Multiuser Interference Alignment based on Outdated Interference State Information

Based on the characteristics of interference seen by a user in a cellular network, we present a very simple multiuser transmission scheme. The transmitprecoding schemes for multi user (MU) MIMO systems are usually sensitive to the delays in the feedback of channel state information. Our scheme exploits the outdated interference state information and the concept of interference alignment. We design the precoding such that the outdated inter-cell interference subspace at the desired receiver is aligned with the current intra-cell interference subspace and the receiver suppresses this aligned subspace. Each transmitter in our scheme requires only the information from serving users hence no coordination whatsoever between users or between the transmitters is required. We have evaluated our scheme with the help of extensive system level simulations and compare it with other state of the art MU-MIMO precoding schemes with respect to the mean user rates. Our results show that our proposed scheme provides considerable gains over the other precodings.