  Various spectrum sensing approaches have been shown to suffer from a
so-called SNR-wall, an SNR value below which a detector cannot perform robustly
no matter how many observations are used. Up to now, the eigenvalue-based
maximum-minimum-eigenvalue (MME) detector has been a notable exception. For
instance, the model uncertainty of imperfect knowledge of the receiver noise
power, which is known to be responsible for the energy detector's fundamental
limits, does not adversely affect the MME detector's performance. While
additive white Gaussian noise (AWGN) is a standard assumption in wireless
communications, it is not a reasonable one for the MME detector. In fact, in
this work we prove that uncertainty in the amount of noise coloring does lead
to an SNR-wall for the MME detector. We derive a lower bound on this SNR-wall
and evaluate it for example scenarios. The findings are supported by numerical
simulations.
