Multi-user HetNets with imperfect CSI

In this manuscript we consider several cells with heterogeneous characteristics, macro and small, working under the same spectrum. These cells serve a set of users, which are split between the two cell types. Under a frequency reuse of one, the users allocated to different cells generate harmful interference between them. We apply interference alignment (IA) at both macro and small-cell users to tackle that interference, which requires the availability of channel state information (CSI) at the transmitters. The more realistic case of imperfect CSI is considered, which leads to imperfectly interference aligned and, consequently, to performance degradation. Iterative space-frequency equalization is performed at the receiver side to cope with this residual interference. The results have shown the robustness of iterative equalization to imperfect CSI and its efficiency in removing interference generated by the poorly aligned interference. Close to matched filter bound performance is achieved with a very few number of iterations.