Relays can provide alignment for the K-user interference channel without channel state information at the transmitters

Channel state information at the transmitters (CSIT) is of importance for interference alignment schemes to achieve the optimal degrees of freedom (DoF) for wireless networks. This paper focuses on the K-user interference channel and shows that, employing relays between the sources and the destinations, interference alignment is possible without CSIT. Furthermore, the optimal DoF can be achieved with the help of relays. Specifically, a transmission strategy is designed and it is shown that the DoF κ/2 can be achieved with a two-slot transmission strategy using either (i) one relay with K - 1 antennas, or (ii) K(K - 2) single antenna relays. It is also shown that when each relay is equipped with L antennas, we need [K(K - 2)/L²] relays to achieve the optimal DoF.