How to compute $|\alpha(e^{j2 \pi f})|^2$, the power spectral density of a discrete-time signal $\alpha_n = \alpha(nT) \in \{\pm1\}$ from the power spectral density of the corresponding continuous-time Fourier Transform of $\alpha(t)$, $|\alpha(f)|^2$?
Also what is the relation between $|\alpha(e^{j2 \pi fT})|^2$ and $|\alpha(e^{j2 \pi f})|^2$, where $T$ is the constant sampling period?