D. Spread Spectrum Technology: OFDM

Orthogonal Frequency Division Multiplexing (OFDM) is a modulation scheme that comprises multicarrier, multisymbol, and multirate techniques using spread spectrum technology. It is converged technologies of spread spectrum, Fast Fourier Transform (FFT), and multiple input multiple output (MIMO) antennae.

Broadband services require transmission of modulation of broadband signal at a high digital data rate. Due to frequency selective fading, the digital pulses in the time domain are spread out, interfering with neighboring digits and thus causing inter-symbol interference (ISI). This is shown in Figure D.1.