When we apply the DFT operation on a real signal $x[n]$ to get $X[k]$, then take the square magnitude of the $X[k]$, $\lvert X[k]\rvert^2$, the power spectrum is symmetrical. You can take the positive frequencies or negative frequencies as the frequency information in $X[k]$.
However this is not true for complex valued signals; the power spectrum is not symmetrical.
- In this case, how would you determine the frequency components in original signal?
- Can we just drop the negative frequency part?