The video introduces modulation, defining it as the process of changing a carrier signal's properties (amplitude, phase, or frequency) according to a baseband signal. It also highlights the different types of modulation based on which property is altered.

One key reason for modulation is to reduce antenna size. The size of an antenna is proportional to the wavelength of the transmitted signal. By modulating a low-frequency signal onto a high-frequency carrier, the wavelength decreases significantly, leading to a much smaller and more practical antenna size.

Modulation reduces interference by allowing multiple signals to be transmitted simultaneously without overlapping. Each signal can be modulated onto a different carrier frequency, preventing them from interfering with each other at the receiver. This also enables multiplexing, such as Frequency Division Multiplexing (FDM).

Modulation is broadly categorized into analog and digital. Analog modulation is used when the message signal is analog. This can be further classified into continuous-wave modulation (using a continuous carrier like a sine wave) and pulse modulation (using a pulse signal as a carrier).

Continuous-wave analog modulation includes Amplitude Modulation (AM), Frequency Modulation (FM), and Phase Modulation (PM). In AM, the carrier's amplitude changes with the message signal. In FM, the carrier's frequency changes, and in PM, its phase varies according to the message signal.

Pulse modulation techniques involve an analog message signal and a pulse train carrier. These include Pulse-Amplitude Modulation (PAM), where pulse height changes; Pulse-Width Modulation (PWM), where pulse duration changes; Pulse-Position Modulation (PPM), where pulse position changes; and Pulse Code Modulation (PCM), where the analog signal is sampled, quantized, and encoded into a digital bitstream.

Digital modulation schemes are used when the message signal is digital (1s and 0s). The main types are Amplitude Shift Keying (ASK), where amplitude changes based on bits; Frequency Shift Keying (FSK), where frequency changes based on bits; and Phase Shift Keying (PSK), where the phase of the carrier changes based on bits (e.g., a 180-degree phase shift for binary 0 or 1).