IQ Processing for Coherent Lidar Ghosting Mitigation
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Solution Overview
Problem
Coherent LIDAR systems face challenges in accurately determining the location and velocity of targets due to ghosting issues caused by Doppler shifts, which result in the misidentification of peak images as true peaks, leading to faulty data processing.
Innovation Solution
The method involves transmitting up-chirp and down-chirp frequencies, receiving returned signals, and performing in-phase quadrature phase (IQ) processing to differentiate between true and image peaks, reducing the magnitude of image peaks and accurately determining target location, velocity, and reflectivity by selecting true peaks based on signal attribute values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Doppler shift compensation is not applied, then the system structure remains simple, but ghosting occurs causing misidentification of peak images as true peaks
Solution Approach 1:
The patent applies parameter changes by performing IQ processing to transform the signal representation from real-valued to complex-valued domain. This changes the frequency domain characteristics, causing image peaks to appear at different locations than true peaks. The processing involves generating in-phase and quadrature components, then combining them to form a complex signal whose FFT spectrum separates true peaks from image peaks, thereby resolving the ghosting problem through parameter transformation.
2Measurement precision
If IQ processing is performed on all signals, then measurement precision is improved, but processing time and computational resources increase
Solution Approach 1:
The patent implements partial action by applying IQ processing selectively rather than uniformly to all received signals. The system determines whether peaks fall within frequency ranges associated with ghosting conditions, and only performs the computationally intensive IQ processing when such conditions are detected. This selective application maintains measurement precision when needed while minimizing unnecessary processing time and resource consumption during normal operating conditions.
3Productivity
If traditional peak detection is used without IQ processing, then processing speed is maintained, but ghosting causes faulty data processing
Solution Approach 1:
The patent introduces an intermediary step between traditional peak detection and final target parameter extraction. The IQ processing acts as a mediator that transforms the received signal into a form where true peaks and image peaks are separated in the frequency domain. This intermediary transformation preserves data processing throughput by using efficient FFT-based methods while eliminating the loss of information caused by ghosting, enabling accurate determination of target velocity and location.
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 effectively mitigates ghosting by reducing the processing of false peak data, enabling reliable identification of target locations, speeds, and velocities in LIDAR systems, even under conditions of relative motion between the LIDAR system and targets.
Implementation Method 1
The set of returned signals includes a Doppler shifted up-chirp frequency shifted from the at least one up-chirp frequency caused by a relative motion between the target and the LIDAR system, and a Doppler shifted down-chirp frequency shifted from the at least one down-chirp frequency caused by the relative motion between the target and the LIDAR system
Data Source
AI summary
A light detection and ranging (LIDAR) system to transmit optical beams including at least up-chirp frequency and at least one down-chirp frequency toward targets in a field of view of the LIDAR system and receive returned signals of the up-chirp and the down-chirp as reflected from the targets. The LIDAR system may perform IQ processing on one or more returned signals to generate baseband signals in the frequency domain of the returned signals during the at least one up-chirp and the at least one down-chirp. The baseband signal includes a first set of peaks associated with the at least one up-chirp frequency and a second set of peaks associated with the at least one down-chirp frequency. The LIDAR system determines the target location using the first set of peaks and the second set of peaks.