  In this paper, an $n$-user Gaussian interference channel, where the power of
the transmitters are subject to some upper-bounds is studied. We obtain a
closed-form expression for the rate region of such a channel based on the
Perron-Frobenius theorem. While the boundary of the rate region for the case of
unconstrained power is a well-established result, this is the first result for
the case of constrained power. We extend this result to the time-varying
channels and obtain a closed-form solution for the rate region of such
channels.
