Quadrature modulation

1. What is meant by quadrature modulation?
2. What is quadrature frequency modulation?
3. Is QAM and QPSK same?
4. Where is QAM modulation used?

What is meant by quadrature modulation?

Quadrature Amplitude Modulation (QAM) is a modulation method in which two signals are used to amplitude-modulate two carriers that are in quadrature (90 degrees out of phase with each other). The two modulated signals are combined. A common application is in PAL and NTSC color television transmission.

What is quadrature frequency modulation?

The carrier signals are of the same frequency but differ in phase by 90 degrees. Since the carriers are in phase quadrature, the modulation scheme described is referred to as, 'Quadrature frequency modulation'.

Is QAM and QPSK same?

Yes, QPSK and 4-QAM are effectively the same. Higher order PSK and QAM would be different, but they reduce to the same thing if you only have 4 constellation points.

Where is QAM modulation used?

QAM is used extensively as a modulation scheme for digital telecommunication systems, such as in 802.11 Wi-Fi standards. Arbitrarily high spectral efficiencies can be achieved with QAM by setting a suitable constellation size, limited only by the noise level and linearity of the communications channel.