Modulator - Definition and Overview

For the musical use of "modulation", see modulation (music).

Modulation describes a range of techniques for encoding information on a carrier signal, typically a sine-wave signal. A device that performs modulation is known as a modulator.

Modulation techniques include:

• Amplitude modulation (AM)
• Phase modulation (PM, includes BPSK, QPSK, etc.)
• Frequency modulation (FM)
• Single-sideband modulation (SSB)
• Vestigial-sideband modulation (VSB, or VSB-AM)
• Quadrature amplitude modulation (QAM)
• Orthogonal frequency division modulation (OFDM), also known as Discrete multitone modulation (DMT)
• Wavelet modulation
• Trellis modulation
• Adaptive modulation
• Sigma-delta modulation (∑Δ)

When OFDM is used in conjunction with channel coding techniques, it is described as Coded orthogonal frequency division modulation (COFDM).

Pulse modulation techniques include:

• Pulse-code modulation (PCM)
• Pulse-width modulation (PWM)
• Pulse-amplitude modulation (PAM)
• Pulse-position modulation (PPM)
• Pulse-density modulation (PDM)

When transmitting digital data, modulation normally involves shifting one or more properties of the carrier wave between a set of states, a process referred to as keying. This type of modulation includes:

• Amplitude-shift keying (ASK) and its most common form, on-off keying (OOK) see Amplitude modulation
• Frequency-shift keying (FSK) and audio frequency-shift keying (AFSK) see Frequency modulation
• Phase-shift keying (PSK) see Phase modulation
• Gaussian Minimum Shift Keying (GMSK)

The use of on-off keying to transmit Morse code at radio frequencies is known as continuous wave (CW) operation.

Modulation is frequently used in conjunction with various channel access methods.

See also:

• Types of radio emissions
• Communications channel
• Channel coding
• Telecommunication
• Modem
• RF modulator
• Codec

External links

• "Data Encoding Techniques" (http://www.rhyshaden.com/encoding.htm) and "Specifications for Data Encoding" (http://www.wildpackets.com/compendium/FE/FE-Encod.html) discuss the various encoding techniques that have been used with various types of Ethernet.