  It was shown in a previous work that some blind methods can be made robust to
channel order overmodeling by using the $\ell_1$ or $\ell_p$ quasi-norms.
However, no theoretical argument has been provided to support this statement.
In this work, we study the robustness of subspace blind based methods using
$\ell_1$ or $\ell_p$ quasi-norms. For the $\ell_1$ norm, we provide the
sufficient and necessary condition that the channel should satisfy in order to
ensure its identifiability in the noise-less case. We then study its frequency
of occurrence, and deduce the effect of channel parameters on the robustness of
blind subspace methods using $\ell_1$ norms.
