Description
Multiple-Input Multiple-Output transmission uses N_T transmit and N_R receive antennas to create N_T × N_R parallel propagation paths. From a sensing perspective, MIMO multiplies the dimensionality of CSI: each TX/RX pair is its own complex channel observation, and the spatial diversity opens up angle-of-arrival, beamforming, and inter-antenna phase-difference techniques that single-antenna systems cannot perform.
When it's used
- Angle-of-arrival and direction estimation
- Inter-antenna phase difference / CSI ratio for sanitised phase
- Spatial diversity to suppress small-scale fading in sensing
- ISAC waveform design over MIMO arrays
Limitations
- Increases CSI matrix size and storage cost linearly per antenna pair
- Antenna geometry must be known to interpret AoA features
- Commodity APs often expose only a subset of antenna pairs