3. Quadrature Amplitude Modulation (QAM)
- Is a modulation scheme used in high speed modems and many different
transmission schemes.
- Is a form of digital modulation where the digital information is
contained in both amplitude and phase of the transmitted carrier.
- Quadrature is a reference to the technique of modulating two sine
waves independently, with 90 o phase shift (sine-cosine) between to create more subtle
phase changes. Amplitude refers to additional changes in signal level.
- The early QAM modem systems used eight phase changes and two
amplitude levels to transmit 4 bits during each baud (change state). So modem running at
1200 baud will transmit 9600 bps.
3.1 8-QAM
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