Carrierless Amplitude Phase Modulation is a non-standard variation of quadrature amplitude modulation (QAM).

CAP divides the available space into three bands. The range from 0 to 4 kHz is allocated for POTS transmissions. The range of 25 kHz to 160 kHz is allocated for upstream data traffic and the range of 240 kHz to 1.5MHz is allocated for downstream data traffic.

History

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CAP was the de facto standard for xDSL deployments up until 1996, deployed in 90 percent of xDSL installs. Now it is deprecated in favour of Discrete MultiTone Modulation (DMT)

Carrier-less Amplitude/Phase Modulation