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CAP

Introduction

Carrier-less Amplitude/Phase modulation (CAP) describes a version of quadrature amplitude modulation (QAM) in which incoming data modulates a single carrier that is then transmitted down a telephone line. The carrier itself is suppressed before transmission (it contains no information and can be reconstructed at the receiver), hence the adjective "carrier-less." CAP was the industry standard for early deployments of ADSL, and it is able to obtain asymmetric transmission speeds from 256 Kbps to 7168 Kbps downstream and 91 Kbps to 1088 Kbps upstream.