Carrierless_amplitude_phase_modulation
Carrierless amplitude phase modulation
Type of amplitude modulation lacking a carrier
Carrierless amplitude phase modulation (CAP) is a variant of quadrature amplitude modulation (QAM). Instead of modulating the amplitude of two carrier waves, CAP generates a QAM signal by combining two PAM signals filtered through two filters designed so that their impulse responses form a Hilbert pair. If the impulse responses of the two filters are chosen as sine and a cosine, the only mathematical difference between QAM and CAP waveforms is that the phase of the carrier is reset at the beginning of each symbol.[1] If the carrier frequency and symbol rates are similar, the main advantage of CAP over QAM is simpler implementation.[1] The modulation of the baseband signal with the quadrature carriers is not necessary with CAP, because it is part of the transmit pulse.[1]