7.4. Multiple-QAM Approaches and Standards
The VDSL system specified in [16] uses either CAP or QAM as a modulation scheme [6], and analog frequency division duplexing (FDD) to separate the upstream and downstream channels. There are two carriers or equivalently center frequencies, both with 20 percent excess bandwidth raised cosine transmission in each direction, following frequency plans 997 (Europe) or 998 (North America). The symbol rate of each of the signals is any integer multiple of 67.5 kHz, and the carrier/center frequencies can also be programmed as any integer multiple of 33.75 kHz. This allows for the receiver for each signal to estimate signal quality and request an appropriate center frequency and symbol rate, as well as corresponding ...
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