High PRF Lidar Pulse Position Modulation Range Ambiguity
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Solution Overview
Problem
Current lidar systems face challenges with high pulse repetition frequency (PRF) due to range ambiguity, increased atmospheric backscatter, and measurement noise, which limit accurate range estimation and target detection, especially in dynamic scenes.
Innovation Solution
The implementation of pulse position modulation (PPM) waveforms with a pulse repetition frequency greater than 500 kHz, combined with asynchronous detectors and streaming cross-correlation algorithms, enables unambiguous range estimation and reduces noise, effectively addressing range ambiguity and atmospheric backscatter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pulses are repeated at higher frequency to decrease integration time, then productivity is improved, but range ambiguity increases making time of flight calculation ambiguous
Solution Approach 1:
The patent applies periodic pulse transmission with pulse position modulation, where pulses are transmitted at regular intervals but with coded position offsets. This periodic structure allows the system to operate at high PRF while the modulation pattern enables unambiguous range determination through correlation processing, resolving the contradiction between high productivity and measurement precision.
Solution Approach 2:
The patent changes the temporal parameter of pulse transmission by applying pulse position modulation offsets to the nominal pulse timing. This parameter modification encodes range information directly in the pulse timing structure, allowing the system to maintain high PRF operation while preserving unambiguous range measurement capability through the modulated timing pattern.
2Measurement precision
If pulse position modulation is applied to encode waveforms for range ambiguity resolution, then measurement precision is improved, but device complexity increases due to computationally intensive waveform construction
Solution Approach 1:
The patent replaces complex computational waveform construction methods with a more efficient implementation using direct pulse position modulation and streaming cross-correlation processing. This substitution reduces computational complexity while maintaining the ability to resolve range ambiguity through the modulated pulse timing structure.
Solution Approach 2:
The patent uses a reference copy of the transmitted pulse timing pattern (including modulation offsets) to perform correlation processing against received pulses. This copying approach simplifies the processing by allowing direct comparison with a stored reference pattern, reducing computational complexity compared to generating waveforms from scratch.
3Measurement precision
If conventional cross-correlation methods are used for time of flight determination, then measurement precision is achieved, but loss of time increases due to post-collection processing latency
Solution Approach 1:
The patent prepares the reference pulse timing pattern (including modulation offsets) in advance before actual measurement begins. This preliminary preparation allows the system to perform streaming cross-correlation processing in real-time as pulses are received, eliminating post-collection processing delays and reducing overall latency while maintaining measurement precision.
4Productivity
If high pulse repetition frequency is used to improve detection speed, then productivity is improved, but object-generated harmful factors increase due to increased atmospheric backscatter and measurement noise
Solution Approach 1:
The patent uses the known pulse position modulation pattern as a reference feedback signal for correlation processing. This feedback mechanism allows the system to distinguish true target returns from atmospheric backscatter and noise by correlating received signals with the expected modulated pulse pattern, enabling high PRF operation while filtering out harmful interference.
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 allows for accurate range and range rate estimation at high PRFs, improving detection accuracy and reducing noise, even in dynamic scenes, by using PPM waveforms and advanced signal processing techniques.
Implementation Method 1
Pulsed laser radar sensors, also known as lidars or ladars, are active sensing systems that determine the range to a target by measuring the time of flight of short laser pulses reflected off the target.
Implementation Method 2
The receiver includes an optical system (which may include an array of detectors) capable of collecting light reflected from the target, and a photodetector that can record the arrival of reflected light.
Data Source
AI summary
A laser detection and ranging system and method for operating thereof. 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; and estimating a range or a range rate of a target based on the pulse transmission times and the return pulse times. Each of the pulse transmission times may be offset from a corresponding nominal pulse transmission time by a respective pulse position modulation offset, the nominal pulse transmission times being uniformly spaced with a period corresponding to a pulse repetition frequency, the pulse repetition frequency being greater than 500 kHz.