How do you handle negative frequencies in the power spectrum of a complex signal?
For a real signal, content at the negative frequencies generated by using the DFT is redundant. This is due to the well-known property of real signals with respect to the Fourier transform family: their transforms are Hermitian symmetric. That is, for any real signal $x[n]$,

$$
X[k] = \sum_{n=0}^{N-1}x[n] e^{-j2\pi n k / N} = (\sum_{n=0}^{N-1}x[n] e^{-j(-2\pi n k / N)})^* = X[-k] = X[N - k]
$$

So, if your input is a real signal, all of the information is in the positive frequency bins; the negative frequencies can be discarded for many applications. However, there is no such proprety for general complex signals. They can have power spectra that are asymmetric about zero frequency, so you may not discard any of the frequency bins of a complex signal's power spectrum without loss of information.