  It is well known that the classical 2 user Gaussian interference channel has
only 1 degree of freedom (DoF), which can be achieved by orthogonal time
division among the 2 users. It is also known that the use of conventional
relays, which introduce a processing delay of at least one symbol duration
relative to the direct paths between sources and destinations, does not
increase the DoF of the 2 user interference channel. The use of instantaneous
relays (relays-without-delay) has been explored for the single user
point-to-point setting and it is known that such a relay, even with memoryless
forwarding at the relay, can achieve a higher capacity than conventional
relays. In this work, we show that the 2 user interference channel with an
instantaneous relay, achieves 3/2 DoF. Thus, an instantaneous relay increases
not only the capacity but also the DoF of the 2 user interference channel. The
achievable scheme is inspired by the aligned interference neutralization scheme
recently proposed for the 2X2X2 interference channel. Remarkably the DoF gain
is achieved with memoryless relays, i.e., with relays that have no memory of
past received symbols.
