The document discusses Orthogonal Frequency Division Multiplexing (OFDM), including its principles, advantages, disadvantages and applications. OFDM divides the available spectrum into multiple orthogonal subcarriers, each modulated with a low data rate stream. This makes OFDM robust to multipath fading and intersymbol interference. While OFDM provides high data rates and spectral efficiency, it suffers from issues like high peak-to-average power ratio and sensitivity to frequency errors. OFDM is used in technologies like WiFi, WiMAX and digital audio/video broadcasting.