary
A GmAPD-based LiDAR system and methods for developing a point-cloud image of a detection region are disclosed. The methods include scanning the detection region during a plurality of detection frames that defines an image frame. In each detection frame, the detection region is interrogated with a different one of a series of optical pulses and reflections of the optical pulse are detected at a GmAPD-based receiver that is gated such that a different sampling region within the detection region is selectively sampled in each detection frame. The sampling regions are defined such that longer-range areas of the detection region are sampled more times in the image frame than shorter-range areas of the detection region. As a result, objects throughout the entire detection region can be detected with high SNR.