Cross-tier interference mitigation for RTDD-based macro-femto networks

This paper considers the cross-tier interference mitigation for macro-femto networks under the reverse time division duplexing (RTDD) mode. A joint interference alignment (IA) and avoidance scheme is proposed. To mitigate the interference caused by femtocells at the macrocell base station (MBS), the signals of femtocells are aligned into the the null-space of the MBS's signal. The problem of the optimal precoding and decoding matrices is formulated to maximize the femtocell capacity while minimizing the interference leaked to the MBS. In addition, interference avoidance is also proposed to deal with the interference between macrocell users (MUs) and nearby femtocells. Numerical results demonstrate that the proposed scheme can significantly improve the MBS's performance with a slight degradation of the femto-cell's performance.