This document discusses multiple access techniques for wireless communications including CDMA, TDMA, and FDMA. It then describes orthogonal frequency-division multiplexing (OFDM), how it works, and its advantages over other techniques. OFDM divides the available bandwidth into multiple orthogonal subcarriers. This eliminates interference between subcarriers and improves spectral efficiency. The document also discusses fast Fourier transforms and their use in implementing OFDM modulation and demodulation.