Let SXX (f) be the PSD function of a WSS discrete- time process X (n). Recall that one way to obtain this PSD function is to compute RXX [n] = E [X[k] X [k+ n]] and then take the DFT of the resulting autocorrelation function. Determine how to find the average power in a discrete- time random process directly from the PSD function, SXX (f).