Discuss the propagation challenges at mmWave frequencies and mitigation techniques.

mmWave (24-100 GHz) faces severe propagation challenges. High path loss: FSPL increases with f², requiring ~20-30 dB more link budget at 28 GHz vs 2 GHz; mitigated by high-gain beamforming (256 elements can provide 24 dBi). Atmospheric absorption: O2 absorption peak at 60 GHz (~15 dB/km), rain attenuation (1-10 dB/km); limits outdoor range. Blockage: Human body causes 20-35 dB loss, materials vary widely; requires beam tracking, multi-connectivity, and dense deployment. Limited diffraction: Minimal propagation around corners; reflection-based NLOS paths critical. Foliage attenuation: Severe loss through vegetation. Solutions include beam tracking algorithms, multi-panel antennas, integrated access and backhaul (IAB), and cell densification with seamless handover.