What is the difference between MIMO and traditional beamforming in automotive radar?
MIMO vs Traditional Beamforming in Automotive Radar
MIMO (Multiple-Input Multiple-Output) radar is the enabling technology for high-resolution automotive radar. Without MIMO, achieving sub-2 degree angular resolution would require impractically large antenna arrays for a compact automotive module.
Frequently Asked Questions
Does MIMO improve range or velocity resolution?
No. MIMO improves angular resolution only. Range resolution depends on chirp bandwidth, and velocity resolution depends on the coherent processing interval. MIMO does not change these parameters. However, the TX orthogonality method may affect maximum unambiguous velocity (TDM-MIMO reduces it by N_TX) or range resolution (FDM-MIMO reduces it per sub-band).
What is the minimum number of TX channels for useful MIMO?
Even 2 TX channels doubles the virtual aperture compared to traditional beamforming, providing a significant improvement. Most production automotive radars use 3 TX channels as the minimum for meaningful MIMO benefit with manageable trade-offs in TDM Doppler ambiguity. High-resolution imaging radars use 12+ TX channels in cascade configurations.
Does MIMO work on transmit as well as receive?
MIMO creates a larger virtual aperture for receive beamforming (angle estimation). On transmit, each TX illuminates a wide area (the individual TX element pattern, typically 90-120 degrees). There is no transmit beam gain advantage in MIMO; the advantage is entirely in the synthetic receive aperture. This means MIMO radar's transmit efficiency is lower than a phased array with a focused transmit beam, partially offset by the MIMO processing gain.