Lidar Interference Resistance via Pulse Modulation
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Solution Overview
Problem
Lidar systems face interference, spoofing, and jamming issues due to the inability to distinguish between true and false returns, which can lead to incorrect target location detection.
Innovation Solution
Modulating the optical pulses with unique characteristics such as varying pulse repetition frequency, optical phase, polarization, or RF subcarriers, and using a processor to filter and identify genuine returns based on these modulations, thereby differentiating between true and spurious signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If narrow field of view optics, angular scanning, or narrow optic filters are used to reduce interference and jamming, then the chance of receiving spurious light is lowered, but a trace amount of light can still be received and confuse the sensor
Solution Approach 1:
The patent changes the temporal parameter of the optical signal by modulating the laser source with a unique code sequence. This allows the receiver to distinguish true returns from spurious light based on whether they carry the expected temporal modulation pattern, resolving the contradiction by adding a new dimension of discrimination beyond spatial and spectral filtering.
Solution Approach 2:
The system uses a matched filter that correlates the received signal with the transmitted code sequence. This feedback mechanism confirms whether received light carries the expected modulation pattern, allowing the sensor to accept or reject signals based on verification of their authenticity, thereby maintaining measurement precision while resisting interference.
2Reliability
If modulation is applied to optical pulses to distinguish true returns from spurious returns, then resistance to interference and hacking is improved, but the device complexity increases due to additional modulators and processing requirements
Solution Approach 1:
The patent replaces complex mechanical or optical modulation devices with direct electrical modulation of the laser source. By modulating the laser current with the code sequence, the system achieves the same effect as external modulators but with simpler electronics, reducing device complexity while maintaining reliability against interference and spoofing.
3Measurement precision
If a processor is used to filter and identify genuine modulated returns, then measurement precision and resistance to spoofing are improved, but the loss of time for signal processing increases
Solution Approach 1:
The system performs preliminary correlation processing by matching the received signal against the known transmitted code sequence. This preliminary action of correlation allows rapid identification of genuine returns versus spurious signals, reducing the overall processing time required while maintaining high measurement precision and spoofing resistance.
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
Enhances the resistance of lidar systems to interference and jamming by ensuring that only modulated returns are considered genuine, improving the accuracy of target location detection and reducing the risk of false readings.
Implementation Method 1
a laser that generates a series of optical pulses
Implementation Method 2
an external modulator that modulates those pulses to produce the modulated series of optical pulses
Implementation Method 3
the transmitter may modulate the pulses by varying a pulse repetition frequency, an optical carrier wavelength, a polarization, or an amplitude of the series of optical pulses
Implementation Method 4
A receiver receives a modulated series of optical returns scattered and/or reflected from at least one object in the scene
Data Source
AI summary
Lidar uses light to sense the range to an object. It can be used as a sensor, e.g., for autonomous vehicle navigation, or to generate detailed maps of terrain. A lidar can also sense target speed, optical reflectivity, and spectroscopic signature. As lidars become more widespread, one lidar could interfere with another nearby lidar. Incoherent (time of flight (TOF)) lidars can also be spoofed or hacked. And both coherent and incoherent lidars can be jammed. Modulating the lidar source makes the lidar more resistant to interference, jamming and hacking. In a TOF lidar, each transmitted pulse is modulated in a prearranged or predetermined fashion. A processor in the receiver distinguishes true returns from actual returns based on the modulation or encoding of the transmitted pulses. If the modulation is present, the return signal considered genuine. If the modulation is not present, it is deemed fake.