Dynamic MIMO Precoding for Femtocell Interference Mitigation

This paper studies interference mitigation in heterogeneous cellular networks consisting of traditional macrocells and newly envisioned femtocells. The mutual interference between macrocells and femtocells arises as a result of decentralized femtocell deployment and backhaul delay. To mitigate downlink interference between the femtocell clients, known as Home User Equipments (HUEs), and macrocell clients, known as Macrocell User Equipments (MUEs), we present methods of dynamic distributed beamforming that are fully compatible with MIMO precoding mechanisms in existing LTE standard releases. We develop three MIMO beamforming schemes for interference mitigation that take into account the Quality of Service (QoS) requirement of both femtocell and macrocell clients. These new heterogeneous MIMO precoding strategies improve flexibility in resource provisioning and signaling requirement while responding to different QoS needs. We also present MUE mean throughput analysis by applying order statistics to our proposed methods. Moreover, we provide an approximate closed form for the mean throughput in terms of basic transmitter, channel, and receiver parameters. Furthermore, we extend our proposed interference control precoding schemes to spatial multiplexing for MIMO transmissions. Finally, we extend our solution to tackle the more general case involving multiple MUEs, multiple HUEs, and multiple femtocells.