Beam subset selection strategy for interference reduction in two-tier femtocell networks

This paper examines an orthogonal random beamforming-based cross-tier interference reduction scheme for two-tier femtocell networks. In order to improve the immunity of both macrocell and femtocell users to cross-tier interference, we adopt a macrocell beam subset selection strategy. This beam subset selection strategy maximizes the throughput of the macrocell by optimizing the trade-off between the multiplexing gain and the multiuser interference. Simultaneously, the max-throughput scheduler suppresses the cross-tier interference with an adaptively reduced number of beams. Since the average cross-tier interference from the macrocell gradually decreases as the number of beams decreases, the beam subset selection strategy is capable of providing a spatial opportunity to the femtocell network. This spatial opportunity enables the femtocell network to take advantage of the selectivity arising from the correlation between the interference channel and the precoding matrix. Therefore, we also propose opportunistic channel selection and distributed power control strategies for the femtocell network. Both analytical and numerical results show that the proposed strategies collaboratively reduce the cross-tier interference in two-tier femtocell networks.