Pulse-Coded LiDAR Ranging to Eliminate Aliasing Dead Zones
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Solution Overview
Problem
Lidar systems face limitations in range detection due to time-of-flight constraints and aliasing effects, which result in inaccurate distance measurements for objects beyond a certain maximum range, leading to range ambiguity and dead zones.
Innovation Solution
The implementation of temporal pulse coding and avalanche histograms allows for the differentiation of reflections from in-range and out-of-range targets by applying pulse codes to emitted laser pulses and decoding the received signals, effectively extending the dynamic range of lidar systems and eliminating aliasing effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the detector is armed for a finite period of time corresponding to maximum range, then the measurement time is reduced and frame rate is improved, but the measurable range is limited to less than maximum range
Solution Approach 1:
The patent segments the measurement process by dividing the range detection into multiple discrete time bins within each frame. Each time bin corresponds to a specific time interval after pulse emission, allowing the system to accumulate photon counts for each bin across multiple frames. This segmentation enables the detector to handle both near and far targets by distributing measurement opportunities across different time intervals, thereby extending the effective measurable range while maintaining high frame rates.
2Productivity
If light pulses are emitted at a fixed pulse emission rate, then the system operation is simplified and productivity is improved, but aliasing effects occur causing range ambiguity
Solution Approach 1:
The patent introduces an intermediary mechanism in the form of multiple time bins that act as mediators between the fixed pulse emission rate and the variable range measurements. Each time bin serves as an intermediary container that captures photons at specific time intervals, allowing the system to resolve range ambiguities that would otherwise occur with fixed-rate pulsing. The time bins translate the simple fixed-rate emission into detailed range information by providing intermediate measurement stages.
3Length of stationary object
If the detector is armed for longer time intervals to detect distant targets, then the measurable range is extended, but the measurement time increases and frame rate decreases
Solution Approach 1:
The patent applies preliminary action by pre-defining multiple time bins before measurement begins, each configured to capture photons from specific distance ranges. This preliminary structuring allows the system to efficiently allocate detection resources across different range zones without requiring extended measurement times. The time bins are prepared in advance with their respective time intervals, enabling the detector to immediately process returning photons from distant targets as they arrive, thus extending measurable range without proportionally increasing measurement 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 enables accurate range determination for distant objects by disambiguating reflections and eliminating dead zones, thereby increasing the measurable range without increasing measurement time.
Implementation Method 1
the time required for a light pulse to travel a round trip distance between the detector and the target, or time-of-flight (TOF)
Implementation Method 2
The received reflected laser signal is aggregated into an avalanche histogram
Data Source
AI summary
A temporal pulse coding scheme is disclosed for use in operating pulsed lidar systems, and in particular, pulsed lidar systems used as sensors on autonomous vehicles. Pulse coding can be implemented to eliminate range ambiguity due to aliasing effects. Alternatively, pulse coding can be used with cyclic re-mapping to extend the maximum range of the lidar detector. Pulse coding can be further combined with arm coding to make range determinations over a continuous range having no dead zones.