What is OFDM and what are its advantages?

OFDM (Orthogonal Frequency Division Multiplexing) divides wideband channel into many narrowband subcarriers, each carrying low-rate data. Subcarriers are mathematically orthogonal, allowing overlap without interference, maximizing spectral efficiency. Implementation uses FFT/IFFT. Advantages: Robust against frequency-selective fading (each subcarrier sees flat fading), simple equalization (one-tap per subcarrier), efficient spectrum use, and easy implementation of MIMO. Cyclic prefix handles multipath. Used in Wi-Fi, LTE, DVB-T, and 5G NR.