Degrees of Freedom Characterization: The 3-User SISO Interference Channel with Blind Interference Alignment

We characterize the degrees of freedom (DoF) of the 3-user Gaussian interference channel where each transmitter is equipped with a single conventional antenna and each receiver is equipped with one multi-mode antenna. By assuming that the channel is unknown to the transmitters and only known to the receivers, we show that by using linear blind interference alignment (BIA) with antenna switching at the receivers only, the sum DoF are 6/5. The new insight behind this result is that any vector of a user aligned at one unintended receiver cannot be aligned at the other unintended receiver. This is the first complete characterization of the sum DoF when using BIA over the Gaussian Interference Channel. The DoF result under the temporal correlated channels is also discussed.