MIMO Radar Velocity Ambiguity Resolution via Doppler Offsets
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Solution Overview
Problem
Traditional MIMO RADAR systems face velocity ambiguity issues due to insufficient maximum Doppler frequency, which complicates the separation of reflections from multiple transmitters and requires complex waveform associations, increasing system implementation costs and complexity.
Innovation Solution
The implementation of a Doppler Division Multiple Access (DDMA) method using transmit center frequency offsets to ensure orthogonality between transmitters, allowing for a single measurement per FMCW chirp and simplifying the system by eliminating the need for up-chirp and down-chirp associations, while using a virtual transmitter to distinguish reflections and increase Signal to Noise Ratio (SNR).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional FMCW waveform with up-chirp and down-chirp is used to prevent velocity ambiguity, then velocity measurement accuracy is improved, but system complexity increases due to the need for waveform association
Solution Approach 1:
The patent extracts the velocity ambiguity resolution problem from the complex up-chirp/down-chirp waveform association system. By using a single chirp waveform with cyclically shifted Doppler spectra, the solution removes the need for pairing multiple waveforms, thereby reducing system complexity while maintaining velocity measurement accuracy through the virtual transmitter approach
Solution Approach 2:
The patent changes the Doppler frequency parameter by introducing cyclic shifts to the Doppler spectra of different transmitters. This parameter transformation allows the system to resolve velocity ambiguity through frequency domain separation rather than temporal waveform pairing, simplifying the measurement system while preserving accuracy
2Measurement precision
If multiple transmit antennas are used to improve angular resolution, then DOA separation capability is improved, but velocity ambiguity occurs due to insufficient maximum Doppler frequency
Solution Approach 1:
The patent resolves the contradiction by moving from the time domain to the frequency domain. By applying cyclic shifts to the Doppler spectra in the frequency domain, the system achieves both high angular resolution through multiple antennas and reliable velocity measurement through spectral separation, effectively adding a frequency dimension to the measurement space
Solution Approach 2:
The patent introduces a virtual transmitter as an intermediary concept that does not physically exist but is created through signal processing. This virtual transmitter's cyclically shifted Doppler spectrum serves as a mediator to separate the responses of multiple physical transmitters, enabling both high angular resolution and unambiguous velocity measurement simultaneously
3Reliability
If Doppler frequency is increased to resolve velocity ambiguity, then velocity measurement reliability is improved, but orthogonality between transmitters is compromised
Solution Approach 1:
The patent applies preliminary action by pre-shifting the Doppler spectra of different transmitters by distinct cyclic amounts before the measurement process. This pre-established frequency separation ensures that when signals are received, the transmitters remain orthogonal and distinguishable, maintaining both velocity reliability and separation accuracy without requiring high Doppler frequencies
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 resolves velocity ambiguity, simplifies system implementation, and enhances the ability to separate reflections from multiple transmitters, improving angular resolution and reducing costs by minimizing hardware complexity and increasing coherence in complex target scenarios.
Implementation Method 1
the maximum Doppler frequency is typically insufficient to prevent velocity ambiguity
Implementation Method 2
transmitting a Frequency Modulated Continuous Wave (FMCW) waveform
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
An apparatus for resolving velocity ambiguity in a MIMO RADAR includes a plurality of transmit channels and a virtual channel. Each transmit channel includes a transmit antenna configured to transmit a plurality of chirps. Each chirp includes a frequency ramp of a transmit frequency of the respective transmit channel. Each transmit channel is orthogonal to another transmit channel and to a virtual transmit channel. A waveform generator is configured to generate a local oscillator (LO) signal for each transmit channel. A frequency offset circuit is configured to modify the LO signal of each transmit channel with a respective frequency offset to generate the respective transmit frequency.