LAUSR

To effectively mitigate interference and improve the performance, we propose a grouping-based two-stage distributed interference alignment (GTDIA) scheme for a two-layered heterogeneous network (HetNet) in multi-user multiple-input-multiple-output (MIMO) Gaussian downlink transmission scenario. In this paper, we first extend the grouping-based interference alignment (GIA) scheme, which is suitable in single-layer multi-cell scenario to a two-layered HetNet. Then, in order to improve the system performance and reduce the computational complexity, we propose a new interference alignment (IA) scheme (i.e., GTDIA) by grouping pico users (PUEs) to align inter-layer interference (inter-layer IF) and design the receive beamforming matrices of PUEs. Since the macro users (MUEs) are located randomly under the coverage of macro base station, the inter-layer IF is between some pico base stations and MUEs. Specifically, two-stage (i.e., a composite of two cascade matrices) transmit beamforming matrices of base stations are designed to cancel both of the inter-layer and intra-layer interference among MUEs. Furthermore, because of the reciprocity of time-division duplex system, a distributed algorithm is used when designing the second stage transmit beamforming matrices. Analysis and simulation results demonstrate that the proposed scheme outperforms the extended GIA and other conventional IA schemes.