What does the term "modulation" refer to in context of OFDM?

In the context of Orthogonal Frequency Division Multiplexing (OFDM), the term "modulation" refers to the process of encoding a signal with another signal. This is achieved by varying certain characteristics of the signal, such as its amplitude, frequency, or phase, to represent the information being transmitted. In OFDM, multiple carrier signals are used, each modulated with a portion of the data. This allows for efficient use of the available bandwidth and helps to increase the robustness of the transmission against interference and fading.

The modulation techniques used in OFDM, such as QAM (Quadrature Amplitude Modulation) or PSK (Phase Shift Keying), ensure that the data can be encoded onto the different subcarriers. This is a fundamental aspect of how OFDM achieves high data rates and maintains signal quality in environments that may be subject to various impairments.