  Channel state information (CSI) at the transmitters (CSIT) is of importance
for interference alignment schemes to achieve the optimal degrees of freedom
(DoF) for wireless networks. This paper investigates the impact of half-duplex
relays on the degrees of freedom (DoF) of the X channel and the interference
channel when the transmitters are blind in the sense that no ISIT is available.
In particular, it is shown that adding relay nodes with global CSI to the
communication model is sufficient to recover the DoF that is the optimal for
these models with global CSI at the transmitters. The relay nodes in essence
help steer the directions of the transmitted signals to facilitate interference
alignment to achieve the optimal DoF with CSIT. The general MxN X channel with
relays and the K-user interference channel are both investigated, and
sufficient conditions on the number of antennas at the relays and the number of
relays needed to achieve the optimal DoF with CSIT are established. Using
relays, the optimal DoF can be achieved in finite channel uses. The DoF for the
case when relays only have delayed CSI is also investigated, and it is shown
that with delayed CSI at the relay the optimal DoF with full CSIT cannot be
achieved. Special cases of the X channel and interference channel are
investigated to obtain further design insights.
