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Common Data for Questions 74, 75:

Two $4$-ary signal constellations are shown. It is given that $\phi_{1}$ and $\phi_{2}$ constitute an orthonormal basis for the two constellations. Assume that the four symbols in both the constellations are equiprobable. Let $\frac{N_{0}}{2}$ denote the power spectral density of white Gaussian noise.

The ratio of the average energy of Constellation $1$ to the average energy of Constellation $2$ is

1. $4 a^{2}$
2. $4$
3. $2$
4. $8$