FMCW Radar Interference Cancellation Using Orthogonal Codes
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Solution Overview
Problem
The increasing number of radar sensors in vehicles leads to a higher likelihood of unwanted interference between sensors, particularly in scenarios like driving in a convoy, where rear sensors of one vehicle can interfere with front sensors of another, and existing methods to suppress these interferences, such as frequency offsetting or signal interpolation, are inadequate.
Innovation Solution
The use of orthogonal code sequences for phase modulation in FMCW radar sensors, where a first Fourier transformation separates objects by distance and a second transformation separates them by speed, with phase demodulation and summation of spectra to suppress interfering signals by ensuring only coherent oscillations with matching code sequences produce power peaks, while orthogonal code sets eliminate interference even with unsynchronized phase modulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of radar sensors is increased to improve detection coverage, then measurement precision and detection capability are improved, but the likelihood of interference between sensors increases
Solution Approach 1:
The patent segments the radar signal space by assigning different orthogonal code sequences to different radar sensors. Each sensor transmits signals modulated with its unique code, creating distinct signal segments that can be independently identified and processed. This segmentation allows multiple sensors to operate simultaneously without mutual interference, resolving the contradiction between increased sensor数量 and interference reduction.
Solution Approach 2:
The patent changes the modulation parameter of the radar signals by applying different orthogonal code sequences (such as phase codes or frequency codes) to different sensors. This parameter differentiation enables the system to distinguish between signals from different sensors, allowing multiple sensors to coexist without interference while maintaining high detection precision.
2Object-affected harmful factors
If frequency offsetting is used to suppress interference, then interference suppression is improved, but distance separation capability deteriorates
Solution Approach 1:
Instead of using frequency offsetting in the frequency domain, the patent transitions to the code domain by applying orthogonal code sequences. This dimensionality change allows interference suppression through code orthogonality rather than frequency separation, thereby maintaining full distance separation capability while effectively suppressing interference.
Solution Approach 2:
The patent changes the modulation parameter from frequency offset to orthogonal code sequence assignment. This parameter change enables interference suppression through code differentiation rather than frequency separation, preserving the distance separation capability that would otherwise be degraded by frequency offsetting.
3Object-affected harmful factors
If signal interpolation is used to suppress interference, then interference suppression is improved, but the method is inadequate for multiple interfering signals
Solution Approach 1:
The patent applies orthogonal code sequences that provide universal interference suppression capability regardless of the number or type of interfering signals. The orthogonality property ensures that each sensor's signal can be independently extracted even in the presence of multiple other signals, making the system universally effective against any number of interferers without requiring signal-specific processing.
Solution Approach 2:
The patent employs correlation-based detection where the received signal is correlated with the known orthogonal code sequences. This feedback mechanism allows the system to identify and extract signals from desired sensors while rejecting interference, effectively handling multiple interfering signals through the orthogonality property of the codes.
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 suppresses both self-interference within a vehicle's radar system and external interference from other vehicles, maintaining accurate distance and speed measurements even with short ramp durations and multiple interfering signals.
Implementation Method 1
Radar sensors are used in motor vehicles, for example to measure the distances, relative speeds and azimuth angles of vehicles or other objects located in front of one's own vehicle
Implementation Method 2
In the second Fourier transformation, the radar objects are separated according to their speeds based on changes in the phase angles over the sequence of the radar echoes
Implementation Method 3
A baseband signal is generated from a received signal by mixing it with the transmitted signal and is then evaluated
Implementation Method 4
a first Fourier transformation of the baseband signal is carried out for the individual frequency ramps of the transmission signal. Then the spectra of the first Fourier transformations of the frequency ramps of a sequence are used as input signal for a second Fourier transformation
Implementation Method 5
the transmission signal is phase-modulated with a code sequence Cm, which associates a phase offset with each frequency ramp of the sequence
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
The invention relates to a radar system in which a transmission signal of an FMCW radar sensor (10) comprises a sequence of frequency modulation ramps (30) and is phase-modulated according to a first code sequence (Cm) that is orthogonal to a respective other code sequence (Cq), a time-synchronized transmission signal of another FMCW radar sensor (10') being phase-modulated according to said other code sequence. The radar echoes are phase-modulated using a code sequence (Cm, fm) which correlates to the first code sequence (Cm), and a distance (d) and/or a relative speed (v) of at least one located object (44) is determined on the basis of a frequency spectrum of a Fourier analysis (32, 38) in a first dimension using respective sampled values of a radar echo of a frequency modulation ramp (30) and in a second dimension using the phase-modulated sequence of the radar echoes of the frequency modulation ramps (30) of the radar sensor (10) transmission signal. The invention also relates to a radar system for a vehicle fleet, wherein a code set (Cm1, Cm2) is used for phase modulation and demodulation purposes in an FMCW radar sensor (10), said code set together with a code set (Cq1, Cq2) used in a radar sensor (10") of another vehicle satisfying a code set orthogonality condition.