Modulation

The process of applying a signal onto a carrier signal.

Carrier signal

A high-frequency continuous signal. Usually sine wave is used. Enables efficient long distance data transmission

Modulation rate

Rate at which the signal level is changed. Measured in bauds or signal elements per second.

Mark

A signal element that represents a binary 1.

Space

A signal element that represents a binary 0.

Modulation Algorithms

QAM

Short for Quadrature Amplitude Modulation. Combination of ASK and PSK. Logical extension of QPSK. Sends 2 different signals simultaneously on same carrier frequency, phase shifted. Each carrier is ASK modulated.

Used on asymmetric digital subscriber line (ADSL).