Modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal that typically contains information to be transmitted. In digital modulation, the properties of the carrier wave—specifically its amplitude, frequency, or phase—are modified to represent digital data (bits). For example, Amplitude Shift Keying (ASK) varies the amplitude, Frequency Shift Keying (FSK) varies the frequency, and Phase Shift Keying (PSK) varies the phase. More complex schemes like Quadrature Amplitude Modulation (QAM) vary both amplitude and phase.

C. A channel is the physical medium or logical path through which the signal is transmitted; it is not a parameter of the carrier wave that is modified during modulation.

1. Huawei. (2020). HCIA-Datacom V1.0 Training Material (Model H12-811). Section: WLAN Overview

Subsection: Basic WLAN Concepts

Chapter: 802.11 Physical Layer Technologies. (This section describes how modulation techniques like PSK and QAM are used to encode data onto radio waves by modifying carrier properties).

2. Stallings

W. (2016). Data and Computer Communications (10th ed.). Pearson. Chapter 5

"Signal Encoding Techniques

" pp. 147-165. (This chapter details how amplitude

frequency

and phase are the fundamental characteristics of a carrier signal altered in digital-to-analog conversion/modulation).