Transmit precoding based on outdated interference alignment for two users multi cell MIMO system

We present a novel downlink transmit precoding scheme for multi user MIMO cellular system where each cell schedules two users on the same resource. Our approach is to exploit the delayed interference state information (INTSI) and the concept of interference alignment (IA). We design the precoding such that the inter-cell interference subspace from the previous transmission is aligned at the intended receiver with the intra-cell interference subspace of the current transmission. Due to this outdated alignment we expect leakage interference in the desired signal space. However, we show that with the help of proper receiver design, we can suppress the interference and minimize the residual leakage interference and get substantial gains even with outdated alignment. We also address the practical issues and limitations related to the receiver design and provide a modified precoding scheme to overcome these limitations. We also present a comparison with other state of the art multiuser MIMO transmit precoding schemes with the help of extensive system level simulations. The simulation results show that our proposed scheme provides considerable gains over the other transmission schemes with ideal as well as practical considerations.