The constellation diagram is very similar to
the vector diagram introduced earlier in the section, and is
a method of representing the symbol states in a carrier modulated bandpass modem in terms
of their amplitude and phase. Typically, the horizontal axis is taken as a reference for
symbols that are in-phase with the carrier cos wct,
and the vertical axis represents the quadrature carrier component, sin wct. With
binary ASK, there are just two symbol states to map onto the constellation space: a(t) = 0 (no carrier amplitude,
giving a point at the origin), and a(t) = A cos wct
(giving a point on the positive
horizontal axis at a distance A from the origin). |
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