Regularized Interference Alignment Transceiver Design for Asymmetric UL-DL Multi-Cell Multi-User MIMO Systems

In a dynamic time division duplex multi-cell system, the uplink (UL) and downlink (DL) transmissions may co-exist. The asymmetric UL-DL modes introduce more complex and diverse interference among the adjacent cells. In this paper, we propose an interference alignment (IA) scheme for asymmetric UL-DL multi-cell multi-user multi-antenna system. This system involves conventional inter-cell and intra-cell interference in symmetric directions and new asymmetric inter-cell interference. We characterize the properties of the new interference and use these properties to implement partial IA and guarantee feasibility of IA. Through minimizing weighted sum minimum mean square error, we design a regularized IA transceiver to compensate the performance degradation in low and moderate signal-noise-ratio region. The numerical simulations demonstrate that the proposed schemes outperform the previous works for the asymmetric UL-DL multi-cell system.