What is MIMO and how does it improve wireless performance?

MIMO (Multiple-Input Multiple-Output) uses multiple antennas at both transmitter and receiver to improve performance. Key MIMO techniques: Spatial Multiplexing transmits different data streams on different antennas, multiplying throughput (up to min(Nt,Nr) streams). Spatial Diversity transmits the same data on multiple paths to combat fading, improving reliability. Beamforming focuses energy toward the receiver using phase/amplitude weighting. MIMO capacity grows linearly with min(Nt,Nr) in rich scattering environments. Modern systems use Massive MIMO with 64-256 antennas for significant capacity gains in 5G networks.