CW-TOF Camera Multipath Interference Detection
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Solution Overview
Problem
Continuous Wave Time of Flight (CW-TOF) cameras face errors in distance measurement due to multipath interference (MPI), which contaminates the photocharge accumulated by pixels, leading to incorrect phase delays and distances calculated.
Innovation Solution
The CW-TOF camera acquires multiple images of a scene with different modulation frequencies, processes the amplitudes and phase angles of the photocharge accumulated by each pixel, and compares these values to detect and mitigate the effects of MPI, thereby determining the presence of multipath interference and correcting for errors in distance measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the CW-TOF camera uses photocharge accumulation to measure distance, then distance measurement capability is achieved, but measurement precision deteriorates due to multipath interference contaminating the photocharge
Solution Approach 1:
The camera segments the photocharge accumulation process into multiple exposure periods with different sampling phase offsets. By dividing the measurement into discrete phase-sampled components, the system can identify and eliminate multipath-contaminated segments through comparison, thereby improving distance measurement precision while addressing the multipath interference problem.
Solution Approach 2:
The system changes the sampling phase offset parameter across different exposure periods to create varied measurement conditions. This parameter variation allows the camera to detect inconsistencies caused by multipath interference and correct distance measurements, resolving the contradiction between achieving distance measurement and maintaining precision against multipath interference.
2Measurement precision
If the camera acquires multiple images with different modulation frequencies to detect MPI, then measurement precision improves, but productivity decreases due to increased acquisition and processing time
Solution Approach 1:
The camera employs periodic modulation of the light source at different frequencies across multiple images, creating a structured sampling pattern. This periodic action enables efficient detection of multipath interference through frequency-based analysis, improving measurement precision while managing the time cost through systematic rather than random sampling.
Solution Approach 2:
The system performs preliminary acquisition of multiple images with different modulation frequencies before final distance calculation. This preliminary sampling at varied frequencies allows the camera to pre-identify multipath interference patterns, enabling corrected distance measurements without requiring excessive processing time during the main measurement phase.
3Reliability
If the camera processes photocharge data to determine phase delays and distances, then distance information is obtained, but reliability deteriorates due to MPI-generated errors in photocharge accumulation
Solution Approach 1:
The camera implements a feedback mechanism where the processed phase delay information from multiple images is analyzed for consistency. When multipath interference is detected through phase inconsistency, the system feeds back to identify and correct the affected measurements, thereby improving distance measurement reliability while compensating for photocharge accuracy loss due to MPI.
Solution Approach 2:
The system combines data from multiple images acquired with different modulation frequencies to create a composite distance measurement. This composite approach integrates information from various frequency responses, allowing the camera to distinguish direct light from multipath light and produce more reliable distance measurements despite individual photocharge accuracy limitations.
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 identifies and reduces the impact of MPI on distance calculations, enhancing the accuracy of CW-TOF cameras by distinguishing between direct and multipath light, resulting in more precise distance measurements.
Implementation Method 1
The camera images the light reflected by the given feature on a pixel of a photosensor for each of a plurality of exposure periods to accumulate electric charge, 'photocharge' that the imaged light generates in the pixel during the exposure period
Implementation Method 2
A 'continuous wave' time of flight (TOF) camera (CW-TOF), transmits a 'continuous wave' of electromagnetic radiation, optionally infrared (IR) light, having intensity that is periodically modulated to illuminate a scene that the camera images
Data Source
AI summary
A method for determining whether a distance that a CW-TOF range camera provides for a scene is degraded by multipath interference (MPI) comprising operating the camera to determine a propagation phase delay and a phase delay coefficient for each of a plurality of modulation frequencies of light that illuminates the scene and using the phase delay coefficient and/or the phase delay to determine whether a distance provided by the camera is compromised by MPI.