LIDAR Pulse Position Modulation for Interference Discrimination
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Solution Overview
Problem
Lidar systems operating in the same environment interfere with each other, leading to erroneous operations due to the inability to discriminate between their return signals, which is critical in safety applications like automotive and industrial settings.
Innovation Solution
The implementation of an integrated circuit that encodes and decodes pulses using orthogonal codes, allowing lidar systems to distinguish their own return signals from those of other systems by modulating the timing of light pulses and using demodulators to process these signals, ensuring interference-free operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple lidar systems operate in the same environment using conventional pulse transmission, then the coverage and functionality of lidar systems are improved, but interference between systems occurs leading to erroneous operations
Solution Approach 1:
The patent divides the continuous light signal into discrete pulses and assigns unique binary codes to different lidar systems. Each system's transmitted light is segmented into coded pulses (e.g., System A: 101010, System B: 010101), allowing simultaneous operation without interference. The receiver identifies which pulses belong to its transmitted sequence, filtering out other systems' signals.
Solution Approach 2:
The patent uses optical code division multiple access (OCDMA) where different lidar systems are assigned unique optical codes that modulate their transmitted light. The codes act as optical 'colors' or signatures, enabling the receiver to distinguish between different systems' return signals through correlation detection, similar to how different colors can be distinguished simultaneously.
2Measurement precision
If lidar systems transmit powerful light pulses to improve detection capability, then the detection precision is improved, but the risk of interference and erroneous operation increases
Solution Approach 1:
The patent applies preliminary encoding to the transmitted light pulses before they leave the lidar system. Each pulse is pre-modulated with a unique binary code sequence. This preliminary action ensures that even when multiple systems transmit simultaneously with high power, the receiver can decode and identify its own return pulses through correlation, preventing interference before it causes errors.
Solution Approach 2:
The patent implements a feedback mechanism where the receiver correlates the received signal with the known transmitted code sequence. This correlation process provides feedback to confirm which received pulses belong to the system's own transmission, enabling the system to adjust its detection threshold and filtering to maintain measurement precision while rejecting other systems' signals.
3Device complexity
If conventional lidar reception methods are used without pulse position modulation, then the device complexity is reduced, but the ability to discriminate return signals from multiple systems is lost
Solution Approach 1:
The patent uses periodic pulse transmission with regular time intervals and assigns each lidar system a unique periodic code sequence. The transmitted pulses follow a periodic pattern (e.g., repeating binary sequences), and the receiver uses this known periodic structure to correlate and identify return signals. This periodic action enables discrimination without requiring overly complex processing, as the regular pattern simplifies correlation detection.
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 solution enables lidar systems to operate interference-free, even in environments with multiple systems, by using unique orthogonal codes that prevent cross-correlation, allowing for accurate distance estimation and reducing the need for powerful lasers, resulting in more efficient and reliable lidar operations.
Implementation Method 1
a source transmits light into a field of view and the light reflects off objects. Sensors receive the reflected light.
Implementation Method 2
The receiver typically estimates the time of flight based on the phase of the received CW signal relative to the transmitted CW signal.
Implementation Method 3
an encoder configured to modulate a driving signal for an optical transmitter with a plurality of encoded pulses corresponding to a code
Data Source
AI summary
Described examples include an integrated circuit that includes an encoder configured to modulate a driving signal for an optical transmitter with a plurality of encoded pulses corresponding to a code, in which the driving signal is transmitted to the optical transmitter periodically. The integrated circuit also includes a demodulator configured to receive a received signal from an optical receiver that is configured to receive a reflection of light transmitted by the optical transmitter off an object, the demodulator configured to discriminate the plurality of encoded pulses in the received signal and estimate a distance of the object.