  This paper fully determines the degree-of-freedom (DoF) region of two-user
interference channels with arbitrary number of transmit and receive antennas
and isotropic fading, where the channel state information is available to the
receivers but not to the transmitters. The result characterizes the capacity
region to the first order of the logarithm of the signal-to-noise ratio (SNR)
in the high-SNR regime. The DoF region is achieved using random Gaussian
codebooks independent of the channel states. Hence the DoF gain due to
beamforming and interference alignment is completely lost in absence of channel
state information at the transmitters (CSIT).
