OFDM

A wide channel is hit unevenly by interference: some frequencies are cancelled by reflections while others get through. Orthogonal frequency-division multiplexing handles this by sending many slow streams side by side rather than one fast one. If some subcarriers are wiped out the rest arrive, and error correction fills the gaps.

Orthogonality means the subcarriers can sit close enough to overlap without interfering, giving excellent spectral efficiency. A cyclic prefix between symbols makes the system insensitive to echoes. The price is sensitivity to frequency error and a high peak-to-average power ratio that stresses the transmitter's amplifier.